Gene-Specific Sex Effects on Susceptibility to Infectious Diseases

Lipoldová, Marie; Demant, Peter

doi:10.3389/fimmu.2021.712688

MINI REVIEW article

Front. Immunol., 14 October 2021

Sec. Inflammation

Volume 12 - 2021 | https://doi.org/10.3389/fimmu.2021.712688

Gene-Specific Sex Effects on Susceptibility to Infectious Diseases

ML
Marie Lipoldová ¹^*
PD
Peter Demant ²

1. Laboratory of Molecular and Cellular Immunology, Institute of Molecular Genetics of the Czech Academy of Sciences, Prague, Czechia
2. Department of Molecular and Cellular Biology, Roswell Park Comprehensive Cancer Center, Buffalo, NY, United States

Abstract

Inflammation is an integral part of defense against most infectious diseases. These pathogen-induced immune responses are in very many instances strongly influenced by host’s sex. As a consequence, sexual dimorphisms were observed in susceptibility to many infectious diseases. They are pathogen dose-dependent, and their outcomes depend on pathogen and even on its species or subspecies. Sex may differentially affect pathology of various organs and its influence is modified by interaction of host’s hormonal status and genotype: sex chromosomes X and Y, as well as autosomal genes. In this Mini Review we summarize the major influences of sex in human infections and subsequently focus on 22 autosomal genes/loci that modify in a sex-dependent way the response to infectious diseases in mouse models. These genes have been observed to influence susceptibility to viruses, bacteria, parasites, fungi and worms. Some sex-dependent genes/loci affect susceptibility only in females or only in males, affect both sexes, but have stronger effect in one sex; still other genes were shown to affect the disease in both sexes, but with opposite direction of effect in females and males. The understanding of mechanisms of sex-dependent differences in the course of infectious diseases may be relevant for their personalized management.

Introduction

Sex plays an important role in immune response, including susceptibility to infectious diseases (), outcome of vaccination (–) and response to treatment (). Sex differences in susceptibility to infectious and inflammatory diseases are widespread – both in terms of number of pathogens and diseases they influence and in terms of the number of vertebrate and invertebrate species and genera where they were observed. In humans they were demonstrated in a number of diseases discussed in detail below and hence they form a significant but hitherto unexplained component of clinical inter-patient heterogeneity. Their individual prediction and functional explanation may therefore significantly improve individual management of disease. A part of this phenomenon may be under genetic control, but there is presently little evidence for this in humans. However, there are extensive data from studies in mice that described 22 autosomal gene-loci controlling the sex differences in response to 12 infectious or inflammatory agents. We are presenting a comprehensive summary of this information, as it may help to proceed to clarification of the manifestations and mechanisms of sex differences in these pathologies.

Sexual dimorphism takes place already in healthy individuals. In most cases, basal immune responses are higher in females than in males. It has been described that women have higher several immunology-related parameters than males: blood levels of mature B cell subsets, IgM-only B cells, proliferating and memory (CD45RA-) Treg cells, NK bright (CD56++CD16-) subsets (), immunoglobulin M (), neutrophil and platelets (), and higher CD4+/CD8+ ratio (). TLR7 ligands induce higher IFNα production in woman peripheral blood lymphocytes (). Neutrophils of men exhibit lower responses to cytokine stimulation and decreased ability to form neutrophil traps (), whereas in women neutrophils were characterized by enhanced type I IFN pathway activity and enhanced proinflammatory responses (). Male and female neutrophils differ also in bioenergetics. Metabolic assays of oxygen consumption rate (OCR), which is a key metric of mitochondrial function, and the extracellular acidification rate (ECAR), which approximates glycolytic activity in male and female neutrophils shown that OCR was higher in male than female neutrophils, whereas there were no differences in ECAR (). As the immune cells differentiation and function crucially depend on mitochondrial bioenergetics (, ), sex differences in mitochondrial functions have a potential to modulate immune responses. Differences in immune responses have been observed also between males and females of other mammals (–), birds (), reptiles (), echinoderms () and insects (). Such baseline differences can contribute to sex biases in response to pathogens (24,25 and see the next section) and to vaccination (–). Females usually have more efficient response to vaccination than males (–), but also develop more often adverse reactions to vaccination (, ). On the other hand, vaccination of healthy volunteers by Bacille Calmette-Guérin (BCG) led to enhanced cytokine responses to restimulation and reduced systemic inflammation. The effect was much stronger in men than in women ().

Sex Biases in Human Infections

Viruses

Male sex was associated with higher death rate in hepatitis A virus-hospitalized cases (). Male sex was also a risk factor for hepatitis B virus (HBV) and hepatitis C Virus (HCV) prevalence and for development of hepatocellular carcinoma subsequent to HBV and/or HCV infection (). Presence of virus stimulates inflammatory responses and appearance of reactive oxygen (ROS) and nitrogen species, which are described as leading cause of series of alterations that led to DNA damage (). Estrogen may serve an inhibitory role in these processes by inhibiting inflammation, tumor progression and invasion and stimulating DNA repair (), whereas androgen induced miR-216a stimulated tumorigenesis (). The lower survival rate was observed among male patients infected with Ebola virus (). The higher COVID-19 case mortality rate and increased severity of disease was described in males (–). Interestingly, gene encoding ACE2 (angiotensin-converting enzyme 2), which plays an essential role in cell entry of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) is localized on X chromosome (Xp22.2), thus females have double gene dose and can be potentially heterozygous compared to males who are definitely hemizygous. It has been speculated that together with X mosaicism it might favor women in counteracting the progression of the SARS-CoV-2 infection (, ). Prevalence of herpes simplex virus type 1 (HSV1) and type 2 (HSV2) in persons aged 14-49 in United States in the years 2015-2016 was higher in women than in men (). Similarly, HSV1 in Europe was more often detected in women than in men (). Sex differences in measles mortality were compared among 78 countries in years between 1950 and 1989. Regional variations showed excess female mortality of 3% in Europe, 6.2% in North America, 5.9% in Far East Asia, 4.3% in Latin America, and 20.9% in the Middle East. The cumulative excess female mortality in comparison with males was small at age 0-4 (+4.2%), larger at age 5-14 (+10.9%), and peaks at ages 15-44 (+42.6%) (). The most probable explanation of these variations is the influence of estrogens (). Several studies have shown that women are more susceptible to human immunodeficiency virus 1 (HIV-1) acquisition than men, as the male-to-female transmission is more efficient than female-to-male transmission (, ). Indeed, in Sub-Saharan Africa higher HIV prevalence is observed in women (). However, in Europe, there are more newly detected HIV infections in males than in woman, because sex between men remains the predominant mode of HIV transmission reported in the EU (European Union)/EEA (European Economic Area) (). Thus, socioeconomic factors most likely contribute to the sex biases in HIV/AIDS (Acquired Immune Deficiency Syndrome).

Bacteria

Sex differences have also been reported in bacterial infections. Analysis of 4742 randomly selected subjects, aged 12-64, from Northern Ireland shown that Helicobacter pylori infection was more common in males than in females (). A retrospective seroepidemiologic survey of Chlamydia pneumoniae infection in patients in Beijing, China between 2008 and 2017 revealed that adult men had both a higher prevalence and higher levels of antibodies than women (). Klebsiella spp. induced bacteremia was higher in males than in females in England, Wales, and Northern Ireland (). 60% of patients hospitalized in the years 2005-2014 in USA with Lyme disease (infectious agent Borrelia burgdorferi) were men (). On the other hand, reinfection with B. burgdorferi in individuals from Sweden that were initially diagnosed with erythema migrans and treated with antibiotics was much higher in women than in men (). Incidence of tuberculosis that is caused by infection with Mycobacterium tuberculosis was described to be higher in men than in women (), however a consistent female excess for tuberculosis at age 5-29 was observed (47). Listeria monocytogenes is a foodborne pathogen that is highly prevalent in pregnant woman, older adults and immunocompromised individuals. Incidence of listeriosis in the years 2008-2016 in USA was higher in males than in non-pregnant females (48). Socioeconomic factors highly influence the spread of syphilis: a sexually transmitted infection caused by Treponema pallidum. Sex differences in its incidence, prevalence and geographical variations have been well described. For example, the incidence of maternal syphilis is higher in low- to middle-income countries as compared to high-income countries where syphilis is more common among men who have sex with men. In Africa the spread of syphilis is also high in female sex workers (49, 50).

Parasites

Male sex is a risk factor for visceral leishmaniasis (51). Men were more susceptible to visceral infection caused by Leishmania donovani (52–54) and L. infantum (55–58). More variability was observed in studies of sex influence on cutaneous leishmaniasis. Some epidemiological studies revealed in male patients a higher incidence of cutaneous leishmaniasis caused by L. major and L. tropica (59, 60), L. major only (61), and also by L. guyanensis (62). However, the study in Afghanistan found that females developed more lesions and scars after L. tropica infection (63) and other analyses reported no significant sex differences in registered cases of cutaneous leishmaniasis caused by L. tropica (64) and L. major (65). No sex bias was observed in intestinal schistosomiasis caused by Schistosoma mansoni in adults (66). Infection rates did not differ significantly among various age and sex groups infected with Schistosoma haematobium (67).

Fungi

Prior to the AIDS epidemics, cryptococcal disease, caused by Cryptococcus neoformans and Cryptococcus gattii was rather rare. It was reported in case series 2-3 times more frequently in men as in women (68). In the AIDS era, in the years 2000-2007 were in USA hospitalized 10077 patients with cryptococcal disease, 26% were females. Males had a higher risk of a disease in both HIV-infected and uninfected cohorts. Age- and sex-adjusted death rates were almost threefold higher in males compared to females (69).

Worms

Females were found to be more predisposed to Ascaris lumbricoides infection than were males (70). Human neurocysticercosis results from the infection of the central nervous system with the larval stage of the intestinal tapeworm, Taenia solium. In Ecuador, the number of transitional cysts in brain was found to be higher in the female than in the male patients (71).

Various Influences on Sex Effects

Thus, differences in susceptibility and prevalence between males and females have been observed in many human infections. The extensive studies showed that some infectious diseases exhibit male (, , –, –, 52–58, 68, 69), the other female bias (–, 70, 71), but there are also epidemiological studies with contradictory results; some studies showing male and the other female bias or no sex bias in the same disease (–, , 47, 59–65). These disparities may be explained by the fact that the occurrence and susceptibility to infectious diseases is influenced by many factors such as presence of pathogen reservoir, presence and properties of pathogen transmission vector in case of vector borne diseases (72), as well as immune status, sex and hormonal status, age, nutrition, microbiome and genotype of the host (72–75) and multiple environmental factors, including climate changes (76). Susceptibility to many human diseases is modified by socio-cultural determinants, behavioral/lifestyle risk factors (50), prevalence of co-morbidities (48) and co-infection with several pathogens (69, 77).

Sex-Dependent Responses Revealed in Animal Experiments

Sex-dependent differences in response to pathogens could be more effectively analyzed in animal studies. Mouse experiments revealed important features of sex-dependent responses to infectious diseases: dose-dependence, pathogen and pathogen species-dependence, organ specificity and genetic modification.

Dose-Dependent Sex Bias

Dose-dependent sex bias was described in responses to viruses and bacteria. The response of the strain C57BL/6 infected intranasally with the mouse adapted influenza A/PR8;H1N1 was sex-dependent when median infection dose [10² or 10³ TCID₅₀ (tissue culture infectious dose)] were used and females exhibited higher mortality than males. The effect of infections with low (10¹ TCID₅₀) or high (10⁴ or 10⁵ TCID₅₀) viral inoculi was sex independent (78). Dose-dependent sex bias was observed also in the animal model of gram-negative sepsis. Wistar rats were injected intraperitoneally with bacteria Escherichia coli LPS in one of two doses: 1.5 or 15 mg/kg. Day after the LPS injection, serum levels of endotoxin, corticosterone, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) activity in the serum and morphological changes in the lung, liver, thymus, and spleen exhibited dose-dependent sex bias. Low-dose LPS led to the serum endotoxin level increase only in males and it was combined with a more pronounced inflammatory response in the lungs (characterized by infiltration of eosinophils and neutrophils) and thymus (characterized by presence of macrophages and dead lymphocytes) and an increase and decrease in ALT and AST activity, in males and females, respectively, without any changes in corticosterone level. High-dose LPS induced systemic inflammatory response syndrome (SIRS) comprises higher blood endotoxin levels in males than in females, lower the volume fraction index of the white pulp of the spleen of males, increase of apoptotic cells in thymus and decrease of corticosteroids in males only. Sex differences of pathological changes in the lungs and liver were not revealed (79). The observed dose-dependent sex differences might be largely caused by different dynamics of induction of different signaling pathways in males and females.

Sex Differences Depend on Species and Sub-Species of Pathogen and on Genotype of the Host

Sex bias in disease susceptibility and prevalence that is dependent on pathogen species is described in Sex Biases in Human Infections. Here we describe, that sex bias can depend also on pathogen sub-species. DBA/2 female mice are highly resistant and males susceptible to lesion development after infection with the parasite L. mexicana. On the contrary, although both female and male mice developed ulcerating lesions after infection with L. major, lesions healed in males, but not females (80). Sex differentially influenced also infection with L. tropica and L. major and the response was modified by genotype. Females of strains BALB/c, CcS-11, CcS-16 and CcS-20 are more susceptible than males to development of skin lesions induced by L. tropica, whereas no sex bias was observed in strains STS, CcS-3, CcS-5, CcS-12 and CcS-18. On the other hand, infection by L. major induced larger skin lesions in males of strains CcS-3, CcS-5 and CcS-18, whereas no difference between males and females was observed in strains BALB/c, STS, CcS-11, CcS-12, CcS-16 and CcS-20 (81).

Sex Affects Pathology of Various Organs Differently and Its Influence Is Modified by the Host Genotype

Strains BALB/c and CcS-11 did not exhibit any sex influence on lesion size induced by L. major, but males of strain CcS-11 contained more parasites in spleens than females, and males of both strains had much higher parasite load in lymph nodes (82). Organ-dependent sex response was observed also in animal model of gram-negative sepsis (79). These phenomena might be explained by presence of different defense mechanisms in different tissues (83, 84), as well as by highly tissue-dependent sex-biases in expression of genes observed in intercross between strains C57BL/6 and C3H/HeJ (85).

Mechanisms of Sex-Dependent Responses

The observed sex-differential responses to disease susceptibility may be explained by direct and indirect influence of sex hormones and non-hormonal sex-biasing influence of X and Y chromosomes. Sex steroid hormones (estrogen, testosterone and progesterone) influence response to infections by 1) direct effect on pathogen metabolism, growth, and expression of virulence factors. It was shown that physiological concentration of progesterone inhibited replication of Coxiella burnetii in JEG-3 cells (86), both testosterone and progesterone inhibited growth of Staphylococcus aureus (87). 2) by modification of immune response and physiology of the host. Effects on sex hormones on the host are exerted via sex hormone-receptor interactions. These receptors are present in cell nucleus and membrane (88) of non-immune and immune cells and tissues (88–91). Complexes of sex hormone-nuclear steroid receptor bind target DNA through hormone response elements to act as transcription factors (88). They can also bind to DNA-protein complexes and epigenetically modify cell functions (90, 91). Sex hormone-receptor complexes can exert their effects also through DNA-independent mechanisms, such as the activation of cytoplasmic signal transduction pathways (90). These interactions influence pro- and anti-inflammatory signaling pathways (92, 93). Indirect influences might include for example sex-dependent organ development (94) or influence of sex hormones on gut microbiota (95).

Non-hormonal sex-bias effects are mediated by genes localized on X and Y chromosomes (, 96, 97). The X chromosome carries a number of immune-related genes (96), such as toll-like receptor 7 (TLR7) and interleukin-1 receptor-associated kinase 1 (IRAK1), as well as a number of immune-associated microRNAs (96). X inactivation, or silencing of one X chromosome, in women would be expected to provide dosage compensation of X-linked genes, however certain regions of the X chromosome escape inactivation (96, 98). This can lead to higher transcription levels of specific genes that are involved in sex-specific responses (96, 99). The Y chromosome also influences immune gene expression, regulation, and susceptibility to infections (97). For example, the Y chromosome mediates susceptibility to cocksackie virus independently of serum testosterone level (100). Genetic variation in chromosome Y regulates susceptibility to influenza A virus infection (101).

Mouse Autosomal Genes That Control Sex-Biased Responses to Infections

Besides X- and Y-linked genes, there are also autosomal genes operating in sex-dependent manner. Sex-dependent autosomal genes modify response to viruses (102–106), bacteria (106, 107), parasites (108–111), fungi (112) and worms (113) (Table 1, Figure 1). Three models were introduced to explain gene-sex-interactions (114). 1. “Environment specific effect”: Sex dependent gene/loci affect susceptibility only in females (102, 104, 107, 111, 112), or males (102–105, 108–110, 112, 113). 2. “A main effect” model for gene by environment (= sex) interaction. A disease can affect both sexes, but is more severe in one sex compared to the other (106, 107, 111). 3. “A flip-flop” model of gene by environment interaction. Gene affects susceptibility in both sexes, but in different directions (102, 108).

Table 1

Pathogen	Locus/Gene	Chromosome	Cross/Strain	Trait (phenotype) controlled	Sex effect	Reference
Viruses
Theiler’s murine encephalomyelitis virus	Tmevd6	1	BALB/c x DBA/2J	virus-induced demyelination	opposite effects on females and males	(102)
	Tmevd7	5	BALB/c x DBA/2J	virus-induced demyelination	males	(102)
	Tmevd8	15	BALB/c x DBA/2J	virus-induced demyelination	males	(102)
	Tmevd9	1	BALB/c x DBA/2J	virus-induced demyelination	females	(102)
mousepox/ectromelia	Rmp-4	1	C57BL/6 x D2	virus titer in spleen and liver, survival	males	(103)
mouse-adapted influenzaH3N2/HK/1/68	NNI1	2	C57BL/6J x A/J	survival	females	(104)
mouse-adapted influenzaH3N2/HK/1/68	NNI2	17	C57BL/6J x A/J	survival	males	(104)
herpes simplex virus 1	Hrl	6	BALB/c x 129S6	survival	males	(105)
reovirus - T3D	Lrrk2- knockout	15	C57BL/6	mortality from encephalitis	females - increased mortality in knockouts	(106)
Bacteria
Chlamydia pneumoniae	NNCH1	5	C57BL/6J x A/J	chlamydial burden in lungs	females	(107)
Chlamydia pneumoniae	NNCH2	17	C57BL/6J x A/J	chlamydial burden in lungs	stronger effects on males	(107)
Salmonella typhimurium	Lrrk2- knockout	15	C57BL/6	bacterial replication in spleen	female knockouts higher bacteria replication than WT; knockin of pG2019S mutation lower bacteria replication than WT, stronger effect on females	(106)
Parasites
Leishmania major	Lmr4	6	BALB/c x CcS-9	parasite load in lymph nodes	males	(108)
	Lmr14	2	CcS-9 x BALB/c	eosinophil infiltration into lymph nodes	males	(109)
	Lmr14	2	BALB/c x CcS-9	parasite load in lymph nodes	males	(108)
	Lmr15	11	BALB/c x CcS-9	parasite load in lymph nodes	opposite effects on females and males	(108)
	Lmr27	17	BALB/c x CcS-9	parasite load in lymph nodes	males	(108)
Leishmania mexicana	Il4ra CD4+ T cell specific expression	7	BALB/c	skin lesions	non-healing phenotype in males	(110)
Trypanosoma brucei brucei	Tbbr1	3	BALB/c x CcS-11	survival	females	(111)
Trypanosoma brucei brucei	Tbbr2	12	BALB/c x CcS-11	survival	stronger effect on females	(111)
Fungi
Cryptococcus neoformans	Cnes1	3	C57BL/6J x CBA/J	lung fungal burden	females	(112)
	Cnes2	17	C57BL/6J x CBA/J	lung fungal burden	females	(112)
	Cnes3	17	C57BL/6J x CBA/J	lung fungal burden	males	(112)
Worms
Trichuris muris	TM5	5	C57BL/6J x DBA/2	Serum IFNγ	males	(113)

Autosomal genes and loci controlling sex-biased responses to infection in mouse.

The Table summarizes position on chromosome, cross used to map certain locus or mouse genetic background, disease phenotype controlled and sex effect.

Cnes, Cryptococcus neoformans susceptibility; Hlr, herpes resistance locus; Il4ra, interleukin 4 receptor alpha; Lmr, Leishmania major response; Lrrk2, leucine-rich repeat kinase-2; NNCH, not named Chlamydia; NNI, not named influenza; Rmp-4, Resistance mousepox 4; Tbbr, Trypanosoma brucei brucei response; TM, Trichuris muris; Tmevd, Theiler’s murine encephalomyelitis virus-induced demyelination.

Figure 1