Glucocorticoid enhances gamma interferon effects on human monocyte antigen expression and ADCC

The expression of HLA-DR antigen by highly enriched human monocytes cultured in serum free medium was found to be markedly elevated by human recombinant gamma interferon (IFN-gamma). This effect was maximal after 48 h in culture with 300 mu/ml IFN-gamma. Class I MHC antigen also increased with IFN-gamma treatment. By contrast, binding of a myeloid-specific monoclonal antibody, AML-2-23, was dramatically decreased by IFN-gamma. The augmentation of MHC antigens was not ablated by an immunosuppressive concentration (2 X 10(-7) M) of the glucocorticoid dexamethasone (DEX). In fact, both the enhancement of Class I and Class II MHC antigen expression and the suppression of AML-2-23 antigen by IFN-gamma were often more profound in the presence of DEX. IFN-gamma treatment also resulted in elevated monocyte effector function, as measured by antibody dependent cellular cytotoxicity (ADCC). This functional activation was not inhibited by DEX. On the contrary, DEX slightly augmented IFN-gamma effects on ADCC. This contrasts with other reports that glucocorticoids inhibit monocyte responsiveness to lymphokines, and suggests that the interplay between lymphokines and the glucocorticoid hormones may be more complex than previously thought.