The effect of apocynin on the gene expression of gp91phox (a), p47phox (b), p22phox (c), and p67phox (d) by leukocytes. PBMC, PMN, and differentiated HL-60 cells were incubated with 1.0 mM of apocynin during 4 hours, RNA was extracted, and gene expression was accessed by real-time PCR. Relative gene expression was calculated considering one PBMC control sample as reference. Data represents at least four separated experiments (^#, Mann-Whitney test).