Age-related alteration in the composition of immunocompetent blood cells in atomic bomb survivors.

A total of 1328 atomic bomb survivors in Hiroshima were studied to determine alterations in the number of blood lymphocytes belonging to T-cell subpopulations, the number of CD19 antigen-positive B cells and the number of Leu 7 and CD16 antigen-positive lymphocytes. Overall, with increasing age, significant decreasing trends in the numbers of some lymphocytes in T-cell subpopulations and of B cells were observed. Furthermore, the number of blood lymphocytes positive for CD5 antigen was significantly lower in the people exposed to radiation (greater than 1 Gy) in the older age group (more than 30 years old at the time of the bombing). A similar tendency for decreases in the numbers of CD4, CD8, and CD19 antigen-positive cells was observed in these older survivors, although the differences were not statistically significant. These results suggest that aging of the T-cell related immune system is accelerated in the irradiated people of advanced age. This may be explained by the age-related decrease in thymic function in those subjects who were older at the time of the bombing resulting in a decreased functional ability of the immune system after radiation injury. On the contrary, the number of Leu 7 or CD16 antigen-positive cells was found to be increased significantly in the older age group compared to the younger group, although there was little dependence on dose.