Isolation of a Factor from Cancer Ascitic Fluid Increasing Susceptibility of Mice to Listeria Infection

Abstract

Abstract

A low-molecular-weight factor (<1000) which impairs the capacity of normal mice to resist Listeria infection has been isolated from the ascitic fluid of tumor-bearing mice. The factor showed potent suppressive activity when as little as 0.2 ml of 1:10⁵ dilution of the factor was given iv to mice. The factor impaired stage 2 (72 hr after infection) of Listeria elimination in the liver when circulating monocytes migrate from the blood to the liver to begin eliminating the bacteria, but not stage 1 (within 24 hr after infection) when Listeria elimination depends on resident liver macrophages. The factor also inhibited macrophage accumulation in the peritoneum of mice after ip injection of phytohemagglutinin and macrophage chemotaxis in vitro. The factor was heat labile and lost its suppressive activity after being heated at 56°C for 30 min. The factor was detectable in the ascitic fluid rather late after tumor implantation and its production was closely related to tumor growth.