The structural basis of blood group A-related glycolipids in an A3 red cell phenotype and a potential explanation to a serological phenomenon.

Glycolipids from the red cells of a rare blood group A subgroup individual, expressing the blood group A(3) phenotype with the classical mixed-field agglutination phenomenon, A(2(539G>A))/O(1) genotype, and an unusual blood group A glycolipid profile, were submitted to a comprehensive biochemical and structural analysis. To determine the nature of blood group A glycolipids in this A(3) phenotype, structural determination was carried out with complementary techniques including proton nuclear magnetic resonance (1D and 2D), mass spectrometry (MS) (nano-electrospray ionization/quadrupole time-of-flight and tandem mass spectrometry) and thin layer chromatography with immunostaining detection. As expected, total blood group A structures were of low abundance, but contrary to expectations extended-A type 2 and A type 3 glycolipids were more dominant than A hexaglycosylceramides based on type 2 chain (A-6-2 glycolipids), which normally is the major A glycolipid. Several para-Forssman (GalNAcß3GbO(4)) structures, including extended forms, were identified but surmised not to contribute to the classic mixed-field agglutination of the A(3) phenotype. It is proposed that the low level of A antigen combined with an absence of extended branched glycolipids may be the factor determining the mixed-field agglutination phenomenon in this individual.

Structural characterization of blood group A glycolipids in blood group A liver tissue in situ perfused with O blood: the dominating presence of type 1 core chain A antigens.

BACKGROUND: Biochemical studies of organ blood group antigen expression show a mixed pattern originating from both the organ tissue and remaining blood cells trapped in the organ despite in vitro perfusion of the vascular tree. The blood group A glycolipid expression was studied in a unique case in which a human liver had been in situ perfused by recipient blood. CASE HISTORY: A blood group O recipient was re-transplanted with an ABO incompatible A1Le (a - b +) liver. Because of discrepancy in size, liver segments II and III were removed 2 h after re-vascularization. Thereafter, the removed A1 liver segment was physiologically in situ perfused with O blood, eliminating a major part of the donor blood cells/plasma. EXPERIMENTAL: Total neutral glycolipids were isolated from the liver tissue and separated by high-performance liquid chromatography. Purified glycolipid fractions were stained with anti-A monoclonal antibodies (mAbs) and structurally characterized by mass spectrometry and proton nuclear magnetic resonance (NMR) spectroscopy. RESULTS: Two blood group A reactive glycolipid compounds were isolated. One component had a thin-layer chromatography (TLC) mobility as a six-sugar glycolipid and reacted with mAbs specific for A type 1 mono-fucosyl structures. The second glycolipid fraction migrated as seven-sugar components and reacted with mAbs specific for type 1 difucosyl (ALeb) as well as Leb determinants. Mass spectrometry of the six-sugar component showed a structure similar to a blood group A hexaglycosylceramide with one fucose. Mass spectrometry and proton NMR spectroscopy of the seven-sugar fraction revealed a mixture of blood group Leb hexa- and ALeb hepta-glycosylceramides, respectively. All fractions were non-reactive with antibodies specific for A antigens based on types 3 and 4 core chain structures. In addition, TLC immunostaining of glycolipids isolated from blood group A livers, harvested for organ transplantation but discarded for various reasons, revealed trace amounts of several A glycolipids with a complex pattern. CONCLUSION: The in situ perfused liver tissue contains blood group A glycolipids based exclusively on type 1 core chains. The secretor gene (Se) codes for a fucosyltransferase acting on all core chain precursors while the H-gene fucosyltransferase only utilizes the type 2 chain precursor. Whether this explains that only A type 1 chain compounds were found has to be established.