CD59 defines an N-glycosylated glycoprotein expressed on various hemopoietic cells. It is anchored to the cell membrane by a glycosylphosphatidylinositol linkage and restricts the action of homologous complement. Monoclonal antibodies 2/24, 1B2, Fib75.1, BRIC 229, MEM-43, and YTH 53.1 were compared by immunoblotting against normal erythrocyte ghosts. All six stained a diffuse band of 17–25 kDa, but BRIC 229 also detected bands at 35 and 80 kDa. 2/24 reacts with all red blood cells (RBCs) tested, including Rhnull; Oh; ii; KO; FY:−1,−2,−3 JK:−1,−2,−3; S-S-U−; p; CO:−1,−2; Yt(a–);Jr(a–); Vel–; At(a–); Cr(a–); GE:−2−3; Wr(a+b−); MkMk; Jo(a–); and Lan–. 2-aminoethylisothiouronium bromide treatment of erythrocytes destroyed blotting and serologic reactivity of all six antibodies. Pronase treatment reduced serologic reactivity and blotting ability of all antibodies except BRIC 229. Reactivity of all six antibodies was reduced with RBCs from paroxysmal nocturnal hemoglobinuria patients. Flow cytometric analysis was used to demonstrate that 1B2, Fib75.1, BRIC 229, YTH 53.1, and MEM-43 competitively inhibited the binding of 2/24 to RBCs, thus demonstrating that all six antibodies detect epitopes on the same molecule. Immunohematology 1993;9:68.
