Rhesus monkeys were individually total body irradiated using a cobalt-60 source at a midline dose rate of 54.6 rads per minute. Immediate and delayed effects on the response capability of lymphoid tissues to a single antigenic stimulus were tested by injecting a nonproliferating antigen (sheep cells) 2 and 24 hours postirradiation. While 800 rads was lethal, 400 rads significantly impaired the immunologic response as indicated by prolongation of both the latent and production periods whether antigen was injected 2 or 24 hours postirradiation. A drop in rate of antibody synthesis included both the γM and γG types. Wide variations in natural anti-sheep cell heterohemagglutinins (γM type) in the rhesus monkey necessitated pretesting and selection of experimental animals to insure an adequate antigenic stimulus. The induction phase of the immune response proved to be most radioresistant with evidence of selective enhancement of peak titers when irradiation preceeded antigen administration by 2 hours.

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