Induction of tumor necrosis factor alpha (TNF-α) production by in vitro-differentiated macrophages after S100A8/A9 stimulation. Monocytes (1 × 106 cells per ml in culture medium with 10% fetal calf serum) were incubated for 7 days with or without 10 ng/ml granulocyte-macrophage colony-stimulating factor (GM-CSF) or 1 ng/ml interferon gamma (IFN-γ). The in vitro-differentiated macrophages were then stimulated for 24 hours with 2 μM S100A8/A9 in the presence of polymyxin B (100 μg/ml). Culture supernatants were measured for TNF-α concentrations by enzyme-linked immunosorbent assay. Values are the mean ± standard error of the mean. n, number of samples tested.