Mucosal Immunity in the Human Female Reproductive Tract

TIME Is Ticking for Cervical Cancer

Cervical cancer (CC) is a major health problem among reproductive-age females and comprises a leading cause of cancer-related deaths. Human papillomavirus (HPV) is the major risk factor associated with CC incidence. However, lifestyle is also a critical factor in CC pathogenesis. Despite HPV vaccination introduction, the incidence of CC is increasing worldwide. Therefore, it becomes critical to understand the CC tumor immune microenvironment (TIME) to develop immune cell-based vaccination and immunotherapeutic approaches. The current article discusses the immune environment in the normal cervix of adult females and its role in HPV infection. The subsequent sections discuss the alteration of different immune cells comprising CC TIME and their targeting as future therapeutic approaches.

Enhanced IgA coating of bacteria in women with Lactobacillus crispatus-dominated vaginal microbiota

BACKGROUND

Immunoglobulin A (IgA) plays an important role in maintaining a healthy intestinal microbiome, but little is known about the interaction between local immunoglobulins and the vaginal microbiome. We assessed immunoglobulins (unbound and bound to bacteria), their association with vaginal microbiota composition and the changes over time in 25 healthy women of reproductive age.

RESULTS

In both Lactobacillus crispatus-dominated and non-L. crispatus-dominated microbiota, IgA and IgG (unbound and bound to bacteria) were higher during menses (T = 1) compared to day 7‑11 (T = 2) and day 17‑25 (T = 3) after menses onset. The majority of vaginal bacteria are coated with IgA and/or IgG. Women with L. crispatus-dominated microbiota have increased IgA coating of vaginal bacteria compared to women with other microbiota compositions, but contained less IgA per bacterium. Presence of a dominantly IgA-coated population at T = 2 and/or T = 3 was also strongly associated with L. crispatus-dominated microbiota. In women with non-L. crispatus-dominated microbiota, more bacteria were uncoated. Unbound IgA, unbound IgG, and bound IgG levels were not associated with microbiota composition.

CONCLUSIONS

In conclusion, L. crispatus-dominated vaginal microbiota have higher levels of bacterial IgA coating compared to non-L. crispatus-dominated vaginal microbiota. Similar to its regulating function in the intestinal tract, we hypothesize that IgA is involved in maintaining L. crispatus-dominated microbiota in the female genital tract. This may play a role in L. crispatus-associated health benefits. Video abstract.

Hormonal Contraception and HIV-1 Acquisition: Biological Mechanisms

Access to effective affordable contraception is critical for individual and public health. A wide range of hormonal contraceptives (HCs), which differ in composition, concentration of the progestin component, frequency of dosage, and method of administration, is currently available globally. However, the options are rather limited in settings with restricted economic resources that frequently overlap with areas of high HIV-1 prevalence. The predominant contraceptive used in sub-Saharan Africa is the progestin-only three-monthly injectable depot medroxyprogesterone acetate. Determination of whether HCs affect HIV-1 acquisition has been hampered by behavioral differences potentially confounding clinical observational data. Meta-analysis of these studies shows a significant association between depot medroxyprogesterone acetate use and increased risk of HIV-1 acquisition, raising important concerns. No association was found for combined oral contraceptives containing levonorgestrel, nor for the two-monthly injectable contraceptive norethisterone enanthate, although data for norethisterone enanthate are limited. Susceptibility to HIV-1 and other sexually transmitted infections may, however, be dependent on the type of progestin present in the formulation. Several underlying biological mechanisms that may mediate the effect of HCs on HIV-1 and other sexually transmitted infection acquisition have been identified in clinical, animal, and ex vivo studies. A substantial gap exists in the translation of basic research into clinical practice and public health policy. To bridge this gap, we review the current knowledge of underlying mechanisms and biological effects of commonly used progestins. The review sheds light on issues critical for an informed choice of progestins for the identification of safe, effective, acceptable, and affordable contraceptive methods.

Esophageal mucosa in HIV infection: A"deeper" look at this little spoken organ

BACKGROUND AND AIM

Although the esophagus is a common site of opportunistic infection in AIDS patients, little is known about the impact of HIV as well as opportunistic infection in the esophageal mucosa. Our aim is to analyze the esophageal immune profile in HIV+ patients with different immunological status with and without the opportunistic Candida infection.

METHODS

Immunohistochemistry to CD4⁺ and CD8⁺ T-cells, γ-interferon, transforming growth factor-β, interleukin (IL)-4, IL-6, IL-13, and IL-17 was performed in esophageal samples of 40 chronically HIV+ patients under highly active antiretroviral therapy (16 with Candida esophagitis, 12 virologically non-supressed with blood CD4 count < 500, and 12 virologically suppressed with blood CD4 count > 500; the latter two groups without esophageal candidiasis). The controls were 12 HIV-negative healthy individuals.

RESULTS

Esophageal CD4⁺ T-cell expression in HIV+ patients did not differ from the control group (P = 0.50). Mucosal CD8⁺ T-cell expression was significantly increased in HIV+ patients (P = 0.0018). Candida esophagitis and virologically non-supressed HIV+ patients with CD4 < 500 showed an increased expression of IL-17 and IL-6 with fewer expressions of γ-interferon, more attenuated in the latter group. Transforming growth factor-β was increased only in virologically suppressed HIV+ patients with CD4 > 500. IL-4 and IL-13 were similar to the control group.

CONCLUSION

In contrast to CD8⁺ T-cell expression, esophageal CD4⁺ T-cell expression does not reflect the HIV+ patient's immunological status. T-helper 17 (Th17) response seems to play a role in the esophageal mucosa of virologically non-supressed HIV+ patients with blood CD4 < 500. Candida esophagitis showed a Th1/Th17 response but seems to be dominantly regulated by the Th17 pathway.

Innate and adaptive immune responses in male and female reproductive tracts in homeostasis and following HIV infection

The male and female reproductive tracts are complex microenvironments that have diverse functional demands. The immune system in the reproductive tract has the demanding task of providing a protective environment for a fetal allograft while simultaneously conferring protection against potential pathogens. As such, it has evolved a unique set of adaptations, primarily under the influence of sex hormones, which make it distinct from other mucosal sites. Here, we discuss the various components of the immune system that are present in both the male and female reproductive tracts, including innate soluble factors and cells and humoral and cell-mediated adaptive immunity under homeostatic conditions. We review the evidence showing unique phenotypic and functional characteristics of immune cells and responses in the male and female reproductive tracts that exhibit compartmentalization from systemic immunity and discuss how these features are influenced by sex hormones. We also examine the interactions among the reproductive tract, sex hormones and immune responses following HIV-1 infection. An improved understanding of the unique characteristics of the male and female reproductive tracts will provide insights into improving clinical treatments of the immunological causes of infertility and the design of prophylactic interventions for the prevention of sexually transmitted infections.

Humoral immune responses to HIV in the mucosal secretions and sera of HIV-infected women

Although sera and all external secretions contain antibodies to human immunodeficiency virus (HIV), their levels, specificity, isotypes, and relevant effector functions display a great degree of variability. Antibodies that bind HIV antigens and neutralize the virus are predominantly associated with the IgG isotype in sera and in all external secretions, even where total levels of IgG are much lower than those of IgA. Rectal fluid that contains high IgA, but low IgG levels, displayed low neutralizing activity independent of antibodies. Therefore, external secretions should be evaluated before and after selective depletion of Ig. At the systemic level, HIV-specific IgA may interfere with the effector functions of IgG, as suggested by recent studies of individuals systemically immunized with an experimental HIV vaccine. Although HIV-specific IgG and IgA antibodies may exhibit their protective activities at mucosal surfaces through interference with viral entry and local neutralization at the systemic level, such antibodies may display discordant effector functions.

Distinct cytokine patterns in semen influence local HIV shedding and HIV target cell activation

BACKGROUND

Semen is the main vector for human immunodeficiency virus (HIV) transmission from men to women. We investigated the influence of cytokines in semen on local HIV burden and activated T cells.

METHODS

Blood and semen were collected from 42 HIV-negative and 38 HIV-positive men. Concentrations of 20 cytokines were measured by Luminex, and frequencies of activated T cells were measured by flow cytometry.

RESULTS

Semen contained higher concentrations of proinflammatory (monocyte chemotactic protein-1, interleukin [IL]-8, IL-6, Fractalkine, macrophage inflammatory protein (MIP)-1β, granulocyte macrophage colony-stimulating factor) and adaptive cytokines (IL-7 and IL-15) and higher frequencies of activated T cells compared to blood. Plasma IL-2, eotaxin, MIP-1β, and IL-15 and semen eotaxin and granulocyte colony-stimulating factor (G-CSF) concentrations were associated with T-cell activation. Cytokines in semen were highly coregulated in HIV-negative men; however, this network was disrupted during HIV infection. Several cytokines in semen correlated with HIV shedding (G-CSF, tumor necrosis factor-alpha [TNF-α], interferon-gamma [IFN-γ], IL-10).

CONCLUSION

Higher levels of inflammation and T-cell activation were observed in semen compared with blood. Seminal G-CSF, which influences neutrophil survival, T-cell function, and dendritic cell activation, was associated with T-cell activation and HIV shedding and may be an important target for reducing HIV shedding or risk.

Endocrine control of mucosal immunity in the female reproductive tract: impact of environmental disruptors

The complexity of the human female reproductive tract (FRT) with its multiple levels of hormonally controlled immune protection has only begun to be understood. Dissecting the functions and roles of the immune system in the FRT is complicated by the differential hormonal regulation of its distinct anatomical structures that vary throughout the menstrual cycle. Although many fundamental mechanisms of steroid regulation of reproductive tract immune function have been determined, the effects of exogenous synthetic steroids or endocrine disruptors on immune function and disease susceptibility in the FRT have yet to be evaluated in detail. There is increasing evidence that environmental or synthetic molecules can alter normal immune function. This review provides an overview of the innate and adaptive immune systems, the current status of immune function in the FRT and the potential risks of environmental or pharmacological molecules that may perturb this system.

Epithelial cell secretions from the human female reproductive tract inhibit sexually transmitted pathogens and Candida albicans but not Lactobacillus

Female reproductive tract (FRT) epithelial cells protect against potential pathogens and sexually transmitted infections. The purpose of this study was to determine if epithelial cells from the upper FRT secrete antimicrobials that inhibit reproductive tract pathogens that threaten women's health. Apical secretions from primary cultures of Fallopian tube, uterine, cervical, and ectocervical epithelial cells were incubated with Neisseria gonorrhoeae, Candida albicans (yeast and hyphal forms), human immunodeficiency virus 1 (HIV-1), and Lactobacillus crispatus before being tested for their ability to grow and/or infect target cells. Epithelial cell secretions from the upper FRT inhibit N. gonorrhoeae and both forms of Candida, as well as reduce HIV-1 (R5) infection of target cells. In contrast, none had an inhibitory effect on L. crispatus. An analysis of cytokines and chemokines in uterine secretions revealed several molecules that could account for pathogen inhibition. These findings provide definitive evidence for the critical role of epithelial cells in protecting the FRT from infections, without comprising the beneficial presence of L. crispatus, which is part of the normal vaginal microflora of humans.

Methods for evaluation of humoral immune responses in human genital tract secretions

The compilation of epidemiological, virological, and immunological data clearly indicates that HIV-1 infection must be considered primarily as a disease of the mucosal immune system. The earliest and most dramatic alterations of the immune system occur in the mucosal compartment. However, the mucosal immune systems of the genital and intestinal tracts display remarkable immunological differences that must be considered in the evaluation of humoral immune responses in HIV-1-infected individuals or in volunteers immunized with experimental HIV vaccines. In this regard, marked differences in the dominant Ig isotypes, molecular forms of HIV-1-specific antibodies, and their distinct effector functions in the genital versus intestinal tracts must be carefully evaluated and considered in the measurement and interpretation of humoral immune responses. Appropriate controls and alternative immunochemical assays should be used to complement and confirm results generated by ELISA, which are prone to false positivity. Special precautions and rigorous controls must be used in the evaluation of antibody-mediated virus neutralization in external secretions of the genital and intestinal tracts.

Tolerance and protection against infection in the genital tract

The genital tract is a unique immunological environment that must support the reproductive function and resist infection. Particularly in the female tract, immunoregulatory and immunosuppressive activities that permit the growth of the fetus create an environment that can readily be exploited by microbes that have become well-adapted to this location. Cellular and molecular mediators of immune responses differ from those found at other mucosal surfaces. Mechanisms of immune response induction and delivery, as well as immune effector functions at the genital mucosae need to be considered in the development of vaccines against infections of the genital tract.

Chlamydia trachomatis, a hidden epidemic: effects on female reproduction and options for treatment

The number of genital tract Chlamydia trachomatis infections is steadily increasing worldwide, with approximately 50-70% of infections asymptomatic. There is currently no uniform screening practice, current antibiotic treatment has failed to prevent the increased incidence, and there is no vaccine available. We examined studies on the epidemiology of C. trachomatis infections, the effects infections have on the female reproductive tract and subsequent reproductive health and what measures are being taken to reduce these problems. Undetected or multiple infections in women can lead to the development of severe reproductive sequelae, including pelvic inflammatory disease and tubal infertility. There are two possible paradigms of chlamydial pathogenesis, the cellular and immunological paradigms. While many vaccine candidates are being extensively tested in animal models, they are still years from clinical trials. With no vaccine available and antibiotic treatment unable to halt the increased incidence, infection rates will continue to increase and cause a significant burden on health care systems.

Dendritic cell-mediated induction of mucosal cytotoxic responses following intravaginal immunization with the nontoxic B subunit of cholera toxin

The use of the nontoxic B subunit of cholera toxin (CTB) as mucosal adjuvant and carrier-delivery system for inducing secretory Ab responses has been documented previously with different soluble Ags. In this study, we have evaluated this approach for inducing CTL responses against a prototype Ag, OVA, in the female genital mucosa. We report here the ability of an immunogen comprised of CTB conjugated to OVA (CTB-OVA) given by intravaginal (ivag) route to induce genital OVA-specific CTLs in mice. Using adoptive transfer models, we demonstrate that ivag application of CTB-OVA activates OVA-specific IFN-gamma-producing CD4 and CD8 T cells in draining lymph nodes (DLN). Moreover, ivag CTB induces an expansion of IFN-gamma-secreting CD8+ T cells in DLN and genital mucosa and promotes Ab responses to OVA. In contrast, ivag administration of OVA alone or coadministered with CTB failed to induce such responses. Importantly, we demonstrate that ivag CTB-OVA generates OVA-specific CTLs in DLN and the genital mucosa. Furthermore, genital CD11b+ CD11c+ dendritic cells (DCs), but not CD8+ CD11c+ or CD11c- APCs, present MHC class I epitopes acquired after ivag CTB-OVA, suggesting a critical role of this DC subset in the priming of genital CTLs. Inhibition studies indicate that the presentation of OVA MHC class I epitopes by DCs conditioned with CTB-OVA involves a proteasome-dependent and chloroquine-sensitive mechanism. These results demonstrate that CTB is an efficient adjuvant-delivery system for DC-mediated induction of genital CTL responses and may have implications for the design of vaccines against sexually transmitted infections.

Mucosal vaccines: the promise and the challenge

Most infectious agents enter the body at mucosal surfaces and therefore mucosal immune responses function as a first line of defence. Protective mucosal immune responses are most effectively induced by mucosal immunization through oral, nasal, rectal or vaginal routes, but the vast majority of vaccines in use today are administered by injection. As discussed in this Review, current research is providing new insights into the function of mucosal tissues and the interplay of innate and adaptive immune responses that results in immune protection at mucosal surfaces. These advances promise to accelerate the development and testing of new mucosal vaccines against many human diseases including HIV/AIDS.

Innate and adaptive immunity in female genital tract: cellular responses and interactions

The mucosal immune system in the female reproductive tract (FRT) has evolved to meet the unique requirements of dealing with sexually transmitted bacterial and viral pathogens, allogeneic spermatozoa, and the immunologically distinct fetus. Analysis of the FRT indicates that the key cells of the innate and adaptive immune systems are present and functionally responsive to antigens. Acting through Toll-like receptors in the Fallopian tubes, uterus, cervix, and in the vagina, epithelial cells, macrophages, natural killer cells, and neutrophils confer protection through the production of chemokines and cytokines, which recruit and activate immune cells, as well as bactericidal and virucidal agents, which confer protection at times when adaptive immunity is downregulated by sex hormones to meet the constraints of procreation. The overall goal of this paper is to define the innate immune system in the FRT and, where possible, to define the regulatory influences that occur during the menstrual cycle that contribute to protection from and susceptibility to potential pathogens. By understanding the nature of this protection and the ways in which innate and adaptive immunity interact, these studies provide the opportunity to contribute to the foundation of information essential for ensuring reproductive health.

Mucosal immunoglobulins

Due to their vast surface area, the mucosal surfaces of the body represent a major site of potential attack by invading pathogens. The secretions that bathe mucosal surfaces contain significant levels of immunoglobulins (Igs), which play key roles in immune defense of these surfaces. IgA is the predominant antibody class in many external secretions and has many functional attributes, both direct and indirect, that serve to prevent infective agents such as bacteria and viruses from breaching the mucosal barrier. This review details current understanding of the structural and functional characteristics of IgA, including interaction with specific receptors (such as Fc(alpha)RI, Fc(alpha)/microR, and CD71) and presents examples of the means by which certain pathogens circumvent the protective properties of this important Ig.

Immunologic Uniqueness of the Genital Tract: Challenge for Vaccine Development

Although the genital tract is considered to be a component of the mucosal immune system, it displays several distinct features not shared by other typical mucosal tissues and external secretions. Both male and female genital tract tissues lack inductive mucosal sites analogous to intestinal Peyer's patches. Consequently, local humoral and cellular immune responses stimulated by infections [with e.g. Neisseria gonorrhoeae, Chlamydia trachomatis, papilloma virus, and human immunodeficiency virus (HIV-1)] are weak or absent, and repeated local intravaginal immunizations result in minimal humoral responses. In contrast to typical external secretions such as intestinal fluid that contain secretory immunoglobulin A (S-IgA) as the dominant isotype, semen and cervico-vaginal fluid contain more IgG than IgA. Furthermore, irrespective of the route of infection, humoral immune responses to HIV-1 are dominated by specific IgG and low or absent IgA antibodies in all external secretions. Because a significant proportion of IgG in genital tract secretions is derived from the circulation, systemic immunization may provide protective IgG antibody-mediated immunity in the genital tract. Furthermore, combined systemic and mucosal (oral, rectal, and especially intranasal) immunization may induce protective humoral responses in both the systemic and mucosal compartments of the immune system.