Evidence for compromise of tumour immunity in rats by a non-specific blocking serum factor that inactivates macrophages.

A factor in the serum of rats infected with the nematode parasite, Nippostrongylus brasiliensis, enhances the growth of Walker carcinosarcoma cells in rats in vivo and also fully reverses inhibition of tumour growth achieved by cellular mechanisms augmented by nematode infection or by RES stimulants. Under specified in vitro conditions, the blocking rat serum factor largely counteracts the elimination of tumour cells in the rat system and also in a mouse effector/target cell system. Moreover, activated peritoneal macrophages cultured in vitro manifest various signs of inactivation upon addition of the serum from rats infested with the parasite.