The effects of cyclosporin and hydrocortisone on human T lymphocyte colony formation

The immunosuppressive activities of two compounds, cyclosporin A and hydrocortisone, were evaluated using a human T lymphocyte colony assay. Both compounds produced a dose-related reduction in colony formation. With cyclosporin, concentrations of 1.0–100 μg/ml virtually abolished PHA-induced lymphocyte growth; as little as 0.01 μg/ml decreased clonal growth by 48%. Suppression was observed as late as 4 days after the addition of PHA. The addition of exogenous IL-2 did not completely restore clonal growth to normal. Similarly, hydrocortisone, in concentrations of 0.4 μg/ml, produced a 96% inhibition in clonal growth. Partial suppression could also be obtained if the drug was added as late as 4 days after PHA. Exogenous IL-2 completely reversed the inhibitory effects of hydrocortisone. By contrast, IL-1 was able to only partially restore growth potential. Parallel studies using TPA indicated that both immunosup-pressants inhibited responses to this mitogen. However, in plates containing both TPA and PHA, hydrocortisone failed to impair clonal growth.