Immunodepression during urethane and N-nitrosomethylurea leukaemogenesis in mice.

Five injections of urethane, 1 mg./g. body weight to suckling mice markedly reduced the primary immune response against sheep red blood cells assessed by splenic plaque forming cells (PFC) determination and haemagglutinin (HA) titration. The immunological impairment lasted for about 50 days after the end of the treatment. The secondary response tested by HA titration was not affected. A lower dose of urethane (0.5 mg./g.) produced only a delay of the primary HA response. A single neonatal dose of N-nitrosomethylurea (NMU) caused a profound immunodepression evaluated as HA titre and number of PFC. Both primary and secondary responses were still depressed when tested at 50 and 90 days of age respectively. No clear correlation between the degree of immunodepression and lymphoma development was found.