Although women constitute half of all HIV-1–infected people worldwide (UNAIDS World AIDS Day Report, 2011), the earliest events in the female reproductive tract (FRT) during heterosexual HIV-1 transmission are poorly understood. Recently, we demonstrated that HIV-1 could directly impair the mucosal epithelial barrier in the FRT. This suggested that the HIV-1 envelope glycoprotein gp120 was being recognized by a membrane receptor on genital epithelial cells, leading to innate immune activation. In this study, we report that pattern-recognition receptors TLR2 and -4 bind to HIV-1 gp120 and trigger proinflammatory cytokine production via activation of NF-κB. The gp120–TLR interaction also required the presence of heparan sulfate (HS). Bead-binding assays showed that gp120 can bind to HS, TLR2, and TLR4, and studies in transfected HEK293 cells demonstrated that HS and TLR2 and -4 were necessary to mediate downstream signaling. Exposure to seminal plasma from HIV-1–infected and uninfected men with gp120 added to it induced a significant proinflammatory cytokine response from genital epithelial cells and disruption of tight junctions, indicating a role for gp120 in mucosal barrier disruption during HIV-1 heterosexual transmission. These studies provide, for the first time to our knowledge, a possible mechanism by which HIV-1 gp120 could directly initiate innate immune activation in the FRT during heterosexual transmission.

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Clinical and experimental studies have shown that estradiol (E2) confers protection against HIV and other sexually transmitted infections. Here, we investigated the underlying mechanism. Better protection in E2-treated mice, immunized against genital HSV-2, coincided with earlier recruitment and higher proportions of Th1 and Th17 effector cells in the vagina post-challenge, compared to placebo-treated controls. Vaginal APCs isolated from E2-treated mice induced 10-fold higher Th17 and Th1 responses, compared to APCs from progesterone-treated, placebo-treated, and estradiol-receptor knockout mice in APC-T cell co-cultures. CD11c+ DCs in the vagina were the predominant APC population responsible for priming these Th17 responses, and a potent source of IL-6 and IL-1β, important factors for Th17 differentiation. Th17 responses were abrogated in APC-T cell co-cultures containing IL-1β KO, but not IL-6 KO vaginal DCs, showing that IL-1β is a critical factor for Th17 induction in the genital tract. E2 treatment in vivo directly induced high expression of IL-1β in vaginal DCs, and addition of IL-1β restored Th17 induction by IL-1β KO APCs in co-cultures. Finally, we examined the role of IL-17 in anti-HSV-2 memory T cell responses. IL-17 KO mice were more susceptible to intravaginal HSV-2 challenge, compared to WT controls, and vaginal DCs from these mice were defective at priming efficient Th1 responses in vitro, indicating that IL-17 is important for the generation of efficient anti-viral memory responses. We conclude that the genital mucosa has a unique microenvironment whereby E2 enhances CD4+ T cell anti-viral immunity by priming vaginal DCs to induce Th17 responses through an IL-1-dependent pathway.

It is well established that interferon gamma (IFN-γ) production by CD4 T cells is critical for antiviral immunity against herpes simplex virus 2 (HSV-2) genital infection. However, the role of interleukin-17A (IL-17A) production by CD4 T cells in HSV-2 antiviral immunity is yet to be elucidated. Here we demonstrate that IL-17A plays an important role in enhancing antiviral T helper type 1 (T1) responses in the female genital tract (FGT) and is essential for effective protection conferred by HSV-2 vaccination. While IL-17A did not play a critical role during primary genital HSV-2 infection, seen by lack of differences in susceptibility between IL-17A-deficient () and wild-type (WT) C57BL/6 mice, it was critical for mediating antiviral responses after challenge/reexposure. Compared to WT mice, mice (i) infected intravaginally and reexposed or (ii) vaccinated intranasally and challenged intravaginally demonstrated poor outcomes. Following intravaginal HSV-2 reexposure or challenge, vaccinated mice had significantly higher mortality, greater disease severity, higher viral shedding, and higher levels of proinflammatory cytokines and chemokines in vaginal secretions. Furthermore, mice had impaired T1 cell responses after challenge/reexposure, with significantly lower proportions of vaginal IFN-γ CD4 T cells. The impaired T1 cell responses in mice coincided with smaller populations of IFN-γ CD4 tissue resident memory T (T) cells in the genital tract postimmunization. Taken together, these findings describe a novel role for IL-17A in regulating antiviral IFN-γ T1 cell immunity in the vaginal tract. This strategy could be exploited to enhance antiviral immunity following HSV-2 vaccination. T helper type 1 (T1) immunity, specifically interferon gamma (IFN-γ) production by CD4 T cells, is critical for protection against genital herpesvirus (HSV-2) infection, and enhancing this response can potentially help improve disease outcomes. Our study demonstrated that interleukin-17A (IL-17A) plays an essential role in enhancing antiviral T1 responses in the female genital tract (FGT). We found that in the absence of IL-17A, preexposed and vaccinated mice showed poor disease outcomes and were unable to overcome HSV-2 reexposure/challenge. IL-17A-deficient mice () had smaller populations of IFN-γ CD4 tissue resident memory T (T) cells in the genital tract postimmunization than did wild-type (WT) mice, which coincided with attenuated T1 responses postchallenge. This has important implications for developing effective vaccines against HSV-2, as we propose that strategies inducing IL-17A in the genital tract may promote more effective T1 cell immunity and better overall protection.

The gonococcal Opa proteins are an antigenically variable family of surface adhesins that bind human carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), CEACAM3, CEACAM5, and/or CEACAM6, cell surface glycoproteins that are differentially expressed on a broad spectrum of human cells and tissues. While they are presumed to be important for infection, the significance of various Opa-CEACAM-mediated cellular interactions in the context of the genital tract has remained unclear. Here, we observed that CEACAM1 and CEACAM5 are differentially expressed on epithelia lining the upper and lower portions of the human female genital tract, respectively. Using transgenic mouse lines expressing human CEACAMs in a manner that reflects this differential pattern, we considered the impact of Opa-CEACAM interactions during uncomplicated lower genital tract infections versus during pelvic inflammatory disease. Our results demonstrate that Opa-CEACAM5 binding on vaginal epithelia facilitates the long-term colonization of the lower genital tract, while Opa protein binding to CEACAM1 on uterine epithelia enhances gonococcal association and penetration into these tissues. While these Opa-dependent interactions with CEACAM-expressing epithelial surfaces promote infection, Opa binding by neutrophil-expressed CEACAMs counterbalances this by facilitating more effective gonococcal clearance. Furthermore, during uterine infections, CEACAM-dependent tissue invasion aggravates disease pathology by increasing the acute inflammatory response. Together, these findings demonstrate that the outcome of infection is determined by both the cell type-specific expression of human CEACAMs and the CEACAM specificity of the Opa variants expressed, which combine to determine the level of gonococcal association with the genital mucosa versus the extent of CEACAM-dependent inflammation and gonococcal clearance by neutrophils.