Dexamethasone suppresses concanavalin A-induced production of chemotactic lymphokines by releasing a soluble factor from splenic T lymphocytes

Treatment of guinea-pig spleen cells with glucocorticoids, such as dexamethasone (DEX), reduces concanavalin A (Con A)-induced production of chemotactic lymphokines (CLK), such as eosinophil chemotactic factor and macrophage chemotactic factor. The decreased CLK production is not caused by a direct effect of DEX on the spleen cells producing CLK, because Con A-induced CLK production is suppressed when the cells are cultured together with cell-free supernatants of the spleen cells which had been pretreated with DEX. A soluble suppressive factor, termed CLK-SF, with a MW of about 20,000, seems to be responsible for the suppression of both CLK production. CLK-SF is produced from DEX-treated T lymphocytes. CLK-SF probably exerts a critical role in the early stage of CLK production. In contrast, CLK-SF fails to inhibit Con A-induced lymphocyte proliferation, although DEX itself suppresses lymphocyte proliferation. This suggests that DEX suppresses Con A-induced CLK production by a different mechanism from that for lymphocyte proliferation.