Figure 4.

Schematic of the multiple functions carried out by epithelial cells throughout the upper female reproductive tract as sentinels of immune protection. Acting as the first line of defense, epithelial cells provide host protection against sexually transmitted diseases, while supporting the process of fertilization, in a number of ways that includes providing a mechanical barrier, producing and/or secreting antimicrobial molecules, transporting IgA, processing and presenting antigen and communicating with underlying immune cells including macrophages, dendritic cells, T cells, NK cells and neutrophils as well as by secreting cytokines, chemokines and growth factors that are important in autocrine and paracrine signaling, growth and differentiation. To accomplish this, epithelial cells communicate with underlying stromal cells and vise-versa via soluble paracrine signals. Sex hormone (estradiol and progesterone) regulation of epithelial cell function is both direct and indirect. In some cases hormone effects are mediated through estradiol receptors (ER) in epithelial cells. Others are indirect and mediated through ER located in the underlying stromal cells (fibroblasts) as well as immune cells.