Flow cytometric characterization of rat thymus cells in a radiation-dominated model of combined injury.

Thymuses of rats that had been: a) gamma-irradiated [500 cGy whole-body radiation (R)], or b) thermally injured [20% BSA dorsal, scald burn (TI)], or c) combined injured [irradiation followed by burn (CI)] were studied for involution and recovery processes after sublethal treatments. The expression of surface antigens on thymic cells before and after injuries was evaluated using the monoclonal antibodies (mcAB) MRC OX4, MRC OX7, MRC OX8, W3/13 HLK, and W3/25 and flow cytometric analysis. Thymic cellularity decreased to less than 1% of normal (N), age-matched rats by 4 days after R or CI. Recovery reached 60% to 70% of N by 28 days post treatments. TI caused a biphasic thymic recovery pattern with nadirs of 40% of N on days 7 and 21. Recovery at day 28 was similar to that after R and CI. Expression of OX7, OX8, W3/13, and W3/25 antigens all reached nadirs of 40% of N by day 4 after R and CI. Recovery of antigen expression, except for W3/25, was near completion by day 7 after R and CI. Changes in antigen expression after TI were less pronounced for all mcAB tested. Decreases in labeling of thymocytes with the helper T-cell marker, W3/25, observed after TI, could not be correlated with elevated expressions of the suppressor/cytotoxic T-lymphocyte antigen, OX8. Variations in relative labeling of nonlymphoid thymic cells with OX4 (Ia-antigen) reflected the disappearance and recovery of radiosensitive lymphoid thymocytes. The similarity of results after R and CI demonstrate that the model of CI is 'radiation-dominated.' The addition of burn injury to radiation trauma had no synergistically damaging effect on the parameters studied.