The suppressive effect of γ-IFN on LPS-induced MIP-1α release is dose-dependent. Macrophages (1 × 106 cells) were incubated for 18 hr with LPS (10 ng/ml) either in the absence or presence of γ-IFN at the indicated doses. Culture medium was then removed and the MIP-1α (solid bars) content quantified by ELISA. Data are from a representative experiment (of 3) and are expressed as the mean ± SD of values obtained from duplicate macrophage stimulations. Lesser relative suppression of MIP-1 β release was observed in γ-IFN-treated cultures (cross-hatched bars).