Evidence That the Human Blood Group Antigens Gya and Hy Are Carried on a Novel Glycosylphosphatidylinositol-linked Erythrocyte Membrane Glycoprotein

Immunoblotting under non-reducing conditions with purified human anti-Gya and anti-Hy locates both antigens to an erythrocyte membrane glycoprotein of apparent Mr 46,750-57,500. The antigens are destroyed on intact red cells by the enzymes pronase, trypsin and chymotrypsin, and by treatment with reducing agents. Immunoblotting with anti-Gya and anti-Hy to membranes prepared from red cells pre-treated with an Endo F preparation caused a mean reduction in apparent Mr of the glycoprotein by 11 kDa at the leading and trailing edges, when compared with control membranes. These results suggest that the glycoprotein has one or more complex N-glycans that are not completely sensitive to Endo F digestion on intact cells. The majority of Gya/Hy-active molecules are not tightly associated with the red cell membrane skeleton. A gross reduction in reactivity with anti-Gya and anti-Hy by immunoblotting was observed in red cell membranes from patients with paroxysmal nocturnal haemoglobinuria, suggesting a possible membrane linkage via glycosylphosphatidylinositol for the glycoprotein that carries the Gya and Hy antigens. Immunoprecipitation of the glycoprotein by anti-Gya showed that the protein migrates faster under reducing conditions (Mr 45,000-54,000). A putative dimer was also evident in the precipitates. The glycoprotein was demonstrated to be distinct from lymphocyte-function-associated antigen-3 (CD58), the LWab-active glycoprotein, the Fya-active glycoprotein, the Oka-active glycoprotein and the BRIC 125 glycoprotein (CD47).