Induction of Human β-Defensin-2 by Vaginal Lactobacillus crispatus Strains in Vaginal Epithelial Cells Correlates With Their Adhesion Abilities

Abstract Background The human vaginal microbiota is dominated by lactobacilli, with Lactobacillus crispatus associated with reproductive health. Human β-defensin-2 (HβD-2), a vaginal fluid antimicrobial peptide, correlates with spontaneous births. However, their relationships remain poorly understood. We identified L. crispatus strains that stimulate vaginal epithelial cells to secrete HβD-2. Methods Human vaginal epithelial cells VK2/E6E7 were co-incubated with live or heat-killed L. crispatus or L. gasseri strains. Complementary DNA was synthesized from cellular RNA, and HβD2, IL8, TNFα, and MUC1 mRNA levels were quantified by quantitative PCR. HβD-2 levels were measured using ELISA. Adherent Lactobacillus cells on VK2/E6E7 were stained with DAPI, and bacterial cell count was determined using a fluorescence microscope. Results Two L. crispatus strains, HMS-115 and HMS-122, significantly increased HβD2 mRNA expression in VK2/E6E7 cells. The remaining eighteen strains showed HβD2 mRNA levels comparable to those of the Dulbecco's phosphate-buffered saline control group. This increase in HβD2 mRNA expression correlated with each strain's adhesion ability towards VK2/E6E7 cells. Heat inactivation of L. crispatus cells did not impair HMS-115's ability to enhance HβD2 mRNA and protein expression, nor did it affect its adherence properties. Furthermore, incubation with live HMS-115 cells induced pro-inflammatory cytokine gene expression in VK2/E6E7 cells; however, heat-killed cells did not. Conclusions Only L. crispatus strains HMS-115 and HMS-122 stimulated HβD-2 production in vaginal epithelial cells. This ability correlated with the adhesion capacity of the Lactobacilli to vaginal epithelial cells, regardless of bacterial viability. Thus, the beneficial effects of L. crispatus strains may include promoting HβD-2 production. Lay Summary Human β-defensin-2 (HβD-2) is a vaginal fluid antimicrobial peptide whose levels correlate with spontaneous births. In this study, we assessed HβD2 mRNA levels in vaginal epithelial cells after incubation with various L. crispatus or L. gasseri strains. We found that the L. crispatus strains HMS-115 and HMS-122 stimulated HβD-2 production in vaginal epithelial cells. The ability to promote HβD-2 production in these cells correlated with strong adherence to vaginal epithelial cells. Therefore, the beneficial effects of L. crispatus strains may also include promoting HβD-2 production.