The humoral immune response in mice after neutron or X-irradiation at different dose rates.

Acute radiation dose rate and radiation quality are two critical, although little studied, variables involved in nonspecific radiation immunosuppression. Mice (C3BF1) were injected with sheep erythrocytes shortly after irradiation, and the humoral immune response measured over a 35-day period. With neutron irradiation, antibody formation was dependent only on the total dose, and not the dose rate. In contrast, the immune response after x-irradiation was dependent on both the dose and dose rate. Maximum dose-rate differences occurred with 500 rads of x-rays. Maximum depression with both neutron and x-irradiation occurred when antigen was given 12 hr after exposure. The exposure-rate effect on immunocompetent cells was directly demonstrated at the cellular level by culturing irradiated spleen cells in lethally irradiated recipients.