Radioprotection by whole body hyperthermia: Possible mechanism(s)

Studies were carried out to gain an insight into the mechanisms underlying WBH induced radioprotection. The plasma levels of IL-Iα, IL-6, TNF-α and GM-CSF, were elevated in WBH treated mice between 2 and 6 h after treatment. The total nucleated cell count of hemopoietic tissues such as spleen, thymus, bone marrow and peripheral blood showed drastic reduction without recovery until death in mice treated with TBI. However, the nucleated cell count in the above tissues showed significant recovery after initial drop in WBH and WBH + TBI treated groups and reached to a normal level by day 7 and day 28, respectively. The total WBC and RBC count in peripheral blood recovered to a control level by day 28 after treatment. Significant number of endogenous spleen colonies were detected, 14 days after TBI in WBH pre-treated mice whereas no such spleen colonies could be detected in TBI treated group. The transplantation of bone marrow derived from control, WBH, TBI and WBH + TBI treated groups of mice to lethally irradiated mice (8 Gy) showed formation of spleen colonies only in mice which received bone marrow from control, WBH and WBH + TBI treated groups. Transplantation of the bone marrow from these groups of mice resulted in prolonged survival of lethally irradiated mice as compared to mice receiving bone marrow from TBI treated mice. These results seem to suggest that WBH induced radioprotection of mice could be due to immunomodulation manifested through induction of cytokines responsible for protection and proliferative response, leading to accelerated recovery from hemopoietic damage-a major cause of radiation induced death.