Organ distribution and fate of newly formed splenic lymphocytes in the pig.

The production of lymphoid cells in the pig spleen was studied autoradiographically after selective labeling of the spleen using an extracorporeal perfusion circuit. Tritiated thymidine was added as a DNA precursor. One to 4 days after local labeling of the spleen the relative and absolute number of spleen-derived lymphocytes were determined in the following organs: mesenteric, cervical and inguinal lymph nodes, thymus, bone marrow, Peyer's patches, tonsils, three different parts of the gut, lung, liver, and blood. The labeled lymphocytes which migrated to these organs were all small lymphocytes, except for some large cells in the lamina propria. In the bone marrow, however, a considerable number of the spleen-derived immigrants were transformed into plasma cells. The total number of labeled lymphocytes decreased dramatically from Day 1 to Day 4 after labeling, indicating a high percentage of short-lived cells. Within the spleen, plasma cells had the highest labeling index of about 30% at Day 1 but this dropped to only 1.5% on Day 3. The organ distribution of the splenic emigrants changed from Day 1 to Day 4 with a relative increase in lymphocytes found in lymph nodes and a decrease in the lung and intestinal wall. The newly formed splenic lymphocytes migrated to T-and B-cell areas in lymph nodes, Peyer's patches and tonsils. In the intestinal wall labeled lymphocytes were found in the lamina propria and also as intraepithelial lymphocytes. There was no obvious redistribution between organ compartments with time after labeling of the spleen. The spleen produces large numbers of lymphocytes, which show typical organ distribution and homing to areas in lymphoid and nonlymphoid organs.