Cell-surface expression of the FcɛRI  chain on human platelets analyzed by flow cytometry. The platelets were incubated with mouse MoAbs to (A) human CD61 as positive control, (B) human FcɛRI  chain (CRA2), and (C) human FcɛRI  chain (CRA3) respectively, and then stained with the FITC-labeled rabbit antimouse IgG + IgM (solid dark line). Mouse IgG₁ was used as isotype-matched control antibody (dashed line).