Long-lasting alterations of the immune system by ionizing radiation exposure: implications for disease development among atomic bomb survivors

PURPOSE: The immune systems of the atomic-bomb (A-bomb) survivors were damaged proportionately to irradiation levels at the time of the bombing over 60 years ago. Although the survivor's immune system repaired and regenerated as the hematopoietic system has recovered, significant residual injury persists, as manifested by abnormalities in lymphoid cell composition and function. This review summarizes the long-lasting alterations in immunological functions associated with atomic-bomb irradiation, and discusses the likelihood that damaging effects of radiation on the immune system may be involved partly in disease development so frequently observed in A-bomb survivors. CONCLUSIONS: Significant immunological alterations noted include: (i) attrition of T-cell functions, as reductions in mitogen-dependent proliferation and interleukin-2 (IL-2) production; (ii) decrease in helper T-cell populations; and (iii) increase in blood inflammatory cytokine levels. These findings suggest that A-bomb radiation exposure perturbed one or more of the primary processes responsible for T-cell homeostasis and the balance between cell renewal and survival and cell death among naive and memory T cells. Such perturbed T-cell homeostasis may result in acceleration of immunological aging. Persistent inflammation, linked in some way to the perturbation of T-cell homeostasis, is key in addressing whether such noted immunological changes observed in A-bomb survivors are in fact associated with disease development.