The gut-associated lymphoid tissue is a secondary lymphoid organ, which is in charge of processing antigens that interact with the intestinal mucosa and of disseminating the immune response. Antigens present in the intestinal lumen are transported into the Peyer's patches through M cells, which are located between the enterocytes in tge epithelium. Once in the Peyer's patches, antigens interact with antigen-presenting cells, which present them to immature B and T cells located in the germinal centers and in the inter-follice regions. These immature B and T cells, after being activated by antigens, are drained by the regional lymph nodes, and migrate through the thoracic duct to the bloodstream. Finally, after recirculating for several days, they differenciate into mature effector cells migrating to the lamina propia, and intra-epithelial lymphocytes) can be distinguuished in the intestine (scheme).