Peritoneal Macrophage Response to Leukemia L1210 in Syngeneic Mice 2

Abstract

DBA/2 mice were inoculated ip with 10³ live L1210 leukemia cells, which caused their death in 14 days. Three days after challenge, the peritoneal cavities of these animals contained about 6–8×10⁶ nucleated cells, and by day 6 this amount increased to 25–50×10⁶. Half the cells on day 3 and two-thirds on day 6 had a morphology typical of macrophages, many of which appeared activated. By tests of adherence and phagocytosis, they were confirmed to be macrophages. The remaining cells were intermediate between lymphocytes and macrophages, typical lymphocytes, polymorphonuclears, or L1210 cells. The ratio of the number of macrophages to the number of L1210 leukemia cells varied from 5:1 to 50:1. This ratio decreased to less than 1:1 on days 9 and 13 after challenge because of the rapid proliferation of the L1210 leukemia, but the absolute number of macrophages remained the same. Whole-body irradiation of mice with 400 R, 1 day before challenge, almost completely suppressed this macrophage response and resulted in a small but statistically significant shortening of survival time. A lower radiation dose, 200 R, only diminished the response and had a variable effect on survival. Athymic (“nude”) mice developed a macrophage response after an ip inoculation of L1210, although the magnitude was variable. It appeared then that the macrophage response was radiosensitive and T-cell-independent and may have had some controlling effect on the growth of L1210 in these syngeneic mice.