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Radiation Dose, Dose Rate, and Quality in Suppression of the Humoral Immune Response¹

From the Medical Division, Oak Ridge Associated Universities, Oak Ridge, Tennessee, 37830

Abstract

Radiation-induced immunosuppression was studied with special emphasis on the factors of dose rate and quality of the radiation. Fission neutrons, x-rays, and ⁶⁰Co -rays at dose rates ranging from 2.8 to 95 rads/min were tested for their biologic effect. Data reported earlier from our laboratory were supplemented as necessary to allow intercomparisons to be made. The biologic systems in the mouse included: a) animal mortality, b) immune response capability of the irradiated animal, and c) antibody formation by irradiated spleen cells cultured in unresponsive hosts. The following empiric relationships were established: a) the three biologic responses were each related to the radiation dose by a probit-type analysis, b) the magnitude of the dose-rate effect was an exponential function of the linear energy transfer (LET), and c) the inverse cube root dose-rate relationship reported earlier was confirmed. Immunosuppression of the whole animal was related to mortality, but not in a simple manner: as the LET of the radiation used declined, the level of immunosuppression at the LD₅₀ increased, indicating that mortality is not necessarily a measure of the level of immune activity. We present an empiric expression relating the radiation dose rate and quality (LET) to the expected biologic effect, anticipating the possible application of these data to clinical situations.

Footnotes

¹ This investigation was supported by the Medical Division, Oak Ridge Associated Universities, Oak Ridge, Tennessee, under contract with the United States Atomic Energy Commission, and by Training Grant T2 GM 730 from the National Institute of General Medical Sciences.

² Submitted in partial fulfillment of the degree Doctor of Philosophy, Institute of Radiation Biology, the University of Tennessee.