CD33-mediated inhibition of FcγRI-induced calcium mobilization in interferon γ-treated (250 U/mL for 48 hours) U937 cells.

Cells were loaded with calcium-sensitive dyes then stimulated with anti-CD64 or anti-CD64 + anti-CD33 as indicated (arrow 1) followed by GAM (arrow 2). Calcium was monitored with cells at 37°C.