THE EXIT OF LYMPHOCYTES AND RBCS FROM THE PERITONEAL-CAVITY OF SHEEP

The purpose of this study was to compare the exit rates and migration pathways of Cr-51-labeled lymphocytes from the peritoneal cavity into the blood with those of a non-motile cell population, In-111-RBCs, in order to determine whether lymphocytes actively migrate from the perit oneal cavity. Radiolabeled cells were infused into the peritoneal cavi ty and multiple samples of lymph draining from the peritoneal cavity a nd/or blood were obtained, then the animal was sacrificed and various tissues were harvested and assayed for radioactivity. The recovery of Cr-51-lymphocytes from the mesenteric nodes was not significantly diff erent from that of nodes anatomically distant from the cavity, so it i s unlikely that large numbers of lymphocytes migrate across the mesoth elial lining of the cavity and into the mesenteric lymphatics. However , the caudal mediastinal node contained about 18-fold more Cr-51-lymph ocytes and 473 times as many In-111-RBCs, confirming the importance of this node in the drainage of cells and fluid from the cavity. The hep atic node also appears to receive cells directly from the peritoneal c avity. We also calculated the recovery of labeled cells at the end of the experiment (T = 40 h), and found that the recovery of Cr-51-lympho cytes (3.87 +/- 1.29 %ID) in the blood was much lower than that of In- 111-RBCs (35.28 +/- 5.02 %ID). This difference can be attributed mainl y to the traffic of labeled lymphocytes out of the blood rather than t he selective retention of lymphocytes within the peritoneal cavity. Ca nnulation of the caudal mediastinal efferent lymphatic and the thoraci c duct, which drain the peritoneal cavity, revealed approximately a 3- fold higher cumulative recovery of In-111-RBCs than Cr-51-lymphocytes over 6 h. However, by 40 h the percentage of labeled RBCs and lymphocy tes remaining in the cavity was not significantly different. While Cr- 51-lymphocytes may leave the peritoneal cavity at a slower rate than I n-111-RBCs, both cell populations appear to exit solely via lymphatic vessels.