Down regulation of human monocyte differentiation antigens by interferon gamma

The role of IFN-gamma in the activation and differentiation of human peripheral blood monocytes was investigated. Recombinant IFN-gamma induced a decrease in the expression of monocyte differentiation antigens (Mo2 and 63D3) and, to a lesser extent, the C3bi receptor. Conversely, class II histocompatibility antigen expression increased on monocytes exposed to IFN-gamma. The antigen modulating effect of IFN-gamma was maximal on freshly isolated monocytes, with diminished potency if added to monocytes that had been cultivated in vitro for 1 to 3 days. Experiments to determine the fate of the down-regulated antigens on interferon-treated cells failed to demonstrate intracellular antigen due to internalization. We suggest that Mo2 and 63D3 may be considered "inverse" activation antigens; i.e., their expression is decreased in monocytes activated by interferon.