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 α‐N ‐acetylhexosaminidase or α‐galactosidase, a branched hybrid‐type molecule with both A and B determinants was not detected.