Effects of the Landschütz ascites carcinoma and ascitic fluid on macrophage activity in C. parvum-injected mice.

I.p. administration of 1.4 mg Corynebacterium parvum (C. parvum) 24 h before inoculation of Landschütz ascites carcinoma (LAC) cells significantly impaired growth of the tumour in MF1 mice. The injection of tumour cells caused a transient inhibition of the activity of the mononuclear phagocyte system (MPS) in both normal and C. parvum-treated hosts, as evidenced by impaired clearance of colloidal carbon from the bloodstream and reduction in hepatic phagocytosis of 51Cr-labelled sheep erythrocytes. Depression in Kupffer-cell activity was associated with a shift in particle distribution towards the spleen. The pronounced hepatosplenomegaly in response to C. parvum was significantly less in animals which also received tumour cells. Histological examination of liver and spleen revealed evidence of depressed MPS activity. Granuloma production in the liver in response to C. parvum was inhibited in tumour-bearing mice, and macrophage proliferation within the spleen was also reduced. Ascitic fluid showed similar inhibitory effects to those of tumour-cell suspensions, suggesting production by LAC of a heat-stable macrophage-inhibitory factor.