Cytokine-mediated priming of neutrophil NADPH oxidase activity in patients in steady-state (A and B) or crisis (C and D) of SCD compared with controls tested on the same day. Whole-blood samples were incubated with either rhTNF-α (A and C), rhGM-CSF (B and D), at the doses indicated, or FCS diluent for 30 minutes at 37°C, followed by stimulation for 15 minutes with 1 μmol/L FMLP or PBS. Neutrophil H₂O₂ production was measured by the oxidation of dichlorodihydrofluorescein (DCF) using flow cytometry, as described in Materials and Methods. Total H₂O₂ production was calculated as the product of the percent of positive cells and their standardized MCF. The data shown are the mean ± 1 SE of (A) 10 experiments, (B) 7 experiments, and (C and D) six experiments. Significant differences between patients and controls (Wilcoxon's matched pairs signed-ranks test) are shown: *P < .01, †P < .005. (-•-), Patient + FMLP; (-○-), control + FMLP; (-▪-), patient + PBS; (-□-), control + PBS.