Inhibition by the Landschütz ascites carcinoma of the granulomatous inflammatory response to C. parvum.

I.p. or i.v. administration of Corynebacterium parvum (CP) to MF1 mice induces a generalized inflammatory response, associated with marked hepatosplenomegaly and accompanied by a pronounced granulomatous response in the liver. Injection of the Landschütz ascites carcinoma (LAC) 24 h after CP substantially reduced the intensity of the inflammatory response, and decreased both the frequency and size of the hepatic granulomas, as revealed by morphometric analysis of histological sections. The difference in cellular composition of the granulomas between the experimental groups, as revealed by light microscopy, was further emphasized and characterized by ultrastructural studies. These revealed the predominance of macrophages within the granulomas in tumour-bearing mice, in contrast to the predominance of epithelioid cells in the lesions which developed in mice given CP alone. Our experimental findings show that the inhibitory effect of the growing LAC on granuloma formation in response to CP cannot be ascribed to (a) sequestration of the microorganism within the growing tumour, (b) a nonspecific inflammatory stimulus, (c) diversion and seqestration of mononuclear phagocytes in the growing tumour or (d) the presence of lactate dehydrogenase-elevating virus in either the host or tumour cells. The inhibition of liver granuloma formation is consistent with an effect mediated by soluble, heat-stable tumour-associated factor(s).