Edited by: Marie-Agnes Dragon-Durey, Université Paris Descartes, France
Reviewed by: Umesh S. Deshmukh, Oklahoma Medical Research Foundation, United States; Batteux Frederic, Université Paris Descartes, France
This article was submitted to Autoimmune and Autoinflammatory Disorders, a section of the journal Frontiers in Immunology
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Systemic lupus erythematosus (SLE) is characterized by high-titer serological autoantibodies, including antibodies that bind to double-stranded DNA (dsDNA). The origin, specificity, and pathogenicity of anti-dsDNA antibodies have been studied from a wider perspective. These autoantibodies have been suggested to contribute to multiple end-organ injuries, especially to lupus nephritis, in patients with SLE. Moreover, serum levels of anti-DNA antibodies fluctuate with disease activity in patients with SLE. By directly binding to self-antigens or indirectly forming immune complexes, anti-dsDNA antibodies can accumulate in the glomerular and tubular basement membrane. These autoantibodies can also trigger the complement cascade, penetrate into living cells, modulate gene expression, and even induce profibrotic phenotypes of renal cells. In addition, the expression of suppressor of cytokine signaling 1 is reduced by anti-DNA antibodies simultaneously with upregulation of profibrotic genes. Anti-dsDNA antibodies may even participate in the pathogenesis of SLE by catalyzing hydrolysis of certain DNA molecules or peptides in cells. Recently, anti-dsDNA antibodies have been explored in greater depth as a therapeutic target in the management of SLE. A substantial amount of data indicates that blockade of pathogenic anti-dsDNA antibodies can prevent or even reverse organ damage in murine models of SLE. This review focuses on the recent research advances regarding the origin, specificity, classification, and pathogenicity of anti-dsDNA antibodies and highlights the emerging therapies associated with them.
Systemic lupus erythematosus (SLE) is a severe disease that involves dysregulation of the immune system, excessive production of pathogenic autoantibodies (and their upregulation in serum), and multiple immune-system-mediated injuries. Anti-double-stranded (ds)DNA antibodies have been some of the classic diagnostic and nosological criteria of SLE since 1982. In 2012, the high titer of anti-dsDNA antibodies in serum accompanied by biopsy-proven lupus nephritis (LN) was accepted as an independent classification criterion for SLE by the Systemic Lupus International Collaborating Clinics (
Normally, nuclear antigens, such as dsDNA, are not accessible to the immune system because they are restricted to the nucleus and mitochondria and are quickly degraded by DNases in the cytoplasm and endosomes. However, nuclear materials can be released from apoptotic cells after exposure to ultraviolet light, infection, and drugs. Cells undergo death via different processes. During NETosis, cells extrude DNA and neutrophil extracellular traps (NETs), in which DNA is covered by anti-bacterial substances (
The released DNA can be recognized by anti-DNA antibodies and compose immune complexes. Extracellular nucleic acids containing immune complexes can be captured by immature dendritic cells (iDCs) via FcγRs; these cells subsequently get activated and migrate from peripheral tissues to lymphatic organs, where iDCs undergo maturation (
Moreover, autophagy is associated with the immune regulation and is essential for the homeostasis in immune cells. LC3-associated phagocytosis is an autophagy pathway that participates in the endocytosis of DNA or immune complexes by immune cells, especially plasmacytoid DCs. LC3 induces production of IFN-α via the TLR9 pathway in plasmacytoid DCs, whereas beclin-1, another member of the autophagy pathway, inhibits the production of IFN-α (
Anti-dsDNA antibodies recognize diverse DNA structures, including single-stranded (ss)DNA, Z-DNA, bent or elongated dsDNA, DNA:RNA hybrids, locked-nucleic acids, and peptide: nucleic acid hybrids (
Antigenic recognition of anti-dsDNA antibodies.
Annexin II | •Mesangial cells |
•Activate p38 MAPK, JNK, and AKT |
( |
Alpha-actinin | •Mesangial cells | •Change cell shape and migration |
( |
Laminin | •Glomerular matrix | •Trigger inflammation |
( |
Collagen III/ IV | •Glomerular basement membrane |
•Exacerbate inflammatory infiltration |
( |
C1q | •Sera | •Induce immune complex deposition |
( |
NMDAR | •Neuronal cells | •Apoptosis of neuronal cells |
( |
Entactin | •Glomerular basement membrane | •Increase production of anti-entactin antibodies |
( |
Ribosomal P | •Hepatocytes |
•Induce production of anti-Rib-P antibody |
( |
Heparan sulfate | •Glomerular basement membrane |
•Mediate penetration of living cells |
( |
Anti-dsDNA antibodies have different subclasses, including IgA, IgE, IgG, and IgM. Nonetheless, not all of them contribute equally to tissue injuries in SLE. It is IgG and IgA but not IgM that correlate with disease activity in humans. Most pathogenic antibodies are affiliated with the IgG class in SLE patients (
Tests for anti-DNA antibodies can be positive at least 2 years before clinical diagnosis of SLE, and a surge in serum levels can present as a predictor for a severe SLE flare-up in the following 6 months (
There are a variety of tests for anti-dsDNA antibody detection, such as the Farr radioimmunoassay (FARR-RIA), Crithidia luciliae indirect immunofluorescence test (CLIFT), and enzyme-linked immunosorbent assays (ELISA) (
Detection methods with strengths and weaknesses.
FARR-RIA | •Detect high-avidity antibodies |
•Low sensitivity |
CLIFT | •Detect high-avidity antibodies |
•Only score the kinetoplast fluorescence since nuclei always contain many antigens other than DNA |
ELISA | •Detect low and high avidity antibodies |
•Low specificity |
Among the affected organs, renal involvement indicates major internal damage in SLE patients. Anti-dsDNA antibodies are present in serum in nearly 80% of patients with LN. Anti-dsDNA antibodies directly or indirectly interact with renal antigens, thus producing immune complexes (
Effects on renal cell types.
Mesangial cells | Increase/Decrease? | •↑ IL-1β, IL-8, IL-6, TNF-α, hyaluronan, lipocalin-2, iNOS, MCP-1 | •↑ PKC, TGF-β1/MAPK, JAK2/STAT1 |
PTECs | Increase | •↑ IL-6, IL-8, TNF-α, MCP-1, (NF)-κB, IP-10, MIP-1a, ICAM-1, VCAM-1 | •↑ TWEAK/Fn14 |
Endothelial cells | Increase/Decrease? | •↑ IL-1β, IL-8, IL-6, TNF-α | •↑ JAK2/STAT1 ↓ SOCS1 |
Most immunoglobulins are unable to penetrate into living cells (
The penetrating anti-DNA antibodies can affect the proliferation and apoptosis of resident cells in LN, but the exact effect remains controversial. The anti-DNA IgG purified from the serum of LN patients has been shown to downregulate miR-10a and to trigger the proliferation of mesangial cells by targeting HOXA1, KLF4, and CREB1. Concomitantly, the expression of IL-6 is also enhanced, which is a crucial cytokine for promotion of the processes of cell proliferation and inflammation (
It is well-known that accumulation of inflammatory cytokines is sufficient for accelerating the recruitment of immune cells and the induction of inflammatory and fibrogenic processes promoting kidney damage. A wealth of proinflammatory factors, including monocyte chemotactic protein 1 (MCP-1), TNF-α, IL-1β, IL-6, IL-8, hyaluronan, lipocalin-2, and inducible nitric oxide synthase, are overexpressed in both human and murine mesangial cells upon stimulation with anti-dsDNA antibodies (
A persistent chronic inflammatory response is always followed by fibrogenesis when there is no effective intervention, thereby leading to abnormal structure and dysfunction of kidneys with characteristic oversecretion of profibrogenic chemokines. Fibronectin is critical for fibrotic progression in glomerulonephritis and is distributed widely in the mesangial matrix, glomerular, and tubular basement membranes, and Bowman's capsule. The formation of glomerular fibronectin is enhanced both in patients and mice with active LN (
The pathogenic mechanism of anti-dsDNA antibodies in LN. After binding to DNA and non-DNA antigens, the penetrating anti-dsDNA antibodies relocate to the cytosol and cell nucleus, cause DNA fragmentation (accompanied by dysfunction of DNase), and induce apoptosis by regulating the gene expression of p53, Fas, or c-myc. The internalized anti-dsDNA antibodies enhance the expression of IL-6, IL-1β, TNF-α, and TGF-β1, activate the PKC, MAPK, TWEAK/Fn14, and EMT signaling pathways, and trigger the fibrotic process. Local deposition of anti-dsDNA IgG—in combination with the secretion of inflammatory or profibrogenic cytokines as well as the recruitment of immune cells—is sufficient for the initiation of renal fibrosis in LN.
Skin is frequently affected by SLE and can be the only affected organ. The serum positivity for an anti-dsDNA antibody is observed in only a subgroup of patients with cutaneous lupus erythematosus. The binding specificity of anti-DNA IgG to skin sections and keratinocytes has been observed
Central nervous system (CNS) diseases are associated with a poor prognosis among patients with SLE and have been increasingly reported during the past decade. Neuropsychiatric complications occur in 30–40% of patients with SLE and may constitute the initial presentation or a flare (
Classically, the variable region is the only part of an antibody that is credited with the antigenic specificity, whereas the functions of antibodies are determined by the constant region. These two domains are believed to be structurally and functionally independent. However, the specificity and affinity of antibodies are believed to be determined by both regions but not solely by the variable one (
To validate the association between subclasses and pathogenicity, we found that different isotypes of anti-dsDNA antibodies differ from each other in the recognition specificity of nuclear and renal antigens when we generated a panel of murine anti-DNA antibodies (IgM, IgG1, IgG2a, IgG2b, and IgG3), which contain identical variable-joining-diversity (VDJ) regions, suggesting that the effect of the constant region on antibody binding is directly associated with autoimmunity (
The first IgG antibody with DNA-related catalytic activity in SLE was found in 1992 (
The catalytic properties of anti-dsDNA IgG. Anti-dsDNA IgG binds to DNA at the thymine repetitive sequences via tyrosine side chains within a hydrophobic pocket. Hydrolysis of DNA is an energy-intensive process and can be activated by the binding of Ca2+ and Mg2+. After binding to DNA, the active site of IgG is converted to a transition state, and the DNA fragments are produced and released. At this point, the free IgG binds to another DNA molecule and begins its new cycle, in which IgG stabilizes the transition state of the reaction and lowers the activation energy, and thereby increases the rate of the reaction.
In the sequence analysis of anti-DNA antibodies from humans and mice, there is a high frequency of somatic mutations in the VH and VL sequences of anti-dsDNA IgG with high affinity (
This therapeutic strategy against SLE is focused on eliminating or controlling active B cells that offer limited benefits but hamper the advancement of treatment for SLE (
The iDCs exert weaker activating effects on T cells by expressing lower amounts of costimulatory cytokines, including IL-6 and IL-12 in patients with SLE; this observation is consistent with iDCs' effects in lupus-like mice where iDCs lower the responses of Th1/Th2 cells and thus inhibit the secretion of IL-2, IL-4, IL-12, and interferon γ and the formation of anti-dsDNA IgG (
Based on the interactions between self-antigens and anti-dsDNA antibodies, novel therapeutic peptides that bind to autoantibodies have attracted increasing attention. These peptides can be synthesized by combining desired amino acid residues or by chemical modification of certain sequences, to ensure higher activity and specificity. To date, therapeutic peptides have proven to be effective against experimental autoimmune diseases, for example, rheumatoid arthritis and multiple sclerosis (
Peptide DWEYS (D/E W D/E Y S/G), a part of NMDAR expressed on neurons, has been shown to bind to anti-dsDNA antibodies, thereby disrupting the neurotoxicity of anti-DNA antibodies through the NMDAR-activated pathway, in which circulating antibodies penetrate the hippocampal pyramidal cells followed by impairment of spatial cognition (
FISLE-412, an analog of a reduced protease inhibitor for the human immunodeficiency virus, has the potential to block DNA recognition of anti-dsDNA antibodies (
ASPVTARVLWKASHV is a 15-mer peptide selected by purified polyclonal anti-dsDNA IgG in lupus patients and can inhibit antigen-IgG binding (
pCons (FIEWNKLRFRQGLEW) is a 15-mer peptide derived from murine anti-dsDNA antibodies; it exerts therapeutic effects by preventing antibody-antigen binding (
hCDR1 (GYYWSWIRQPPGKGEEWIG) is a 19-mer peptide that is based on CDR1 sequences from human anti-DNA antibodies. hCDR1 has suppressive effects on T cells by reducing apoptosis of T cells with less secretion of interferon-γ and upregulation of IL-10 in lupus-prone mice (
Anti-dsDNA antibodies, the hallmark of SLE, constitute a potent parameter for classifying and diagnosing SLE. Their contribution to damage to the kidneys, skin, and brain in SLE has been well-documented. The production of anti-dsDNA antibodies results from combining multiple factors, including abnormalities of dendritic cells, B cells, or T cells and deficiency of a DNase that leads to failure of cleaning released nuclear materials; however, it still need further studies. The effects of penetrating autoantibodies on triggering a complicated inflammatory and fibrotic process underlie the role of anti-DNA antibodies in damaging target cells and organs. The pathogenicity of antibodies highlights the promising therapeutic potential of DNA-mimicking peptides that react with these autoantibodies in SLE, which can ameliorate the manifestations of SLE in murine models. However, the clinical trials progress slowly in which the timing, dosages, route of administration, alteration of bioactivity, and possible adverse effects of such peptides should be taken into account for developing more efficient therapies for SLE.
YX conceived this paper. XW wrote this manuscript. XW and YX read and approved the final manuscript.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.