Representative flow-cytometric histograms show the effects of priming on the FMLP-stimulated neutrophil respiratory burst. Shown are data from a healthy control (histograms A, B, and C), a SCD patient in steady-state (histograms D, E, and F), and a SCD patient in crisis (histograms G, H, and I). Whole-blood samples were incubated with either growth-factor diluent (histograms A, D, and G), 100 U/mL TNFα (histograms B, E, and H), or 10 ng/mL GM-CSF (histograms C, F, and I) for 30 minutes, followed by stimulation for 15 minutes with 1 μmol/L FMLP. Neutrophil H₂O₂ production was measured by the oxidation of DCF as described in Materials and Methods. Shown for comparison in histograms A, D, and G are the overlaid distributions of nonprimed samples stimulated with and without FMLP. In histograms A and G, the distributions ± FMLP were identical; in D, the stimulated distribution is marked with an arrow.