Background of the antigen
Glycophorins A (GPA) and B (GPB) are single pass membrane sialoglycoproteins. GPA is the carrier of blood group M and N specificities, while GPB accounts for S and U specificities. Glycophorin A is the major intrinsic membrane protein of the erythrocyte. The N terminal glycosylated segment, which lies outside the erythrocyte membrane, has MN blood group receptors and also binds influenza virus.