Lymphocyte disappearance and reappearance after a single whole-body irradiation dose of 5 Gy.

The effects of a single exposure to 5 Grays of caesium gamma rays administered at a high-dose rate were investigated in rat lymphocyte populations. Such a dose completely depleted the B-cell population but never totally depleted the T-cell population. T and B lymphocytes reappeared in the spleen after 10-15 days and somewhat later in the mesenteric lymph nodes and Peyer's patches. In the spleen, non-circulating B lymphocytes of the marginal zone reappeared after a few days, as did the B lymphocytes of the follicles. Lymphoid tissues were observed to have recovered their normal aspect between days 50 and 60 after irradiation; however, even at that time, the germinal centres had not yet returned to normal.