Recent studies suggest that m cells do not break down orally administered antigens; this function, and the subsequent presentation of processed antigens to T cells, is carried out by bone marrow-derived APC, probably DC.2 Precursors of m cells, enterocytes (EC), are also implicated in transcytosis of some intact particles and, indirectly, in presentation of processed antigens to T cells.
What happens to antigens that pass the intestinal transepithelial barrier? Intact macromolecules, including dietary proteins, can be found in blood, suggesting existence of a direct pathway for circulating undigested, gut-derived proteins into remote tissues. More interesting is the fate of antigens entering mucosal immune tissue. It is here that the immune system starts to sort out the antigens into harmless dietary proteins that need to be tolerated, and potentially dangerous pathogens that must be met with an effective immune response to prevent the spread of infection to other organs. The key ...
