Influence of mouse hepatitis virus on the growth of human melanoma in the peritoneal cavity of the athymic mouse.

Mouse hepatitis virus (MHV) infection was found in 15 of 40 athymic mice (Balb/c nu/nu) used in an experimental model designed to study the effect of cell mediated immunity on target human melanoma cells growing in the peritoneal cavity. Most non-MHV-infected mice died of peritoneal tumor within predictable periods following injection of the melanoma cells. Twelve of 15 MHV-infected mice which showed either poor or no tumor growth died of MHV infection, whereas only 3 showed good tumor growth. Peritoneal macrophages in the ascites from the MHV-infected mice were greatly reduced in number compared to those in the ascites from the non-MHV-infected mice. Although the fibrohistiocytic reaction was more prominent in the MHV-infected mice, other aspects of spleen and lymph node lymphocytic reactions exhibited no remarkable differences between the two groups. The possible mechanisms whereby MHV infection influences tumor growth in nude mice are discussed.