DYNAMICS OF LEUKOCYTE MIGRATION INTO THE MOUSE ASCITES TUMOR

There is a marked increase in the number of peritoneal leukocytes (lymphocytes, monocytes and granulocytes) during the growth of Ehrlich ascites tumor in mice. No local proliferation (as indicated by a labeling at 1 hr following a single ³H-TdR injection) was observed in the normal peritoneal leukocytes or those in the ascites tumor, except for a very minor labeling of some tumor macrophages. Kinetics of peritoneal leukocytes was studied with a series of twelve injections of ³H-thymidine (20 μCi every 8 hr) in normal mice as well as mice injected with 10⁶ tumor cells i.p. 2 hr after the last ³H-TdR injection. Animals were sacrificed at intervals up to 6 days. Granulocyte labeling in the blood as well as peritoneal space was near 100% in both groups of animals at all the intervals. Temporal changes in the labeling of lymphocytes (from 10% at 0 day to 22% at day 6), and monocytes (from 20% at 0 day to 57% at day 6) were identical in the blood and peritoneal space of normal animals, indicating a free exchange of cells between these compartments. Higher labeling indices than those in the controls were attained in the blood of tumor-bearing hosts (viz 40% for lymphocytes and 80% for monocytes at 6 days) suggesting an increased turnover of these cells in the circulation. In addition, peritoneal mononuclear cells of tumor-bearing mice showed even a higher labeling than those in the blood (viz 65% for lymphocytes and 92% for monocytes at 6 days) indicating a selective migration and/or retention of newly formed cells within the tumor, in contrast to a random migration into the normal peritoneal cavity. Furthermore, an identical labeling of macrophages to that of monocytes within the tumor indicated a short monocyte-macrophage transition. The preferential accumulation of young mononuclear cells into the tumor may be of functional importance.