Influence of lactic acid on endogenous and viral RNA-induced immune mediator production by vaginal epithelial cells.

Objective: To evaluate the influence of lactic acid on immune mediator release from vaginal epithelial cells.
Methods: The human vaginal epithelial cell line, VK2/E6E7, was cultured in the presence or absence of physiological concentrations of lactic acid, and in the presence or absence of the viral Toll-like receptor 3 agonist, poly (inosinic acid:cytidylic acid). Supernatants were assayed by enzyme-linked immunosorbent assay (ELISA) for interleukin (IL)-1β, IL-6, IL-8, IL-23, transforming growth factor (TGF)-β and secretory leukocyte protease inhibitor.
Results: Vaginal epithelial cells spontaneously released IL-1β (25.9 pg/mL), IL-8 (1.0 ng/mL), TGF-β (175 pg/mL), and secretory leukocyte protease inhibitor (33.8 ng/mL). Only TGF-β production was marginally enhanced (49%) by addition of lactic acid alone. Poly (inosinic acid:cytidylic acid) by itself stimulated the release of IL-6 (305 pg/mL) and enhanced IL-8 production (2.8 ng/mL). The combination of poly (inosinic acid:cytidylic acid) and lactic acid markedly increased IL-8 production (5.0 ng/mL) and induced the release of IL-1β (96.2 pg/mL). The poly (inosinic acid:cytidylic acid)-mediated lactic acid effect on IL-1β and IL-8 release was abrogated when the lactic acid was neutralized or if acetic acid was substituted for lactic acid.
Conclusion: Lactic acid enhances the release of selective mediators from vaginal epithelial cells and stimulates antiviral immune responses.