DEX affects Lck-CD4 and Fyn-CD3 associations. Cells were preincubated with DEX for 10 minutes and subsequently stimulated with anti-CD3/anti-CD28 Abs for 15 minutes. Lck and Fyn were then immunoprecipitated, and samples were analyzed for CD4 and CD3 expression on Western blot. To test for equal loading, blots were analyzed for total Lck and Fyn expression. Upon TCR ligation, CD4 and CD3 expression is increased in Lck and Fyn immunoprecipitates, respectively. Reduced CD4 expression was observed in Lck immunoprecipitates prepared from activated cells treated with DEX. Similarly, Fyn-immunoprecipitated lysates demonstrated decreased CD3 protein levels upon DEX treatment. CD3 expression was analyzed in Lck immunoprecipitates, and CD4 protein levels were studied in Fyn immunoprecipitates to ensure specificity in this experiment. Three experiments were performed and comparable results were obtained. DEX indicates dexamethasone; IB, immunoblotting; IP, immunoprecipitation.