CD59 is transferred to patient granulocytes following transfusion. To exclude hemolysis as an explanation for the RBC results, we examined transfer of a GPI–anchored protein, CD59, to granulocytes. Whole blood was diluted as described in “Patients, materials, and methods” and stained with FITC-conjugated CD15-specific mAb and PE-CD59-specific mAb. Gates were drawn to include only cells staining with FITC (cells of group A₁ blood). Above are scattergrams showing staining of patient granulocytes with PE-conjugated antibody to CD59.