Our results demonstrate that epithelial cells respond to factors present in semen by secreting CCL20, leading to the enhancement of LCp recruitment. These data argue in favour of the implication of epithelial cells in the heterosexual transmission of HIV.

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Mucosa represents the main site of pathogen/cell interactions. The two main types of cells forming the epithelial structure [epithelial cells and Langerhans cells (LC)] coordinate the first defense responses to avoid infection. To evaluate the involvement of epithelial cells in the early steps leading to a specific adaptive immune response, we have studied the interactions between vaginal epithelial and LC through the establishment of a human vaginal epithelial mucosa. We demonstrate that normal human vaginal epithelial cells constitutively secrete the chemokine macrophage inflammatory protein 3alpha/CC chemokine ligand 20 (CCL20), known to recruit LC precursors (LCps) selectively via its cognate CC chemokine receptor 6 (CCR6). This secretion is up-regulated by the proinflammatory cytokine interleukin-1beta through the nuclear factor-kappaB pathway. Similar results were obtained with the human vaginal epithelial cell line SiHa, which displays numerous homologies with normal vaginal cells. The chemotactic activity of the secreted CCL20 was demonstrated by its ability to attract LCp CCR6+. Moreover, the use of neutralizing polyclonal antibodies directed against the CCL20 molecule abolished this migration completely, suggesting that CCL20 is the main attracting factor for LCps, which is produced by the vaginal cells. These data indicate that vaginal epithelial cells play an important role in the immunological defense by attracting immune cells to the site of epithelial/pathogen contact.