Effects of Radiation Exposure on Reactive Oxygen Production in Vivo and Inflammatory Immune Response

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Chronic inflammation seems to be significantly associated with development of cancer, myocardial infarction, and other diseases. Although more than fifty years have passed since the A-bomb was dropped, the risk for developing "diseases of aging" such as cancer, heart disease, and diabetes is still high among A-bomb survivors. On the assumption that effects of radiation exposure might have accelerated inflammation among A-bomb survivors, which may increase the risk of developing various diseases, we measured plasma levels of IL-6,TNF-α,IFN-γ,CRP, and IL-10 using blood specimens of A-bomb survivors to review their relationship with radiation exposure dose. We also developed a practical assay system for measurement of serum levels of reactive oxygen species(ROS) based on use of multi-well plates, and thereby investigated the effects of radiation exposure. As a result, we observed that the inflammation markers IL-6,TNF-α,IFN-γ,IL-10,and CRP were significantly elevated with increased radiation dose, and that the production of ROS significantly and statistically increased with increase of radiation dose. The increase in ROS levels was proportional to the increase of inflammatory markers IL-6 and CRP. In addition, we measured changes in lymphocyte fraction and inflammatory marker levels in mice after exposure to radiation. The study showed that the number of lymphocytes in the blood, thymus, spleen, and lymph nodes decreased in exposed mice, but there was no significant difference in inflammatory cytokines in the plasma or cellular cytokine levels in the thymus, spleen, or lymph nodes between exposed and non-exposed mice. These results suggest that inflammation induced by infection, along with decreased immunocompetent cells resulting from radiation exposure, may play an important role in the persistent inflammation observed among A-bomb survivors.