The impact of testosterone on murine models of infection and vaccination

In men, low testosterone is associated with an increased risk of all-cause and cardiovascular related mortality, and although its immunomodulatory properties have been well characterized, the impact of testosterone on both the severity of viral infection and the efficacy of vaccination remain poorly understood. The severity of influenza increases with age in men, and as circulating testosterone concentrations also decline with age in men, I hypothesized that reduced testosterone contributes to age-associated increases in influenza severity. A murine model was used, and consistent with in humans, young male mice had greater testosterone concentrations than did aged males. Following IAV infection, aged male mice experienced greater disease severity, mortality, and pulmonary inflammation than young males, while control of viral replication was delayed. Removal of testosterone in young males increased disease severity, and pulmonary inflammation independent of changes in viral replication. Because testosterone in young male mice reduced pulmonary inflammation, I further hypothesized that testosterone was altering the immune response to IAV infection. Testosterone reduced IAV severity not by changing pulmonary cytokine activity, but instead by accelerating pulmonary leukocyte contraction. To identify which immune cell types were persisting in testosterone-depleted males, we further characterized the composition of pulmonary cellular infiltrates. Testosterone depletion accelerated the contraction of IAV-specific CD8+ T cells, while inhibiting the influx of eosinophils into the lungs following clearance of virus from the lungs. The effects of testosterone on IAV-specific CD8+ T cells were mediated androgen receptor signaling and dependent on the environment in which they reside. In contrast with IAV infection where the immune suppressive effects of testosterone are protective, in the context of vaccination any reduction in immune response may be detrimental. Adult females tend to develop greater adaptive immune responses than males following vaccination in both preclinical animal studies and human clinical trials. Following vaccination with irradiated transgenic P. berghei sporozoites expressing the P. falciparum CSP protein, adult female mice mounted greater adaptive immune responses and were better protected against challenge than adult males. No sex differences in adaptive immune responses or protection were observed in mice vaccinated prior to puberty, suggesting a role for sex steroid hormones. Depletion of testosterone in males increased, whereas rescue of testosterone decreased, adaptive immune responses and protection in males following parasite challenge. Taken together, these data suggest that testosterone confers protection during IAV infection by modulating the immune response, while testosterone concentrations in males reduce adaptive immunity and contributes to reduced malaria vaccine efficacy

The hypothesized relationship between host damage and the host immune response following infection, as presented in the context of the damage-response framework [17].

<p>When an immune response is “weak” (i.e., not sufficient to clear a pathogen), the damage caused by infection is high, and when an immune response is too “strong” (i.e., excessive enough to cause tissue damage), the damage caused by infection can also be high. Based on the literature presented, we hypothesize that a male bias in disease risk may be observed when weak immune responses underlie high levels of host damage and a female bias in disease risk may be observed when strong immune responses contribute to host damage. Several host factors, including sex chromosomal complement, concentrations of sex hormones, and behaviors can contribute to biases in the outcome of infection.</p

Sex differences in the intensity (i.e., pathogen load), prevalence (i.e., proportion of population with disease), incidence (i.e., new cases of disease), and severity (i.e., hospitalization or progression of disease state) of disease following microbial infections in humans.

<p>Sex differences in the intensity (i.e., pathogen load), prevalence (i.e., proportion of population with disease), incidence (i.e., new cases of disease), and severity (i.e., hospitalization or progression of disease state) of disease following microbial infections in humans.</p

Sex Reporting in Preclinical Microbiological and Immunological Research

Both sex (i.e., biological construct of male and female) and gender (i.e., social construct of masculine and feminine) impact the pathogenesis of diseases, including those caused by microbial infections. Following the 2015 NIH policy for consideration of sex as a biological variable in preclinical research, in 2018, authors of papers published in primary-research American Society for Microbiology (ASM) journals will be asked to report the sex of the research subjects and animals and of materials derived directly from them. To address the need for sex reporting in ASM journals, we systematically reviewed 2,928 primary-research articles published in six primary-research ASM journals (Antimicrobial Agents and Chemotherapy, Clinical and Vaccine Immunology, Infection and Immunity, Journal of Bacteriology, Journal of Virology, and mBio) in 2016. Approximately 37% of animal studies and 9% of primary cell culture papers published in 2016 would have been affected by the new sex-reporting policy. For animal studies (i.e., studies with any nonhuman vertebrate hosts), most published papers either did not report the sex of the animals or used only female animals, and a minority used only males or both sexes. For published studies using primary cells from diverse animal species (i.e., humans and nonhuman vertebrates), almost all studies failed to report the sex of donors from which the cells were isolated. We believe that reporting the sex of animals and even of the donors of derived cells could improve the rigor and reproducibility of research conducted in microbiology and immunology and published in ASM journals

Androgen receptor signaling in the lungs mitigates inflammation and improves the outcome of influenza in mice.

Circulating androgens can modulate immune cell activity, but the impact of androgens on viral pathogenesis remains unclear. Previous data demonstrate that testosterone reduces the severity of influenza A virus (IAV) infection in male mice by mitigating pulmonary inflammation rather than by affecting viral replication. To examine the immune responses mediated by testosterone to mitigate IAV-induced inflammation, adult male mice remained gonadally intact or were gonadectomized and treated with either placebo or androgen-filled (i.e., testosterone or dihydrotestosterone) capsules prior to sublethal IAV infection. Like intact males, treatment of gonadectomized males with androgens improved the outcome of IAV infection, which was not mediated by changes in the control of virus replication or pulmonary cytokine activity. Instead, androgens accelerated pulmonary leukocyte contraction to limit inflammation. To identify which immune cells were contracting in response to androgens, the composition of pulmonary cellular infiltrates was analyzed and revealed that androgens specifically accelerated the contraction of total pulmonary inflammatory monocytes during peak disease, as well as CD8+ T cells, IAV-specific CD8+ T numbers, cytokine production and degranulation by IAV-specific CD8+ T cells, and the influx of eosinophils into the lungs following clearance of IAV. Neither depletion of eosinophils nor adoptive transfer of CD8+ T cells could reverse the ability of testosterone to protect males against IAV suggesting these were secondary immunologic effects. The effects of testosterone on the contraction of immune cell numbers and activity were blocked by co-administration of the androgen receptor antagonist flutamide and mimicked by treatment with dihydrotestosterone, which was also able to reduce the severity of IAV in female mice. These data suggest that androgen receptor signaling creates a local pulmonary environment that promotes downregulation of detrimental inflammatory immune responses to protect against prolonged influenza disease

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

Abstract 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