Differential modulation of surface antigens on human macrophages by IFN-gamma and GM-CSF: effect on susceptibility to LAK lysis.

We have previously reported that cultured human monocytes are lysed by autologous lymphokine-activated killer (LAK) cells in vitro and that treatment of monocytes with interferon-gamma (IFN-gamma) decreased their sensitivity to lysis. Conversely, incubation of monocytes with granulocyte-macrophage colony-stimulating factor (GM-CSF) significantly enhanced their susceptibility to LAK-mediated cytotoxicity. To determine if certain antigens were differentially modulated on macrophages by IFN-gamma and GM-CSF, cytokine-treated and untreated monocytes were analyzed for the expression of a variety of cell surface markers by flow cytometry. Cytotoxicity assays were performed to assess the ability of antibodies to each of these markers to block LAK lysis of macrophage target cells. While several of the surface structures were differentially modulated by cytokine treatment, it was found that only monoclonal antibodies to the adhesion proteins CD11a and CD18 were capable of blocking lysis of either cytokine-treated or untreated target macrophages.