EFFECTS OF COMBINED RADIATION AND THERMAL BURN INJURY ON THE SURVIVALOF SKIN ALLOGRAFT AND IMMUNE FUNCTION IN RATS

Objectives To investigate the effects of combined radiation and therma l bum injury on the survival of skin allografts and to analyze the rel ationship between the prolongation of allograft survival and the chang es of immune functions of the thymocytes and splenocytes in rats. Meth ods Wistar rats were irradiated with 3, 4, 5, 6 and 8 Gy of gamma rays . Thirty minutes after radiation, 15% TBSA m-degree bum was inflicted to the rats. Twenty-four hours after the bum injury, allografts were u sed to cover the bum wounds. In the 8 Gy group, 1 hour before skin gra fting, the bone marrow cells (4 x 10(8)) from the same donor were also transplanted. All rats were carefully observed after injury. The rats with single radiation injury of 5 Gy gamma rays, with single bum inju ry and with combined radiation-bum injury were killed 3, 7, 10, 15 and 30 days after skin grafting for immunological assay and pathological study. Results All the allografts in the single bum group were rejecte d in 10 days. In the combined injury groups, the survival rates of the allografts in rats undergoing 3 and 4 Gy radiation were 20% and 30%, respectively. In the combined injury groups undergoing 5, 6 and 8 Gy r adiation, the 10-day survival rates of the allografts were 69%, 88% an d 100% respectively, and the 30-day survival rates in the three groups were 36%, 42% and 100% separately. The grafted allogenic skin, with n ormal epithelial cells and good vascularity, healed well with the reci pient's skin. Hairs grew well from the allografts 30 days after grafti ng. Three, 7 and 15 days after allografting, in the single bum group, the proliferative activities of the thymocytes were 90%, 185% and 130% of the preinjury level, and the antibody forming capacities of the sp lenocytes were 200%, 171% and 300% of the preinjury level, respectivel y; in the combined injury groups, the proliferative activities were 6% , 99% and 91% of the preinjury level, and the forming capacities were 2%, 36% and 90% of the preinjury level. Conclusions The survival rate of allograft in rats undergoing combined radiation and thermal burn in jury rises with the increase in radiation dosage. The allograft coveri ng single bun injury is severely rejected by immune reaction. The prol ongation of the survival of allograft in combined injury group mainly results from radiation that suppresses immune functions.