Differential Effect of Immunosuppression on the Induction of Nervous System and Bladder Tumors by N-Methyl N-Nitrosourea23

Abstract

Administration of antilymphocyte serum (ALS) to rats treated with N-methyl N-nitrosourea (MNU), a potent neurotropic carcinogen, did not increase the incidence of tumors of the nervous system. Approximately 25% of the rats given ALS and MNU, however, developed carcinoma of the urinary bladder. None treated with either ALS or MNU alone developed bladder tumors. The incidence of other non-neural neoplasms was unaffected by ALS treatment. Deaths in both MNU-treated groups resulted primarily from tumors of the nervous system. Cell susceptibility to neoplastic transformation by MNU appears more important in determining tissue tropism than are immunologic influences after the transformed cells proliferate.