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Objective: To investigate interactions of vaginal epithelial cells (VEC) with Candida albicans and the protective effect of Lactobacillus crispatus on VEC. Methods: VK2/E6E7 VEC cell line was cultured. Candida albicans and Lactobacillus crispatus suspension were prepared respectively. Ultrastructural morphological changes of VEC infected with Candida albicans and treated with Lactobacillus crispatus were observed by scanning electron microscope (SEM). Results: Candida albicans invaded into VEC mainly through endocytosis after an early infection of 6 hours. Pseudopods of VEC increased, contacted and covered the surface of pseudohyphae. After 12 hours infection, active penetration developed into the predominant invasion mechanism. Candida albicans directly penetrated through VEC, destroyed the surface structures, and even led to cell death. A reduction of pseudopods on VEC was observed. After co-incubation with Lactobacillus crispatus, SEM revealed a morphological recovery of VEC and destruction of pseudohyphae. Conclusion: s Candida albicans invade VEC mainly through endocytosis and active penetration. Lactobacillus crispatus could utilize occupying effect to exert protective effect on VEC during the infection with Candida albicans.

Background: Vulvovaginal candidiasis is caused by Candida albicans. The vaginal epithelium, as the first site of the initial stage of infection by pathogens, plays an important role in resisting genital tract infections. Moreover, lactobacilli are predominant members of the vaginal microbiota that help to maintain a normal vaginal microenvironment. Therefore, Lactobacillus crispatus was explored for its capacity to intervene in the immune response of vaginal epithelial cells VK2/E6E7 to C. albicans., Methods: We examined the interleukin-2 (IL-2), 4, 6, 8, and 17 produced by VK2/E6E7 cells infected with C. albicans and treated with L. crispatus in vitro. The capacity of L. crispatus to adhere to VK2/E6E7 and inhibit C. albicans growth was also tested by scanning electron microscopy (SEM) and adhesion experiments., Results: Compared with group VK2/E6E7 with C. albicans, when treated with L. crispatus, the adhesion of C. albicans to VK2/E6E7 cells decreased significantly by 52.87 ± 1.22%, 47.03 ± 1.35%, and 42.20 ± 1.55% under competition, exclusion, and displacement conditions, respectively. SEM revealed that the invasion of C. albicans into VK2/E6E7 cells was caused by induced endocytosis and active penetration. L. crispatus could effectively protect the cells from the virulence of hyphae and spores of C. albicans and enhance the local immune function of the VK2/E6E7 cells. The concentrations of IL-2, 6, and 17 were upregulated significantly (P < 0.01) and that of IL-8 were downregulated significantly (P < 0.01) in infected VK2/E6E7 cells treated with L. crispatus. The concentration of IL-4 was similar to that of the group VK2/E6E7 with C. albicans (24.10 ± 0.97 vs. 23.12 ± 0.76 pg/ml, P = 0.221)., Conclusions: L. crispatus can attenuate the virulence of C. albicans, modulate the secretion of cytokines and chemokines, and enhance the immune response of VK2/E6E7 cells in vitro. The vaginal mucosa has a potential function in the local immune responses against pathogens that can be promoted by L. crispatus., Competing Interests: There are no conflicts of interest.

Objective: To investigate the function of IgG secreted by vaginal epithelial cells in natural resistance to vulvovaginal candidiasis. Methods: (1)Immunohistochemical method was used to determine the expression of IgG secreted by normal vaginal epithelial cells VK2/E6E7.(2)Samples were divided into three groups by different proportions of VK2/E6E7 cells to Candida albicans ,including Candida albicans: VK2/E6E7 cells were 1∶10, 1∶1[yeast+ cells(1∶10)group and yeast+ cells(1∶1)group]and VK2/E6E7 cells as blank control group. The growth status of 3 groups were observed under inverted microscope after 24 hours. ELISA method was used to detect the production of IgG in 3 groups after 0, 3, 6, 12, 24, 48 hours. Results: (1)Immunohistochemical method showed normal vaginal epithelial cells were polygonal with pale blue nucleus and cytoplasm were distributed by brown granules, which indicated that IgG were strongly positive. While negative control group just had light blue nuclei.(2)Inverted microscope observation represented that control group had a clear outline, strong refraction and large nuclei with cobblestone-like appearance. After yeast+cells(1∶10)group co-cultured for 24 hours, Candida albicans begin to sprout and transformed to hyphae. VK2/E6E7 cells and Candida albicans were close to each other with vacuoles and small black granules in the cytoplasm. The morphology of cells were complete. Yeast+ cells(1∶1)group showed obvious invasion effect of Candida albicans to VK2/E6E7 cells with vigorous growth of hyphae, the decreased number and incomplete morphology of cells. Moreover, the connection of cells were loose. ELISA assay showed that there were statistically significant difference of IgG secretions between the 3 groups after 0, 3, 6, 12, 24, 48 hours( P <0.05). After stimulation of Candida albicans, secretion of IgG was significantly lower than that in the control group. The statistical difference of IgG secretions between yeast+ cells(1∶10)group and yeast+ cells(1∶1)group after 3, 6, 12, 24 hours were dramatic( P <0.05). The peak of IgG production showed when the ratio of Candida albicans and VK2/E6E7 was 1∶1 after 24 hours co-cultured(1.61±0.05)μg/ml. Conclusions: Candida albicans has a significant invasion role on epithelial cells. With increasing concentrations of Candida albicans, the invasion effect will be enhenced. While, after the vaginal epithelial cells co-cultured with Candida albicans, the secretion of IgG decreased significantly.