Effects of Continuous Low-Level Gamma Irradiation on Circulating and Peritoneal Mononuclear Leukocytes of Mice

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Abstract
LAF1 mice were exposed continuously to Co60 gamma-radiations at a dose rate of 1.4 rads per hour. The number of lymphocytes in the circulating blood fell sharply during the first week of exposure (190 rads) and decreased thereafter at a very gradual but statistically significant rate for the duration of the experiment (15 weeks, 3450 rads). The disappearance of small lymphocytes (6 microns in diameter) from the peritoneal cavity was also more rapid during the first week of irradiation than during subsequent weeks. Medium peritoneal lymphocytes (8 to 10 microns in diameter) and peritoneal macrophages disappeared at constant rates over the entire observation period. After the first week of exposure, the disappearance rates of small and medium peritoneal lymphocytes were identical. This rate was greater than that for peritoneal macrophages or that for circulating lymphocytes. Based on the fraction of cells surviving any given exposure, the mono-nuclear leukocytes may be arranged in the following order of decreasing sensitivity to continuous low-dose-rate gamma-irradiation: circulating lymphocytes, small peritoneal lymphocytes, medium peritoneal lymphocytes, peritoneal macrophages. This order is the same as that after acute exposure to X-rays.