Functional studies of Peyer's patches: evidence for their participation in intestinal immune responses.

The pattern of responsiveness of lymphocytes from Peyer's patches, spleen, mesenteric, and inguinal nodes of guinea pigs was compared after oral and parenteral immunization. After oral immunization with BCG, Peyer's patch lymphocytes showed the best in vitro proliferative responses to PPD (tuberculin). Responsiveness to Clostridia, normal constituents of the intestinal microflora, also was significant in Peyer's patches, and low or absent in the other lymphoid tissues examined. In animals immunized parenterally with heat-killed Mycobacterium tuberculosis, lymphocytes from the spleen reacted best to PPD and those from Peyer's patches least. Selective elimination of B or T cells from PPD-reactive Peter's patch lymphocyte populations showed that the T-cell-rich fraction remained responsive to PPD, the B cell-rich fraction became unresponsive; but both fractions reacted to Clostridia. We conclude from this experiment that a functional T cell population is present in these organs. Peyer's patches in the guinea pig are immunocompetent lymphoid organs which seem to be primarily engaged in immune responses to antigens presented from the intestinal lumen.