Colony-forming lymphocytes in man. I. In vivo effect of hydrocortisone on phytohaemagglutinin-induced T cell colony formation.

The effect of a single dose (300 mg) of intravenous hydrocortisone on T cell colony and cluster formation was examined in healthy normal volunteers. Peripheral venous blood was drawn before and 4 and 24 hr following administration of the drug T cell colonies (greater than 50 cells/aggregate) and clusters (10-50 cells/aggregate) in response to PHA were assayed by one-stage stimulation in the microagar culture using glass capillaries. The maximum numbers of colonies and clusters were observed between days 7 and 8 of culture. At 4 hr following administration of the drug, both colony and cluster counts were significantly reduced (P less than 0.01). Colony and cluster counts returned to the initial levels 24 hr following administration of the drug. These changes in T cell clusters and colonies were accompanied with changes in the proportions of T cells with IgM (T micro) and IgG (T gamma) receptors. This study demonstrates that a single dose of i.v. hydrocortisone depresses T cell clonal expansion and suggests that this effect could be secondary to the redistribution of a subpopulation of T cells among peripheral blood and other lymphoid tissues and is perhaps not due to a direct suppression of the proliferative response. The significance of these observations is discussed.