Granulocyte-macrophage colony-stimulating factor enhances selective effector functions of tissue-derived macrophages

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is produced by a variety of cells at sites of exposure to antigens. GM-CSF has a stimulatory effect on a number of neutrophil functions, but the effect on macrophage function is less clear. We investigated the effect of purified murine recombinant GM-CSF on murine peritoneal macrophage oxidative metabolism, Fc-dependent phagocytosis, anti-Toxoplasma activity, and expression of class II major histocompatibility antigen (Iad). GM-CSF significantly increased phorbol myristate acetate- and zymosan-elicited H2O2 release by resident and thioglycollate-elicited macrophages after 48 hours in vitro. The effect of recombinant GM-CSF was blocked by polyclonal anti-GM-CSF antibody and was not altered by lipopolysaccharide (0.01 to 1.0 microgram/mL). GM-CSF also stimulated Fc-dependent phagocytosis by peritoneal macrophages, although the stimulation of resident macrophages (1.4-fold) was less dramatic than that of thioglycollate-elicited cells (2.1-fold). GM-CSF (at doses up to 100 U/mL) had no effect on macrophage anti-Toxoplasma activity or on expression of Iad. In addition to stimulating macrophage growth, GM-CSF selectively promotes the functional capacity of tissue-derived macrophages.