Decreased amount of the Rh antigen D in hereditary spherocytosis (HS)

Eosin-5-maleimide binding to band 3 and Rh-related proteins forms the basis of a screening test for hereditary spherocytosis

Flow cytometric analysis of eosin-5-maleimide (EMA) binding to red cells is a screening test for the diagnosis of hereditary spherocytosis (HS). The present study used chemical modifications to determine the integral membrane proteins that react with EMA. The predominant interaction of EMA, contributing c. 80% of fluorescence, was with the epsilon-NH2 group of lysine in band 3 protein, as previously reported. The remainder of the EMA fluorescence was attributable to labelling of accessible sulfhydryl groups on intact red cells. This reaction was heat labile. Three molecules containing sulfhydryl groups were shown to be associated with the Rh blood group protein complex by sodium dodecyl sulphate polyacrylamide gel electrophoresis. These were CD47 and the Rh-associated glycoprotein, both in the Mr 40-60 kD region, and the Rh blood group proteins in the 30-32 kD region. Immunoprecipitation, using specific monoclonal antibodies and antibody binding studies by flow cytometry, showed that the relative content of these three membrane proteins was lower in HS than normal red cells. Thus, the high predictive value of the EMA binding test for HS reflects changes in the relative amounts of the Rh-related integral membrane proteins as well as band 3 in HS red cells.

Biochemistry of rhesus (Rh) blood group antigens

Although the molecular nature of several blood group antigens was established in 1950-1980, the identification and characteristics of the Rh-antigens long remained unsolved. In 1982 two groups were able to conclusively identify the RhO(D) antigen as a cell surface polypeptide with an apparent molecular weight of about 30,000. This protein has now been relatively well characterized. It seems to lack carbohydrate, it is strongly bound to the membrane skeleton, and it is posttranslationally modified by fatty acid acylation. Its NH2-terminal amino acid sequence has been determined. It is relatively hydrophobic, and its absence or decrease results in fragile erythrocytes or spherocytes. Its wide distribution in erythrocytes of various animals indicates that it plays an important physiological role.