CD59, and to a lesser extent CD55, are transferred to deficient RBCs in PNH patients following transfusion. Erythrocytes were washed as described in “Patients, materials, and methods” and stained with FITC-conjugated Dolichos biflorus and either PE-conjugated mAbs to CD55 or CD59. Above are scattergrams showing isotype controls stained with PE-IgG and staining of group A₁ donor cells with PE-CD59 mAb (A) and PE-CD55 mAb (B) before transfusion and at varying intervals following transfusion. The transfused cells, which were lectin negative, appear in the posttransfusion samples, but transfer was not seen in the samples obtained 1 hour after transfusion. The percentages in the right upper quadrant of the scattergrams reflect lectin-positive cells (ie, group A₁ patient cells), which are CD59⁺ or CD55⁺. Transfer of CD59 appeared to be more efficient than transfer of CD55.