Radiation Effects On Immune System

Ruth Neta, Office of International Health Programs, Department of Energy, Germantown, Maryland, USA

Gayle E Woloschak, Center for Mechanistic Biology and Biotechnology, Argonne National Laboratory, Argonne, Illinois, USA

Copyright © 1998 Elsevier Ltd. All Rights Reserved. Published by Elsevier Ltd.

Ionizing radiation (e.g. X- and gamma rays, neutrons and charged particles) damages DNA and other cellular components. Organized lymphoid tissues and recirculating lymphocytes are the most radiosensitive cells in the body. Following exposure to radiation, most cells of other lineages maintain their viability for one or two mitotic cycles. Small lymphocytes are unique in that even small doses of radiation (as low as 0.25 Gy (25 rad)) result in programmed cell death (apoptosis). Myeloid progenitor cells, also vital to host defenses, are similarly radiosensitive, but the mode of their death remains to be established.

At the cellular and tissue level, sensitivity to radiation has been evaluated by determining cell viability and functional capacity. The sensitivity of the immune system to radiation is reflected by 1 ) the magnitude of the suppression of the primary or secondary immune response, 2) the reduction in size of the lymphoid organs, and 3) the decrease in the number of surviving lymphoid cells. Despite the exquisite radiosensitivity of most lymphoid cells, a number of radioresistant immune functions (and cells) are maintained, even after doses of radiation that may lead to the death of the animal. Thus, although radiation-induced death of mice, within a dose range below 16 Gy (1600 rad) is often caused by opportunistic infections, the reduced resistance of the host is caused primarily by the ablation of the hematopoietic tissues, rather than total ablation of the immune system. This condition is referred to as the hematopoietic syndrome.

Consequently, to understand the effects of radiation on the immune system and host resistance, we must consider the deleterious effects of radiation not only on lymphocytes but additionally on the leukocytes which mediate nonspecific host responses.

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