Characterization of blood-group-ABO(H)-active glycosphingolipids in type-AB human erythrocytes

Neutral glycolipids in Folch's upper phase were isolated from human erythrocyte membranes of 22 individuals with blood type AB. On immunostaining by TLC with anti-A IgG, all reactive glycolipids in type A corresponded to reactive glycolipids in type-AB erythrocytes. With anti-B IgM, all reactive glycolipids in type-B erythrocytes also corresponded to reactive glycolipids in type-AB erythrocytes. By comparison of the reactivity to that of the anti-A and anti-B antibodies, it was found that, in type-AB erythrocytes, all glycolipids reactive with either one of the anti-A or anti-B antibodies were detected in both type-A and type-B erythrocytes, and that A-active glycolipids had higher Rf values than B-active glycolipids on TLC plates. A series of glycolipids reactive with both antibodies were purified from the Folch's upper neutral glycolipid fraction of erythrocyte membranes by column chromatography, and was characterized by TLC-immunostaining and negative secondary-ion mass spectrometry. The results strongly suggested that A-active and B-active carbohydrate chain epitopes existed separately as glycolipid molecules in blood-type-AB erythrocytes. It was also confirmed that these phenotypes observed in erythrocyte membranes were exhibited by blood-group-active glycosphingolipids in the small intestine of blood-type-AB individuals. Furthermore, upon treatment of fractions obtained from silicic acid column chromatography with alpha-N-acetylhexosaminidase or alpha-galactosidase, a branched hybrid-type molecule with both A and B determinants was not detected.