The impact of semen exposure on the immune and microbial environments of the female genital tract.

Abstract

Background: Semen is an immunomodulatory fluid that induces mucosal changes at the female genital tract (FGT) for sperm survival and conception. Semen-induced alterations necessary for reproduction may also modulate the inflammatory environment related to HIV risk in women. This thesis investigated the impact of semen exposure on biomarkers of female genital inflammation (GI) and the persistence of these associations over time. Methods: Stored genital specimens were assessed from HIV-negative women participating in the CAPRISA 008 trial. Cervicovaginal lavage (CVL) samples were screened for Y-chromosome DNA (YcDNA) by real-time PCR as a biomarker of semen exposure within 15 days of genital sampling. Prostate-specific antigen (PSA) detection by ELISA stratified CVLs into semen exposure within 48 hours (PSA+YcDNA+) and between 3-15 days (PSA-YcDNA+). Vaginal cytokine concentrations, matrix metalloproteinases (MMPs), and tissue inhibitors of metalloproteinases (TIMPs) were assessed in CVLs using multiplexed ELISA. Endocervical T-cell frequencies were measured in cytobrushes by flow-cytometry. Vaginal microbes and sexually transmitted infections (STIs) were detected in vulvovaginal swabs by PCR. Results: Self-reported condom use as a measure of semen exposure was not associated with changes in the FGT microenvironments. Conversely, YcDNA detection predicted significant increases in several cytokines, barrier-related proteins, and Prevotella bivia detection (p=0.001). Since YcDNA detection alone was not associated with the immune environment linked to HIV risk, this thesis further investigated the contribution of more recent sex to female GI. PSA detection (semen exposure within 48 hours) was associated with higher YcDNA concentrations (p<0.0001), suggesting a relationship between the timing of semen exposure and vaginal YcDNA concentrations after condomless sex. In support of this, both PSA detection and higher YcDNA concentrations predicted significant increases in several cytokines, barrier-related proteins (MMP-2, TIMP-1, TIMP-4), and higher frequencies of activated CD4+HLA-DR+ T-cells (p=0.032) and CD4+CCR5+HLA-DR+ HIV targets (p=0.046). PSA detection was also associated with increased detection of several bacterial vaginosis (BV)-associated microbes and reduced Lactobacillus jensenii detection. Conclusion: Recent semen exposure contributes to the inflammatory environment associated with HIV risk in women. These studies highlight the need for clinical and immunological studies of STIs and their biomedical interventions to consider semen’s contribution to the immune and microbial microenvironments of the FGT.