Chemical carcinogenesis and immunity: immunologic status of rats treated with methylnitrosourea.

During the treatment of outbred Sprague-Dawley rats with methylnitrosourea (MNU) or the noncarcinogenic analog diphenylnitrosamine, antibody levels to teichoic acid as well as several parameters of lymphocyte and macrophage function were assessed in animals not overtly stimulated with antigen. Treatment with MNU did not appear to alter most immunologic parameters studied. Some alterations occurred in natural antibody levels, in spleen weight, and in peripheral blood differentials of rats that had received the highest carcinogen dose (4.5 mg/kg). These alterations, however, appeared to coincide with the development of tumors and were not observed in animals with premalignant lesions. Levels of chemical carcinogens that were capable of inducing tumors did not necessarily suppress the immune response.