More newly formed T than B lymphocytes leave the intestinal mucosa via lymphatics.

Many lymphocytes are produced in the intestinal mucosa, especially in the Peyer's patches. These newly formed lymphoid cells leave the gut wall, undergo further maturation and many reach the lamina propria of the intestinal mucosa where they function as effector and regulator cells of the intestinal immune response. However, the number and subset composition of these newly formed lymphocytes emigrating from the gut wall are not known. Therefore, the intestinal lymph duct was cannulated in eight minipigs, in which the mesenteric lymph nodes had been removed 3 months earlier. Thus, it was possible to obtain all lymphocytes leaving the intestinal mucosa including the Peyer's patches via lymphatics. The hourly output of lymphocyte subsets was examined over the course of 93 h. The percentage and the absolute numbers of newly formed T cells (CD2+, CD8+) and B cells (IgA+, IgM+) were determined by examining the incorporation of the DNA precursor bromodeoxyuridine. After a single i.v. bromodeoxyuridine injection 8.5% of the T, 55% of the IgA+ and 25% of the IgM+ cells were labeled. In absolute numbers (1.9 +/- 0.7) x 10(6) newly formed T cells, (0.4 +/- 0.3) x 10(6) IgA+ cells and (0.5 +/- 0.4) x 10(6) IgM+ cells emigrated from the gut wall per hour. Both T and B lymphocyte subpopulations that are produced in the intestinal mucosa leave the gut wall via lymphatics; interesting, the T cells outnumber the B cells. Obviously the induction and maintenance of mucosal immunity depend to a large extent on the function of newly formed T lymphocytes emigrating from the Peyer's patches and/or from the mucosa without Peyer's patches.