The Role of Sex Hormones and the Tissue Environment in Immune Protection Against HIV in the Female Reproductive Tract

Despite extensive studies of the mucosal immune system in the female reproductive tract (FRT) and its regulation by sex hormones, relatively little attention has been paid to the tissue environment in the FRT that regulates immune cell function. Consisting of secretions from epithelial cells, stromal fibroblasts and immune cells in tissues from the upper (Fallopian tubes, uterus and endocervix) and lower (ectocervix and vagina) tracts, each tissue compartment is unique and precisely regulates immune cells to optimize conditions for successful pregnancy and protection against sexually transmitted diseases including HIV. Our goal in this Review is to focus on the mucosal (tissue) environment in the upper and lower FRT. Specifically, this review will identify the contributions of epithelial cells and fibroblasts to the tissue environment and examine the impact of this environment on HIV-target cells. Much remains to be learned about the complex interactions with the tissue environment at different sites in the FRT and the ways in which they are regulated by sex hormones and chemical contraceptives. Awareness of the involvement of the tissue environment in determining immune cell function and HIV acquisition is crucial for the understanding the mechanisms that lead to HIV prevention, acquisition and the development of new therapeutic modalities of immune protection.