The effect of recombinant interferon-gamma on human monocyte-derived macrophages

The effect of recombinant interferon-gamma (rIFN-gamma) on human macrophage functions was studied, using monocytes which had matured to macrophages within hydrophobic containers. Following exposure to rIFN-gamma, the number of surface-expressed specific IgG-binding sites was increased. This increase was restricted to high-affinity Fc receptors (FcR), however; low-affinity FcR were not increased in number. Exposure to rIFN-gamma led to an enhanced chemiluminescence (CL) signal in the presence of luminol and a variety of respiratory burst stimuli, such as zymosan, phorbol 12-myristate 13-acetate or IgG-sensitized sheep erythrocytes (EA). In contrast, phagocytosis of EA was markedly depressed in rIFN-gamma-treated cells. Both increase in CL response and decrease in phagocytic activity were manifest after 1 day of treatment and were more pronounced after 2 days. While 5 U/ml of rIFN-gamma was an insufficient dose, 50 to 5000 U/ml yielded significant dose-dependent changes in both functional assays. Thus, using rIFN-gamma as a biological response-modifier, FcR expression and FcR-mediated CL can be dissociated from FcR-mediated phagocytosis.