T-Cell Responses to Mitogens in Atomic Bomb Survivors: A Decreased Capacity to Produce Interleukin 2 Characterizes the T Cells of Heavily Irradiated Individuals

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Abstract
Kusunoki, Y., Hayashi, T., Morishita, Y., Yamaoka, M., Maki, M., Hakoda, M., Kodama, K., Bean, M. A. and Kyoizumi, S. T-Cell Responses to Mitogens in Atomic Bomb Survivors: A Decreased Capacity to Produce Interleukin 2 Characterizes the T Cells of Heavily Irradiated Individuals. Significant decreases in the fraction of lymphocytes that are CD4 and increases in serum levels of some classes of immunoglobulin have been reported to occur in atomic bomb (A-bomb) survivors and in victims of the Chernobyl nuclear plant accident. To investigate the long-term effects of nuclear radiation on cellular immunity in more detail, we used limiting dilution assays with peripheral blood mononuclear cell preparations to analyze the T-cell responses of 251 A-bomb survivors exposed to less than 0.005 Gy and 159 survivors exposed to more than 1.5 Gy. The percentages of CD2-positive cells that were capable of proliferating in response to phytohemagglutinin (PHA) in the presence of exogenous interleukin 2 (IL2) did not differ substantially between distally exposed and more heavily exposed survivors. The heavily exposed survivors appeared to possess fewer T cells that were capable of proliferating in response to concanavalin A (Con A) or of producing interleukin 2. Assuming that CD4 T cells were the ones primarily responsible for producing IL2 in response to Con A, we were able to estimate how many cells in any given CD4 T-cell population were actually producing IL2. The results indicated that peripheral blood samples from heavily exposed survivors contained significantly fewer IL2-producing CD4 T cells than did similar samples from distally exposed survivors, indicating that significant exposure to A-bomb radiation may have a long-lasting negative effect on the capacity of CD4 T-cell populations to produce IL2.

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