Abstract
The UNSCEAR documents are currently shifting more to the re-evaluation or overview, rather than database update, on radiation effects viewed from the rapidly growing biosciences and technology. Two topics presented here are not exceptions. Radiation effects on immune system were extensively discussed in 1977 report, but in terms of the crisis of the immune system. The present document was prepared from the entirely different view as a "tissue response". The document begins with the general outline of the functional differentiation of immune system and their interplay. The radiation effects are considered as a deregulation of stem cells and its recovery to the stable accommodation phase (stimulatory, sensitive, degradative phases inclusive therein). They are rate limiting process and hence constitute the reason for some controversies among experiments in the experimental animals. In contrast, changes seen after long-time stabilization (A-bomb cohort, and Techa river cohort) are relatively consistent and provide important information on the late effects of radiation. Untargeted and delayed effects have long been known; in bacterial system in 1970s and in sea urchin in 1940s, respectively. Recent development of the microbeam irradiation systems regained the interest on the issues in mammalian cells. They include untargeted mutagenesis, bystander effects, genetic instability and delayed mutagenesis. They are particularly important as they are beyond the scope of classical target theory of radiation action and hence have impact on the current estimate of radiation risk. Reviews in literature are consistent with the untargeted and delayed effects. However, some controversies among experimental systems and paucity of assessments in vivo remain the issues for further confirmation and more rigorous tests.
