The effect of recombinant interferon‐γ on human monocyte‐derived macrophages

The effect of recombinant interferon‐gamma (rIFN‐γ) on human macrophage functions was studied, using monocytes which had matured to macrophages within hydrophobic containers. Following exposure to rIFN‐γ, 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‐γ 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‐γ‐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‐γ was an insufficient dose, 50 to 5000 U/ml yielded significant dose‐dependent changes in both functional assays. Thus, using rIFN‐γ as a biological response‐modifier, FcR expression and FcR‐mediated CL can be dissociated from FcR‐mediated phagocytosis.