Expression of the FcɛRI in normal human megakaryocytes. (A) The cell-surface expression of the FcɛRI  chain in normal human megakaryocytes was analyzed by two-color flow cytometry. Cells were isolated from the bone marrow aspirate (as described in the text) and were incubated with PE-conjugated antihuman CD61 MoAb and the FITC-conjugated antihuman FcɛRI  chain MoAb (CRA2) (solid line) and analyzed using the FACScan after gating on the polymorphonuclear cells that were CD61 positive (CD61⁺ PMN). FITC-conjugated mouse IgG1 was used as isotype-matched control antibody. (B) The intracytoplasmic expression of the FcɛRI  chain in normal human megakaryocytes. Cells were first incubated with the PE-conjugated antihuman CD61 MoAb, treated with the permeabilization solution (Becton Dickinson) and then incubated with FITC-conjugated antihuman FcɛRI  chain MoAb, and analyzed using the FACScan after gating on the CD61⁺ PMN. FITC-conjugated mouse IgG1 was used as isotype-matched control antibody (thin line).