Lymphocyte migration in the intestinal mucosa: entry, transit and emigration of lymphoid cells and the influence of antigen.

Lymphocyte migration is important to transport immunological information between the different compartments of the intestinal immune system. Large numbers of lymphocytes emigrate from the Peyer's patches and reach the blood circulation after expansion and maturation within the mesenteric lymph nodes. So far the frequency of antigen specific lymphocytes emigrating from the Peyer's patches after oral stimulation is not known. After mesenteric lymph node resection those cells emigrating from the intestinal wall are accessible by calculating the major intestinal lymph duct. The first antigen specific cells draining from the intestines are obviously not lymphocytes but dendritic cells, thus the antigen is rapidly trapped in the parenchyma of the lymph nodes in vivo. When lymphocytes were taken from intestinal lymph, labeled in vitro and retransfused, marked numbers of B-cells were re-detected in intestinal lymph. Later preferentially T-cells recirculated through the gut wall. After immigration into the intestinal lamina propria the lymphocytes may enter the space between epithelial cells, where they are present as intraepithelial lymphocytes. Lymphoid cells in the S-phase of the cell cycle have been detected in all compartments of the intestinal wall. Apoptosis is probably a further important mechanism for the regulation of intestinal immunity in removing cells reacting against harmless dietary antigens to maintain oral tolerance.