The effect of N-nitroso-N-methylurea and N-dimethylnitrosamine on cell mediated and humoral immune responses in rats and mice.

N-Nitroso-N-methylurea (NMU) induced a marked dose dependent leucopoenia which was associated with an increased survival of skin allografts in adult rats and in 2 strains of mice. The humoral immune response to NMU as assessed by haemolytic plaque formation and haemagglutination was also much reduced. Dimethylnitrosamine (DMN) which, like NMU is a powerful carcinogen and an alkylating agent, showed no immunosuppressive activity after a single dose in rats on either a normal diet or fed a protein-free diet which enhances kidney tumourigenesis. In mice DMN at a near LD(50) dose (14 mg/kg) had no effect on skin graft survival but did reduce the humoral response. At half this dose level, however, no immunosuppressive effect was seen. The results support the conclusion that the immunosuppressive activity of a chemical carcinogen is not necessarily associated with the expression of its carcinogenicity.