Proliferation and emigration of newly formed lymphocytes from pig spleens during an immune response.

Normal young pigs were immunized intravenously with sheep red blood cells (SRBC). At various times after a second SRBC injection the spleens were connected to an extracorporeal perfusion system, and proliferating lymphoid cells in the spleens were selectively labelled with tritiated thymidine. One day later the relative and absolute numbers of spleen-derived lymphocytes were determined by autoradiography in the following organs: various parts of the spleen, mesenteric and cervical lymph nodes, thymus, bone marrow, Peyer's patches, tonsils, intestine, lung, liver and blood. From 1 to 7 days after the second SRBC injection, the spleens produced increasing numbers of lymphocytes, and labelled cells were found especially in the blood and bone marrow. The newly formed splenic lymphocytes migrated preferentially to T- but also to B-cell areas in lymph nodes, Peyer's patches and tonsils. In all organs outside the spleen nearly all labelled spleen-derived lymphocytes were small lymphocytes. However, the bone marrow contained a high proportion of labelled immature and mature plasma cells. The spleen produced large numbers of lymphocytes during the secondary immune response, many of which migrated to different organs probably as memory cells, while others were found in the bone marrow as effector cells from the immune response.