Stimulation of reactive oxygen species (ROS) in neutrophils by IgG Fcγ receptor engagement. Purified neutrophils were incubated with DHR-123 and stimulated with heat-aggregated IgG (HAIgG) or antibodies against IgG Fcγ receptors (FcγR) followed by streptavidin. Homologous cross-linking was completed by using iv.3–biotin (FcγRII) or 3g8–biotin (FcγRIII), and heterologous cross-linking by using both FcγRII and FcγRIII with streptavidin. Data are expressed at maximum fluorescence (45 minutes after stimulation). Experiments were performed in duplicate (n = 7). Comparisons between stimulations were completed by using a one-way analysis of variance with post hoc Bonferroni Dunn test. Significant differences from the streptavidin control are shown (*p < 0.05). Comparisons between rheumatoid arthritis and controls were performed by unpaired t-test (#p < 0.05). MFI, median fluorescence intensity.