Thymic response to thermal injury in mice: I. Alterations of thymocyte subsets studied by flow cytometry and immunohistochemistry.

The dynamics of thymocyte subset changes in mice subjected to sublethal thermal injury were studied in cell suspensions by flow cytometry and in situ by immunohistochemistry. Thermal injury caused acute thymic involution in the first 2 days which was the consequence of a considerable decrease in numbers of Thyl.2high+ CD4+ CD8+, cortical thymocytes. Medullary, Thyl.2low+ thymocytes were more resistant and their relative values increased. In the regenerative phase (2-14 days) the recovery of large CD4- CD8-, early thymocytes, mainly localized in the subcapsular area of the thymus, preceded the regeneration thymocytes of the cortical phenotype. Judged by the absolute numbers of medullary thymocytes it can be seen that CD4+ CD8- (T-helper/inducer cells) were more sensitive to the effect of thermal injury than CD4- CD8+ (T-suppressor/cytotoxic cells). While values of CD4+ CD8- cells were constantly and progressively lower during 2 weeks after thermal injury, absolute numbers of CD4- CD8+ cells showed cyclic changes with lower and higher values compared to controls. An increase in the numbers of CD4- CD8+ cells was found at day 6 after thermal injury.