Innate immune responses of vaginal epithelium and activity of monoclonal antibody-based microbicide in the presence of lactic acid, a lactobacillus metabolite
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Sexually transmitted infections (STIs) such as gonorrhea, herpes simplex virus 2 (HSV 2), hepatitis C, human papilloma viruses (HPV) and human immunodeficiency virus type 1 (HIV) are a global health concern affecting millions of lives. Although extensive efforts have been geared towards prevention and treatment of STIs, little progress has been achieved. Recently, efforts to develop microbicides have been focused on the commensal bacterial species that comprise the vaginal microbiome and their role in immunity and disease pathogenesis. The lower FRT which includes the cervix and vagina has endogenous bacterial species that are supported by the mucosal epithelium. Lactobaccilli are the dominant endogenous bacterial species in the vagina of most women; lactobacilli convert glycogen to lactic acid (LA) which maintains a low pH environment in the vagina and serves as a deterrent to infectious organisms. The purpose of this research project was to determine the effects of LA on vaginal integrity and inflammation in a vaginal epithelial cell (VEC) tissue model, and on the ability of the broadly neutralizing anti-HIV antibody, VRCO1, to inactivate HIV in vitro. Effects of LA exposure on the viability and integrity of vaginal epithelium were determined by histology, MTT assay and measurement of transepithelial electric resistance (TEER). In addition, an enzyme-linked immunosorbent assay (ELISA) was used to measure concentrations of cytokines secreted by the VEC epithelial cells in response to different doses of LA. Using TLR agonists to simulate infection in the VEC model, we tested the hypothesis that LA has anti-inflammatory properties that modulate immune responses of the vaginal epithelium. We assessed the effect of LA on the neutralization activity of the anti-HIV-1 monoclonal antibody VRCO1 in the TZM-bl HIV neutralization assay. Tissue morphology and integrity were not affected by exposure to LA. Low concentrations of IL-1β and RANTES were expressed by VEC tissues in response to L-LA treatment. VEC tissues expressed significantly elevated concentrations of IL-1RA (p<0.0001), an anti-inflammatory cytokine, in response to LA regardless of incubation time and LA doses. In addition, treatment of VEC tissues with Poly I: C in the presence of LA dampened upregulated expression of IL-1β, TNF-alpha and IL-6 in response to the TLR 3 agonist. LA also elicited significantly higher IL-1RA concentrations when apically added to the TLR agonist-treated VEC tissues. These data suggest that LA elicits an anti-inflammatory response in the vaginal epithelium. LA acidic conditions as low as pH 3.5 did not affect the ability of VRC01, to prevent HIV infection. We found that LA, at concentrations present in vaginal secretions of normal women, inhibited the inflammatory response to a TLR agonist, possibly due to upregulated Il-1RA synthesis. In addition, the functionality of VRCO1 in an acidic milieu was not diminished, providing evidence that antibodies can function in the low pH vaginal environment. This report highlights the potential use of LA in the vagina as a microbicide due to its virucidal activity and anti-inflammatory properties. It also indicates that monoclonal antibody-based vaginal microbicides will not be neutralized by LA. There is still a need to elucidate the exact mechanisms by which LA confers immuno-modulatory properties within the female reproductive tract.