Induction of proinflammatory cytokine production by monocytes after stimulation with S100A8, S100A9, and S100A8/9. Monocytes were purified by negative selection from peripheral blood mononuclear cells of healthy individuals. The monocyte suspensions (1 × 106 cells per ml in culture medium with 10% fetal calf serum) were incubated with or without S100A8, S100A9, and S100A8/A9 (0.1–10 μM) in the presence of polymyxin B (100 μg/ml). Culture supernatants were harvested 24 hours later. Cytokine concentrations were measured by cytometric beads array (using anticytokine monoclonal antibody [mAb]-coated beads and phycoerythrin-conjugated anticytokine mAbs). Values are the mean ± standard error of the mean. IL, interleukin; n, number of samples tested; TNF-α, tumor necrosis factor alpha.