The effect of irradiation on the fever of delayed hypersensitivity.

The effect of total body irradiation on the development of delayed hypersensitivity and on the febrile response to specific antigen has been studied in guinea-pigs with the following results: 1. 200 R. whole body irradiation in guinea-pigs, while suppressing circulating antibody response, did not prevent the development of delayed hypersensitivity. 2. Irradiated and non-irradiated hypersensitive animals had an equal febrile response to systemic challenge with specific antigen. 3. Serum from antigen-challenged, irradiated, hypersensitive animals contained a pyrogenic factor of the endogenous serum type capable of producing fever in normal recipients. These results support the conclusion that production of circulating specific antibody is not essential either for development of delayed hypersensitivity or for the febrile response of the hypersensitive animal to specific antigen.