Yamaoka, M., Kusunoki, Y., Kasagi, F., Hayashi, T., Nakachi, K. and Kyoizumi, S. Decreases in Percentages of Naïve CD4 and CD8 T Cells and Increases in Percentages of Memory CD8 T-Cell Subsets in the Peripheral Blood Lymphocyte Populations of A-Bomb Survivors. Radiat. Res. 161, 290–298 (2004).

Our previous studies have revealed a clear dose-dependent decrease in the percentage of naïve CD4 T cells that are phenotypically CD45RA in PBL among A-bomb survivors. However, whether there is a similar radiation effect on CD8 T cells has remained undetermined because of the unreliability of CD45 isoforms as markers of naïve and memory subsets among the CD8 T-cell population. In the present study, we used double labeling with CD45RO and CD62L for reliable identification of naïve and memory cell subsets in both CD4 and CD8 T-cell populations among 533 Hiroshima A-bomb survivors. Statistically significant dose-dependent decreases in the percentages of CD45RO⁻/CD62L naïve cells were found in the CD8 T-cell population as well as in the CD4 T-cell population. Furthermore, the percentages of CD45RO / CD62L and CD45RO /CD62L⁻memory T cells were found to increase significantly with increasing radiation dose in the CD8 T-cell population but not in the CD4 T-cell population. These results suggest that the prior A-bomb exposure has induced long-lasting deficits in both naïve CD4 and CD8 T- cell populations along with increased proportions of these particular subsets of the memory CD8 T-cell population.