Differential cytokine/chemokine release triggered by FcγRI versus FcγRIIa activation. U937 cells were cross-linked with anti-CD32 (antibody 3D3) and/or anti-CD64 (antibody 10.1) plus goat anti–mouse IgG F(ab)′₂ for 10 minutes and cells were placed in culture for 24 hours. Culture supernatants were harvested 24 hours later and assayed for 17 different cytokine targets by Bioplex cytokine array analysis. Higher levels of (A) IL-8, (B) TNF-α, (C) MIP-1β, (D) IFN-γ, (E) IL-6, and (F) G-CSF were secreted after cross-linking of FcγRI versus FcγRIIa. Results are expressed as the mean ± SD of triplicate samples from 4 independent experiments.