Differential expression of complement Properdin and Factor H in the placentae and umbilical cords of mothers with Preeclampsia, Gestational Diabetes Mellitus and Recurrent Pregnancy Loss

Abstract

Background:

Properdin and factor H (FH), the two regulatory proteins of the alternative complement pathway, oppose each other to maintain the complement system’s activation. While properdin upregulates, FH downregulates the complement alternative pathway. The current study evaluated the expression of properdin and FH transcripts and proteins in the placental tissues and umbilical cords (UC) of preeclampsia (PE), gestational diabetes mellitus (GDM), and recurrent pregnancy loss (RPL) compared to normal healthy pregnancy (N).

Methods:

The tissue histology of PE, GDM and RPL were observed using haematoxylin-eosin and Masson’s trichrome staining. To understand the expression and distribution of properdin and FH, RT-qPCR, western blot, and immunohistochemistry were carried out. The expressions of two additional complement components, C3 and C5, were also detected by western blot.

Results:

The placentae from PE and GDM showed substantial collagen and fibrinoid deposition, thicker foetal blood capillaries, and a considerable number of syncytial knots. There was a significant rise in the level of properdin and significant decline in the level of FH at both mRNA and protein levels in the placentae and umbilical cord of PE compared to N; in GDM placentae, both properdin and FH were significantly elevated compared to N. In the case of RPL placentae, similar to PE, properdin expression was high while FH expression level was low. In both PE and RPL placentae, C3 and C5 levels were high, suggesting possibility of overactivation of complement proteins in the placenta.

Discussion:

The observed elevated properdin level can contribute to the heightened inflammatory response in PE, GDM and RPL placentae. Low FH and high C3 and C5 in the placenta possibly suggests dysregulated complement activation in PE and RPL.

Introduction

Human placenta is an extraembryonic selective barrier between the foetus and the mother, acting as a conduit system supporting the growing foetus. Placenta, in conjunction with the umbilical cord, serves as a vital interface for the exchange of gases, nutrients, and waste products between maternal and foetal circulation, thereby supporting optimal foetal development (1–3). Foetal villi are bathed in the maternal blood, and thus, stress-related factors such as maternal circulating inflammatory cytokines (4), oxidative stress markers (5, 6), Damage-associated molecular patterns (DAMPs) (6), and endocrine/metabolic mediators (7) released in the maternal circulation during pathogenic assault can have detrimental effects leading to adverse pregnancy outcomes. Despite these adverse conditions, the establishment of immune privilege at the maternal-foetal interface, along with coordinated vascular remodelling and cellular adaptations, ensures the successful continuation of pregnancy (8–11).

Complement is one of the important innate immune systems, which plays a vital role in pregnancy and parturition (12, 13). There are more than 50 membrane-bound and soluble components of complement system which are involved in protection against invading pathogens and can generate membrane attack complex (MAC) for lysis, via three independent pathways– classical, lectin and alternative (14). Some of the complement components can also offer defence against pathogens without participating the complement pathway (15, 16). Despite being mostly derived from the liver (17), complement components are also synthesised at the extra-hepatic locations in different tissues and organs (18). In the cervico-vaginal mucosa, mannan-binding lectin (MBL) and C3 can bind to bacteria colonizing on clue cells (19, 20). As a physiological response, complement activity increases in pregnant women, and thus, there is a rise in the circulating complement proteins in the plasma. A prospective study carried out by He et al. showed that serum C3 and C4 levels increase gradually as the pregnancy progresses while C1q, C5a and sC5b‐9 levels remain similar to non‐pregnant condition in the plasma (21). The C-reactive protein (CRP), C4d, C3a and C9 levels are high whereas C1-inhibitor is low in the circulation in pregnant subjects compared to non-pregnant women (22). In the first trimester placenta, C1q, C3 and C4 are localized mostly in the fibrin and fibrinoid areas (23); C1q, C4, C3, C3d, C5, C6 and C9 are present in both pre-term and term placentae in varied locations (24), suggesting the relevance of complement proteins in a healthy pregnancy. Several mechanistic studies involving placental cell lines and gene knock-out mice, and observational studies in human samples have suggested that complement proteins play key roles in immune protection, inflammation regulation, immune tolerance, and host-pathogen interactions; in addition, they also support pre-implantation (25–27), implantation (12, 28), vascular remodelling (29, 30) placental development (28), trophoblast invasion (29, 31–33) and parturition (19). Thus, dysregulated complement activation, either inadequate or overstimulated, can lead to pregnancy complications.

Nearly all the biological consequences of complement subcomponents are dependent on the resultant cleavage products, and their levels have been found to be altered in adverse pregnancies (34). Increased deposition of C1q, C3d and C9 in chorionic villi (33), high C4d (35), and C3 and C4BP localization in syncytial bodies (32) have been observed in preeclampsia (PE) placentae. Increased levels of complement components such as factor B (36), C3b (37), C5a (38, 39), terminal complement complex (sC5b-9) (40, 41), MBL (42), C4d (35), H-ficolin, L-ficolin (43), C5a (44), aberrant C3a-C5a serum level (45) and decreased levels of C1q (32) were also observed in PE. Similarly, elevated levels of C4d placental deposition in unexplained recurrent miscarriage (46), Bb activation in early pregnancy and spontaneous preterm birth (47), and increased serum mannan-binding lectin-associated serine proteases (MASP1 and MASP2) (48) were associated with gestational diabetes mellitus (GDM). Thus, a range of studies appear to indicate dysregulated/altered complement activation in pregnancy-related complications; however, research gap exists in understanding factors and circumstances that can influence complement activation.

Local control by surface-bound and soluble complement regulators is critical to prevent complement-mediated tissue damage in normal pregnancy. An optimal degree of continuous low- grade complement activation is thus maintained and regulated at the level of initiation, amplification, and generation of effectors such as opsonin, MAC, and pro-inflammatory anaphylatoxins by complement regulators (49–54). Among the complement regulators, properdin and factor H (FH) are two vital soluble complement proteins that are secreted in the maternal circulation and in the placenta, tightly controlling the complement activation (54–56). Properdin, 53 kDa glycoprotein, which is dispersed in plasma at a concentration of about 25µg/ml (55) in a 26:54:20 ratio (55, 57), is the only upregulator of complement alternative pathway (AP) and can induce inflammation (58, 59), resulting in tissue damage (60, 61), immune cell infiltration (62) and pro-inflammatory cytokine release (63, 64). Properdin binds to and stabilizes the alternative pathway C3 convertase, C3bBb, extending its half--life by 5- to 10-fold, and enhances deposition of C3b, and thus, increasing the alternative pathway amplification loop (55, 65). Complement Factor H (FH), a 155 kDa soluble protein present in plasma in the range of 116 to 562 μg/ml, is a key negative regulator of the complement alternative pathway that promotes the proteolytic breakdown of C3b, downregulating the alternative pathway (66–69). FH influences the C3bBb convertase in two ways: it competes with factor B for binding to C3b, thus preventing formation of the C3bBb convertase, and it also accelerates the decay of this convertase once already formed. In addition, FH regulates the C3b-containing C5 convertases and acts as a cofactor for factor I and inactivates C3b (68–72). FH also inhibits complement from being amplified on target cells and on the host tissues’ extracellular matrix, preventing complement-mediated tissue damage and minimizing pro-inflammatory response that leads to a range of diseases (73–78).

Both properdin and FH perform key functions as complement regulators and as modulator of several cellular immune functions (55). Although a complex protective microenvironment exists at the maternal-foetal interface, maternal health can often influence the homeostasis of this communicating barrier compromising the foetal health under pathological conditions. The balance between properdin and FH is therefore crucial at the maternal–foetal interface, where complement must defend against pathogens without damaging foetal tissues. Thus, the current study examines the expression, distribution and localization of these two opposing complement alternative pathway regulators in adverse pregnancy cases (PE, GDM and RPL) in the placentae as well as in the umbilical cords that serves as the primary conduit between the mother and the foetus. The properdin and FH expressions were examined at gene as well as protein levels via RT-qPCR, western blot (WB) and immunohistochemistry (IHC). In addition, to understand the possible connection with complement dysregulation, local levels of C3 and C5 were also assessed. This study provides a novel insight into the potential role of properdin and FH in adverse pregnancy, thus, offering new avenues for the development of biomarkers for early detection risk stratification and/or therapeutic targeting in PE, GDM and RPL.

Materials and methods

Study design and sample collection

The current study was undertaken to evaluate the importance of properdin and factor H in PE, GDM and RPL for diagnostic and therapeutic intervention. Pregnant women between the age of 20 and 30 years admitted to Maharaja Jitendra Narayan Medical College and Hospital (MJNMCH), Cooch Behar, West Bengal, India, between the year 2020 and 2024 were recruited for the study. Four study groups were considered in this study: Group 1/Case group I/Preeclampsia (PE) (n=6), Group 2/Case group II/Gestational diabetes mellitus (GDM) (n=4), Group 3/Case group III/Recurrent pregnancy loss (RPL) (n=4) and Group 4/Control group/Normal healthy pregnancy (N) (n=6).

PE was diagnosed in accordance with the American College of Obstetricians and Gynaecologists (ACOG) guidelines (79). The inclusion criteria for Group 1/PE are new onset of hypertension where systolic ≥ 140mmHg and diastolic ≥ 90mmHg at two occasions at least 4 h apart after 20^th week of gestation, or a systolic ≥ 160mmHg and/or a diastolic ≥ 110mmHg within short interval, or proteinuria ≥ 300 mg in a 24 h urine collection, or a protein/creatinine ratio ≥ 0.3 or a dipstick reading of ≥ 1+ after 20^th week of gestation and in the absence of proteinuria new onset of any among, thrombocytopenia (Platelet count <1,00,000/µL), renal insufficiency, pulmonary edema, impaired liver function, or cerebral/visual symptoms. GDM is the onset or first recognition of glucose intolerance during pregnancy. Group 2/GDM mothers were considered for the study following OGTT (75 g oral glucose tolerance test) with fasting PG≥5.1 mmol/l, 1-h PG≥10.0 mmol/l, and 2-h PG of 8.5–11.0 mmol/l. Those who were diagnosed with diabetes mellitus or prediabetes (impaired fasting glucose or impaired glucose tolerance) before pregnancy or unable to complete OGTT (oral glucose tolerance test) by 32-week gestation were excluded from the study. Inclusion and exclusion criteria of GDM were followed as per the HAPO (Hyperglycaemia and adverse pregnancy outcomes) Study Cooperative Research Group and International Association of Diabetes and Pregnancy (IADP) Study Groups Consensus Panel (80, 81). For group 3/RPL, the criteria considered were continuous two or more episodes of the natural loss of pregnancy prior to the 20th gestational week of pregnancy and no previous successful pregnancy with the same partner. Patients with previous venous or arterial thrombosis or a family history of thromboembolism were also excluded. For RPL, guidelines were followed as mentioned in ACOG, 2018 and by the practice Committee of the American Society for Reproductive Medicine (82–84). For group 4/Control group, normal pregnant women (N) were matched controls (with the cases) with regards to age and gravida (number of pregnancy). Healthy pregnant mothers with no hypertension, no proteinuria, non-diabetes, and with no chronic disease or therapy, were included in this group. Women with any form of ailment or disease mentioned for the group 1/2/3 or with hypertension observed after 3 months of delivery were excluded. The present study excluded all subjects with the following: a history of antibiotic use longer than 7 days, with thyroid disease, cancer, mental illness, premature birth history, intrahepatic cholestasis during pregnancy, hypertensive disorder complicating pregnancy, smokers, previously known systemic disease, multifetal gestation, conception using gonadotropin ovulation induction or by in vitro fertilization. This investigation also excluded pregnant women having either HELLP syndrome (haemolysis, high liver enzymes, and low platelet count), or eclampsia. The clinical data on the human subjects are summarised in Table 1. The proposed work was carried out as per the Indian Council of Medical Research (ICMR) guidelines for Approval of Research Activity involving Human Subjects and was approved by the Institutional Ethics Committee (IEC/CBPBU/200/2020/001, MJNMC/IEC/77/2024 and MJNMC/IEC-78/2024). Informed and written consent were obtained from each subject participating in the study as per the ICMR guidelines.

Human placental (including chorionic villi and decidua) and umbilical cord tissues were collected within an hour following the delivery. They were dissected (1cm) into small pieces (five different sample sites across each placenta), kept in a vial containing phosphate buffered saline (PBS), and immediately transferred to the laboratory (CBPBU) in a cold storage container. For group1/PE, group 2/GDM and group 4/N, third trimester (term end) placentae were collected; for group 3/RPL, first trimester (early term) placentae was collected. Tissues were washed thoroughly 2 to 3 times in fresh PBS to remove blood. For gene expression profiling, tissues were kept overnight in RNA Liv (HiMedia) solution; next day, RNA Liv was discarded and tissues were kept at -80°C. For protein expression profiling and biochemical analysis, tissues were snap-frozen and stored at -80°C, and for histopathology and immunohistochemistry, tissue samples were formalin-fixed.

RNA isolation and reverse transcriptase quantitative polymerase chain reaction (qPCR)

Following the manufacturer’s instructions, 40 mg of placental and umbilical cord tissues were homogenised in RNA Xpress (HiMedia) and centrifuged at 12000×g for 10 min and the RNA containing supernatant was collected. Initially, total RNA was isolated using chloroform (0.2ml v/v), and then precipitated using isopropanol (0.5ml v/v) by centrifuging at 15000×g at 4°C. Next, the pellet containing RNA samples were treated with RNase free DNase I (GeNei™, 065560001A), extracted with chloroform, and precipitated with isopropanol in order to prevent the contamination with genomic DNA. After being cleaned with 75% ethanol and resuspend the RNA pellet in nuclease-free water, RNA was quantified using NanoDrop^® spectrometer (Thermo Scientific, NanoDrop one) at 260 nm. First strand cDNA was synthesized using the iScript Reverse Transcription Supermix (Bio-Rad, 1708841) with 1ng of total RNA. The resulting cDNA was subjected to qPCR with SsoAdvanced Universal SYBR^® Green Supermix (Bio-Rad, 1725270) using the Biorad CFX Maestro (CFX Connect™ Real-Time System). 40 cycles of denaturation (30 sec at 95°C) and annealing (30 sec at 54.6°C to 57.2°C, annealing temperature of the primers) were carried out. Housekeeping gene (β-actin) expression was used to normalise the data. After normalizing with β-actin abundance in the same sample, the ΔΔCT comparative technique was used to semi-quantitate the relative target mRNA (85). Supplementary Table 1 provides specific primer sequence information, product size, annealing temperature, and primer pair sequences.

Protein isolation from placental tissue and umbilical cord and immunoblot analysis

Protease inhibitor cocktail (ML051; HiMedia) and RIPA lysis buffer were used to homogenise placental and umbilical cord tissues (~50 mg each). Following homogenisation for 10 min, the samples were centrifuged for 20 min (14,800 rpm) at 4°C. Using Folin-Lowry’s method, the total protein content in the supernatant was measured. 40µg of protein was loaded on to each well and resolved under reducing conditions using 10% v/v SDS-PAGE for properdin and FH, and 8% v/v SDS-PAGE for C3 and C5. The proteins that have been resolved were wet transferred to a nitrocellulose membrane (Biorad). The membrane was then blocked for 45 min at room temperature using 2% BSA (bovine serum albumin) (Sigma Aldrich) in TBST [Tris-buffered saline containing 0.1% (v/v) Tween-20]. The membrane was probed overnight at 4° C with their respective primary antibodies. The following day, the blots were washed in TBST and probed for 2 h with HRP-conjugated secondary antibodies at room temperature. Finally, the protein bands were revealed using the Immobilon substrate (Millipore) via ChemiDoc machine (Biorad). Quantitative densitometric analysis was carried out via ImageJ software. Antibody details, blocking reagents and dilutions are summarised in Supplementary Table 2.

Immunohistochemistry

For Haematoxylin and Eosin (H&E) and Masson’s trichrome (MT) staining, 1cm thick sections of placental (sampled from the marginal zone bordering the yolk sac) and umbilical cord tissues were processed through ethanol gradient (70%→80%→90%→99% ethanol), cleared in xylene (Merck) and infiltrated with paraffin at 60°C to prepare the paraffin block. A manual rotary microtome (Leica) was used to slice 4 μm thin tissue sections of the paraffin-embedded samples. After stretching the tissue samples on a glass slide, it was deparaffinized in xylene and rehydrated in graded ethanol followed by haematoxylin (Rankem) staining and then dehydrated. The tissue samples were then stained with eosin (SRL), washed in ethanol, dealcoholized, cleared in xylene and mounted using DPX (di-butyl-phthalate polystyrene xylene). MT staining was carried out with Anneline blue (SRL) to study collagen deposition. H&E and MT-stained tissues were photographed via bright field microscope (Axiolab 5, ZEISS).

For IHC, 4 µm sliced tissue sections were placed on poly-L-lysine coated glass slides. Tissue sections were deparaffinizing in xylene and then rehydrated progressively, using 90%, 70%, 50%, 30% (v/v) ethanol and distilled water. After 30 min of endogenous peroxidase blocking with a 3% v/v hydrogen peroxide solution, the slides were replaced in sodium citrate buffer, pH 6.0 (Thermo Fisher Scientific) and microwaved for antigen retrieval. The tissue sections were blocked in 5% w/v BSA for 1 h at room temperature and incubated overnight with mouse anti-human properdin monoclonal antibody (0.9mg/ml in PBS; 1:200 dilution in 1% BSA in PBS) and sheep anti-human FH polyclonal antibody (1:500 dilution in 1% BSA in PBS) at 4°C in a humidified chamber separately. Next day, the slides were washed with PBS, incubated with HRP-conjugated goat anti-mouse IgG (H+L) (1:1000 dilution in 1% BSA in PBS) for properdin and HRP-conjugated rabbit anti-sheep IgG (H+L) (1:1000 dilution in 1%BSA in PBS) for FH for 2 h in a moist chamber at room temperature. The sections were counter-stained with haematoxylin (Rankem) after being treated with DAB (3,3-Diaminobenzidine) (SRL) substrate for three min in the dark. Slides were mounted using Dibutylphthalate Polystyrene Xylene (DPX) and observed under phase contrast microscope (Zeiss). Images were captured at 10X magnification. The amount of immunostaining was measured using a digital image analysis tool, the open-source IHC profiler plug-in for ImageJ (86, 87).

Statistical analysis

For statistical analysis, non-parametric Mann-Whitney test was performed in between control (N) versus PE, control (N) versus GDM and control (N) versus RPL for RT-qPCR and WB. For IHC, non-parametric Mann-Whitney test was performed in between control (N) versus PE, control versus (N) GDM and PE versus GDM. The data were displayed as the average ± standard deviation of the mean (SD). For each analysis, the results were shown as statistically significant, when *p <0.05, **p <0.01, *** p<0.001 and ns=not significant.

Results

High mRNA expression of properdin in PE and GDM placentae, whereas low expression of FH in PE and high in GDM placentae compared to normal healthy placentae

Initially, to confirm the histopathological characteristics in PE and GDM, H&E and MT staining of placental tissue were carried out. The H&E results showed term placenta with thickened foetal blood capillaries, excessive fibrinoid deposition and a considerable number of syncytial knots in the placental tissue of PE and GDM as compared to N placentae (Figure 1A). Earlier studies have demonstrated a substantial collagen deposition in PE placentae which is associated with fibrosis, one of the well-known pathological attributes of PE (88–90). This collagen deposition in the sample groups was also examined via MT staining. A characteristic of PE is maladapted spiral artery remodelling, which is shown by the loss of smooth muscle (red stained) and its replacement by collagen (blue stain). Dense collagen deposition (blue stained) around the foetal blood capillaries and inside the villous stroma of PE and GDM placentae compared to N placentae were observed (Figure 1B).

Figure 1

In the RT-qPCR analysis, a significantly higher level of properdin transcript was observed in PE and GDM placentae as compared to N (Figure 1Ci, ii). Conversely, a significantly low expression level of FH transcript in the PE was noted (Figure 1Di), whereas, the FH mRNA gene expression level in the GDM placentae was significantly higher compared to the N placenta (Figure 1Dii).

High mRNA expression of properdin in the umbilical cord of PE and GDM, whereas low FH mRNA expression in PE and high in GDM compared to normal healthy placentae

In addition to PE and GDM placentae, we examined the histology of umbilical cord, which revealed narrow umbilical arterial lumen (UAL) compared to the control (N-UC) (Figure 2A). A large gap in the Warton’s jelly was also observed in PE-UC, which indicates oedema-like pathological condition. MT staining of PE/GDM-UC did not reveal any difference in the collagen intensity compared to N-UC (Figure 2B).

Figure 2

Properdin and FH transcript levels in the PE-UC and GDM-UC were examined via RT-qPCR. The results showed significantly high properdin transcript expression in the PE and GDM in contrast to the normal healthy UC (N-UC) (Figure 2Ci, ii). As seen in the placentae of PE and GDM, FH mRNA expression significantly decreased in PE-UC (Figure 2Di); GDM-UC showed significantly higher FH transcript expression compared to N-UC (Figure 2Dii).

Higher properdin protein expression in placentae of PE and GDM, whereas lower protein expression of FH in PE and higher FH in GDM in the placentae

The expression of properdin and FH at the protein level was assessed by WB. The results were consistent with RT-qPCR data, revealing significantly higher properdin expression in PE (Figures 3Ai, 3Aii) and GDM (Figures 3Aiii, iv) placentae as compared to N. However, FH protein level was significantly low in PE (Figures 3Av, vi), while higher in GDM (Figures 3Avii, viii). Therefore, the results corroborate the gene expression results.

Figure 3

We also investigated the properdin and FH protein expression in the UC of term sample groups (PE, GDM and N). Protein expression of properdin did not vary among the PE-UC (Figures 3Bi, ii) and GDM-UC (Figures 3Biii, iv) compared to N-UC. However, FH protein expression followed the similar trend, being significantly lower in PE (Figures 3Bv, vi) and higher in GDM (Figures 3Bvii, viii) compared to N-UC.

Localization via IHC of properdin and FH in the PE and GDM placental tissues

To assess the expression along with the localization of properdin and FH in the placental tissues of PE and GDM compared to the N, immunohistochemistry (IHC) was performed. PE, GDM and N placentae were probed with anti-human properdin and anti-human FH antibodies separately; the positively stained sites showed deep brown colour. Properdin expression was observed in all placental types, but at different intensities. In comparison with the N placentae (Figure 4Ai), the properdin expression was higher in both the PE (Figure 4Aii) and the GDM (Figure 4Aiii) placentae. Higher expression was observed throughout the syncytiotrophoblast layer and in the syncytial knots (Figure 4A). FH expression was very low, almost undetectable in PE placentae (Figure 4Bii); in N (Figure 4Bi) and GDM placentae (Figure 4Biii), FH was found to be localized in the syncytiotrophoblast region, in the foetal villous endothelium as well as in the villous stroma region (Figure 4B). The IHC results revealed significantly higher properdin (Figure 4Aiv) and lower FH (Figure 4Biv) expression in PE in comparison to N. Unlike PE, in GDM placentae, both properdin (Figure 4Aiv) and FH levels (Figure 4Biv) were higher compared to N. Our IHC results corroborated the RT-qPCR and WB results, which revealed higher properdin expression in both PE and GDM placentae, and significantly lower FH expression in PE and high in GDM compared to N, suggesting association of properdin and FH levels with PE and GDM-associated pathologies.

Figure 4

Higher expression of key complement components, C3 and C5, in PE placentae, whereas low C3 level in the umbilical cord of PE and GDM

In the case of PE, both the C3 (Figures 5Ai, ii) and C5 (Figures 5Bi, ii) protein expressions in placentae were significantly higher compared to the N placentae, suggesting complement overactivation in the PE placenta. GDM placentae did not show any significant differences in C3 and C5 expression compared to N (Figures 5Av, 5Avi, 5Bv, 5Bvi).

Figure 5

In umbilical cord tissue, the complement protein expression maintained a similar pattern in both PE and GDM. C3 protein expression was significantly lower over the control (N-UC) in both PE-UC (Figures 5Aiii, iv) and GDM-UC (Figures 5Avii, viii). Unlike placentae, C3 level was low in the umbilical cord tissue of PE. However, no differences in the expression of C5 were observed in PE-UC (Figures 5Biii, iv) as well as GDM-UC (Figure 5Bvii, viii) when compared to N-UC.

Higher protein expression of properdin, C3 and C5, and lower FH protein in first trimester RPL placentae

The 3^rd adverse pregnancy group considered in this study was recurrent pregnancy loss (RPL); here the available placental tissue was at its first trimester decidua. Due to the unavailability of the matched control placenta, RT-qPCR and WB results of RPL were compared with 3^rd trimester healthy placental tissues (N) that were used as a healthy control for PE and GDM. The H&E staining of RPL showed dilated blood vessels in the decidua, fibrinoid deposition and intervillous haemorrhage (Figure 6A). MT staining revealed dense collagen deposition (blue stain) throughout the placental section (Figure 6B). Due to unavailability of the control tissue as mentioned above, IHC analysis comparison couldn’t be done with N tissue. Our IHC staining revealed presence of properdin (Figure 6Ci) as well as FH (Figure 6Cii) inside the chorionic villi and decidual vessels (Figure 6C). In our earlier report, we have shown the presence of FH in the syncytiotrophoblasts of 1^st trimester healthy placenta (56).

Figure 6

At the protein level, significantly increased properdin expression (Figures 6Ei, ii) in RPL was found in comparison to N, together with C3 (Figures 6Ev, vi) and C5 (Figures 6Evii, viii) protein expression, indicating more complement activation in RPL. Following the same pattern as PE, significantly low levels of FH mRNA (Figure 6Dii) and protein (Figures 6Eiii, iv) were observed in RPL, indicating dysregulated complement activation in RPL similar to PE.

Discussion

Complement system is one of the primitive multi-tiered interacting pathways that is a crucial part of the innate immunity in humans. This complex complement proteolytic cascade can be triggered, initially by engaging with soluble pattern recognition molecules, off shooting bioactive fragments that act as anaphylatoxins and generating MAC, controlling the infectious non-self. The bioactive fragments generated through complement pathways are capable of binding complement receptors expressed on a range of cell types to mediate diverse cellular and molecular responses. During pregnancy, in order to safeguard the foetus, complement regulators at the feto-maternal interface maintain an appropriate complement activation, neither less nor more. With time, the importance of this sentinel system has gained importance, reshaping our understanding to complement pathobiology in pregnancy. In this study, we have considered two important complement regulators, properdin and FH, which if modulated, can fuel the inflammatory response in the placenta risking the life of both mother and the foetus. Healthy term-end (third trimester) placenta was considered as control for comparison with the pathological cases. The limitation of the study is lack of a gestational age-matched placenta, while comparing with RPL placenta. Using a first trimester healthy placenta would have been scientifically ideal as epigenetic remodelling in about 7519 of 12000 genes took place from first to third trimester placenta (91). Ethical constrains precluded the availability of such samples. Thus, we compared the properdin and FH levels in RPL with the available third trimester healthy placenta (control). However, to the best of our knowledge, this is the first study which compares two opposing complement regulators in three adverse pregnancy conditions.

Properdin, which is the only known up-regulator of complement alternative pathway, was significantly high in the placenta at both mRNA and protein level in all the three adverse pregnancy cases, PE, GDM and RPL. Properdin was also significantly high in the umbilical cord of both PE and GDM at mRNA level; however, the expression was not significant at the protein level. This discordance between transcript and protein expression in UC could be due to post-transcriptional or post-translational modifications, or due to protein degradation. To consider samples matching, the gestational age GDM cohort were reduced down to four; considering larger cohort studies might lead to significant findings. The PE and GDM placental tissue considered in the study had thickened foetal blood capillaries and higher syncytial knots compared to healthy placenta. The placental tissues of RPL exhibited dilated blood vessels, fibrinoid deposition and intervillous haemorrhage. PE and GDM placental tissues had excessive and irregular collagen deposition. Fibrotic alterations were frequently seen in PE and GDM placentae, especially in the villous stroma or perivillous fibrinoid regions, which implies tissue remodelling brought about by persistent hypoxia or ischaemia. Excessive collagen deposition in fibrotic villi indicates prolonged ischaemic damage and compromised placental perfusion (88–90, 92). Altered extracellular matrix (ECM) remodelling affects nutrient and oxygen exchange between mother and foetus, and impaired placental function causes poor vascularization or abnormal development of placenta in PE and GDM. Immunohistochemistry results also showed significantly higher level of properdin expression in PE and GDM at the syncytiotrophoblast regions and syncytial knots compared to healthy placentae (N). When compared with GDM, the properdin expression in PE placentae was significantly higher, which possibly explains exaggerated inflammatory condition in PE.

The observed overexpression of properdin in the diseased placentae (PE, GDM and RPL) compared to healthy placentae (N) can be correlated with the local inflammatory environment evident in adverse pregnancies. Immune system dysfunction, particularly a Th1/Th2 cytokine imbalance at the foetal-maternal interface, is observed in PE, GDM and in RPL (93–99). In response to placental ischemia and hypoxia in PE, NK and CD4⁺ T cells are activated, generating pro-inflammatory mediators and reactive oxygen species, which promote the cycle of oxidative stress and endothelial damage (94, 100). TNF-α, IL-6 and IL-17 are among the inflammatory cytokines that are increased in PE, along with persistent immunological activation (101). An imbalance of T-helper cell subsets, with a reduction in regulatory T cells (Tregs) and a rise in Th1 and Th17 cells, further characterizes the pro-inflammatory state in PE (95, 96, 102, 103). In GDM placenta, overexpression of inflammatory markers and hormones exacerbates maternal insulin resistance. The inflammation could spread systemically (throughout the body), contributing to insulin resistance, which is a key problem in GDM. Th1/Th2 cytokine imbalance is caused by increased pro-inflammatory cytokines (e.g., TNF-α, IL-6, IL-8) and reduced anti-inflammatory cytokines (like IL-10), often due to abnormal leukocyte infiltration (104). The metabolic disturbances that cause GDM often continue post-partum and may progress to Type 2 Diabetes Mellitus (T2DM). In GDM, CD68⁺ and CD14⁺ macrophages are increased, suggesting their contribution to inflammation. Cytokines released by these cells (IL-6 and TNF) can trigger inflammation within the placenta (97). In the case of RPL, little is known about its underlying immunological mechanisms; however, predominance of Th1 pro-inflammatory immune response is indicated (99).

In PE placenta, enhanced neutrophil infiltration with higher NETosis has been observed (105). NET-derived cell-free DNA, complexed with myeloperoxidase (MPO; a neutrophil granular protein), was was considerably higher in PE serum compared to healthy mothers that gradually increased towards the term end (106). Similarly, neutrophil infiltrates were higher in the chorionic villi of GDM mothers in their median gestational age when compared to healthy mothers at term end. This study also showed that neutrophils isolated from GDM mothers exhibited greater tendency to perform NETosis and high glucose condition can further promote pro-NETosis activity (107). Interestingly a recent study also suggested an increase in the NETosis markers (MPO, H2A and H2B) in RPL mothers that might contribute to its pathology (108). It is important to note that MPO degranulation from activated neutrophils can influence properdin-mediated complement alternative pathway (109). Neutrophils are a key extrahepatic and local source of properdin (110), which is secreted upon stimulation by inflammatory signals. Properdin amplifies the alternative pathway, enhancing immune responses against pathogens. Properdin can offer a platform for de novo assembly of C3 convertase, which will go on to activate the alternative pathway. Properdin binds and stabilises C3 convertase and makes it easier for C3b to engage with factor B, which causes C3bBb to assemble on the cell surface and mediate complement activation (111). Properdin can also initiate the alternative pathway activation on neutrophils and platelets attached to NETs and enhance C5a generation, by stabilizing convertase and acting as a positive feedback loop for the alternative pathway amplification (59). This uncontrolled activation of the alternative pathway by neutrophil-derived properdin can worsen inflammation, contributing to autoimmune diseases (e.g., vasculitis, rheumatoid arthritis) and tissue damage (112). In pregnancy, this excessive activation can disrupt embryo implantation and placental development, cause placental ischemia/hypoxia, impair foetal growth, and create a cytotoxic, pro-inflammatory environment by disturbing angiogenic factor balance (104). In our study, the GDM placentae showed no difference in the C3 and C5 protein levels compared to N placentae. This possibly indicates complement-independent function of properdin in GDM. Properdin can mediate both complement-dependent as well as complement-independent functions, aggravating the inflammatory conditions. Properdin can act as an opsonin promoting phagocytic clearance of apoptotic or necrotic target cells independent of complement activation (113). Properdin can directly bind to NKp46, a mature NK cell ligand; cfp (properdin gene) silencing can abolish NKp46 reporter cell activation. Properdin-deficient individuals frequently acquire Neisseria meningitidis (Nm) infection. However, properdin treatment during Nm infection were found to be dependent on NKp46 (114). In a study involving a non-obese GDM mouse model, a significant increase in CD11b⁺ NK cells was observed in the peripheral blood. After pregnancy, when these GDM mice were intraperitoneally injected with streptozotocin (STZ), intrauterine growth restriction occurred with significant increase in the number of CD27^-CD11b⁺ NK cells in the decidua with enhanced cytotoxic activity (115). Thus, properdin in PE and RPL could be involved in both complement-dependent and -independent pathways, but in GDM, it could be following complement independent pathway as both C3 and C5 levels were low in the placenta.

The other regulator considered in this study is FH, which mainly controls the complement alternative pathway by preventing excessive immune activation. FH inhibits the formation and promotes the breakdown of C3 and C5 convertases (116). FH can prevent complement-mediated tissue damage (73, 74, 117). Recent research shows that by competing with C1q for binding to targets such as cardiolipin, lipid A, E. coli (118), and beta-amyloid, FH also negatively controls the classical pathway (119), thereby reducing inflammation. It is primarily produced in the liver (hepatocytes and Kupffer cells), but also in kidney, spleen, heart, lungs, brain, eyes, pancreas, placenta and adipose tissue (120). In the present study, unlike properdin, which was significantly high in the placenta of all the three diseases (PE, GDM and RPL), FH was high only in case of GDM and significantly low in PE and RPL. In PE placenta, where FH was significantly very low, the C3 and C5 protein levels were significantly high. Other studies have also reported higher level of C3, C3b, C3d, C4d C5a, factor B, MBL, C9 and sC5b-9 in PE (32, 33, 35–39, 41, 42, 44, 121). We have recently demonstrated that FH serum level significantly declines in PE mothers with increase in gestational age (3^rd trimester < 1^st trimester) (56). This near absence of FH in PE placenta could be one of the likely reasons for dysregulated complement activation. Reduced FH expression in PE can also be due to its mutation. Severe PE is predisposed to develop in five rare variants of the FH gene: L3V, R127H, R166Q, C1077S, and N1176K (122). Additionally, anti-FH autoantibodies (123), FH intake, or the fact that a significant illness load overburdens FH can all contribute to FH reduction (54). In the case of 1^st trimester placentae of RPL, FH mRNA as well as protein levels were significantly lower when compared to 3^rd trimester healthy placentae (N). FH polymorphism (CFH rs1065489 G>T/CFH rs1061170 T>C) has been associated with reduced risk of RPL (124). In our study, RPL placentae showed significantly higher C3 and C5 protein levels when compared with term end healthy placenta. Previous studies have pointed towards the role of complement in spontaneous abortion, where high C5a level was observed in maternal circulation while the complement regulators, CD46 and CD55, were found three-fold decreased compared to control (125). Thus, low levels of complement inhibitors in RPL could be one possible reason for higher complement activation. Upregulation of properdin and downregulation of FH in PE and RPL, as observed in this study, could be the causal drivers of pathology or secondary consequences of the inflammatory milieu characteristic of these pregnancy-related disorders. Whilst altered properdin and FH expression may contribute to local complement dysregulation, it is also likely to be amplified by upstream inflammatory processes inherent to PE and RPL. Together, these findings identify a previously uncharacterized properdin-FH imbalance that may contribute to the distinct pathophysiological profiles in PE and RPL.

As opposed to PE and RPL, GDM placenta as well as GDM-UC showed higher FH compared to N. Our result is consistent with the previous report that demonstrated high FH level in GDM compared to non-GDM serum samples collected in the third trimester of pregnancy (126). High FH level in GDM could be for avoiding unwanted complement activation in the placenta as we have observed low C3 and C5 levels in GDM. Thus, the pathological condition may not be related to complement over-activation in our GDM cohorts. In the umbilical cord, C3 protein expression was significantly lower in GDM compared to healthy ones. We have recently shown that in the case of healthy pregnancy, FH mRNA was highly expressed in human umbilical vein endothelial cells (HUVECs) derived from the UC, compared to decidual endothelial cells, extravillous trophoblasts and decidual stromal cells (56). Higher expression of FH in HUVECs is possibly for maintaining tight regulation on complement activation in the UC, which directly communicates with the foetus. In adipose tissue, high level of FH is linked with obesity, inflammation, insulin resistance, and decreased high density lipoprotein (HDL) cholesterol, suggesting a role of FH in metabolic diseases (127). In addition to its well-known role in defending the body against infections, the complement system is also crucial for metabolism. Human metabolic disorders are regularly associated with elevated levels of certain complement proteins. The metabolic syndrome (MetS) is more likely to develop in patients with greater levels of C3 and C4 (128, 129). High blood glucose, high triglycerides (TG), insulin resistance, and diabetes are all linked to elevated C3, which is especially effective in predicting future risk (130–132). Increased expression of C1 components (C1q, C1r, and C1s) in fat cells (adipocytes) in insulin-resistant individuals suggests that complement is activated in response to metabolic stress (133). FH levels increase with obesity, presumably as a defence mechanism against excessive complement activation. Research on human clinical samples showed that human fat tissue produces FH, particularly in stromal cells and, to a lesser extent, in adipocytes. Insulin resistance and worse metabolic health (such as lower HDL and greater obesity markers) are correlated with higher levels of FH. Higher FH expression, however, may aid in lowering detrimental inflammation in subcutaneous fat (127, 134). In a study involving Chinese mothers who were in their early pregnancy, high level of mannan-binding lectin-associated serine protease (MASP1 and MASP2) were found associated with GDM (48). In second trimester GDM mothers, increase levels of C3, C4 and FH were also observed (126, 135). A recent study in women with GDM, who developed PE during mid-pregnancy, showed high factor B (FB), FH and C3 levels in circulation compared to GDM subjects without PE (136). FB, an alternative pathway activator, can compete with FH for binding with C3b. Thus, when FH level declines in GDM patients, FB can activate the alternative pathway, increasing the risk of developing PE in GDM subjects. At the same time, activation of the lectin pathway in GDM could lead to the production of inflammatory mediators that may influence the local expression of properdin. This possibly explains the concurrent high levels of properdin and FH in GDM compared to healthy subjects.

In addition to the unavoidable limitation of unmatched gestational ages for RPL samples, the relatively small sample size for cohorts as well as a lack of functional complement activity assays are the limitations of our study. However, the present work shows how upregulation of the positive regulator properdin coincides with a reduction in the key negative regulator FH in adverse pregnancies. This study highlights the paradigm of dysregulated expression of two vital but diabolically opposite complement regulators at the feto-maternal interface in pathological conditions, offering an opportunity for future mechanistic and functional studies.

Conclusions

The primary conclusions of this investigation were that properdin, the the only upregulator of complement alternative pathway, showed very high expression in PE, GDM and RPL and could add to the high inflammatory condition of the placenta and contribute to the pathobiology. Lower level of FH in PE and RPL could contribute to dysregulated complement activation in the placenta. In GDM, the pathogenic pathway may not be directly complement activation mediated due to the high presence of FH in the placenta and in the umbilical cord. In GDM, several other factors contributing to insulin resistance may be in crosstalk with the complement proteins accounting for the pathogenesis. Thus, understanding the mechanistic pathway that leads to the differential distribution of properdin and FH in PE, GDM and RPL at the feto-maternal interface will be of paramount for complement-related diagnosis and therapeutics.

References

• 1

  Burton GJ Fowden AL . The placenta: a multifaceted, transient organ. Philos Trans R Soc B: Biol Sci. (2015) 370:20140066. doi: 10.1098/rstb.2014.0066

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 2

  Gaccioli F Lager S . Placental nutrient transport and intrauterine growth restriction. Front Physiol. (2016) 7:40. doi: 10.3389/fphys.2016.00040

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 3

  Hay WW . The placenta. Not just a conduit for maternal fuels. Diabetes. (1991) 40 Suppl 2:44–50. doi: 10.2337/diab.40.2.s44

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 4

  Puttaiah A Kirthan JPA Sadanandan DM Somannavar MS . Inflammatory markers and their association with preeclampsia among pregnant women: A systematic review and meta-analysis. Clin Biochem. (2024) 129:110778. doi: 10.1016/j.clinbiochem.2024.110778

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 5

  Assani A-D Boldeanu L Siloşi I Boldeanu MV Dijmărescu AL Assani M-Z et al . Pregnancy under pressure: oxidative stress as a common thread in maternal disorders. Life (Basel). (2025) 15(9):1348. doi: 10.3390/life15091348

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 6

  Baker BC Heazell AEP Sibley C Wright R Bischof H Beards F et al . Hypoxia and oxidative stress induce sterile placental inflammation in vitro. Sci Rep. (2021) 11:7281. doi: 10.1038/s41598-021-86268-1

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 7

  Louwen F Kreis N-N Ritter A Yuan J . Maternal obesity and placental function: impaired maternal-fetal axis. Arch Gynecol Obstet. (2024) 309:2279–88. doi: 10.1007/s00404-024-07462-w

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 8

  Mor G Cardenas I . The immune system in pregnancy: A unique complexity. Am J Reprod Immunol. (2010) 63:425–33. doi: 10.1111/j.1600-0897.2010.00836.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 9

  Reichhardt MP Lundin K Lokki AI Recher G Vuoristo S Katayama S et al . Complement in human pre-implantation embryos: attack and defense. Front Immunol. (2019) 10:2234. doi: 10.3389/fimmu.2019.02234

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 10

  Yoshinaga K . A sequence of events in the uterus prior to implantation in the mouse. J Assist Reprod Genet. (2013) 30:1017–22. doi: 10.1007/s10815-013-0093-z

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 11

  Madhukaran SP Yasmin H Kishore U . Innate immune mechanisms in normal and adverse pregnancy. Adv Exp Med Biol. (2025) 1476:339–79. doi: 10.1007/978-3-031-85340-1_14

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 12

  Bulla R Bossi F Tedesco F . The complement system at the embryo implantation site: Friend or foe? Front Immunol. (2012) 3:55. doi: 10.3389/fimmu.2012.00055

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 13

  Girardi G Lingo JJ Fleming SD Regal JF . Essential role of complement in pregnancy: from implantation to parturition and beyond. Front Immunol. (2020) 11:1681. doi: 10.3389/fimmu.2020.01681

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 14

  Merle NS Church SE Fremeaux-Bacchi V Roumenina LT . Complement system part I - molecular mechanisms of activation and regulation. Front Immunol. (2015) 6:262. doi: 10.3389/fimmu.2015.00262

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 15

  Murugaiah V Varghese PM Beirag N De Cordova S Sim RB Kishore U . Complement proteins as soluble pattern recognition receptors for pathogenic viruses. Viruses. (2021) 13(5):824. doi: 10.3390/v13050824

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 16

  Sahu SK Kulkarni DH Ozanturk AN Ma L Kulkarni HS . Emerging roles of the complement system in host-pathogen interactions. Trends Microbiol. (2022) 30:390–402. doi: 10.1016/j.tim.2021.09.002

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 17

  Morris KM Aden DP Knowles BB Colten HR . Complement biosynthesis by the human hepatoma-derived cell line HepG2. J Clin Invest. (1982) 70:906–13. doi: 10.1172/jci110687

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 18

  Morgan BP Gasque P . Extrahepatic complement biosynthesis: where, when and why? Clin Exp Immunol. (1997) 107:1–7. doi: 10.1046/j.1365-2249.1997.d01-890.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 19

  Madhukaran SP Alhamlan FS Kale K Vatish M Madan T Kishore U . Role of collectins and complement protein C1q in pregnancy and parturition. Immunobiology. (2016) 221:1273–88. doi: 10.1016/j.imbio.2016.06.002

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 20

  Pellis V De Seta F Crovella S Bossi F Bulla R Guaschino S et al . Mannose binding lectin and C3 act as recognition molecules for infectious agents in the vagina. Clin Exp Immunol. (2005) 139:120–6. doi: 10.1111/j.1365-2249.2005.02660.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 21

  He Y-D Xu B-N Song D Wang Y-Q Yu F Chen Q et al . Normal range of complement components during pregnancy: A prospective study. Am J Reprod Immunol. (2020) 83:e13202. doi: 10.1111/aji.13202

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 22

  Derzsy Z Prohászka Z Rigó J Füst G Molvarec A . Activation of the complement system in normal pregnancy and preeclampsia. Mol Immunol. (2010) 47:1500–6. doi: 10.1016/j.molimm.2010.01.021

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 23

  Johnson PM Faulk WP . Immunological studies of human placentae: identification and distribution of proteins in immature chorionic villi. Immunology. (1978) 34:1027–35.

  • Pubmed Abstract
  • Google Scholar

• 24

  Faulk WP Jarret R Keane M Johnson PM Boackle RJ . Immunological studies of human placentae: complement components in immature and mature chorionic villi. Clin Exp Immunol. (1980) 40:299–305.

  • Pubmed Abstract
  • Google Scholar

• 25

  Reichhardt MP Meri S . Intracellular complement activation-An alarm raising mechanism? Semin Immunol. (2018) 38:54–62. doi: 10.1016/j.smim.2018.03.003

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 26

  King BC Renström E Blom AM . Intracellular cytosolic complement component C3 regulates cytoprotective autophagy in pancreatic beta cells by interaction with ATG16L1. Autophagy. (2019) 15:919–21. doi: 10.1080/15548627.2019.1580515

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 27

  Lee Y Cheong AWY Chow W Lee K Yeung WSB . Regulation of complement-3 protein expression in human and mouse oviducts. Mol Reprod Dev. (2009) 76:301–8. doi: 10.1002/mrd.20955

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 28

  Chow W Lee Y Wong P Chung M Lee K Yeung WS . Complement 3 deficiency impairs early pregnancy in mice. Mol Reprod Dev. (2009) 76:647–55. doi: 10.1002/mrd.21013

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 29

  Agostinis C Bulla R Tripodo C Gismondi A Stabile H Bossi F et al . An alternative role of C1q in cell migration and tissue remodeling: contribution to trophoblast invasion and placental development. J Immunol. (2010) 185:4420–9. doi: 10.4049/jimmunol.0903215

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 30

  Agostinis C Mangogna A Balduit A Kishore U Bulla R . A non-redundant role of complement protein C1q in normal and adverse pregnancy. Explor Immunol. (2022) 2:622–36. doi: 10.37349/ei.2022.00072

  • CrossRef
  • Google Scholar

• 31

  Bulla R Agostinis C Bossi F Rizzi L Debeus A Tripodo C et al . Decidual endothelial cells express surface-bound C1q as a molecular bridge between endovascular trophoblast and decidual endothelium. Mol Immunol. (2008) 45:2629–40. doi: 10.1016/j.molimm.2007.12.025

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 32

  Lokki AI Heikkinen-Eloranta J Jarva H Saisto T Lokki ML Laivuori H et al . Complement activation and regulation in preeclamptic placenta. Front Immunol. (2014) 5:312. doi: 10.3389/fimmu.2014.00312

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 33

  Sinha D Wells M Faulk WP . Immunological studies of human placentae: complement components in pre-eclamptic chorionic villi. Clin Exp Immunol. (1984) 56:175–84.

  • Pubmed Abstract
  • Google Scholar

• 34

  Regal JF Gilbert JS Burwick RM . The complement system and adverse pregnancy outcomes. Mol Immunol. (2015) 67:56–70. doi: 10.1016/j.molimm.2015.02.030

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 35

  Buurma A Cohen D Veraar K Schonkeren D Claas FH Bruijn JA et al . Preeclampsia is characterized by placental complement dysregulation. Hypertension. (2012) 60:1332–7. doi: 10.1161/HYPERTENSIONAHA.112.194324

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 36

  Velickovic I Dalloul M Wong KA Bakare O Schweis F Garala M et al . Complement factor B activation in patients with preeclampsia. J Reprod Immunol. (2015) 109:94–100. doi: 10.1016/j.jri.2014.12.002

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 37

  Lynch AM Eckel RH Murphy JR Gibbs RS West NA Giclas PC et al . Prepregnancy obesity and complement system activation in early pregnancy and the subsequent development of preeclampsia. Am J Obstet Gynecol. (2012) 206:428.e1–8. doi: 10.1016/j.ajog.2012.02.035

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 38

  Girardi G Yarilin D Thurman JM Holers VM Salmon JE . Complement activation induces dysregulation of angiogenic factors and causes fetal rejection and growth restriction. J Exp Med. (2006) 203:2165–75. doi: 10.1084/jem.20061022

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 39

  Denny KJ Woodruff TM Taylor SM Callaway LK . Complement in pregnancy: A delicate balance. Am J Reprod Immunol. (2013) 69:3–11. doi: 10.1111/aji.12000

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 40

  Burwick RM Java A Regal JF . The role of complement in normal pregnancy and preeclampsia. Front Immunol. (2025) 16:1643896. doi: 10.3389/fimmu.2025.1643896

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 41

  Rampersad R Barton A Sadovsky Y Nelson DM . The C5b-9 Membrane Attack Complex of Complement Activation Localizes to Villous Trophoblast Injury in vivo and Modulates Human Trophoblast Function in vitro. Placenta. (2008) 29:855–61. doi: 10.1016/j.placenta.2008.07.008

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 42

  Agostinis C Bossi F Masat E Radillo O Tonon M De Seta F et al . MBL interferes with endovascular trophoblast invasion in pre-eclampsia. Clin Dev Immunol. (2012) 2012:484321. doi: 10.1155/2012/484321

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 43

  Wang CC Yim KW Poon TCW Choy KW Chu CY Lui WT et al . Innate immune response by ficolin binding in apoptotic placenta is associated with the clinical syndrome of preeclampsia. Clin Chem. (2007) 53:42–52. doi: 10.1373/clinchem.2007.074401

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 44

  Denny KJ Coulthard LG Finnell RH Callaway LK Taylor SM Woodruff TM . Elevated complement factor C5a in maternal and umbilical cord plasma in preeclampsia. J Reprod Immunol. (2013) 97:211–6. doi: 10.1016/j.jri.2012.11.006

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 45

  He Y-D Xu B-N Wang M-L Wang Y-Q Yu F Chen Q et al . Dysregulation of complement system during pregnancy in patients with preeclampsia: A prospective study. Mol Immunol. (2020) 122:69–79. doi: 10.1016/j.molimm.2020.03.021

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 46

  Meuleman T Cohen D Swings GMJS Veraar K Claas FHJ Bloemenkamp KWM . Increased complement C4d deposition at the maternal-fetal interface in unexplained recurrent miscarriage. J Reprod Immunol. (2016) 113:54–60. doi: 10.1016/j.jri.2015.12.001

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 47

  Lynch AM Gibbs RS Murphy JR Byers T Neville MC Giclas PC et al . Complement activation fragment Bb in early pregnancy and spontaneous preterm birth. Am J Obstet Gynecol. (2008) 199:354.e1–8. doi: 10.1016/j.ajog.2008.07.044

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 48

  Gao M Li J Zhang R Li N Li W Zhang S et al . Serum mannan-binding lectin-associated serine proteases in early pregnancy for gestational diabetes in Chinese pregnant women. Front Endocrinol (Lausanne). (2023) 14:1230244. doi: 10.3389/fendo.2023.1230244

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 49

  Holmes CH Simpson KL Okada H Okada N Wainwright SD Purcell DF et al . Complement regulatory proteins at the feto-maternal interface during human placental development: distribution of CD59 by comparison with membrane cofactor protein (CD46) and decay accelerating factor (CD55). Eur J Immunol. (1992) 22:1579–85. doi: 10.1002/eji.1830220635

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 50

  Holmes CH Simpson KL Wainwright SD Tate CG Houlihan JM Sawyer IH et al . Preferential expression of the complement regulatory protein decay accelerating factor at the fetomaternal interface during human pregnancy. J Immunol. (1990) 144:3099–105. doi: 10.4049/jimmunol.144.8.3099

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 51

  Nishikori K Noma J Hirakawa S Amano T Kudo T . The change of membrane complement regulatory protein in chorion of early pregnancy. Clin Immunol Immunopathol. (1993) 69:167–74. doi: 10.1006/clin.1993.1166

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 52

  Hsi BL Hunt JS Atkinson JP . Differential expression of complement regulatory proteins on subpopulations of human trophoblast cells. J Reprod Immunol. (1991) 19:209–23. doi: 10.1016/0165-0378(91)90036-p

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 53

  Meri S Waldmann H Lachmann PJ . Distribution of protectin (CD59), a complement membrane attack inhibitor, in normal human tissues. Lab Invest. (1991) 65:532–7.

  • Pubmed Abstract
  • Google Scholar

• 54

  Cortes C Desler C Mazzoli A Chen JY Ferreira VP . The role of properdin and Factor H in disease. Adv Immunol. (2022) 153:1–90. doi: 10.1016/bs.ai.2021.12.001

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 55

  Kouser L Abdul-Aziz M Nayak A Stover CM Sim RB Kishore U . Properdin and factor H: Opposing players on the alternative complement pathway “see-saw. Front Immunol. (2013) 4:93. doi: 10.3389/fimmu.2013.00093

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 56

  Yasmin H Agostinis C Toffoli M Roy T Pegoraro S Balduit A et al . Protective role of complement factor H against the development of preeclampsia. Front Immunol. (2024) 15:1351898. doi: 10.3389/fimmu.2024.1351898

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 57

  Smith CA Pangburn MK Vogel CW Muller-Eberhard HJ . Molecular architecture of human properdin, a positive regulator of the alternative pathway of complement. J Biol Chem. (1984) 259:4582–8. doi: 10.1016/s0021-9258(17)43086-9

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 58

  Blatt AZ Saggu G Kulkarni KV Cortes C Thurman JM Ricklin D et al . Properdin-mediated C5a production enhances stable binding of platelets to granulocytes in human whole blood. J Immunol. (2016) 196:4671–80. doi: 10.4049/jimmunol.1600040

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 59

  Camous L Roumenina L Bigot S Brachemi S Frémeaux-Bacchi V Lesavre P et al . Complement alternative pathway acts as a positive feedback amplification of neutrophil activation. Blood. (2011) 117:1340–9. doi: 10.1182/blood-2010-05-283564

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 60

  Hilhorst M van Paassen P van Rie H Bijnens N Heerings-Rewinkel P van Breda Vriesman P et al . Complement in ANCA-associated glomerulonephritis. Nephrol Dial Transplant. (2017) 32:1302–13. doi: 10.1093/ndt/gfv288

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 61

  Maillard N Wyatt RJ Julian BA Kiryluk K Gharavi A Fremeaux-Bacchi V et al . Current understanding of the role of complement in igA nephropathy. J Am Soc Nephrol. (2015) 26:1503–12. doi: 10.1681/ASN.2014101000

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 62

  Chen JY Cortes C Ferreira VP . Properdin: A multifaceted molecule involved in inflammation and diseases. Mol Immunol. (2018) 102:58–72. doi: 10.1016/j.molimm.2018.05.018

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 63

  Al-Mozaini MA Tsolaki AG Abdul-Aziz M Abozaid SM Al-Ahdal MN Pathan AA et al . Human Properdin Modulates Macrophage: Mycobacterium bovis BCG Interaction via Thrombospondin Repeats 4 and 5. Front Immunol. (2018) 9:533. doi: 10.3389/fimmu.2018.00533

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 64

  Wang Y Miwa T Ducka-Kokalari B Redai IG Sato S Gullipalli D et al . Properdin contributes to allergic airway inflammation through local C3a generation. J Immunol. (2015) 195:1171–81. doi: 10.4049/jimmunol.1401819

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 65

  Kemper C Hourcade DE . Properdin: New roles in pattern recognition and target clearance. Mol Immunol. (2008) 45:4048–56. doi: 10.1016/j.molimm.2008.06.034

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 66

  Sim RB DiScipio RG . Purification and structural studies on the complement-system control protein beta 1H (Factor H). Biochem J. (1982) 205:285–93. doi: 10.1042/bj2050285

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 67

  Whaley K Ruddy S . Modulation of the alternative complement pathways by beta 1 H globulin. J Exp Med. (1976) 144:1147–63. doi: 10.1084/jem.144.5.1147

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 68

  Kishore U Sim RB . Factor H as a regulator of the classical pathway activation. Immunobiology. (2012) 217:162–8. doi: 10.1016/j.imbio.2011.07.024

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 69

  Perkins SJ Nan R Li K Khan S Miller A . Complement Factor H-ligand interactions: Self-association, multivalency and dissociation constants. Immunobiology. (2012) 217:281–97. doi: 10.1016/j.imbio.2011.10.003

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 70

  Weiler JM Daha MR Austen KF Fearon DT . Control of the amplification convertase of complement by the plasma protein beta1H. Proc Natl Acad Sci U.S.A. (1976) 73:3268–72. doi: 10.1073/pnas.73.9.3268

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 71

  Conrad DH Carlo JR Ruddy S . Interaction of beta1H globulin with cell-bound C3b: quantitative analysis of binding and influence of alternative pathway components on binding. J Exp Med. (1978) 147:1792–805. doi: 10.1084/jem.147.6.1792

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 72

  Morgan HP Schmidt CQ Guariento M Blaum BS Gillespie D Herbert AP et al . Structural basis for engagement by complement factor H of C3b on a self surface. Nat Struct Mol Biol. (2011) 18:463–71. doi: 10.1038/nsmb.2018

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 73

  Józsi M . Factor H family proteins in complement evasion of microorganisms. Front Immunol. (2017) 8:571. doi: 10.3389/fimmu.2017.00571

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 74

  Meri S Haapasalo K . Function and dysfunction of complement factor H during formation of lipid-rich deposits. Front Immunol. (2020) 11:611830. doi: 10.3389/fimmu.2020.611830

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 75

  Ferreira VP Pangburn MK Cortés C . Complement control protein factor H: the good, the bad, and the inadequate. Mol Immunol. (2010) 47:2187–97. doi: 10.1016/j.molimm.2010.05.007

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 76

  Parente R Clark SJ Inforzato A Day AJ . Complement factor H in host defense and immune evasion. Cell Mol Life Sci. (2017) 74:1605–24. doi: 10.1007/s00018-016-2418-4

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 77

  Leffler J Herbert AP Norström E Schmidt CQ Barlow PN Blom AM et al . Annexin-II, DNA, and histones serve as factor H ligands on the surface of apoptotic cells. J Biol Chem. (2010) 285:3766–76. doi: 10.1074/jbc.M109.045427

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 78

  Ferluga J Kouser L Murugaiah V Sim RB Kishore U . Potential influences of complement factor H in autoimmune inflammatory and thrombotic disorders. Mol Immunol. (2017) 84:84–106. doi: 10.1016/j.molimm.2017.01.015

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 79

  Hypertension in pregnancy . Report of the american college of obstetricians and gynecologists’ Task force on hypertension in pregnancy. Obstet Gynecol. (2013) 122:1122–31. doi: 10.1097/01.AOG.0000437382.03963.88

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 80

  HAPO Study Cooperative Research Group Metzger BE Lowe LP Dyer AR Trimble ER Chaovarindr U et al . Hyperglycemia and adverse pregnancy outcomes. N Engl J Med. (2008) 358:1991–2002. doi: 10.1056/NEJMoa0707943

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 81

  International Association of Diabetes and Pregnancy Study Groups Consensus Panel Metzger BE Gabbe SG Persson B Buchanan TA Catalano PA et al . International association of diabetes and pregnancy study groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care. (2010) 33:676–82. doi: 10.2337/dc09-1848

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 82

  Clement EG Horvath S McAllister A Koelper NC Sammel MD Schreiber CA . The language of first-trimester nonviable pregnancy: patient-reported preferences and clarity. Obstet Gynecol. (2019) 133:149–54. doi: 10.1097/AOG.0000000000002997

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 83

  American College of Obstetricians and Gynecologists' Committee on Practice Bulletins—Gynecology . ACOG practice bulletin no. 200: early pregnancy loss. Obstet Gynecol. (2018) 132:e197–207. doi: 10.1097/AOG.0000000000002899

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 84

  Practice Committee of the American Society for Reproductive Medicine . Electronic address: asrm@asrm.org. Definitions of infertility and recurrent pregnancy loss: a committee opinion. Fertil Steril. (2020) 113:533–5. doi: 10.1016/j.fertnstert.2019.11.025

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 85

  Kale K Vishwekar P Balsarkar G Jassawalla MJ Sawant G Madan T . Differential levels of surfactant protein A, surfactant protein D, and progesterone to estradiol ratio in maternal serum before and after the onset of severe early-onset preeclampsia. Am J Reprod Immunol. (2020) 83(2):e13208. doi: 10.1111/aji.13208

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 86

  Pirker R Pereira JR von Pawel J Krzakowski M Ramlau R Park K et al . EGFR expression as a predictor of survival for first-line chemotherapy plus cetuximab in patients with advanced non-small-cell lung cancer: analysis of data from the phase 3 FLEX study. Lancet Oncol. (2012) 13:33–42. doi: 10.1016/S1470-2045(11)70318-7

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 87

  Varghese F Bukhari AB Malhotra R De A . IHC Profiler: an open source plugin for the quantitative evaluation and automated scoring of immunohistochemistry images of human tissue samples. PloS One. (2014) 9:e96801. doi: 10.1371/journal.pone.0096801

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 88

  Nikitina ER Mikhailov AV Nikandrova ES Frolova EV Fadeev AV Shman VV et al . In preeclampsia endogenous cardiotonic steroids induce vascular fibrosis and impair relaxation of umbilical arteries. J Hypertens. (2011) 29:769–76. doi: 10.1097/HJH.0b013e32834436a7

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 89

  Ohmaru-Nakanishi T Asanoma K Fujikawa M Fujita Y Yagi H Onoyama I et al . Fibrosis in preeclamptic placentas is associated with stromal fibroblasts activated by the transforming growth factor-β1 signaling pathway. Am J Pathol. (2018) 188:683–95. doi: 10.1016/j.ajpath.2017.11.008

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 90

  Feng Y Chen X Wang H Chen X Lan Z Li P et al . Collagen I induces preeclampsia-like symptoms by suppressing proliferation and invasion of trophoblasts. Front Endocrinol (Lausanne). (2021) 12:664766. doi: 10.3389/fendo.2021.664766

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 91

  Sitras V Fenton C Paulssen R Vårtun Å Acharya G . Differences in gene expression between first and third trimester human placenta: a microarray study. PloS One. (2012) 7:e33294. doi: 10.1371/journal.pone.0033294

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 92

  Shi J-W Lai Z-Z Yang H-L Yang S-L Wang C-J Ao D et al . Collagen at the maternal-fetal interface in human pregnancy. Int J Biol Sci. (2020) 16:2220–34. doi: 10.7150/ijbs.45586

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 93

  Powe CE Levine RJ Karumanchi SA . Preeclampsia, a disease of the maternal endothelium: the role of antiangiogenic factors and implications for later cardiovascular disease. Circulation. (2011) 123:2856–69. doi: 10.1161/CIRCULATIONAHA.109.853127

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 94

  Shah DA Khalil RA . Bioactive factors in uteroplacental and systemic circulation link placental ischemia to generalized vascular dysfunction in hypertensive pregnancy and preeclampsia. Biochem Pharmacol. (2015) 95:211–26. doi: 10.1016/j.bcp.2015.04.012

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 95

  Ribeiro VR Romao-Veiga M Romagnoli GG Matias ML Nunes PR Borges VTM et al . Association between cytokine profile and transcription factors produced by T-cell subsets in early- and late-onset pre-eclampsia. Immunology. (2017) 152:163–73. doi: 10.1111/imm.12757

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 96

  Rahimzadeh M Norouzian M Arabpour F Naderi N . Regulatory T-cells and preeclampsia: an overview of literature. Expert Rev Clin Immunol. (2016) 12:209–27. doi: 10.1586/1744666X.2016.1105740

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 97

  Lekva T Norwitz ER Aukrust P Ueland T . Impact of systemic inflammation on the progression of gestational diabetes mellitus. Curr Diabetes Rep. (2016) 16:26. doi: 10.1007/s11892-016-0715-9

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 98

  Plows JF Stanley JL Baker PN Reynolds CM Vickers MH . The pathophysiology of gestational diabetes mellitus. Int J Mol Sci. (2018) 19(11):3342. doi: 10.3390/ijms19113342

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 99

  Talukdar A Sharma KA Rai R Deka D Rao DN . Effect of coenzyme Q10 on th1/th2 paradigm in females with idiopathic recurrent pregnancy loss. Am J Reprod Immunol. (2015) 74:169–80. doi: 10.1111/aji.12376

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 100

  Vaka R Deer E LaMarca B . Is mitochondrial oxidative stress a viable therapeutic target in preeclampsia? Antioxid (Basel). (2022) 11(2):210. doi: 10.3390/antiox11020210

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 101

  Cornelius DC . Preeclampsia: from inflammation to immunoregulation. Clin Med Insights Blood Disord. (2018) 11:1179545X17752325. doi: 10.1177/1179545X17752325

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 102

  Boij R Mjösberg J Svensson-Arvelund J Hjorth M Berg G Matthiesen L et al . Regulatory T-cell subpopulations in severe or early-onset preeclampsia. Am J Reprod Immunol. (2015) 74:368–78. doi: 10.1111/aji.12410

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 103

  Steinborn A Schmitt E Kisielewicz A Rechenberg S Seissler N Mahnke K et al . Pregnancy-associated diseases are characterized by the composition of the systemic regulatory T cell (Treg) pool with distinct subsets of Tregs. Clin Exp Immunol. (2012) 167:84–98. doi: 10.1111/j.1365-2249.2011.04493.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 104

  Laresgoiti-Servitje E . A leading role for the immune system in the pathophysiology of preeclampsia. J Leukoc Biol. (2013) 94:247–57. doi: 10.1189/jlb.1112603

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 105

  Gupta A Hasler P Gebhardt S Holzgreve W Hahn S . Occurrence of neutrophil extracellular DNA traps (NETs) in pre-eclampsia: a link with elevated levels of cell-free DNA? Ann N Y Acad Sci. (2006) 1075:118–22. doi: 10.1196/annals.1368.015

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 106

  Sur Chowdhury C Hahn S Hasler P Hoesli I Lapaire O Giaglis S . Elevated levels of total cell-free DNA in maternal serum samples arise from the generation of neutrophil extracellular traps. Fetal Diagn Ther. (2016) 40:263–7. doi: 10.1159/000444853

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 107

  Stoikou M Grimolizzi F Giaglis S Schäfer G van Breda SV Hoesli IM et al . Gestational diabetes mellitus is associated with altered neutrophil activity. Front Immunol. (2017) 8:702. doi: 10.3389/fimmu.2017.00702

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 108

  Abed S Shani WS Alharoon DS . Immunohistochemical expression of netosis markers (MPO, H2A, H2B) in placenta of RPL women in Basrah Province. Romanian J Med Pract. (2024) 19:213–8. doi: 10.37897/RJMP.2024.3.4

  • CrossRef
  • Google Scholar

• 109

  O’Flynn J Dixon KO Faber Krol MC Daha MR van Kooten C . Myeloperoxidase directs properdin-mediated complement activation. J Innate Immun. (2014) 6:417–25. doi: 10.1159/000356980

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 110

  Wirthmueller U Dewald B Thelen M Schäfer MK Stover C Whaley K et al . Properdin, a positive regulator of complement activation, is released from secondary granules of stimulated peripheral blood neutrophils. J Immunol. (1997) 158:4444–51. doi: 10.4049/jimmunol.158.9.4444

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 111

  Pillemer L Blum L Lepow IH Ross OA Todd EW Wardlaw AC . The properdin system and immunity: demonstration and isolation of a new serum protein, properdin, and its role in immune phenomena. Science (New York, N.Y.). (1954) 120(3112):279–85. doi: 10.1126/science.120.3112.279

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 112

  Kimura Y Zhou L Miwa T Song W-C . Genetic and therapeutic targeting of properdin in mice prevents complement-mediated tissue injury. J Clin Invest. (2010) 120:3545–54. doi: 10.1172/jci41782

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 113

  Kemper C Atkinson JP Hourcade DE . Properdin: emerging roles of a pattern-recognition molecule. Annu Rev Immunol. (2010) 28:131–55. doi: 10.1146/annurev-immunol-030409-101250

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 114

  Narni-Mancinelli E Gauthier L Baratin M Guia S Fenis A Deghmane AE et al . Complement factor P is a ligand for the natural killer cell–activating receptor NKp46. Sci Immunol. (2017) 2(10):eaam9628. doi: 10.1126/sciimmunol.aam9628

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 115

  Xiong Y Wang Y Wu M Chen S Lei H Mu H et al . Aberrant NK cell profile in gestational diabetes mellitus with fetal growth restriction. Front Immunol. (2024) 15:1346231. doi: 10.3389/fimmu.2024.1346231

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 116

  Sim RB Day AJ Moffatt BE Fontaine M . Complement factor I and cofactors in control of complement system convertase enzymes. Methods Enzymol. (1993) 223:13–35. doi: 10.1016/0076-6879(93)23035-l

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 117

  Ferreira VP Cortes C Pangburn MK . Native polymeric forms of properdin selectively bind to targets and promote activation of the alternative pathway of complement. Immunobiology. (2010) 215:932–40. doi: 10.1016/j.imbio.2010.02.002

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 118

  Tan LA Yang AC Kishore U Sim RB . Interactions of complement proteins C1q and factor H with lipid A and Escherichia coli: further evidence that factor H regulates the classical complement pathway. Protein Cell. (2011) 2:320–32. doi: 10.1007/s13238-011-1029-y

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 119

  Tan LA Yu B Sim FCJ Kishore U Sim RB . Complement activation by phospholipids: the interplay of factor H and C1q. Protein Cell. (2010) 1:1033–49. doi: 10.1007/s13238-010-0125-8

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 120

  Mandal MNA Ayyagari R . Complement factor H: spatial and temporal expression and localization in the eye. Invest Ophthalmol Vis Sci. (2006) 47:4091–7. doi: 10.1167/iovs.05-1655

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 121

  Burwick RM Velásquez JA Valencia CM Gutiérrez-Marín J Edna-Estrada F Silva JL et al . Terminal complement activation in preeclampsia. Obstet Gynecol. (2018) 132:1477–85. doi: 10.1097/AOG.0000000000002980

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 122

  Lokki AI Ren Z Triebwasser M Daly E FINNPEC Perola M et al . Identification of complement factor H variants that predispose to pre-eclampsia: A genetic and functional study. BJOG. (2023) 130:1473–82. doi: 10.1111/1471-0528.17529

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 123

  Dijkstra DJ Lokki AI Gierman LM Borggreven NV van der Keur C Eikmans M et al . Circulating levels of anti-C1q and anti-factor H autoantibodies and their targets in normal pregnancy and preeclampsia. Front Immunol. (2022) 13:842451. doi: 10.3389/fimmu.2022.842451

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 124

  Chen S Zhang J Chen J Ke J Huang Y Du X et al . Compromised C3b-VSIG4 axis between decidual NK cells and macrophages contributes to recurrent spontaneous abortion. J Transl Med. (2024) 22:1017. doi: 10.1186/s12967-024-05829-w

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 125

  Banadakoppa M Chauhan MS Havemann D Balakrishnan M Dominic JS Yallampalli C . Spontaneous abortion is associated with elevated systemic C5a and reduced mRNA of complement inhibitory proteins in placenta. Clin Exp Immunol. (2014) 177:743–9. doi: 10.1111/cei.12371

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 126

  Li J Shen Y Tian H Xie S Ji Y Li Z et al . The role of complement factor H in gestational diabetes mellitus and pregnancy. BMC Pregnancy Childbirth. (2021) 21(1):562. doi: 10.1186/s12884-021-04031-w

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 127

  Moreno-Navarrete JM Martínez-Barricarte R Catalán V Sabater M Gómez-Ambrosi J Ortega FJ et al . Complement factor H is expressed in adipose tissue in association with insulin resistance. Diabetes. (2010) 59:200–9. doi: 10.2337/db09-0700

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 128

  Nilsson B Hamad OA Ahlström H Kullberg J Johansson L Lindhagen L et al . C3 and C4 are strongly related to adipose tissue variables and cardiovascular risk factors. Eur J Clin Invest. (2014) 44:587–96. doi: 10.1111/eci.12275

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 129

  Liu Z Tang Q Wen J Tang Y Huang D Huang Y et al . Elevated serum complement factors 3 and 4 are strong inflammatory markers of the metabolic syndrome development: a longitudinal cohort study. Sci Rep. (2016) 6:18713. doi: 10.1038/srep18713

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 130

  Grant RW Dixit VD . Adipose tissue as an immunological organ. Obes (Silver Spring). (2015) 23:512–8. doi: 10.1002/oby.21003

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 131

  Gregor MF Hotamisligil GS . Inflammatory mechanisms in obesity. Annu Rev Immunol. (2011) 29:415–45. doi: 10.1146/annurev-immunol-031210-101322

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 132

  Onat A Uzunlar B Hergenç G Yazici M Sari I Uyarel H et al . Cross-sectional study of complement C3 as a coronary risk factor among men and women. Clin Sci (Lond). (2005) 108:129–35. doi: 10.1042/CS20040198

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 133

  Zhang J Wright W Bernlohr DA Cushman SW Chen X . Alterations of the classic pathway of complement in adipose tissue of obesity and insulin resistance. Am J Physiol Endocrinol Metab. (2007) 292:E1433–40. doi: 10.1152/ajpendo.00664.2006

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 134

  King BC Blom AM . Non-traditional roles of complement in type 2 diabetes: Metabolism, insulin secretion and homeostasis. Mol Immunol. (2017) 84:34–42. doi: 10.1016/j.molimm.2016.12.009

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 135

  Ramanjaneya M Butler AE Alkasem M Bashir M Jerobin J Godwin A et al . Association of complement-related proteins in subjects with and without second trimester gestational diabetes. Front Endocrinol (Lausanne). (2021) 12:641361. doi: 10.3389/fendo.2021.641361

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 136

  Xue Y Yang N Ma L Gu X Jia K . Predictive value of the complement factors B and H for women with gestational diabetes mellitus who are at risk of preeclampsia. Pregnancy Hypertens. (2022) 30:210–4. doi: 10.1016/j.preghy.2022.10.010

  • Pubmed Abstract
  • CrossRef
  • Google Scholar