The intestinal epithelial cell: processing and presentation of antigen to the mucosal immune system

The immunologic tone of the intestinal tract is one of suppressed or highly regulated responses. While there are several components (intrinsic and ext rinsic to the gut-associated lymphoid tissue) responsible for this immunolo gically suppressed tone, the intestinal epithelial call (IEC) has been prop osed as a key player in this process. IECs can take up and process antigen but distinct surface molecules and restriction elements allow them to prese nt these antigens to unique regulatory T cells. These include the expressio n of the class Ib molecule CD1d as well as a novel CD8 ligand, gp180. These molecules come together to activate a subpopulation of CD8(+) regulatory c ells whose function is to suppress immune responses in an antigen non-speci fic fashion most likely through cognate interactions. This form of regulati on may be unique to the gut-associated lymphoid tissue which is consistent with the unsual demands upon this part of the immune system.