Memory CD4 T-cell subsets discriminated by CD43 expression level in A-bomb survivors

Purpose: Our previous study showed that radiation exposure reduced the diversity of repertoires of memory thymus-derived cells (T cells) with cluster of differentiation (CD)-4 among atomic-bomb (A-bomb) survivors. To evaluate the maintenance of T-cell memory within A-bomb survivors 60 years after radiation exposure, we examined functionally distinct memory CD4 T-cell subsets in the peripheral blood lymphocytes of the survivors. Methods: Three functionally different subsets of memory CD4 T cells were identified by differential CD43 expression levels and measured using flow cytometry. These subsets consist of functionally mature memory cells, cells weakly responsive to antigenic stimulation, and those cells functionally anergic and prone to spontaneous apoptosis. Results: The percentages of these subsets within the peripheral blood CD4 T-cell pool all significantly increased with age. Percentages of functionally weak and anergic subsets were also found to increase with radiation dose, fitting to a log linear model. Within the memory CD4 T-cell pool, however, there was an inverse association between radiation dose and the percentage of functionally mature memory cells. Conclusion: These results suggest that the steady state of T cell memory, which is regulated by cell activation and/or cell survival processes in subsets, may have been perturbed by prior radiation exposure among A-bomb survivors.