Intestinal epithelial cells control dendritic cell function

Dendritic cells (DCs) comprise a family of cells specializing in antigen capture and presentation to T cells. We have recently shown that DC play an active role in bacterial uptake across mucosal surfaces. Indeed, DC are able to open tight junctions and to sample antigens directly across epithelia, both in vitro and in vivo. Because DC express tight junction proteins, the integrity of the epithelial barrier is preserved. In this study we have analyzed the possible involvement of epithelial cells in controlling DC function. We developed an in vitro model in our laboratory consisting of a three-player system of dendritic cells, epithelial cell monolayers, and bacteria. The crosstalk between epithelial cells and dendritic cells was analyzed, and epithelial cells were tested for their capacity to release cytokines and chemokines that induce the migration and activation of DC. We show that the capacity of epithelial cells to produce cytokines and activate DC is dependent on the invasiveness of the bacteria tested. In particular, invasive bacteria stimulate epithelial cells to release proinflammatory cytokines and to induce the maturation state of DC. By contrast, noninvasive bacteria are unable to stimulate epithelial cells, but can activate DC directly when DC translocate to the apical side. In conclusion, epithelial cells are not simply a barrier to bacteria entering via the oral route, but actively influence the activating properties of bystander DC.