The sugar chain structures of ABO blood group active glycoproteins obtained from human erythrocyte membrane

Negative ion CID fragmentation of O-linked oligosaccharide aldoses--charge induced and charge remote fragmentation

Collision induced dissociation (CID) fragmentation was compared between reducing and reduced sulfated, sialylated, and neutral O-linked oligosaccharides. It was found that fragmentation of the [M - H](-) ions of aldoses with acidic residues gave unique Z-fragmentation of the reducing end GalNAc containing the acidic C-6 branch, where the entire C-3 branch was lost. This fragmentation pathway, which is not seen in the alditols, showed that the process involved charge remote fragmentation catalyzed by a reducing end acidic anomeric proton. With structures containing sialic acid on both the C-3 and C-6 branch, the [M - H](-) ions were dominated by the loss of sialic acid. This fragmentation pathway was also pronounced in the [M - 2H](2-) ions revealing both the C-6 Z-fragment plus its complementary C-3 C-fragment in addition to glycosidic and cross ring fragmentation. This generation of the Z/C-fragment pairs from GalNAc showed that the charges were not participating in their generation. Fragmentation of neutral aldoses showed pronounced Z-fragmentation believed to be generated by proton migration from the C-6 branch to the negatively charged GalNAc residue followed by charge remote fragmentation similar to the acidic oligosaccharides. In addition, A-type fragments generated by charge induced fragmentation of neutral oligosaccharides were observed when the charge migrated from C-1 of the GalNAc to the GlcNAc residue followed by rearrangement to accommodate the (0,2)A-fragmentation. LC-MS also showed that O-linked aldoses existed as interchangeable α/β pyranose anomers, in addition to a third isomer (25% of the total free aldose) believed to be the furanose form.

ABH blood group antigens in N-glycan of human glycophorin A

We previously showed that a small proportion of the O-linked oligosaccharide chains of human glycophorin A (GPA) contains blood group A, B or H antigens, relevant to the ABO phenotype of the donor. The structures of these minor O-glycans have been established (Podbielska et al. (2004) [20]). By the use of immunochemical methods we obtained results indicating that ABH blood group epitopes are also present in N-glycan of human GPA (Podbielska and Krotkiewski (2000) [22]). In the present paper we report a detailed analysis of GPA N-glycans using nanoflow electrospray ionization tandem mass spectrometry. N-glycans containing A-, B- and H-related sequences were identified in GPA preparations obtained from erythrocytes of blood group A, B and O donors, respectively. The ABH blood group epitopes are present on one antenna of the N-glycan, whereas a known sialylated sequence NeuAcalpha2-6Galbeta1-4GlcNAc- occurs on the other antenna and other details are in agreement with the known major structure of the GPA N-glycan. In the bulk of the biantennary sialylated N-glycans released from GPA preparations, the blood group ABH epitopes-containing N-glycans, similarly O-glycans, constituted only a minor part. The amount relative to other N-glycans was estimated to 2-6% of blood group H epitope-containing glycans released from GPA-O preparations and 1-2% of blood group A and B epitope-containing glycans, released from GPA-A and GPA-B, respectively.

A genome-wide association study identifies new loci for ACE activity: potential implications for response to ACE inhibitor

Because angiotensin-converting enzyme (ACE) activity is implicated widely in biological systems, we aimed to identify its novel quantitative trait loci for the purposes of understanding ACE activity regulation and pharmacogenetics relating to ACE inhibitor (ACEI). We performed a two-stage genome-wide association study: (1) from 400 young-onset hypertension (YOH) subjects and (2) a confirmation study with an additional 623 YOH subjects. In the first stage, eight single nucleotide polymorphisms (SNPs) of the ACE structural gene and one SNP of ABO genes were significantly associated with ACE activity. SNP rs4343 in exon17 near the well-known insertion/deletion polymorphism had the strongest association. We confirmed in the second stage that three SNPs: rs4343 in ACE gene (P=3.0 x 10⁻²⁵), rs495828 (P=3.5 x 10⁻⁸) and rs8176746 (P=9.3 x 10⁻⁵) in ABO gene were significantly associated with ACE activity. We further replicated the association between ABO genotype/blood types and ACE activity in an independent YOH family study (428 hypertension pedigrees), and showed a potential differential blood pressure response to ACEI in subjects with varied numbers of ACE-activity-raising alleles. These findings may broaden our understanding of the mechanisms controlling ACE activity and advance our pharmacogenetic knowledge on ACEI.

Terminal Sialic Acid Residues on Human Glycophorin A Are Recognized by Porcine Kupffer Cells

BACKGROUND

We have previously shown that recognition of human erythrocytes by porcine Kupffer cells is mediated by a carbohydrate-dependent mechanism. The present study explores the possible ligands existing on human glycophorin A and tests their ability to inhibit erythrocyte rosette formation.

METHODS

Human erythrocytes were tested for ABO and MN specificity and used as targets in a 51Chromium quantitative erythrocyte rosette assay. Monosaccharides present on human glycophorin A, neuraminyl lactoses, bovine and porcine submaxillary mucins (BSM and PSM), and hyaluronic acid as well as proteoglycan N-linked glycosidase F(PNGaseF)- and sialidase A-treated human erythrocyte glycoproteins (hEGP) and human erythrocytes were all tested for inhibitory potential in the rosetting assay.

RESULTS

Porcine Kupffer-cell recognition of human erythrocytes was insensitive to differences in blood groups A, B, O, or MN. At 30 mM, the monosaccharide, N-acetylneuraminic acid, and the trisaccharide mixture, neuraminyl lactoses, disrupted human erythrocyte recognition by 25% and 30%, respectively. A dilution of BSM but not PSM inhibited the rosetting assay by 17% (.2 mg/mL), 33% (1 mg/mL), and 53% (2 mg/mL). The same dilution of hyaluronic acid had no effect on rosetting. Removal of N-linked oligosaccharides from hEGP with PNGaseF did not impair its ability to inhibit the rosetting assay. In contrast, removal of sialic acid completely abrogated its inhibitory ability. Treatment of whole human erythrocytes with sialidase A likewise prevented recognition by porcine Kupffer cells.

CONCLUSIONS

Terminal sialic acid on human erythrocytes is a target recognized by porcine Kupffer cells, suggesting a role for a sialic-acid receptor in innate cellular recognition of xenogeneic epitopes. Inasmuch as this work reveals a carbohydrate-recognition mechanism for cellular rejection, we shed light on a potential new boundary that will need to be overcome within xenotransplantation.

ABH blood group antigens in O-glycans of human glycophorin A

The major O-linked oligosaccharide structures attached to human glycophorin A (GPA) have been extensively characterized previously. Our own recent findings, obtained by immunochemical methods, suggested the presence of blood group A and B determinants in O-glycans of human glycophorin originating from blood group A or B erythrocytes, respectively. Here, we elucidate the structure of O-glycans, isolated from GPA of blood group A, B, and O individuals by reductive beta-elimination, carrying A, B or H blood group epitopes, respectively. Structural studies based on nanoflow electrospray-ionization tandem mass spectrometry and earlier reported data on the carbohydrate moiety of GPA and ABH antigens allowed us to conclude that these blood group epitopes are elongations of the beta-GlcNAc branch attached to C-6 of the reducing GalNAc. The galactose linked to C-3 of the reducing GalNAc carries NeuAcalpha2-3 linked residue. Identified here O-glycans were found in low amounts, their content estimated at about one percent of all GPA O-glycans. These O-glycans with type-2 core, carrying the blood group A, B or H determinants, have not been identified in GPA so far. Our results demonstrate the efficacy of nanoESI MS/MS in detecting minor oligosaccharide components present in a mixture with much more abundant structures.

Absorption of anti-blood group A antibodies on P-selectin glycoprotein ligand-1/immunoglobulin chimeras carrying blood group A determinants: core saccharide chain specificity of the Se and H gene encoded alpha1,2 fucosyltransferases in different host cells

To specifically eliminate recipient anti-blood group ABO antibodies prior to ABO-incompatible organ or bone marrow transplantation, an efficient absorber of ABO antibodies has been developed in which blood group determinants may be carried at high density and by different core saccharide chains on a mucin-type protein backbone. The absorber was made by transfecting different host cells with cDNAs encoding a P-selectin glycoprotein ligand-1/mouse immunoglobulin G(2b) chimera (PSGL-1/mIgG(2b)), the H- or Se-gene encoded alpha1,2-fucosyltransferases (FUT1 or FUT2) and the blood group A gene encoded alpha1,3 N-acetylgalactosaminyltransferase (alpha1,3 GalNAcT). Western blot analysis of affinity-purified recombinant PSGL-1/mIgG(2b) revealed that different precursor chains were produced in 293T, COS-7m6, and Chinese hamster ovary (CHO)-K1 host cells coexpressing FUT1 or FUT2. FUT1 directed expression of H type 2 structures mainly, whereas FUT2 preferentially made H type 3 structures. None of the host cells expressing either FUT1 or FUT2 supported expression of H type 1 structures. Furthermore, the highest A epitope density was on PSGL-1/mIgG2(2b) made in CHO-K1 cells coexpressing FUT2 and the alpha1,3 GalNAcT. This PSGL-1/mIgG(2b) was used for absorption of anti-blood group A antibodies in human blood group O serum. At least 80 times less A trisaccharides on PSGL-1/mIgG(2b) in comparison to A trisaccharides covalently linked to macroporous glass beads were needed for the same level of antibody absorption. In conclusion, PSGL-1/mIgG(2b), if substituted with A epitopes, was shown to be an efficient absorber of anti-blood group A antibodies and a suitable model protein for studies on protein glycosylation.

Changes in immunologic properties of group A RBCs during treatment with an A-degrading exo-alpha-N-acetylgalactosaminidase

BACKGROUND

Blood group A RBCs theoretically can be converted to universal-donor group O cells by incubation with alpha-N-acetylgalactosaminidase (A-zyme). The purpose of this study was to compare the extent of A-zyme treatment required to abolish several immunologic responses of group B or O recipients to group A RBCs.

STUDY DESIGN AND METHODS

A(1) RBCs were incubated for 2 hours at 37 degrees C in buffer alone (control) or with 0.1 to 5.0 units (U) of A-zyme per mL of packed cells. They were then tested for 1) immune adherence (% rosetting) and activation of monocytic cells (% erythrophagocytosis, TNFalpha production), 2) activation of immune hemolysis, and 3) hemagglutination with Dolichos biflorus lectin and pooled human anti-A serum.

RESULTS

A 2-hour incubation with < or =5.0 U of A-zyme per mL of packed cells abolished monocytic cell adherence and phagocytosis of group A(1) RBCs coated with IgG(3) A MoAb. Epitopes of A binding to IgG(3) anti-A A005 MoAb and BG-2 MoAb differed in A-zyme sensitivity. TNFalpha production in group B or O whole blood in response to the addition of A(1) cells varied, but it essentially was abolished when group A cells were treated with 0.1 to 1.0 U of A-zyme per mL of packed cells. A epitopes mediating immune hemolysis and hemagglutination with D. biflorus lectin were also cleaved by <5 U of A-zyme per mL of packed cells. In contrast, hemagglutination with polyclonal anti-A typing serum was diminished by only 1 to 2 serial titer dilutions.

CONCLUSION

A epitopes mediating immune hemolysis and immune adherence to and activation of monocytic cells are highly sensitive to A-zyme cleavage, as compared to those mediating hemagglutination with monoclonal and polyclonal anti-A.

Structural analysis of O-linked oligosaccharide-alditols by electrospray-tandem mass spectrometry after mild periodate oxidation and derivatization with 2-aminopyridine

O-linked oligosaccharide-alditols were analyzed by a combination of high-performance liquid chromatography (HPLC) and electrospray-tandem mass spectrometry (ESI-MS/MS). First, oligosaccharide-alditols were treated with sodium meta-periodate under conditions where core N-acetylgalactosaminitol is specifically degraded. The resulting fragments were labeled with 2-aminopyridine and purified on a reversed-phase column. Pyridylamino oligosaccharides yielded protonated molecular ions in positive-ion ES-MS and gave Y-series sequence ions, arising from glycosidic cleavages, by ESI-tandem mass spectrometry. Information on sugar sequence and branching of oligosaccharides linked at C6 and C3 to the N-acetylgalactosaminitol can be obtained. A systematic study of various oligosaccharide-alditols demonstrated that this approach constitutes a powerful tool for the structural characterization of O-glycans available only in limited quantities.

Analysis of O-linked oligosaccharide alditols by high-pH anion-exchange chromatography with pulsed amperometric detection

To apply high-pH anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) to the accurate and sensitive analysis of O-linked oligosaccharide alditol, removal of glycopeptides and peptides from oligosaccharide samples obtained by beta-elimination was first investigated. The results obtained by using fetuin as a model glycoprotein indicated that (glyco)peptides derivatized by fluorescamine are easily removed from the beta-eliminated oligosaccharide sample by means of a Sep-Pak C18 cartridge due to their increased hydrophobicity. This clean-up procedure was also effectively applied to the beta-eliminated oligosaccharide sample obtained from delipidated sheep erythrocyte ghosts. Furthermore, structural analysis of the oligosaccharide alditols by HPAEC-PAD was successfully performed in combination with partial and complete desialylation, composition analysis, periodate oxidation, and glycosidase digestion and revealed that sheep erythrocyte membrane glycoproteins contain Gal beta 1-->3Gal-NAc and Gal beta 1-->4GlcNAc beta 1-->3Gal beta 1-->3GalNac, to which one or two residues of Neu5Ac and Neu5Gc are attached in different combinations.

O-linked neutral sugar chains of porcine zona pellucida glycoproteins

The O-linked sugar chains were liberated from porcine zona pellucida glycoproteins by alkaline-borohydride treatment and the structures of neutral oligosaccharides were determined. The major oligosaccharides had the following structures with type-1 cores, (Gal beta 1-->4GlcNAc beta 1-->3)1 3-Gal bdta 1-->3N-acetylgalactosaminitol (54%) and GlcNAc beta 1-->3(Gal beta 1-->4GlcNAc beta 1-->3)0-1Gal beta 1-->3N- acetylgalactosaminitol (16%). Approximately 6% of the oligosaccharides had the structure with a type-3 core, Gal beta 1-->4GlcNAc beta 1-->3N-acetylgalactosaminitol. Oligosaccharides having alpha-galactose (2%) and beta-GalNAc (4%) at their non-reducing termini were also found as minor components.

An improved approach to the analysis of the structure of small oligosaccharides of glycoproteins: application to the O-linked oligosaccharides from human glycophorin A

Treatment of purified human glycophorin A with alkaline borohydride cleaved the oligosaccharide side chains to yield alditol derivatives that were separated by gel filtration into three mixtures of low molecular weight compounds. Each mixture was oxidised with periodate, and the products were reduced with borohydride and analysed after acetylation or methylation by GLC-MS and FABMS. The resulting data allowed the monosaccharide sequence and linkage positions to be assigned to each component of the mixtures. The anomeric configuration was determined by 1H NMR spectroscopy of the intact fractions. The structures of a desialylated tetrasaccharide, two monosialylated trisaccharides, and five other minor products were defined.

Histochemical and cytochemical localization of blood group antigens

The oligosaccharide structures of blood group antigens are not the primary gene products; they are constructed in a stepwise manner by adding particular sugar to precursor oligosaccharides via several glycosyltransferases coded for by different blood group genes (Watkins 1966, 1978, 1980). Consequently, final profiles of antigens expressed in each cell type are influenced by many different factors such as the intrinsic composition of glycosyltransferase species which are defined by the genotype of the individuals, relative activity or amount of these enzymes (repression, derepression or induction of the enzymes), competition between enzymes with overlapping substrate specificity, the organization of the enzymes in membranes, utilizability of precursors and specific substrate sugars, and the activity level of degradating enzymes. Changes in the antigen profiles during maturation, differentiation and malignant transformation are thought to be intimately related to the variability of these factors. Although great importance attaches to histo- and cytochemical information on the distribution and levels of glycosyltransferases and messenger RNA corresponding to the relevant enzyme, detailed and precise localization of the blood group antigens and their variants is the base line for analyzing these complex factors. On the basis of individual genotype and histochemical findings about the antigen distribution and the interrelationship between cells and cellular components producing different antigenic structures (cellular and subcellular mosaicism), we can deduce precursor oligosaccharide levels as well as the status of gene activation and its primary product, glycosyltransferases. Thus, these findings are a prerequisite for further analysis at the molecular genetic level. As emphasized in this article, lectin staining or immunostaining methods with MAbs combined with glycosidase digestion procedures are powerful tools for in situ analysis of carbohydrate structures in histochemical systems. Although in some cases valuable results have been obtained by applying the technique, our knowledge concerning the distribution of complex carbohydrate structures is still far from satisfactory. Along with well defined MAbs and lectins, the key to developing our methods further is successful introduction of glycosidases, in particular, endoglycosidases since these reagents are indispensable for analyzing the inner core structures and glycoconjugate species of the blood group antigens. Application of these techniques at the ultrastructural level is an alluring possibility, even though many difficulties must be overcome. Although their functional roles have not yet been determined, a diverse array of macromolecules is known to be decorated with blood group-related antigens.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of the heterogeneity of the binding site specificities of hyperimmune human anti-A and -A, B sera: the application of competition assays using murine monoclonal antibodies

Monoclonal antibodies PL41 and AL62 have previously been shown to recognize two distinct blood group A epitopes on the red cell surface. Competitive inhibition of the binding of 125I-PL41 and 125I-AL62 to group A1 red cells, by hyperimmune polyclonal human antibodies, has been employed to investigate the binding site specificities of 15 anti-A and 8 anti-A,B sera. Differences in the degree of inhibition of the binding of the two MABs by individual anti-A or -A,B samples indicate that polyclonal reagents are composed of varying proportions of up to 3 (or more) different antibody specificities, each recognizing a distinct epitope: PL41-like, AL62-like and a third (as yet undefined) category of antibody. In general, those anti-A sera with PL41-like specificities are superior agglutinators of A2B cells with weakly expressed A antigens; similarly, the specificity of potent anti-A,B, sera capable of strongly agglutinating Ax cells was likewise directed towards PL41-binding blood group A trisaccharide haptens.

ABH and related histo-blood group antigens; immunochemical differences in carrier isotypes and their distribution

This review summarizes present knowledge of the chemistry of histo-blood group ABH and related antigens. Recent advances in analytical carbohydrate chemistry (particularly mass spectrometry and NMR spectroscopy) and the introduction of monoclonal antibodies (MoAbs) have made it possible to distinguish structural variants of histo-blood group ABH antigens. Polymorphism of ABH antigens is induced by: (i) variations in peripheral core structure, of which four (type 1, 2, 3 and 4) are known in man; (ii) variation in inner core by branching process (blood group iI), leading to variation of unbranched vs. branched ABH determinants; (iii) biosynthetic interaction with other glycosyltransferases (Lewis, P. T/Tn blood systems) capable of acting on the same substrate as the ABH-defined transferases, and finally (iv) the nature of the glycoconjugate (glycolipid, glycoprotein of N- or O-linked type). ABH variants induced by item (i) above have been clearly distinguished qualitatively by MoAbs; e.g., at least six types of A determinants can be distinguished by qualitatively different classes of antibody. The variants induced by item (ii) create mono- vs. bivalent antigens which may be responsible for observed differences in antibody-binding affinity. Detailed studies of the chemistry of these antigens have increased our insight into blood groups, providing the basis for blood group iI and A subgrouping, as well as a relation between the ABH and Lewis, P, and T/Tn systems. A survey of the literature on distribution patterns of ABH variants is presented. It has been assumed that expression of histo-blood group antigens is developmentally regulated. Relationships between histo-blood group expression, development, differentiation and maturation, as well as malignant transformation, are discussed.

Further characterization of type 2 and type 3 chain blood group A glycosphingolipids from human erythrocyte membranes

Blood group A glycosphingolipids with slow chromatographic mobilities have been separated systematically with an improved chromatographic procedure, and their structures have been analyzed by application of a panel of monoclonal antibodies defining A determinants carried by type 1, type 2, type 3, and type 4 carbohydrate chains as well as by 1H NMR spectroscopy and methylation analysis. Of several A-active fractions, previously termed Aa, Ab, Ac, and Ad, in decreasing order of thin-layer chromatographic mobility, the third fraction (Ac) was characterized as containing one type 3 chain A component and one type 2 chain A component without branching, which have been termed type 3 chain Ab and nor-Ac, respectively. (Formula: see text). The major component present in the fourth A-active fraction (Ad) was isolated and characterized as a branched type 2 chain glycolipid formerly termed Ac. The major component in the fifth A-active fraction (Ae) was identified as a branched type 2 chain A previously termed Ad. The structures of Ac (n = 1) and Ad (n = 2) are (Formula: see text).

Genetics of ABO, H, Lewis, X and related antigens

The present knowledge on chemical, enzymatic, serologic and genetic aspects of ABH antigens is reviewed in an effort to produce a simple and coherent genetic model for the biosynthesis of these antigens and chemically related structures. The genetic control of type 1 (Le(a), Le(b), Le(c) and Le(d)), type 2 (X, Y, I, and H), type 3 and type 4 ABH and related antigens in different animal and human tissues is analyzed, taking into account the properties of the glycosyltransferases which are involved in their synthesis and considering possible competition for common acceptor and donor substrates. The phylogeny of ABH determinants shows that they appeared as tissular antigens much earlier than as red cell antigens. The ontogeny of ABH antigens suggests that they behave as differentiation antigens, and an effort is made to correlate their tissular distribution in the adult with the embryological origin of each tissue.

Characterization of blood group active glycopeptides derived from porcine kidneys

Sialoglycopeptide fractions were prepared from the pronase digest of porcine kidneys by DEAE-Sephadex A-25 column chromatography and gel-filtration through Sephadex G-100. Their chemical compositions and large molecular size suggested that these glycopeptides were derived from mucin-type glycoprotein(s). The results of the beta-elimination reaction indicated that they have the O-glycosidic linkages between N-acetylgalactosamine and serine/threonine. The glycopeptides exhibited blood group A and H activities. The present study revealed that the porcine kidney contains the blood group antigens of glycoprotein nature.

Structure and blood-group I activity of poly(glycosyl)-ceramides

Nitrous acid deamination of N-deacetylated blood-group O poly(glycosyl)ceramides resulted in a complete degradation of the glycolipids to give O-beta-D-galactopyranosyl-(1 leads to 4)-2,5-anhydro-D-mannose, O-alpha-L-fucopyranosyl-(1 leads to 2)-O-beta-D-galactopyranosyl-(1 leads to 4)-2,5-anhydro-D-mannose, lactosylceramide, and small proportions of free 2,5-anhydro-D-mannose. A series of straight-chain glycolipids containing up to six glycosyl residues and comprising alternating 3-O-substituted D-galactosyl and 4-O-substituted 2-acetamido-2-deoxy-D-glucosyl residues was isolated from partial acid hydrolyzates of poly(glycosyl)ceramides. Branching points of 3,6-di-O-substituted and 6-O-substituted D-galactosyl residues were observed only in fractions containing more than six glycosyl residues. Sequential periodate oxidation of poly(glycosyl)ceramides gradually eliminated the branching points. This elimination was not complete, even after four cycles of degradation. The ability of poly(glycosyl)ceramides to precipitate with anti-I serums disappeared after two cycles of degradation. These results suggest a general structure for poly(glycosyl)ceramides. I blood-group activity of the glycolipids would depend on the periodical arrangement of branched side-chains.

A-active trisaccharides isolated from A1 and A2 blood-group-specific glycoproteins

Blood-group-specific glycoproteins obtained from ovarian cyst fluids of A1 and A2 persons were degraded with NaOH/NaBH4. The oligosaccharides released were de-N-acetylated with Ba(OH)2 and then hydrolysed with dilute H2SO4. The products were fractionated on columns of ion-exchange resin and the components isolated were re-N-acetylated with 14C-labelled acetic anhydride; further purification was effected by paper chromatography. The following trisaccharides: type 1, GalNAc(alpha 1-3)Gal(beta 1-3)GlcNAc; type 2, GalNAc(alpha 1-3)-Gal(beta 1-4)GlcNAc; type 3 (reduced), GalNAc(alpha 1-3)Gal (beta 1-3)GalNAcOH (where Gal is galactose; GalNAc is N-acetylgalactosamine, GlcNAc is N-acetylglucosamine and GalNAcOH is N-acetylgalactosaminitol) were isolated and characterised from both the A1 and A2 materials. The type 3 (reduced) trisaccharide has not previously been obtained from human glycoproteins. Chromatographic evidence indicated that the three trisaccharide structures were also present in other A1, A2, A1B and A2B ovarian cyst glycoproteins and in A1 and A2 salivary glycoproteins. These findings are not indicative of structural differences between the A determinants of A1 and A2 glycoproteins.

Further evidence that carbohydrates are the immunodeterminant structures of blood group M and N specificities

Terminal beta-D-galactopyranosyl (Gal) groups are implied in blood group N but not M specificity by the following findings: (a) Rabbit anti-asialoganglioside sera specific for terminal beta-Gal-(1 leads to 3)-GalNac agglutinate human group 0 M and N erythrocytes, the latter to a significantly higher titer, while rabbit anti-ganglioside GMl sera, whereas sialic acid modifies the antibody specificity, do not. The agglutination score with N erythrocytes was about twice that with M red blood cells. The asialoganglioside antibodies were readily absorbed by group 0 N erythrocytes, which were up to 10 times more efficient than group 0 M erythrocytes. Erythrocyte agglutination by the anti-asialoganglioside sera was inhibited by M and N antigen preparations isolated from group 0 red cells ghosts. N antigen was a better inhibitor. Asialoganglioside effectively inhibited the red cell agglutinations by anti-asialoganglioside serum. Ganglioside GMl did not inhibit. (b) Horse anti-pneumococcus Type XIV serum, which has anti-beta-Gal specificity, precipitated highly active N but not M substances. This precipitation was specifically inhibitable by oligosaccharides with terminal beta-Gal. (c) Beta galactosidase specifically inactivated native N and "acid-produced' N substances with the release of about three moles Gal per subunit of N antigen. It did not affect M antigen.

Blood group ABH antigens on human cord red cells. Number of H antigenic sites and their distribution among different classes of membrane constituents

When the blood group H sites of cord erythrocytes obtained from newborn infants of groups O, A, B and AB were labelled specifically by incubation of the whole cells with the A1 gene dependent alpha-N-acetylgalactosaminyl transferase in the presence of UDP-N-acetyl [14C]-galactosamine, the incorporation of radioactivity was considerably lower than that found for cells from adults. Based on the amount of label recovered in the membranes, average values of 326,000 H sites per single O cell and 68,000 H sites per single A, B and AB cell were calculated. Following fractionation of the stromal blood group substances thus labelled, it was found that, on the average, 66% of the radioactivity was bound to glycoprotein material, 2.7% to glycosphingolipids with short carbohydrate chains, and about 24% to polyglycosylceramides. As these values are similar to those previously determined for O cells from adults, this result shows that there are probably no substantial differences between erythrocytes from adults and newborn infants concerning the overall membrane disposition, but rather provides evidence for variations in the carbohydrate chains of the stromal glycoconjugates.

Identification of blood group A-active glycoproteins in the human erythrocyte membrane

Normal human erythrocytes of blood groups A1, A2, B and O, and En (a-) erythrocytes lacking glycophorin A, but with A1B-activity, were surface-labeled with tritiated sodium borohydride after oxidation of terminal galactosyl and N-acetylgalactosaminyl residues with galactose oxidase. A1 cells were also labeled by lactoperoxidase catalyzed iodination. After solubilization in Triton X-100, the blood group A-active glycoconjugates were isolated using the A-specific lectin from Vicia cracca coupled to Sepharose. No radioactivity was bound from erythrocytes of B and O blood groups. The glycoconjugates from A cell membranes which bound to the lectin and were eluted with 0.01 M N-acetyl-D-galactosamine were analyzed using cylindrical or slab gel electrophoresis in the presence of sodium dodecyl sulfate. The A-active glycoproteins included the major integral glycoprotein, band 3, and many minor, previously poorly defined components. Glycophorins A and B did not contain A-activity.

Blood-group-ABH antigens of human erythrocytes. Quantitative studies on the distribution of H antigenic sites among different classes of membrane components

The contribution of blood-group-active glycolipids and glycoproteins to the blood-group-ABH character of human erythrocytes was investigated. For that purpose the blood-group-H sites of human O cells were converted in vitro into group-A sites by transfer of alpha-N-acetyl-D-[14C]galactosamine residues with the aid of the blood-group-A gene-dependent alpha-N-acetylgalactosaminyl transferase prepared from human A1 plasma. Upon partition of the red cell membranes between water and organic solvent, about 5% of the label was found in the organic phase and about 20% in the water phase, thus reflecting the distribution of blood-group antigenic sites between glycosphingolipids with short carbohydrate chains and polyglycosylceramides, respectively. The fact that about 70% of the radioactivity remained tightly bound to the membranes and could only be released by treatment with pronase provided good evidence that the bulk of blood-group-H determinants is bound to glycoprotein material. Following these results it can thus be assumed that blood-group-ABH activity of human erythrocytes is determined preferentially by group-specific glycoproteins rather than glycolipids.

Comparison of alkal-labile oligosaccharide chains of M and N blood-group glycopeptides from human erythrocyte membrane

Alkali-borohydride degradation of M or N blood-group active, tryptic glycopeptides and glycoproteins was performed under conditions giving the reduced oligosaccharides in a yield significantly improved over that reported earlier. Degradation of desialosylated glycoproteins yielded beta-D-Galp-(1 leads to 3)-D-GalNAcol, D-GalNA-col, and Galol in a ratio of approximately 30:1:1. GalNAc was shown to be alpha-D-linked to the polypeptide chain. Degradation of the glycopeptides gave the tetrasaccharide, NeuAc-(2 leads to 3)-beta-D-Galp-(leads to 3)-[NeuAc-(2 leads to 6)]-D-GalNAcol, and two trisaccharides, NeuAc-(2 leads to 3)-beta-D-Galp-(1 leads to 3)-D-GalNAcol and beta-D-Galp-(1 leads to 3)-[NeuAc-(2 leads to 6)]-D-GalNAcol, in a molar ratio of approximately 8:3:1. These oligosaccharides were accompanied by minor amounts of unidentified compounds showing identical electrophoretic mobility when derived from M and N glycopeptides. During isolation of the reduced oligosaccharides, the release of sialic acid did not exceed 5.5%, indicating that only a part of the trisaccharide portion might have arisen as a result of desialosylation of the tetrasaccharide. No differences between the degradation products derived from M and N glycoproteins were found, and the presence of significant amounts of larger, alkali-labile oligosaccharides was not observed.