Figure 1.

Intestinal mucosal immune responses to enteric bacterial antigens. Enteric bacterial antigens may enter the Peyer’s patches (PPs) via transport by the M cells where they are endocytosed by dendritic cells (DCs) within the subepithelial dome region. Antigen-loaded DCs may then interact with T cells within the PPs to prime the lymphocytes or they may migrate from the PPs to the gut-draining mesenteric lymph nodes (MLNs) by way of the afferent lymphatics. Naive T cells that enter the MLNs may interact with these antigen-loaded DCs resulting in the priming, polarization, and expansion of the T cells to yield effector cells. These effector cells then exit the MLNs via the efferent lymphatics, return to the systemic circulation, and home to the gut lamina propria. Enteric antigens may also be endocytosed by DCs within the gut lamina propria and migrate to the MLNs via the afferent lymphatics. Finally, free enteric antigens may be absorbed by the intestinal blood supply and transported to the spleen by way of the systemic circulation. Once in the spleen, free antigen may be processed and presented by splenic DCs thereby initiating potential immune responses within the spleen. Modified from Mowat et al.,¹³ with permission.