SeXX Matters in Infectious Disease Pathogenesis

Vitamin D Deficiency is Associated with Increased Use of Antimicrobials among Preschool Girls in Ethiopia

Preschool children in Addis Ababa, Ethiopia, are highly exposed to influenza viruses. Factors related to infections, nutrition, and environmental conditions that might explain the burden of influenza among these children were investigated. Ninety-five preschool children, 48 girls and 47 boys, were followed clinically for 12 months. Illness and immune responses to influenza; three other respiratory viruses; five airway pathogenic bacteria; and levels of vitamins D, A, and B12 were assessed. Most of the children had antibodies to numerous respiratory viral and bacterial agents at study start, and many were infected during follow-up. Twenty-five girls and 25 boys fell ill during the study, and were treated with one or more courses of systemic antimicrobials. Ninety percent of both girls and boys had 25-hydroxyvitamin D [25(OH)D] levels below the recommended levels. While there was no overall difference in the levels of vitamins D, A, and B12 between girls and boys, treated girls had significantly lower 25(OH)D levels than non-treated girls and treated boys. There was a considerable number of short for age children, but only the short treated girls had significantly lower 25(OH)D levels than the non-treated children. Preschool girls with low 25(OH)D levels were more vulnerable to pathogenic microbes than boys.

Sex and sex steroids impact influenza pathogenesis across the life course

Males and females differ in the outcome of influenza A virus (IAV) infections, which depends significantly on age. During a typical seasonal influenza epidemic, young children (< 10 years of age) and aged adults (65+ years of age) are at greatest risk for severe disease, and among these age groups, males tend to suffer a worse outcome from IAV infection than females. Following infection with either pandemic or outbreak strains of IAVs, females of reproductive ages (i.e., 15-49 years of age) experience a worse outcome than their male counterparts. Among females of reproductive ages, pregnancy is one factor linked to an increased risk of severe outcome of influenza, although it is not the sole factor explaining the female-preponderance of severe disease. Small animal models of influenza virus infection illustrate that inflammatory immune responses and repair of damaged tissue following IAV infection also differ between the sexes and impact the outcome of infection. There also is growing evidence that sex steroid hormones, including estrogens, progesterone, and testosterone, directly impact immune responses during IAV infection to alter outcomes. Greater consideration of the combined effects of sex and age as biological variables in epidemiological, clinical, and animal studies of influenza pathogenesis is needed.

Sex-Related Differences in Immune Response and Symptomatic Manifestations to Infection with Leishmania Species

Worldwide, an estimated 12 million people are infected with Leishmania spp. and an additional 350 million are at risk of infection. Leishmania are intracellular parasites that cause disease by suppressing macrophage microbicidal responses. Infection can remain asymptomatic or lead to a spectrum of diseases including cutaneous, mucocutaneous, and visceral leishmaniasis. Ultimately, the combination of both pathogen and host factors determines the outcome of infection. Leishmaniasis, as well as numerous other infectious diseases, exhibits sex-related differences that cannot be explained solely in terms of environmental exposure or healthcare access. Furthermore, transcriptomic evidence is revealing that biological sex is a variable impacting physiology, immune response, drug metabolism, and consequently, the progression of disease. Herein, we review the distribution, morbidity, and mortality among male and female leishmaniasis patients. Additionally, we discuss experimental findings and new avenues of research concerning sex-specific responses in cutaneous and visceral leishmaniasis. The limitations of current therapies and the emergence of drug-resistant parasites underscore the need for new treatments that could harness the host immune response. As such, understanding the mechanisms driving the differential immune response and disease outcome of males versus females is a necessary step in the development of safer and more effective treatments against leishmaniasis.

The X chromosome and sex-specific effects in infectious disease susceptibility

The X chromosome and X-linked variants have largely been ignored in genome-wide and candidate association studies of infectious diseases due to the complexity of statistical analysis of the X chromosome. This exclusion is significant, since the X chromosome contains a high density of immune-related genes and regulatory elements that are extensively involved in both the innate and adaptive immune responses. Many diseases present with a clear sex bias, and apart from the influence of sex hormones and socioeconomic and behavioural factors, the X chromosome, X-linked genes and X chromosome inactivation mechanisms contribute to this difference. Females are functional mosaics for X-linked genes due to X chromosome inactivation and this, combined with other X chromosome inactivation mechanisms such as genes that escape silencing and skewed inactivation, could contribute to an immunological advantage for females in many infections. In this review, we discuss the involvement of the X chromosome and X inactivation in immunity and address its role in sexual dimorphism of infectious diseases using tuberculosis susceptibility as an example, in which male sex bias is clear, yet not fully explored.

Sex differences in neuroimmunity as an inherent risk factor

Identifying and understanding the sources of inherent risk to neurodevelopmental disorders is a fundamental goal of neuroscience. Being male or being exposed to inflammation early in life are two known risk factors, but they are only infrequently associated with each other. Cellular and molecular mechanisms mediating the masculinization of the brain in animal models reveal a consistent role for inflammatory signaling molecules and immune cells in the healthy male brain. Why this is so remains in the realm of speculation but may have its origins in the maternal immune system. Masculinization of the brain occurs during a restricted critical period that begins in utero and overlaps with the sensitive period during which maternal immune activation negatively impacts the developing brain. The convergence of maleness and early life inflammation as risk factors for neuropsychiatric disorders compels us to consider whether sexual differentiation of the brain in males creates an inherent and greater risk than that experienced by females.

The Wonder Years: What Can Primary School Children Teach Us About Immunity to Mycobacterium tuberculosis?

In high burden settings, the risk of infection with Mycobacterium tuberculosis increases throughout childhood due to cumulative exposure. However, the risk of progressing from tuberculosis (TB) infection to disease varies by age. Young children (<5 years) have high risk of disease progression following infection. The risk falls in primary school children (5 to <10 years), but rises again during puberty. TB disease phenotype also varies by age: generally, young children have intrathoracic lymph node disease or disseminated disease, while adolescents (10 to <20 years) have adult-type pulmonary disease. TB risk also exhibits a gender difference: compared to adolescent boys, adolescent girls have an earlier rise in disease progression risk and higher TB incidence until early adulthood. Understanding why primary school children, during what we term the "Wonder Years," have low TB risk has implications for vaccine development, therapeutic interventions, and diagnostics. To understand why this group is at low risk, we need a better comprehension of why younger children and adolescents have higher risks, and why risk varies by gender. Immunological response to M. tuberculosis is central to these issues. Host response at key stages in the immunopathological interaction with M. tuberculosis influences risk and disease phenotype. Cell numbers and function change dramatically with age and sexual maturation. Young children have poorly functioning innate cells and a Th2 skew. During the "Wonder Years," there is a lymphocyte predominance and a Th1 skew. During puberty, neutrophils become more central to host response, and CD4+ T cells increase in number. Sex hormones (dehydroepiandrosterone, adiponectin, leptin, oestradiol, progesterone, and testosterone) profoundly affect immunity. Compared to girls, boys have a stronger Th1 profile and increased numbers of CD8+ T cells and NK cells. Girls are more Th2-skewed and elicit more enhanced inflammatory responses. Non-immunological factors (including exposure intensity, behavior, and co-infections) may impact disease. However, given the consistent patterns seen across time and geography, these factors likely are less central. Strategies to protect children and adolescents from TB may need to differ by age and sex. Further work is required to better understand the contribution of age and sex to M. tuberculosis immunity.

Epidemiological and Experimental Evidence for Sex-Dependent Differences in the Outcome of Leishmania infantum Infection

Leishmania infantum causes visceral leishmaniasis (VL) in Brazil. We previously observed that VL is more common in males than females living in endemic neighborhoods, despite similar exposure. Using a larger sample, we document that VL is more common in males than females, but only after puberty. BALB/c and C57BL/6 mouse models confirmed that there is a biological basis for male susceptibility to symptomatic VL, showing higher parasite burdens in males than females. Female C57BL/6 mice generated more antigen-induced cytokines associated with curative responses (interferon-γ, interleukin [IL]-1β). Males expressed higher levels of IL-10 and tumor necrosis factor, which are linked to exacerbated disease. Different parasite lines entered or survived at a higher rate in macrophages of male- than female-origin. These results suggest that males are inherently more susceptible to L. infantum than females and that mice are a valid model to study this sex-dependent difference.

The Human Microbiome and Gender Medicine

Discoveries in molecular genetics over the last two decades have broadened our information about the genomics of complex microbial communities. As in all other fields of medicine, there is an undeniable need to explore the microbiome and the way it is impacted by biological sex. A number, although small, of recent studies have demonstrated that women and men have striking differences in the species that constitute their microbiomes. This effects pathological physiology in fields such as hepatology, oncology, autoimmune disease (most notably diabetes mellitus), autism, and obstetrics. There is still an unfortunate lack of research being done on the “microgenderome”: the interaction between microbiota, sex hormones, and the immune system. This review will highlight some of the main areas to be affected by microgenderome physiology, with an in depth focus on obstetrics.

Epidemiology of pulmonary disease due to nontuberculous mycobacteria in Southern China, 2013-2016

Background

Pulmonary nontuberculous mycobacteria (NTM) disease is of increasing public health concern in China. Information is limited regarding risk factors associated with this disease in China. The objective of this study was to describe the epidemiology of pulmonary disease due to NTM in Southern China.

Methods

We retrospectively reviewed the medical records of pulmonary NTM patients registered in the Guangzhou Chest Hospital with positive mycobacterial cultures during 2013–2016. We described sex, age, residence, treatment history, laboratory examination results and comorbidities of pulmonary NTM patients.

Results

Among the 607 NTM cases, the most prevalent species were Mycobacterium avium complex (44.5%), Mycobacterium abscessus complex (40.5%), Mycobacterium kansasii (10.0%) and Mycobacterium fortuitum (2.8%). The male:female ratio was significantly lower among patients infected with rapidly growing mycobacteria (RGM) than among those with slowly growing mycobacteria (SGM). The risk of developing SGM disease significantly increased with advancing age. In addition, pulmonary RGM diseases were more common in migrant population than resident population. Notably, patients with pulmonary RGM diseases were significantly more likely to have bronchiectasis underlying noted than those with SGM diseases. No significant difference was observed in in vitro drug susceptibility among NTM species.

Conclusion

Our data illustrate that the M. avium complex is the most predominant causative agent of pulmonary NTM disease in Southern China. Female, migrant population, the presence of bronchiectasis are independent risk factors for pulmonary diseases due to RGM. In addition, the prevalence of SGM increases significantly with advancing age.

Sex differences in miRNA as therapies for ischemic stroke

MicroRNAs, a subset of non-coding RNAs, are present in virtually all tissues including body fluids and are global regulators of the transcriptome. In view of the expanding number of microRNAs and the large number of gene targets that each microRNA can potentially regulate, they have been compared to hormones in the scope of their effects. MicroRNA have been implicated as biomarkers for several diseases including stroke, as well as chronic conditions that are associated with stroke. Recent research has focused on manipulating miRNA to improve stroke outcomes. Although several miRNAs have been shown to have neuroprotective properties, the overwhelming majority of these studies have employed only male animals. This review will focus on two miRNAs, Let7f and mir363-3p, whose effectiveness as a stroke neuroprotectant is sex-specific.

Sex Matters: Male Hamsters Are More Susceptible to Lethal Infection with Lower Doses of Pathogenic Leptospira than Female Hamsters

A somewhat contradictory published body of evidence suggests that sex impacts severity outcomes of human leptospirosis. In this study, we used an acute animal model of disease to analyze leptospirosis in male and female hamsters infected side by side with low but increasing doses of Leptospira interrogans serovar Copenhageni. We found that male hamsters were considerably more susceptible to leptospirosis, given that only 6.3% survived infection, whereas 68.7% of the females survived the same infection doses. In contrast to the females, male hamsters had high burdens of L. interrogans in kidney and high histopathological scores after exposure to low infection doses (∼10³ bacteria). In hamsters infected with higher doses of L. interrogans (∼10⁴ bacteria), differences in pathogen burdens as well as cytokine and fibrosis transcript levels in kidney were not distinct between sexes. Our results indicate that male hamsters infected with L. interrogans are more susceptible to severe leptospirosis after exposure to lower infectious doses than females.

Sexual dimorphism in Drosophila melanogaster survival of Beauveria bassiana infection depends on core immune signaling

In many animal species, females and males differ in physiology, lifespan, and immune function. The magnitude and direction of the sexual dimorphism in immune function varies greatly and the genetic and mechanistic bases for this dimorphism are often unknown. Here we show that Drosophila melanogaster females are more likely than males to die from infection with several strains of the fungal entomopathogen Beauveria bassiana. The sexual dimorphism is not exclusively due to barrier defenses and persists when flies are inoculated by injection as well as by surface exposure. Loss of function mutations of Toll pathway genes remove the dimorphism in survivorship. Surprisingly, loss of function mutation of relish, a gene in the Imd pathway, also removes the dimorphism, but the dimorphism persists in flies carrying other Imd pathway mutations. The robust sexual dimorphism in D. melanogaster survival to B. bassiana presents opportunities to further dissect its mechanistic details, with applications for biological control of insect vectors of human disease and insect crop pests.

Relapse Versus Reinfection of Recurrent Tuberculosis Patients in a National Tuberculosis Specialized Hospital in Beijing, China

Tuberculosis (TB) recurrence can result from either relapse of an original infection or exogenous reinfection with a new strain of Mycobacterium tuberculosis (MTB). The aim of this study was to assess the roles of relapse and reinfection among recurrent TB cases characterized by a high prevalence rate of drug-resistant TB within a hospital setting. After 58 paired recurrent TB cases were genotyped to distinguish relapse from reinfection, 37 (63.8%) were demonstrated to be relapse cases, while the remaining 21 were classified as reinfection cases. Statistical analysis revealed that male gender was a risk factor for TB reinfection, odds ratios and 95% confidence interval (OR [95% CI]: 4.188[1.012–17.392], P = 0.049). Of MTB isolates obtained from the 37 relapse cases, 11 exhibited conversion from susceptible to resistance to at least one antibiotic, with the most frequent emergence of drug resistance observed to be levofloxacin. For reinfection cases, reemergence of rifampicin-resistant isolates harboring double gene mutations, of codon 531 of rpoB and codon 306 of embB, were observed. In conclusion, our data demonstrate that relapse is a major mechanism leading to TB recurrence in Beijing Chest Hospital, a national hospital specialized in TB treatment. Moreover, male patients are at higher risk for reinfection. The extremely high rate of multidrug-resistant tuberculosis (MDR-TB) among reinfection cases reflects more successful transmission of MDR-TB strains versus non-resistant strains overall.

Differential Redox State Contributes to Sex Disparities in the Response to Influenza Virus Infection in Male and Female Mice

Influenza virus replicates intracellularly exploiting several pathways involved in the regulation of host responses. The outcome and the severity of the infection are thus strongly conditioned by multiple host factors, including age, sex, metabolic, and redox conditions of the target cells. Hormones are also important determinants of host immune responses to influenza and are recently proposed in the prophylaxis and treatment. This study shows that female mice are less susceptible than males to mouse-adapted influenza virus (A/PR8/H1N1). Compared with males, PR8-infected females display higher survival rate (+36%), milder clinical disease, and less weight loss. They also have milder histopathological signs, especially free alveolar area is higher than that in males, even if pro-inflammatory cytokine production shows slight differences between sexes; hormone levels, moreover, do not vary significantly with infection in our model. Importantly, viral loads (both in terms of viral M1 RNA copies and tissue culture infectious dose 50%) are lower in PR8-infected females. An analysis of the mechanisms contributing to sex disparities observed during infection reveals that the female animals have higher total antioxidant power in serum and their lungs are characterized by increase in (i) the content and biosynthesis of glutathione, (ii) the expression and activity of antioxidant enzymes (peroxiredoxin 1, catalase, and glutathione peroxidase), and (iii) the expression of the anti-apoptotic protein Bcl-2. By contrast, infected males are characterized by high expression of NADPH oxidase 4 oxidase and phosphorylation of p38 MAPK, both enzymes promoting viral replication. All these factors are critical for cell homeostasis and susceptibility to infection. Reappraisal of the importance of the host cell redox state and sex-related effects may be useful in the attempt to develop more tailored therapeutic interventions in the fight against influenza.

Sex Hormones Regulate Innate Immune Cells and Promote Sex Differences in Respiratory Virus Infection

Sex differences in the incidence and severity of respiratory virus infection are widely documented in humans and murine models and correlate with sex biases in numbers and/or functional responses of innate immune cells in homeostasis and lung infection. Similarly, changes in sex hormone levels upon puberty, pregnancy, and menopause/aging are associated with qualitative and quantitative differences in innate immunity. Immune cells express receptors for estrogens (ERα and ERβ), androgens (AR), and progesterone (PR), and experimental manipulation of sex hormone levels or receptors has revealed that sex hormone receptor activity often underlies sex differences in immune cell numbers and/or functional responses in the respiratory tract. While elegant studies have defined mechanistic roles for sex hormones and receptors in innate immune cells, much remains to be learned about the cellular and molecular mechanisms of action of ER, PR, and AR in myeloid cells and innate lymphocytes to promote the initiation and resolution of antiviral immunity in the lung. Here, we review the literature on sex differences and sex hormone regulation in innate immune cells in the lung in homeostasis and upon respiratory virus infection.

Production of amphiregulin and recovery from influenza is greater in males than females

Background

Amphiregulin (AREG) is an epidermal growth factor that is a significant mediator of tissue repair at mucosal sites, including in the lungs during influenza A virus (IAV) infection. Previous research illustrates that males of reproductive ages experience less severe disease and recover faster than females following infection with IAV.

Methods

Whether males and females differentially produce and utilize AREG for pulmonary repair after IAV infection was investigated using murine models on a C57BL/6 background and primary mouse and human epithelial cell culture systems.

Results

Following sublethal infection with 2009 H1N1 IAV, adult female mice experienced greater morbidity and pulmonary inflammation during the acute phase of infection as well as worse pulmonary function during the recovery phase of infection than males, despite having similar virus clearance kinetics. As compared with females, AREG expression was greater in the lungs of male mice as well as in primary respiratory epithelial cells derived from mouse and human male donors, in response to H1N1 IAVs. Internalization of the epidermal growth factor receptor (EGFR) was also greater in respiratory epithelial cells derived from male than female mice. IAV infection of Areg knock-out (Areg^−/−) mice eliminated sex differences in IAV pathogenesis, with a more significant role for AREG in infection of male compared to female mice. Deletion of Areg had no effect on virus replication kinetics in either sex. Gonadectomy and treatment of either wild-type or Areg^−/− males with testosterone improved the outcome of IAV as compared with their placebo-treated conspecifics.

Conclusions

Taken together, these data show that elevated levels of testosterone and AREG, either independently or in combination, improve resilience (i.e., repair and recovery of damaged tissue) and contribute to better influenza outcomes in males compared with females.

Sex Differences in HIV Infection: Mystique Versus Machismo

Biological sex is a determinant of both susceptibility to and pathogenesis of multiple infections, including HIV. These differences have effects on the spectrum of HIV disease from acquisition to eradication, with diverse mechanisms including distinct chromosomal complements, variation in microbiota composition, hormonal effects on transcriptional profiles, and expression of different immunoregulatory elements. With a comparative biology approach, these sex differences can be used to highlight protective and detrimental immune activation pathways, to identify strategies for effective prevention, treatment, and curative interventions.

Cancer immunotherapy efficacy and patients' sex: a systematic review and meta-analysis

BACKGROUND

Despite the acknowledged sex-related dimorphism in immune system response, little is known about the effect of patients' sex on the efficacy of immune checkpoint inhibitors as cancer treatments. We did a systematic review and meta-analysis to assess the heterogeneity of immune checkpoint inhibitor efficacy between men and women.

METHODS

We systematically searched PubMed, MEDLINE, Embase, and Scopus, from database inception to Nov 30, 2017, for randomised controlled trials of immune checkpoint inhibitors (inhibitors of PD-1, CTLA-4, or both) that had available hazard ratios (HRs) for death according to patients' sex. We also reviewed abstracts and presentations from all major conference proceedings. We excluded non-randomised trials and considered only papers published in English. The primary endpoint was to assess the difference in efficacy of immune checkpoint inhibitors between men and women, measured in terms of the difference in overall survival log(HR) reported in male and female study participants. We calculated the pooled overall survival HR and 95% CI in men and women using a random-effects model, and assessed the heterogeneity between the two estimates using an interaction test.

FINDINGS

Of 7133 studies identified in our search, there were 20 eligible randomised controlled trials of immune checkpoint inhibitors (ipilimumab, tremelimumab, nivolumab, or pembrolizumab) that reported overall survival according to patients' sex. Overall, 11 351 patients with advanced or metastatic cancers (7646 [67%] men and 3705 [33%] women) were included in the analysis; the most common types of cancer were melanoma (3632 [32%]) and non-small-cell lung cancer (3482 [31%]). The pooled overall survival HR was 0·72 (95% CI 0·65-0·79) in male patients treated with immune checkpoint inhibitors, compared with men treated in control groups. In women treated with immune checkpoint inhibitors, the pooled overall survival HR compared with control groups was 0·86 (95% CI 0·79-0·93). The difference in efficacy between men and women treated with immune checkpoint inhibitors was significant (p=0·0019).

INTERPRETATION

Immune checkpoint inhibitors can improve overall survival for patients with advanced cancers such as melanoma and non-small-cell lung cancer, but the magnitude of benefit is sex-dependent. Future research should guarantee greater inclusion of women in trials and focus on improving the effectiveness of immunotherapies in women, perhaps exploring different immunotherapeutic approaches in men and women.

FUNDING

None.

Sex Differences in HIV Infection

PURPOSE OF REVIEW

This review will outline the multilevel effects of biological sex on HIV acquisition, pathogenesis, treatment response, and prospects for cure. Potential mechanisms will be discussed along with future research directions.

RECENT FINDINGS

HIV acquisition risk is modified by sex hormones and the vaginal microbiome, with the latter acting through both inflammation and local metabolism of pre-exposure prophylaxis drugs. Female sex associates with enhanced risk for non-AIDS morbidities including cardiovascular and cerebrovascular disease, suggesting different inflammatory profiles in men and women. Data from research on HIV cure points to sex differences in viral reservoir dynamics and a direct role for sex hormones in latency maintenance. Biological sex remains an important variable in determining the risk of HIV infection and subsequent viral pathogenesis, and emerging data suggest sex differences relevant to curative interventions. Recruitment of women in HIV clinical research is a pathway to both optimize care for women and to identify novel therapeutics for use in both men and women.

What Is a Host? Attributes of Individual Susceptibility

In every epidemic some individuals become sick and some may die, whereas others recover from illness and still others show no signs or symptoms of disease. These differences highlight a fundamental question of microbial pathogenesis: why are some individuals susceptible to infectious diseases while others who acquire the same microbe remain well? For most of human history, the answer assumed the hand of providence. With the advent of the germ theory of disease, the focus on disease causality became the microbe, but this did not explain how there can be different outcomes of infection in different individuals with the same microbe. Here we examine the attributes of susceptibility in the context of the "damage-response framework" of microbial pathogenesis. We identify 11 attributes that, although not independent, are sufficiently distinct to be considered separately: microbiome, inoculum, sex, temperature, environment, age, chance, history, immunity, nutrition, and genetics. We use the first letter of each to create the mnemonic MISTEACHING, underscoring the need for caution in accepting dogma and attributing disease causality to any single factor. For both populations and individuals, variations in the attributes that assemble into MISTEACHING can create an enormity of combinations that can in turn translate into different outcomes of host-microbe encounters. Combinatorial diversity among the 11 attributes makes identifying "signatures" of susceptibility possible. However, with their inevitable uncertainties and propensity to change, there may still be a low likelihood for prediction with regard to individual host-microbe interactions, although probabilistic prediction may be possible.

Innate Sex Bias of Staphylococcus aureus Skin Infection Is Driven by α-Hemolysin

Numerous studies have reported sex bias in infectious diseases, with bias direction dependent on pathogen and site of infection. Staphylococcus aureus is the most common cause of skin and soft tissue infections (SSTIs), yet sex bias in susceptibility to S. aureus SSTI has not been described. A search of electronic health records revealed an odds ratio of 2.4 for S. aureus SSTI in males versus females. To investigate the physiological basis of this bias, we compared outcomes between male and female mice in a model of S. aureus dermonecrosis. Consistent with the epidemiological data, female mice were better protected against SSTI, with reduced dermonecrosis followed later by increased bacterial clearance. Protection in females was disrupted by ovariectomy and restored by short-term estrogen administration. Importantly, this sex bias was mediated by a sex-specific response to the S. aureus-secreted virulence factor α-hemolysin (Hla). Infection with wild-type S. aureus suppressed inflammatory cytokine production in the skin of female, but not male, mice when compared with infection with an isogenic hla deletion mutant. This differential response was conserved following injection with Hla alone, demonstrating a direct response to Hla independent of bacterial burden. Additionally, neutrophils, essential for clearing S. aureus, demonstrated sex-specific S. aureus bactericidal capacity ex vivo. This work suggests that sex-specific skin innate responsiveness to Hla and neutrophil bactericidal capacity play important roles in limiting S. aureus SSTI in females. Understanding the molecular mechanisms controlling this sex bias may reveal novel targets to promote host innate defense against S. aureus skin infection.

Transcriptomics and Targeted Proteomics Analysis to Gain Insights Into the Immune-control Mechanisms of HIV-1 Infected Elite Controllers

A small subset of HIV-1 infected individuals, the "Elite Controllers" (EC), can control viral replication and restrain progression to immunodeficiency without antiretroviral therapy (ART). In this study, a cross-sectional transcriptomics and targeted proteomics analysis were performed in a well-defined Swedish cohort of untreated EC (n=19), treatment naïve patients with viremia (VP, n=32) and HIV-1-negative healthy controls (HC, n=23). The blood transcriptome identified 151 protein-coding genes that were differentially expressed (DE) in VP compared to EC. Genes like CXCR6 and SIGLEC1 were downregulated in EC compared to VP. A definite distinction in gene expression between males and females among all patient-groups were observed. The gene expression profile between female EC and the healthy females was similar but did differ between male EC and healthy males. At targeted proteomics analysis, 90% (29/32) of VPs clustered together while EC and HC clustered separately from VP. Among the soluble factors, 33 were distinctive to be statistically significant (False discovery rate=0.02). Cell surface receptor signaling pathway, programmed cell death, response to cytokine and cytokine-mediated signaling seem to synergistically play an essential role in HIV-1 control in EC.

Distinctive roles of age, sex, and genetics in shaping transcriptional variation of human immune responses to microbial challenges

Identifying the drivers of the interindividual diversity of the human immune system is crucial to understand their consequences on immune-mediated diseases. By examining the transcriptional responses of 1,000 individuals to various microbial challenges, we show that age and sex influence the expression of many immune-related genes, but their effects are overall moderate, whereas genetic factors affect a smaller gene set but with a stronger effect. We identify numerous genetic variants that affect transcriptional variation on infection, many of which are associated with autoimmune or inflammatory disorders. These results enable additional exploration of the role of regulatory variants in the pathogenesis of immune-related diseases and improve our understanding of the respective effects of age, sex, and genetics on immune response variation.

The contribution of host genetic and nongenetic factors to immunological differences in humans remains largely undefined. Here, we generated bacterial-, fungal-, and viral-induced immune transcriptional profiles in an age- and sex-balanced cohort of 1,000 healthy individuals and searched for the determinants of immune response variation. We found that age and sex affected the transcriptional response of most immune-related genes, with age effects being more stimulus-specific relative to sex effects, which were largely shared across conditions. Although specific cell populations mediated the effects of age and sex on gene expression, including CD8⁺ T cells for age and CD4⁺ T cells and monocytes for sex, we detected a direct effect of these intrinsic factors for the majority of immune genes. The mapping of expression quantitative trait loci (eQTLs) revealed that genetic factors had a stronger effect on immune gene regulation than age and sex, yet they affected a smaller number of genes. Importantly, we identified numerous genetic variants that manifested their regulatory effects exclusively on immune stimulation, including a Candida albicans-specific master regulator at the CR1 locus. These response eQTLs were enriched in disease-associated variants, particularly for autoimmune and inflammatory disorders, indicating that differences in disease risk may result from regulatory variants exerting their effects only in the presence of immune stress. Together, this study quantifies the respective effects of age, sex, genetics, and cellular heterogeneity on the interindividual variability of immune responses and constitutes a valuable resource for further exploration in the context of different infection risks or disease outcomes.

The Toll pathway underlies host sexual dimorphism in resistance to both Gram-negative and Gram-positive bacteria in mated Drosophila

BACKGROUND

Host sexual dimorphism is being increasingly recognized to generate strong differences in the outcome of infectious disease, but the mechanisms underlying immunological differences between males and females remain poorly characterized. Here, we used Drosophila melanogaster to assess and dissect sexual dimorphism in the innate response to systemic bacterial infection.

RESULTS

We demonstrated sexual dimorphism in susceptibility to infection by a broad spectrum of Gram-positive and Gram-negative bacteria. We found that both virgin and mated females are more susceptible than mated males to most, but not all, infections. We investigated in more detail the lower resistance of females to infection with Providencia rettgeri, a Gram-negative bacterium that naturally infects D. melanogaster. We found that females have a higher number of phagocytes than males and that ablation of hemocytes does not eliminate the dimorphism in resistance to P. rettgeri, so the observed dimorphism does not stem from differences in the cellular response. The Imd pathway is critical for the production of antimicrobial peptides in response to Gram-negative bacteria, but mutants for Imd signaling continued to exhibit dimorphism even though both sexes showed strongly reduced resistance. Instead, we found that the Toll pathway is responsible for the dimorphism in resistance. The Toll pathway is dimorphic in genome-wide constitutive gene expression and in induced response to infection. Toll signaling is dimorphic in both constitutive signaling and in induced activation in response to P. rettgeri infection. The dimorphism in pathway activation can be specifically attributed to Persephone-mediated immune stimulation, by which the Toll pathway is triggered in response to pathogen-derived virulence factors. We additionally found that, in absence of Toll signaling, males become more susceptible than females to the Gram-positive Enterococcus faecalis. This reversal in susceptibility between male and female Toll pathway mutants compared to wildtype hosts highlights the key role of the Toll pathway in D. melanogaster sexual dimorphism in resistance to infection.

CONCLUSION

Altogether, our data demonstrate that Toll pathway activity differs between male and female D. melanogaster in response to bacterial infection, thus identifying innate immune signaling as a determinant of sexual immune dimorphism.

Estrogen Stimulation Differentially Impacts Human Male and Female Antigen-Specific T Cell Anti-Tumor Function and Polyfunctionality

Sex-specific differences exist in innate and adaptive immune responses and are mediated by hormone signaling. Estrogen is able to differentially modulate the development and differentiation of immune cells, including T cells. However, the effect of estrogen on T cell function, especially at concentrations other than physiological, remains controversial and incompletely understood. Immunotherapy is one of the most promising cancer treatments to date with a high probability of future enhancements. The adoptive transfer of genetically modified T cells can mediate tumor regression but there are still many hurdles to enhancing the proficiency of this treatment. This study demonstrates for the first time that one major aspect to consider for designing potent immunotherapies for cancer is the impact of the patient's sex. Herein, using two different Ag-specific T cell groups, we investigated the effect of sex and estrogen in antitumor effector responses, T helper cytokine secretion, and, importantly, on T cell whole polyfunctionality important for memory T cell development and survival. Major differences were observed in T cell function and polyfunctionality between sexes and on E2 treatment. The findings of this study may be critical to understand the results of immunotherapy on different patients and for the enhancement of immunotherapy for cancer.

Estrogen protects both sexes against EAE by promoting common regulatory cell subtypes independent of endogenous estrogen

Autoimmune diseases including multiple sclerosis predominantly affect females. Although high levels of sex hormones, particularly estrogen (E2), can reduce proinflammatory immune responses, it remains unclear if a lack of endogenous sex hormones might affect treatment with exogenous sex hormones. Pretreatment with E2 almost completely prevents intact female and male mice from developing clinical and histological signs of experimental autoimmune encephalomyelitis (EAE) by promoting various regulatory immune cell phenotypes. To evaluate the effects of exogenous estrogen in the absence of endogenous sex hormones, the current study compared EAE severity and the emergence of different immunoregulatory cell populations after E2 pretreatment of ovariectomized (OVX) female versus male mice. We found that E2 equally protected both OVX females and males from EAE over a 21 day observation period concomitant with reduced total cell numbers in spleen and spinal cord (males only), but enhanced percentages of CD19⁺CD5⁺CD1d^hi, CD19⁺CD138⁺CD44^hi and CD19⁺Tim-1⁺ Breg cells, CD8⁺CD122⁺ Treg cells and CD11b⁺CD 206⁺ARG-1⁺ anti-inflammatory M2-like monocytes/macrophages in both groups. In contrast, E2 decreased the percentage of CD4⁺CD25⁺FoxP3⁺ Treg cells in OVX females but increased these Treg cells in males and intact female mice. These data suggest that with the exception of CD4⁺CD25⁺FoxP3⁺ Treg cells, E2 protection against EAE promotes highly overlapping immunoregulatory subsets in OVX females and males.

Sex Drives Dimorphic Immune Responses to Viral Infections

New attention to sexual dimorphism in normal mammalian physiology and disease has uncovered a previously unappreciated breadth of mechanisms by which females and males differentially exhibit quantitative phenotypes. Thus, in addition to the established modifying effects of hormones, which prenatally and postpubertally pattern cells and tissues in a sexually dimorphic fashion, sex differences are caused by extragonadal and dosage effects of genes encoded on sex chromosomes. Sex differences in immune responses, especially during autoimmunity, have been studied predominantly within the context of sex hormone effects. More recently, immune response genes have been localized to sex chromosomes themselves or found to be regulated by sex chromosome genes. Thus, understanding how sex impacts immunity requires the elucidation of complex interactions among sex hormones, sex chromosomes, and immune response genes. In this Brief Review, we discuss current knowledge and new insights into these intricate relationships in the context of viral infections.

Associations Between Low Serum Testosterone and All-Cause Mortality and Infection-Related Hospitalization in Male Hemodialysis Patients: A Prospective Cohort Study

Introduction

Infectious diseases are the second highest cause of death in patients on dialysis. In addition, testosterone deficiency or hypogonadism is prevalent in dialysis patients. However, to our knowledge, no studies have investigated the association between testosterone levels and infectious events. We aimed to evaluate whether serum testosterone levels are associated with infection-related hospitalization in male hemodialysis patients in a prospective cohort study.

Methods

We divided the study population into 3 groups based on serum testosterone levels. Associations between testosterone levels and clinical outcomes of infection-related hospitalization, all-cause mortality, and cardiovascular disease (CVD) events were analyzed using the Cox proportional hazard model.

Results

Nine hundred two male patients were enrolled and followed up for a median of 24.7 months. Their mean ± SD age was 63.4 ± 11.8 years, and their median (interquartile range) of total testosterone was 11.7 nmol/l (7.9–14.9 nmol/l). During follow-up, 123 participants died. Infection-related hospitalization and CVD events occurred in 116 and 151 patients, respectively. Infection-related hospitalization was more frequent in the lower testosterone tertile than in the higher testosterone tertile (hazard ratio [HR]: 2.12; 95% confidence interval [CI]: 1.18–3.79; P = 0.01) in adjusted models. Moreover, all-cause mortality was significantly greater in the lower testosterone tertile than in the higher testosterone tertile in adjusted analysis (HR: 2.26; 95% CI: 1.21–4.23; P = 0.01). In contrast, there were no significant differences in CVD events by testosterone level.

Discussion

Low levels of testosterone may be associated with higher rates of infection-related hospitalization and all-cause mortality in male hemodialysis patients.

The Sex and Gender Intersection in Chronic Periodontitis

Periodontitis, a complex polymicrobial inflammatory disease, is a public health burden affecting more than 100 million people and being partially responsible for tooth loss. Interestingly, periodontitis has a documented higher prevalence in men as compared to women signifying a possible sex/gender entanglement in the disease pathogenesis. Although relevant evidence has treated sex/gender in a simplistic dichotomous manner, periodontitis may represent a complex inflammatory disease model, in which sex biology may interfere with gender social and behavioral constructs affecting disease clinical phenotype. Even when it became clear that experimental oral health research needed to incorporate gender (and/or sex) framework in the hypothesis, researchers overwhelmingly ignored it unless the research question was directly related to reproductive system or sex-specific cancer. With the recognition of gender medicine as an independent field of research, this study challenged the current notion regarding sex/gender roles in periodontal disease. We aimed to develop the methodological and analytical framework with the recognition of sex/gender as important determinants of disease pathogenesis that require special attention. First, we aim to present relevant sex biologic evidence to understand the plausibility of the epidemiologic data. In periodontitis pathogenesis, sex dimorphism has been implicated in the disease etiology possibly affecting the bacterial component and the host immune response both in the innate and adaptive levels. With the clear distinction between sex and gender, gender oral health disparities have been explained by socioeconomic factors, cultural attitudes as well as access to preventive and regular care. Economic inequality and hardship for women have resulted in limited access to oral care. As a result, gender emerged as a complex socioeconomic and behavioral factor influencing oral health outcomes. Taken together, as disease phenotypic presentation is a multifactorial product of biology, behavior and the environment, sex dimorphism in immunity as well as gender socio-behavioral construct might play a role in the above model. Therefore, this paper will provide the conceptual framework and principles intergrading sex and gender within periodontal research in a complex biologic and socio-behavioral dimension.

The Impact of Gut Microbiota on Gender-Specific Differences in Immunity

Males and females are known to have gender-specific differences in their immune system and gut microbiota composition. Whether these differences in gut microbiota composition are a cause or consequence of differences in the immune system is not known. To investigate this issue, gut microbiota from conventional males or females was transferred to germ-free (GF) animals of the same or opposing gender. We demonstrate that microbiota-independent gender differences in immunity are already present in GF mice. In particular, type I interferon signaling was enhanced in the intestine of GF females. Presumably, due to these immune differences bacterial groups, such as Alistipes, Rikenella, and Porphyromonadaceae, known to expand in the absence of innate immune defense mechanism were overrepresented in the male microbiota. The presence of these bacterial groups was associated with induction of weight loss, inflammation, and DNA damage upon transfer of the male microbiota to female GF recipients. In summary, our data suggest that microbiota-independent gender differences in the immune system select a gender-specific gut microbiota composition, which in turn further contributes to gender differences in the immune system.

Progesterone-Based Contraceptives Reduce Adaptive Immune Responses and Protection against Sequential Influenza A Virus Infections

In addition to their intended use, progesterone (P4)-based contraceptives promote anti-inflammatory immune responses, yet their effects on the outcome of infectious diseases, including influenza A virus (IAV) infection, are rarely evaluated. To evaluate their impact on immune responses to sequential IAV infections, adult female mice were treated with placebo or one of two progestins, P4 or levonorgestrel (LNG), and infected with a mouse-adapted H1N1 (maH1N1) virus. Treatment with P4 or LNG reduced morbidity but had no effect on pulmonary virus titers during primary H1N1 infection compared to placebo treatment. In serum and bronchoalveolar lavage fluid, total anti-IAV IgG and IgA titers and virus-neutralizing antibody titers but not hemagglutinin stalk antibody titers were lower in progestin-treated mice than placebo-treated mice. Females were challenged 6 weeks later with either an maH1N1 drift variant (maH1N1dv) or maH3N2 IAV. The level of protection following infection with the maH1N1dv was similar among all groups. In contrast, following challenge with maH3N2, progestin treatment reduced survival as well as the numbers and activity of H1N1- and H3N2-specific memory CD8⁺ T cells, including tissue-resident cells, compared with placebo treatment. In contrast to primary IAV infection, progestin treatment increased the titers of neutralizing and IgG antibodies against both challenge viruses compared with those achieved with placebo treatment. While the immunomodulatory properties of progestins protected immunologically naive female mice from the severe outcomes from IAV infection, it made them more susceptible to secondary challenge with a heterologous IAV, despite improving their antibody responses against a secondary IAV infection. Taken together, the immunomodulatory effects of progestins differentially regulate the outcome of infection depending on exposure history.IMPORTANCE The impact of hormone-based contraceptives on the outcome of infectious diseases outside the reproductive tract is rarely considered. Using a mouse model, we have made the novel observation that treatment with either progesterone or a synthetic analog found in hormonal contraceptives, levonorgestrel, impacts sequential influenza A virus infection by modulating antibody responses and decreasing the numbers and activity of memory CD8⁺ T cells. Progestins reduced the antibody responses during primary H1N1 virus infection but increased antibody titers following a sequential infection with either an H1N1 drift variant or an H3N2 virus. Following challenge with an H3N2 virus, female mice treated with progestins experienced greater mortality with increased pulmonary inflammation and reduced numbers and activity of CD8⁺ T cells. This study suggests that progestins significantly affect adaptive immune responses to influenza A virus infection, with their effect on the outcome of infection depending on exposure history.

Sex-Dependent Intestinal Replication of an Enteric Virus

Coxsackievirus is an enteric virus that initiates infection in the gastrointestinal tract before disseminating to peripheral tissues to cause disease, but intestinal factors that influence viral replication are understudied. Furthermore, a sex bias for severe sequelae from coxsackievirus infections has been observed in humans. While mouse models mimicking human pathogenesis have been well characterized, many of these experiments use intraperitoneal injection of coxsackievirus to infect mice, bypassing the intestine. In light of recent studies identifying intestinal factors, such as the microbiota, that alter enteric viral replication, we sought to investigate coxsackievirus replication within the intestine. Here, we orally infected mice with coxsackievirus B3 (CVB3) and found that CVB3 replication in the intestine is sex dependent. CVB3 replicated efficiently in the intestine of male mice but not female mice. Additionally, we found that the type I interferon response and sex hormones can alter both viral replication and lethality. Overall, these data suggest that sex and the immune response play a vital role in CVB3 replication in the intestine and should be considered in light of the sex bias observed in human disease.IMPORTANCE Sex bias in severe sequelae from enteric viral infections has been observed. Since viruses have evolved to achieve optimal levels of fitness in their environmental niches, it is imperative to study viruses at the site of initial replication. Here, we used an oral inoculation system for CVB3, which follows the natural route of infection in the gastrointestinal tract. We found that sex can influence the replication of CVB3 in the intestine. Additionally, the type I interferon response and sex hormones alter both CVB3 intestinal replication and lethality. Overall this work highlights the fact that sex should be considered in investigations of enteric viral replication and pathogenesis.

Sex Steroids Mediate Bidirectional Interactions Between Hosts and Microbes

The outcome of microbial infections in mammals, including humans, is affected by the age, sex, and reproductive status of the host suggesting a role for sex steroid hormones. Testosterone, estradiol, and progesterone, signaling through their respective steroid receptors, affect the functioning of immune cells to cause differential susceptibility to parasitic, bacterial, and viral infections. Microbes, including fungi, bacteria, parasites, and viruses, can also use sex steroid hormones and manipulate sex steroid receptor signaling mechanisms to increase their own survival and replication rate. The multifaceted use of sex steroid hormones by both microbes and hosts during infection forms the basis of this review. In the arms race between microbes and hosts, both hosts and microbes have evolved to utilize sex steroid hormone signaling mechanisms for survival.

(Putative) sex differences in neuroimmune modulation of memory

The neuroimmune system is significantly sexually dimorphic, with sex differences evident in the number and activation states of microglia, in the activation of astrocytes, and in cytokine release and function. Neuroimmune cells and signaling are now recognized as critical for many neural functions throughout the life span, including synaptic plasticity and memory function. Here we address the question of how cytokines, astrocytes, and microglia contribute to memory, and specifically how neuroimmune modulation of memory differentially affects males and females. Understanding sex differences in both normal memory processes and dysregulation of memory in psychiatric and neurological disorders is critical for developing treatment and preventive strategies for memory disorders that are effective for both men and women. © 2016 Wiley Periodicals, Inc.

Age and testosterone mediate influenza pathogenesis in male mice

Influenza severity increases with age, with hospitalization and mortality rates during seasonal influenza epidemics being higher in older men than age-matched women. As it is known that with age, circulating testosterone levels decline in males, we hypothesized that reduced testosterone contributes to age-associated increases in influenza severity. A murine model was used to test this hypothesis. As in men, testosterone concentrations were lower in aged (18 mo) than young (2 mo) male C57BL/6 mice. Following inoculation with influenza A virus (IAV), aged males experienced greater morbidity, clinical disease, and pulmonary inflammation than young males, and had lower neutralizing and total anti-influenza IgG antibody responses. Peak titers of virus in the lungs did not differ between aged and young males, but virus clearance was delayed in aged males. In young males, removal of the gonads increased-whereas treatment of gonadectomized males with testosterone reduced-morbidity, clinical illness, and pulmonary pathology, but viral replication was not altered by hormone manipulation in young males. Treatment of aged males with testosterone improved survival following infection but did not alter either virus replication or pulmonary pathology. These results indicate that low concentrations of testosterone, whether induced surgically in young males or naturally occurring in aged males, negatively impact the outcome of influenza.

Gene-specific sex effects on eosinophil infiltration in leishmaniasis

Background

Sex influences susceptibility to many infectious diseases, including some manifestations of leishmaniasis. The disease is caused by parasites that enter to the skin and can spread to the lymph nodes, spleen, liver, bone marrow, and sometimes lungs. Parasites induce host defenses including cell infiltration, leading to protective or ineffective inflammation. These responses are often influenced by host genotype and sex. We analyzed the role of sex in the impact of specific gene loci on eosinophil infiltration and its functional relevance.

Methods

We studied the genetic control of infiltration of eosinophils into the inguinal lymph nodes after 8 weeks of Leishmania major infection using mouse strains BALB/c, STS, and recombinant congenic strains CcS-1,-3,-4,-5,-7,-9,-11,-12,-15,-16,-18, and -20, each of which contains a different random set of 12.5% genes from the parental “donor” strain STS and 87.5% genes from the “background” strain BALB/c. Numbers of eosinophils were counted in hematoxylin-eosin-stained sections of the inguinal lymph nodes under a light microscope. Parasite load was determined using PCR-ELISA.

Results

The lymph nodes of resistant STS and susceptible BALB/c mice contained very low and intermediate numbers of eosinophils, respectively. Unexpectedly, eosinophil infiltration in strain CcS-9 exceeded that in BALB/c and STS and was higher in males than in females. We searched for genes controlling high eosinophil infiltration in CcS-9 mice by linkage analysis in F₂ hybrids between BALB/c and CcS-9 and detected four loci controlling eosinophil numbers. Lmr14 (chromosome 2) and Lmr25 (chromosome 5) operate independently from other genes (main effects). Lmr14 functions only in males, the effect of Lmr25 is sex independent. Lmr15 (chromosome 11) and Lmr26 (chromosome 9) operate in cooperation (non-additive interaction) with each other. This interaction was significant in males only, but sex-marker interaction was not significant. Eosinophil infiltration was positively correlated with parasite load in lymph nodes of F₂ hybrids in males, but not in females.

Conclusions

We demonstrated a strong influence of sex on numbers of eosinophils in the lymph nodes after L. major infection and present the first identification of sex-dependent autosomal loci controlling eosinophilic infiltration. The positive correlation between eosinophil infiltration and parasite load in males suggests that this sex-dependent eosinophilic infiltration reflects ineffective inflammation.

Sex differences in immune responses

Males and females differ in their immunological responses to foreign and self-antigens and show distinctions in innate and adaptive immune responses. Certain immunological sex differences are present throughout life, whereas others are only apparent after puberty and before reproductive senescence, suggesting that both genes and hormones are involved. Furthermore, early environmental exposures influence the microbiome and have sex-dependent effects on immune function. Importantly, these sex-based immunological differences contribute to variations in the incidence of autoimmune diseases and malignancies, susceptibility to infectious diseases and responses to vaccines in males and females. Here, we discuss these differences and emphasize that sex is a biological variable that should be considered in immunological studies.