Priming of fMLP-stimulated O₂ production by GM-CSF is significantly decreased in neutrophils from MDS patients compared with healthy subjects.

Freshly isolated neutrophils were (A) stimulated with 1 μM fMLP, (B) primed with 5 ng/mL GM-CSF for 15 minutes before fMLP stimulation, or (C) stimulated with 100 ng/mL PMA, and plates were scanned repetitively at 550 nm using an automated microplate reader. Superoxide production was expressed as the difference in OD₅₅₀ nm (Δ OD 550) between the ferricytochrome c reduction test in the absence and in the presence of 13.16 U/mL SOD. Each test was performed in quadruplicate. Mean O₂ production levels for 3 healthy volunteers and 4 MDS patients are shown. Differences between MDS patients and healthy controls were calculated using the Wilcoxon nonparametric test (*P < .05).