Abstract
The lower female reproductive tract (FRT) is comprised of the cervix and vagina, surfaces that are continuously exposed to a variety of commensal and pathogenic organisms. Sexually transmitted viruses, such as herpes simplex virus type 2 (HSV-2), have to traverse the mucosal epithelial lining of the FRT to establish infection. The majority of current culture systems that model the host-pathogen interactions in the mucosal epithelium have limitations in simulating physiological conditions as they employ a liquid-liquid interface (LLI), in which both apical and basolateral surfaces are submerged in growth medium. We designed the current study to simulate in vivo conditions by growing an immortalized vaginal epithelial cell line (Vk2/E6E7) in culture with an air-liquid interface (ALI) and examined the effects of female sex hormones on their growth, differentiation, and susceptibility to HSV-2 under these conditions, in comparison to LLI cultures. ALI conditions induced Vk2/E6E7 cells to grow into multi-layered cultures compared to the monolayers present in LLI conditions. Vk2 cells in ALI showed higher production of cytokeratin in the presence of estradiol (E2), compared to cells grown in progesterone (P4). Cells grown under ALI conditions were exposed to HSV-2-green fluorescent protein (GFP) and the highest infection and replication was observed in the presence of P4. Altogether, this study suggests that ALI cultures more closely simulate the in vivo conditions of the FRT compared to the conventional LLI cultures. Furthermore, under these conditions P4 was found to confer higher susceptibility to HSV-2 infection in vaginal cells. The vaginal ALI culture system offers a better alternative to study host-pathogen interactions.
Highlights
417 million people worldwide are seropositive for herpes simplex virus type 2 (HSV-2) with an incidence of 19.2 million [1]
These results indicate that the effect of hormones on cytokeratin expression in vaginal cells was more pronounced under air-liquid interface (ALI) conditions
We examined the effects of female sex hormones in Vk2 cell lines in terms of growth, differentiation, as well as HSV-2 infection under both ALI
Summary
417 million people (range: 274–678 million) worldwide are seropositive for herpes simplex virus type 2 (HSV-2) with an incidence of 19.2 million [1]. More females (267 million) are infected with HSV-2 than males (150 million), and data indicates that seroprevalence is higher in women (25.6%) compared to men (17.8%) in the USA [1,2]. Viruses 2016, 8, 241 the higher infection rates in females to the greater surface area of the female reproductive tract (FRT). Compared to the male reproductive tract, other studies suggest that other biological factors such as presence of female sex hormones contribute to the difference in infectivity and seroprevalence [3,4,5,6,7]. Transmission of HSV-2 in women occurs predominantly in the FRT through the direct infection of genital epithelium [8]. Epithelial cells of the FRT mucosa are the primary barriers against other sexually transmitted viruses, such as human immunodeficiency virus (HIV) and pathogenic bacteria [9,10,11]
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