Pharmacological HIV-1 reactivation to reverse latent infection has been extensively studied. However, HIV-1 reactivation also occurs naturally, as evidenced by occasional low-level viremia (“viral blips”) during antiretroviral treatment (ART). Clarifying where blips originate from and how they happen could provide clues to stimulate latency reversal more effectively and safely or to prevent viral rebound following ART cessation. We studied HIV-1 reactivation in the female genital tract, a dynamic anatomical target for HIV-1 infection throughout all disease stages. We found that primary endocervical epithelial cells from several women reactivated HIV-1 from latently infected T cells. The endocervical cells’ HIV-1 reactivation capacity further increased upon Toll-like receptor 3 stimulation with poly(I·C) double-stranded RNA or infection with herpes simplex virus 2 (HSV-2). Notably, acyclovir did not eliminate HSV-2-induced HIV-1 reactivation. While endocervical epithelial cells secreted large amounts of several cytokines and chemokines, especially tumor necrosis factor alpha (TNF-α), CCL3, CCL4, and CCL20, their HIV-1 reactivation capacity was almost completely blocked by TNF-α neutralization alone. Thus, immunosurveillance activities by columnar epithelial cells in the endocervix can cause endogenous HIV-1 reactivation, which may contribute to viral blips during ART or rebound following ART interruption. IMPORTANCE A reason that there is no universal cure for HIV-1 is that the virus can hide in the genome of infected cells in the form of latent proviral DNA. This hidden provirus is protected from antiviral drugs until it eventually reactivates to produce new virions. It is not well understood where in the body or how this reactivation occurs. We studied HIV-1 reactivation in the female genital tract, which is often the portal of HIV-1 entry and which remains a site of infection throughout the disease. We found that the columnar epithelial cells lining the endocervix, the lower part of the uterus, are particularly effective in reactivating HIV-1 from infected T cells. This activity was enhanced by certain microbial stimuli, including herpes simplex virus 2, and blocked by antibodies against the inflammatory cytokine TNF-α. Avoiding HIV-1 reactivation could be important for maintaining a functional HIV-1 cure when antiviral therapy is stopped.

Bacterial vaginosis (BV) is a vaginal dysbiotic condition linked to negative gynecological and reproductive sequelae. Flagellated bacteria have been identified in women with BV, including Mobiluncus spp. and BV-associated bacterium-1 (BVAB1), an uncultivated, putatively flagellated species. The host response to flagellin mediated through toll-like receptor-5 (TLR5) has not been explored in BV. Using independent discovery and validation cohorts, we examined the hypothesis that TLR5 deficiency–defined by a dominant negative stop codon polymorphism rs5744168–is associated with an increased risk for BV and increased colonization with flagellated bacteria associated with BV (BVAB1, Mobiluncus curtisii, Mobiluncus mulieris). TLR5 deficiency was not associated with BV status and TLR5 deficient women had decreased colonization with BVAB1 in both cohorts. We stimulated HEK-hTLR5-overexpressing, NF-kB reporter cells with whole, heat-killed M. mulieris or M. curtisii, and with partially purified flagellin from these species; as BVAB1 is uncultivated, we used cervicovaginal lavage (CVL) supernatant from women colonized with BVAB1 for stimulation. While heat-killed M. mulieris and CVL from women colonized with BVAB1 stimulate a TLR5-mediated response, heat-killed M. curtisii did not. In contrast, partially purified flagellin from both Mobiluncus species stimulated a TLR5-mediated response in vitro. We observed no correlation between vaginal IL-8 and flagellated BVAB concentrations among TLR5 sufficient women. Inter-species variation in accessibility of flagellin recognition domains may be responsible for these observations as reflected in the potentially novel flagellin products encoded by Mobiluncus species versus those encoded by BVAB1.