EFFECTS OF IRRADIATION, GLUCOCORTICOID AND FK506 ON CELL-SURFACE ANTIGEN EXPRESSION BY RAT THYMOCYTES - A 3-COLOR FLOW CYTOFLUOROMETRIC ANALYSIS

The expression of T-cell antigen receptor (TCR) alpha beta was investi gated in rat CD4(-) CD8(-) thymocytes during thymic reconstitution aft er the exposure of animals to irradiation or glucocorticoid. The effec t of the immunosuppressant FK506 on the expression of TCR alpha beta i n rat CD4(-) CD8(-) thymocytes was also examined. The percentage of CD 4(-) CD8(-) thymocytes constituted 2.6% of total thymocytes and that o f CD4(-) CD8(-) TCR alpha beta(high) cells constituted 12.6% of CD4(-) CD8(-) thymocytes in normal adult Lewis rats. The percentage of CD4(- ) CD8(-) TCR alpha beta(high) cells increased during thymic reconstitu tion after irradiation, and maximally constituted 28.6% of CD4(-) CD8( -) thymocytes on day 7. Similar results were obtained during thymic re constitution after glucocorticoid treatment. In contrast, continuous t reatment with FK506 for 7 days markedly decreased not only the percent ages of CD4(+) CD8(-) TCR alpha beta(high) and CD4(-) CD8(+) TCR alpha beta(high) thymocytes, but also that of CD4(-) CD8(-) TCR alpha beta( high) thymocytes. These results indicate that rat CD4(-) CD8(-) thymoc ytes contain a subpopulation of mature (TCR alpha beta(high)) cells. T he possible implications of the existence of this subpopulation with r egard to thymocyte differentiation and maturation are discussed.