Different N-terminal amino acids in the MN-glycoprotein from MM and NN erythrocytes

Large-scale blood group genotyping: clinical implications

The molecular background of blood group antigen expression of the major clinically significant blood group antigens has been largely accomplished. Despite this large body of work, blood group phenotype prediction by genotyping has a marginal supporting role in the routine blood bank. It has however had a major impact in the prenatal determination of fetal blood group status in the management of haemolytic disease of the fetus and newborn. In the past few years several high throughput systems have been in development that have the potential capacity to perform genotyping on a mass scale. Such systems have been designed for use on donor- and patient-derived DNA and provide much more comprehensive information regarding an individuals blood group than is possible by using serological methods alone. DNA-based typing methodology is easier to standardize than serology and has the potential to replace it as a front line diagnostic in blood banks. This review overviews the current situation in this area and attempts to predict how blood group genotyping will evolve in the future.

Glycoprotein identification and localization of O-glycosylation sites by mass spectrometric analysis of deglycosylated/alkylaminylated peptide fragments

In-gel digestion of densely O-glycosylated proteins, an essential step in proteome analysis, is often hampered by steric hindrance of the proteases. To overcome this technical problem a simple and convenient method has been developed, which combines several advantages: (1) Approximately 70% of the oligosaccharides are cleaved without significant protein hydrolysis at the optimal reaction conditions of 70% ethylamine, and quantitative cleavage is achieved with 40% methylamine, at 50 degrees C. (2) To the unsaturated derivatives of Ser and Thr the alkylamine is added as a label of previous O-glycosylation sites. (3) The alkylaminylated protein is effectively cleaved by proteolysis. (4) The modified peptides are identified by MALDI mass spectrometry under consideration of incremental mass increases. (5) The alkylamine label is stable under MALDI post-source-decay analysis as well as in collision-induced dissociation experiments allowing sequencing and peptide localization of O-glycosylation sites. Applicability of the method is evaluated with a series of synthetic glycopeptides, the densely O-glycosylated human glycophorin A, and with the mucin MUC1 from human milk fat globule membranes.

Only Selected Light Chains Combine with a Given Heavy Chain to Confer Specificity for a Model Glycopeptide Antigen

The M and N human blood group glycopeptide Ags are carried on RBCs by glycophorin A. Previous results suggested that the murine humoral immune response against the N, but not the M, Ag is restricted. In addition, these results suggested that particular highly homologous heavy chains might be able to combine promiscuously with various light chains to yield anti-N specificity. To examine this, the current study used Fab phage methodology to couple an array of light chains, obtained from cDNA libraries isolated from immunized mice, to single Fd obtained from N61, N92, and 425/2B hybridomas. Interestingly, for the chimeric Fab to retain M or N specificity, the new light chains needed to belong to the same Vk gene family as the light chain from the parental, hybridoma-derived mAb. In some cases the new light chains modified the Fab affinity and fine specificity. For example, library-derived light chains coupled with the N92 Fd yielded chimeric Fab with increased affinity. In particular, the affinity of these univalent chimeric Fab for the N Ag was equivalent to that of the bivalent parental IgG mAb. Taken together, these results demonstrate that particular structures formed by the light chain V region are required to cooperate with a particular heavy chain V region to create a functional binding site for these glycopeptide Ags. They also demonstrate a lack of heavy chain promiscuity in the formation of murine anti-M and anti-N Abs.

Restricted VH gene usage by murine hybridomas directed against the human N, but not M, blood group antigen

The M and N human blood group antigens are complex glycopeptide determinants at the amino terminus of the red blood cell membrane glycoprotein, glycophorin A. The heavy and light chain variable region cDNA sequences were determined for seven murine monoclonal antibodies recognizing glycophorin A. Three of the antibodies were anti-M and four were anti-N. Each of the anti-M antibodies was composed of VH and VL regions derived from distinct germline gene families (VH1 (J558), VH4 (X24), VH5 (7183), VK5, VK8, and VK19). In contrast, all four anti-N heavy chains were composed of VH regions derived from the VH2 (Q52) germline gene family and all used the same J4 gene segment. In addition, two of the anti-N light chains were composed of VK regions from the VK8 germline gene family and used the J1 gene segment. Since each anti-N hybridoma was derived from different mice immunized by different protocols, these results suggest that the murine immune response to the N, but not the M, human blood group antigen is restricted.

Human erythrocyte glycophorins: protein and gene structure analyses

Human RBCs glycophorins are integral membrane proteins rich in sialic acids that carry blood group antigenic determinants and serve as ligands for viruses, bacteria, and parasites. These molecules have long been used as a general model of membrane proteins and as markers to study normal and pathological differentiation of the erythroid tissue. The RBC glycophorins known as GPA, GPB, GPC, GPD, and GPE have recently been fully characterized at both the protein and the DNA levels, and these studies have demonstrated conclusively that these molecules can be subdivided into two groups that are distinguished by distinct properties. The first group includes the major proteins GPA and GPB, which carry the MN and Ss blood group antigens, respectively, and a recently characterized protein, GPE, presumably expressed at a low level on RBCs. All three proteins are structurally homologous and are essentially erythroid specific. The respective genes are also strikingly homologous up to a transition site defined by an Alu repeat sequence located about 1 Kb downstream from the exon encoding the transmembrane regions. Downstream of the transition site, the GPB and GPE sequences are still homologous, but diverge completely from those of GPA. The three glycophorin genes are organized in tandem on chromosome 4q28-q31, and define a small gene cluster that presumably evolved by duplication from a common ancestral gene. Most likely two sequential duplications occurred, the first, about 9 to 35 million years ago, generated a direct precursor of the GPA gene, and the second, about 5 to 21 million years ago, generated the GPB and GPE genes and that involved a gene that acquired its specific 3' end by homologous recombination through Alu repeats. Numerous variants of GPA and GPB usually detected by abnormal expression of the blood group MNSs antigens are known. An increasing number of these variants have been structurally defined by protein and molecular genetic analyses, and have been shown to result from point mutations, gene deletions, hybrid gene fusion products generated by unequal crossing-over (not at Alu repeats), and microconversion events. The second group of RBC membrane glycophorins includes the minor proteins GPC and GPD both of which carry blood group Gerbich antigens. Protein and nucleic acid analysis indicated that GPD is a truncated form of GPC in its N-terminal region, and that both proteins are produced by a unique gene called GE (Gerbich), which is present as a single copy per haploid genome and is located on chromosome 2q14-q21.(ABSTRACT TRUNCATED AT 400 WORDS)

Monoclonal antibodies as blood grouping reagents

The large volume requirements for high quality ABO and Rh(D) typing reagents can now be supplied by selected monoclonal antibodies. Superior anti-A and anti-B monoclonal reagents can be prepared, from blends of at least two antibodies, to optimize the intensity of agglutination for slide tests and the potency for the detection of the weaker sub-groups, including Ax and Bw, by tube techniques. New quality control steps have been described for some highly sensitive anti-A/anti-B antibodies to avoid the detection of traces of A on B cells or traces of B on A1 cells, which results from the non-specific activity of A and B transferases. Excellent anti-A,B reagents may also be made by blends of at least two antibodies to optimize both A and B reactions, but the need for their continued use is now debatable. The development of high titre IgM monoclonal anti-D reagents offers simple rapid saline Rh(D) typing of both patients and donors, but they cannot reliably detect weak D (Du) and some D variants, e.g. the epitopes on D category VI cells. However, this can be achieved by blending an IgM anti-D with IgG (polyclonal) anti-D which can detect these types after conversion of negative saline tests to an antiglobulin phase. In addition, high grade Du, D categories and variants can be reliably detected (for typing donors) by selected monoclonal IgM and IgG anti-Ds by use of suitably enhanced tests without the use of an antiglobulin test.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of cDNA clones for human glycophorin A. Use for gene localization and for analysis of normal of glycophorin-A-deficient (Finnish type) genomic DNA

Glycophorin A is the major membrane sialoglycoprotein of human erythrocytes and represents a typical example of a transmembrane glycoprotein. The functional role of this cell-surface component is not known but it represents a receptor for viruses, bacteria and parasites like Plasmodium falciparum. 1. Two cDNA clones encoding glycophorin A have been characterized from human fetal cDNA libraries. The longer cDNA extended from the coding region of glycophorin A (residues 4-131) to the 3' untranslated region which included two polyadenylation signals and a poly(A) tail. 2. The structural gene for glycophorin A is located on chromosome 4, q28-q31 as shown by in situ hybridization, thus confirming the previous localization by genetic linkage analysis. 3. Three distinct mRNA species (1.0 kb, 1.7 kb and 2.2 kb) have been identified in erythroid spleen. Northern blot analyses with a probe directed against the 3' untranslated region of the mRNAs indicated that all these species share a homologous 3' non-coding region and that the first polyadenylation signal downstream the stop codon is not used. 4. Preliminary studies by Southern blot analysis of the genomic DNA from normal En(a+) and rare En(a-) donors suggest that the glycophorin A gene has a complex organization and is largely deleted in donors of the En(a-) phenotype (Finnish type) who lack glycophorin A on their red cells.

Monoclonal antibodies against glycophorin A

Two mouse IgM monoclonal antibodies, 177.1 and 179.3, are directed against glycophorin A, the major sialoglycoprotein of human erythrocytes. Both antibodies agglutinate blood group M and N erythrocytes equally well, both before and after treatment with neuraminidase or trypsin, but fail to agglutinate erythrocytes treated with papain. Antibody 179.3 agglutinates MiVII(K.T.) cells, whose glycophorin A probably contains some alterations in amino acid sequence between residues 46-56, but antibody 177.1 does not agglutinate these cells. Neither antibody agglutinates En(a-)G.W. cells, which lack glycophorin A completely. The hemagglutinating activity of antibody 177.1 is inhibited by purified glycophorin A and its chymotryptic glycopeptides CH1 (amino acid residues 1-64) and CH3 (amino acid residues 35-64), whereas the hemagglutinating activity of 179.3 is inhibited weakly by glycophorin A but not by chymotryptic peptides. These antibodies both are classified as anti-En(a-)FS but apparently bind different epitopes.

Number and distribution density of ABH and MN antigen sites on young and old human erythrocyte surfaces

There were no differences in the number of A and M antigen sites between young and old human erythrocyte surfaces. No essential differences in the number of A1, N and Vicia graminea N antigen sites could be observed between young and old erythrocytes. The number of B and H antigen sites on cell surface was significantly higher in young erythrocytes than in old ones. The distribution density of A and M antigen sites on young erythrocyte was remarkably higher than that on old ones. Compared with young erythrocytes, significant increases in the distribution density of A1, B, H, N and Vicia graminea N antigen sites were observed in aged erythrocytes. It is suggested from these and other observations that human erythrocyte aging is accompanied by elimination of a small amount of B and H antigens from cell membranes, while A, A1, M, N and Vicia graminea N antigens are not released from cell membranes during in vivo aging.

The Dantu erythrocyte phenotype of the NE variety. I. Dodecylsulfate polyacrylamide gel electrophoretic studies

Red cell membranes from patient NE, Mr. Dantu and 16 additional Black individuals, positive for the low-frequency MNSs-system antigen Dantu, were studied by dodecylsulfate polyacrylamide gel electrophoretic techniques. The content of the major, blood group M- or N-active sialoglycoprotein (glycophorin A, GP A) was found to be decreased by about 57%. The blood group S- or s-active sialoglycoprotein (GP B) was decreased by about 51% in membranes from proven Dantu/U heterozygotes and not detectable in those from patient NE and other Dantu+U- individuals. Donor NE was shown to exhibit the genotype Dantu/u. Dantu-positive cells exhibit a proteinase-resistant GP B-GP A hybrid with an apparent molecular mass of 29 KDa whose intramembraneous and cytoplasmic domains were shown to be similar to those of GP A. The molar hybrid: GP A ratio in all cells was found to be about 2.4: 1, indicating that the NE variety of the Dantu phenotype is much more frequent than the Ph or MD types. The significance of an additional minor 'new' component (molecular mass 21 KDa) in Dantu+ membranes and the minor component J (molecular mass 22 KDa) occurring in normal and Dantu+U+ GP preparations, but not in those from Dantu+U- cells, has not been resolved. The apparent molecular mass of the anion channel protein (band 3) in all cells of the NE variety was shown to be decreased by about 3 KDa, due to a shortening of carbohydrate chains. This suggests that the hybrid, just like GP A, might form a complex with band 3.

A monoclonal anti-glycophorin A antibody recognizing the blood group M determinant: studies on the subspecificity

A mouse monoclonal antibody (425/2B, IgM) was obtained which shows specificity for blood group M determinant of glycophorin A. The antibody is pH-dependent. At pH 6-7 it reacted strongly with blood group M antigen, but also cross-reacted distinctly with N antigen. At pH 8.3 the antibody showed moderately decreased reactivity with M antigen, but no interaction with N antigen was detectable by hemagglutination, immunoblotting, or microplate ELISA. The direct binding studies and inhibition of 425/B antibody by untreated or modified blood group M and N glycoproteins or tryptic glycopeptides showed that the binding to the antigens was not affected by acetylation of their amino groups, or removal of amino-terminal amino acid residue. Desialylation of the antigens decreased their reactivity with the antibody and this effect was distinctly stronger at pH 7 than 8.3. The antibody reacted strongly at pH 7 and 8.3 with glycophorin B of Henshaw phenotype, whereas its reactivity with normal glycophorin B was weak or undetectable at these pH values, respectively. The results obtained indicated that anti-M specificity of 425/2B antibody is related to the 5th amino acid residue of glycophorin A (anti-Mgly specificity) and that pH shift from 7 to 8.3 changes the fine specificity of the antibody. At pH 8.3 the reactivity of the antibody is more dependent on glycine residue (higher anti-M specificity) and less dependent on sialic acid residues in the antigen.

The blood group U antigen is not located on glycophorin B

Erythrocytes from twelve individuals with the S-s-U- phenotype and from ten with the S-S-U+ phenotype were analyzed and compared to control cells with S+/s+U+ determinants. No red cell abnormality was detected in S-s-U+ or S-s-U- carriers. Sialic acid content was similar (P greater than 0.05) for S-s-U+ and S-s-U- erythrocytes (74.6 +/- 7.14 and 71.4 +/- 8.53 nmol/10(9) red blood cells, respectively) but significantly less (P less than 0.001) than controls with 89.5 +/- 11.4 nmol/10(9) red blood cells, n = 16. Fluorographs of SDS-polyacrylamide gels showed no glycophorin B in membranes from S-s-U+ and S-s-U- erythrocytes labeled with NaB3H4. Glycophorins were extracted from red cell membranes in chloroform/methanol, labeled with 125I and analyzed by SDS-polyacrylamide gel electrophoresis. Periodic acid Schiff stain and autoradiographs of these gels also showed absence of glycophorin B in both S-s-U+ and S-s-U- cells. These findings suggested that the U antigen is not located on glycophorin B. This hypothesis was tested by determining blood group antigenicity on red cell membranes and on extracted sialoglycoproteins by the hemagglutination inhibition technique. Although U and S/s activities were detected in control red cell membranes, extracted glycoproteins demonstrated S/s activity but no U activity. Together the data indicate that both S-s-U+ and S-s-U- erythrocytes lack glycophorin B and that the U antigen is not located on glycophorin B. This deletion does not seem to affect the structure-function of the red cell.

Reactions of murine monoclonal antibodies to blood group MN antigens

BALB/c mice were immunized by intraperitoneal injections with human blood group substances; 4 mice with M and 4 with N. Immune spleen cells were fused with murine myeloma cells X63-Ag-8.653. Two clones secreting monoclonal anti-M and seven secreting monoclonal anti-N were identified. All antibodies were of IgG1 subclass and had kappa light chains. Three clones have been maintained that produced antibodies useful for typing purposes: anti-M, A09 originating from a mouse injected with M, anti-N, AH7 originating from a mouse injected with N, and anti-N BO10 originated from a mouse injected with M substance. In typing 370 erythrocyte samples, monoclonal reagents gave identical results with commercial anti-M or anti-N typing sera of rabbit origin. Significantly, anti-N reagent AH7 obtained by immunization with N substance showed serological differences from anti-N reagent BO10 obtained by immunization with M substance in that AH7 had apparently higher avidity to N specificity on glycophorin A of N erythrocytes than BO10, whereas BO10 showed higher avidity for 'N' specificity on glycophorin B of M and N erythrocytes than AH7. These two reagents showed also somewhat different patterns of reaction with enzymatically digested erythrocytes. This apparent serologic difference between N and 'N' specificities is at variance with current immunochemical data.

Identification of the O-linked sialyloligosaccharides of glycophorin A as the erythrocyte receptors for S-fimbriated Escherichia coli

The erythrocyte receptors for S-fimbriated Escherichia coli, which causes sepsis and meningitis in newborn infants, were investigated. Neuraminidase and trypsin treatments of erythrocytes abolished the hemagglutination ability of the bacteria. To identify the receptor glycoproteins, we separated erythrocyte membrane proteins by gel electrophoresis, blotted them to nitrocellulose, and incubated them with 125I-labeled bacteria. The only bacterium-binding bands identified corresponded to glycophorin A dimer and monomer, and the binding was abolished by neuraminidase treatment of the blot. Radiolabeled bacteria also bound to purified glycophorin A adsorbed to polyvinyl chloride microwells, and the binding was inhibited by other sialoglycoproteins and isolated sialyloligosaccharides containing the NeuAc alpha 2-3Gal sequence. Oligosaccharides which contain the NeuAc alpha 2-3Gal beta 1-3GalNAc and NeuAc alpha 2-3Gal beta 1-3(NeuAc alpha 2-6)GalNAc sequence and which are identical to the O-linked saccharides of glycophorin A were twofold more effective inhibitors of binding than were other oligosaccharides containing the NeuAc alpha 2-3Gal sequence. The replacement of sialic acid in asialoerythrocytes with a purified Gal beta 1-3GalNAc alpha 2-3 sialyltransferase, which forms the O-linked NeuAc alpha 2-3Gal beta 1-3GalNAc sequence in asialoglycophorins, restored bacterial hemagglutination. These results indicated that the major erythrocyte receptor for S-fimbriated E. coli is the NeuAc alpha 2-3Gal beta 1-3GalNAc sequence of the O-linked oligosaccharide chains of glycophorin A.

Differences in carbohydrate specificities and complement-activating capacity of guinea pig and human antibodies to neuraminidase-treated autologous erythrocytes

Guinea pig erythrocytes desialated by treatment with neuraminidase from Vibrio cholerae were lyzed in autologous serum through a natural-antibody-dependent activation of the classical complement pathway. Lysis was inhibited when a mannose, glucose, galactose or N-acetyl-glucosamine was added to the incubation mixture. Methyl-alpha- or -beta-D-galactopyranosides were poorly effective and N-acetyl-D-galactosamine was not effective at all. Inhibition of lysis by the carbohydrates was due neither to an anti-complementary effect nor to a modification of the osmotic pressure since: (a) they did not alter the total complement haemolytic activity of guinea pig serum, and (b) they did not inhibit lysis of desialated guinea pig erythrocytes in human serum through activation of the alternative complement pathway. The presence of mannose, glucose, galactose or N-acetyl-glucosamine in the incubation mixture resulted in an impaired fixation of natural auto-antibodies on antigenic sites, namely the T-antigen (Thomsen-Friedenreich), which were unmasked following membrane sialic acid removal. When tested under the same conditions, only small percentage of the normal human population showed the phenomenon of lysis of desialated erythrocytes in autologous serum. Lysis was not due to a particular susceptibility of erythrocytes from these individuals to complement-mediated lysis but to the presence in their serum of complement-activating anti-T antibodies. As expected, the activity of human anti-T antibodies was inhibited by galactose and N-acetyl-galactosamine, which are the immunodominant sugars of the human T-antigen. Mannose and glucose had no effect, and methyl- alpha- or - beta-D-galactopyranosides were almost as effective as galactose. The heterogeneity of the human population with regard to the complement-activating capacity of anti-T antibodies could be of significance for the individual response of the host to an infection by a neuraminidase-producing microorganism. That the immunodominant sugars of the T-antigen were different between humans and guinea pigs was further assessed by absorption experiments. We have demonstrated that guinea pig anti-T antibodies were not removed during contact with desialated human red cells which do not have the mannose specificity, whereas human antibodies were almost entirely retained on desialated guinea pig red cells which, beside mannose, express galactose. These results also suggest that guinea pig antibodies are mostly directed towards mannose and glucose.

Two blood group M epitopes disclosed by monoclonal antibodies

Two cloned mouse hybridomas, designated G8 and E3, produced anti-M of immunoglobulin classes IgG2b and IgG1, respectively. No discrepancies were observed in testing over 5,000 normal donor blood samples with appropriately diluted G8 and E3 culture supernatant fluids in parallel with rabbit anti-M and anti-N typing reagents. The specificity and titer of antibodies produced by G8 and E3 were minimally affected by changes in temperature (37 degrees C, 22 degrees C, 4 degrees C). G8 and E3 showed reduced activity with type MM red cells that had been treated with either neuraminidase or papain, but differences were observed in the susceptibility of the respective epitopes to treatment with neuraminidase. Furthermore, G8 and E3 exhibited different specificities when used to test the red cells of nonhuman primates and erythrocytes of the rare MgMg human blood type. These results indicate the existence of at least two M antigen epitopes.

Studies on Mv red cells. II. Immunochemical investigations

The properties of the Mv antigen, a low incidence receptor of the MNSs blood group system, were investigated by serological tests with protease treated red cells and inhibition assays with glycoproteins or peptides from normal and Mv erythrocytes. Our data demonstrate that the Mv receptor represents an allelomorphic form of the 'N' antigen on the Ss sialoglycoprotein, rather than variant of the M receptor on the MN sialoglycoprotein. Anti-Mv plus -N (serum Arm.) reacts with the N, 'N' and Mv antigens, whereas anti-Mv (serum Arch.) is specifically directed against the latter receptor.

Effect of pH on the binding of Vicia graminea lectin to erythrocytes. Dependence on the chemical character of red-cell receptors

Binding of the radioactive Vicia graminea lectin to human blood-group M and N erythrocytes and to horse erythrocytes was studied at pH 6-10. Binding of the lectin to untreated human erythrocytes and to those treated with Vibrio cholerae neuraminidase increased severalfold from pH 6 to pH 8 and was maintained at the maximal level up to pH 9/9.5. On the other hand, interaction of V. graminea lectin with native or desialylated horse erythrocytes was not significantly affected by pH and small differences in the binding were opposite to those found with human erythrocytes: the binding decreased when pH increased from 6 to 9.5. Binding of the lectin to all erythrocytes tested at pH 10 was lowered to about 80% of the maximal values. The differences in pH dependence of V. graminea lectin binding to human and horse erythrocytes most probably resulted from the presence of amino groups in human red-cell receptors and their absence from receptors of horse erythrocytes. The earlier data on the enhancing effect of amino group modification on the interaction of human red-cell glycopeptides with V. graminea lectin support the conclusion that an increase in the lectin binding to human erythrocytes at pH 6-8 is confined to the decreased protonization of the receptor amino groups. V. graminea lectin was irreversibly inactivated at pH 3 and was inactivated by EDTA at pH 7.4 and reactivated by Ca2+ or Mn2+. This suggested that the lectin is a metaloprotein, requiring bivalent cations for the full binding activity. Some quantitative differences between the binding properties of V. graminea lectin, prepared from different batches of seeds, are reported.

The MNSs antigen Ridley (Ria)

After more than 20 years the extended pedigree of the only known kindred carrying the low frequency antigen Ria (Ridley) was reinvestigated. It is established that Ria is governed by a gene which is part of or very closely linked to the MNSs locus. Further serological and frequency studies are reported.

Structural analysis of the Ss sialoglycoprotein specific for Henshaw blood group from human erythrocyte membranes

The N-terminal structures of the MN and Ss erythrocyte membrane sialoglycoproteins (glycophorins A, B) from two Henshaw (He) blood-group heterozygotes were determined by manual sequencing of tryptic glycopeptides and various secondary fragments. No structural alteration of the MN glycoprotein could be detected. The He-specific portion of the Ss glycoprotein was found to exhibit the N-terminal sequence Trp-Ser+-Thr+-Ser+-Gly-(+ = glycosylation). Thus it differs at three positions from its normal counterpart which possesses 'N' activity and exhibits the N-terminal structure Leu-Ser+-Thr+-Thr+-Glu-. Analysis of the Ss glycoprotein from 15 He-negative erythrocyte samples did not reveal any of the three He-specific structural alterations. The presence of a glycine residue at the fifth position of the blood-group-M-active MN glycoprotein as well as in the He-specific Ss glycoprotein provides an explanation for the occurrence of antisera (anti-Me) reacting with the M and He antigens.

Structures of Miltenberger class I and II specific major human erythrocyte membrane sialoglycoproteins

The N-terminal structures of the Miltenberger (Mi-) blood group class I and II specific human MN erythrocyte membrane sialoglycoproteins were determined by manual sequencing of tryptic glycopeptides and various secondary fragments. The Mi-I and Mi-II active glycoproteins were found to exhibit a threonine leads to methionine and threonine leads to lysine exchange, respectively, at position 28 which prevents N-glycosylation of asparagine 26. Due to the absence of the N-glycosidic oligosaccharide chain, the monomeric form of the Mi-I and Mi-II specific glycoproteins possesses a slightly increased sodium dodecyl sulfate/polyacrylamide gel electrophoretic mobility, in comparison to its normal counterpart. Serological studies suggest that antibodies, specific for Mi-I or Mi-II red cells, react with the structurally altered region of the MN glycoprotein.

Monoclonal antibodies specific for the M- and N-forms of human glycophorin A

Four mouse monoclonal antibodies directed against the red cell membrane protein glycophorin A have been isolated and characterized. They are produced by hybridomas derived from SP2/0 myeloma cells and spleen cells from Biozzi mice immunized with a mixture of human erythrocytes from homozygous blood group M and N individuals. These antibodies recognize and bind to purified glycophorin A and to glycophorin on the red cell surface. All are of the IgGl, kappa light chain subclass and bind to determinants presented on the 39 amino acid, trypsin-sensitive, N-terminal peptide of glycophorin A. Three display differential specificities for the two allelic forms of glycophorin A; two are exquisitely specific for the M-form and one preferentially binds the N-form. Treatment of red cells with neuraminidase, which removes N-acetylneuraminic acid from glycophorin A, abolishes the binding of these three antibodies. The binding of the N-specific antibody is also sensitive to modification of the amino-terminal residue of the antigen. The fourth antibody binds equally well to both the M- and N-forms as well as to neuraminidase-treated red cells; thus it recognizes a public, N-acetylneuraminic acid independent glycophorin A determinant.

Blood group antigens: synthesis of TN glycopeptide related to human glycophorin AM

Three 2-acetamido-2-deoxy-alpha-D-galactopyranose residues attached to Ser2, Thr3 and Thr4 of the amino-terminal portion of glycophorin AM are responsible for the so-called TN blood group specificity. In a continuation of earlier work, this report describes the first chemical synthesis of the triglycosylated pentapeptide H2N-Ser1-Ser2*-Thr3*-Thr4*-Gly5-OH, in which (*) represents the 2-acetamido-2-deoxy-alpha-D-galactopyranosyl residue. This compound constitutes the G1-G5 sequence of the amino-terminal portion of human glycophorin AM, the main erythrocyte membrane glycoprotein. The above compound was obtained by a stepwise peptide coupling strategy alternatively using aminoacids and adequately protected and/or activated O-glycosyl-aminoacids. Since the desired sequence possesses both unglycosylated and glycosylated serine this route was preferred to that in which the glycosylation is carried out on the preformed pentapeptide H2N-Ser-Ser-Thr-Thr-Gly-OH. Carbohydrate residues were introduced into the sequence as 2-azido-2-deoxy-alpha-D-galactopyranosyl-L-serine and L-threonine derivatives. The azido functions were further converted into the corresponding acetamido groups by treatment of the final triglyco-pentapeptide with sodium borohydride in the presence of nickel chloride followed by acetylation.

Miltenberger Class I and II erythrocytes carry a variant of glycophorin A

The membranes from Miltenberger Class I (Mi I) and II (Mi II) erythrocytes, two rare variants at the blood group MNSs locus, exhibited an abnormal glycoprotein of 32 kDa apparent molecular mass sharply stained by the periodic acid/Schiff procedure and a decreased content of glycoprotein alpha (synonym glycophorin A, glycoprotein MN) as seen on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Purified 125I-labelled Vicia graminea lectin binds to the unusual 32 kDa glycoprotein separated from Mi I and Mi II erythrocyte membrane of blood group NN or MN, but no significant labelling of this band was observed with Mi samples typed MM. On the basis of such lectin-labelling experiments we have described two heterozygous MN, Mi I individuals that carry one copy of an M gene producing a normal alpha-glycoprotein with M-specificity and one copy of a MiI gene producing a 32 kDa glycoprotein with N-specificity. Further investigations have shown that the 32 kDa glycoprotein was immunoprecipitated by two mouse monoclonal antibodies (R18 and R10) reacting specifically with the external domain of glycoprotein alpha. These results demonstrate that Mi I and Mi II erythrocytes carry an unusual variant of glycoprotein alpha.

N-terminal amino acid sequence of sialoglycoprotein D (glycophorin C) from human erythrocyte membranes

The amino acid sequence of the N-terminal tryptic glycopeptide from a minor human erythrocyte membrane sialoglycoprotein (component D or glycophorin C) was determined by manual sequencing. The glycosylation sites were identified by a new procedure for the detection of the glycosylated derivatives released by Edman degradation. The fragment, comprising 47 residues, was found to contain an average of about 12 O-glycosidically linked oligosaccharides and one asparagine-linked carbohydrate chain. An identical hexapeptide sequence occurring in two regions of the glycopeptide provides evidence that it has developed by an internal gene duplication during evolution. In addition, a part of its structure shows a striking similarity to the sequence of a certain region of the MN and Ss erythrocyte membrane sialoglycoproteins (glycophorins A and B), suggesting that the molecules might be related.

Pj variant, a new hybrid MNSs glycoprotein of the human red-cell membrane

An unusual glycoprotein variant (Pj) was found inherited through a caucasian family exhibiting atypical N and Nvg blood-group reactivities. Pj erythrocytes are blood-group-MS homozygous and have a normal sialic acid content. On sodium dodecyl sulphate/polyacrylamide-gel electrophoresis the variant contains a new component Pj of 24kDa apparent molecular mass in the monomeric state which is sharply stained by periodic acid/Schiff reagent. Both blood-group-MN (alpha) and -Ss (delta) glycoproteins were present. Homodimers (Pj2) as well as heterodimers with MN-glycoprotein (alpha Pj) and the Ss-glycoprotein (delta Pj) were also identified. The new sialoglycoprotein Pj is trypsin- and chymotrypsin-resistant in situ and carries N- and Nvg- but not M- and S-reactivities. The Pj component is labelled by lactoperoxidase-catalysed radioiodination. A 3H label is also easily introduced into the sialic acid or the galactose and galactosamine of the Pj glycoprotein. It is proposed that the Pj is a hybrid glycoprotein containing the N-terminal end of delta-glycoprotein and the C-terminal end of the alpha-glycoprotein. This proposal is supported by the finding that Pj carries a leucine residue at its N-terminus and is not immunoprecipitated by a monoclonal mouse antibody (R18) reacting specifically with the external domain of glycoprotein alpha. The red cells from the proposita Pj were found positive for a very low frequency MN antigen named Sta.

HLA-restricted responses to M and N determinants in the primed lymphocyte test

We have studied the role of MNSs determinants in the primed lymphocyte test (PLT). The data demonstrate that incompatibility associated with the M or N antigens causes HLA-restricted proliferative responses in PLT. Responses to the M or N determinants required the presence of the same HLA-A antigen(s) on both the stimulator and the responder cells. No effects of S or s incompatibility were observed in this test. This is the first report of lymphocyte proliferative responses to "minor" alloantigens that require corecognition of the MHC determinants. These observations suggest possible new biological functions of these blood group antigens.

Vicia graminea anti-N lectin: partial characterization of the purified lectin and its binding to erythrocytes

Vicia graminea lectin, purified by affinity chromatography, was homogeneous in sodium dodecylsulphate/polyacrylamide gel electrophoresis and migrated with a velocity corresponding to a molecular weight of 125 000. Heating of 0.1% sodium dodecylsulphate at 100 degrees C caused dissociation of the lectin into subunits with an apparent molecular weight of 31 000. The results of isoelectric focusing suggested non-identity of the lectin subunits and existence of several molecular forms of the lectin. The lectin was neither dissociated nor activated by succinylation, but was irreversibly inactivated by 8 M urea. The lectin was totally bound to concanavalin-A-Sepharose and could be eluted with alpha-D-mannopyranoside. Binding of the 125I-labeled Vicia graminea lectin to untreated and desialylated human erythrocytes of blood groups M and N, horse and bovine erythrocytes was characterized. The lectin was bound specifically to sites specific for blood group N on untreated human erythrocytes with an uniform affinity, and association constant Ka = 1.5 X 10(8) M-1. Desialylated human NN and MM erythrocytes bound more lectin, with a distinctly higher, but non-uniform affinity. Vicia graminea lectin bound weakly to horse erythrocytes, and the effect of their desialylation was similar to that obtained with human erythrocytes. The lectin was not bound either to untreated or to desialylated bovine erythrocytes. Binding of the labeled lectin to human NN erythrocytes was inhibited by desialylated glycoproteins of the M and N blood groups, by untreated N glycoprotein, and weakly by untreated M glycoprotein.

Immunochemical properties of Mg erythrocytes

The major erythrocyte membrane (MN) sialoglycoprotein in Mg red cells was found to exhibit a slightly decreased sodium-dodecyl-sulphate polyacrylamide gel electrophoretic molecular weight and periodic and/Schiff staining intensity. Mg antigen activity was shown to be associated with this molecule. As judged from chemical modification experiments, no carbohydrate but the glycoprotein's N-terminal amino acid is involved in the Mg receptor site. The endgroup of the glycoprotein was found to leucine and studies involving Staphylococcus aureus V8 protease suggest that a glutamic acid is located at the fifth position of its peptide chain. This indicates that the Mgs gene complex evolved from a mutation of an Ns allele. An amino acido substitution or deletion at the second, third and/or fourth position(s), preventing the glycosylation of all or some of these amino acids, provides an explanation for the properties of Mg erythrocytes.

Cell-free synthesis and glycosylation of the major human-red-cell sialoglycoprotein, glycophorin A

The human erythroid cell line, K562, synthesizes the major red cell sialoglycoprotein, glycophorin A. We have isolated an mRNA fraction which codes for glycophorin A from K562 cells and studied the synthesis of the sialoglycoprotein in a rabbit reticulocyte cell-free system. In the absence of membranes a precursor form of glycophorin A was synthesized. This was identified using specific anti-(glycophorin A) serum. The apparent molecular weight of the carbohydrate-free precursor of glycophorin A was 19 500. This exceeds the molecular weight of the glycophorin A apoprotein by approximately 5000. In the presence of membranes from dog pancreas, the synthesized glycophorin A precursor was N-glycosylated and probably also O-glycosylated. The oligosaccharide chains remained incomplete and the glycoprotein synthesized in vitro corresponded to the glycosylated precursor of glycophorin A obtained in intact cells.

An immunochemical study on anti-N antibodies from dialysis patients

The specificity of anti-N antibodies from dialysis patients was investigated by hemagglutination in-hibition tests, using various fractionation, fragmentation and modification products of human erythrocytic membrane sialoglycoproteins. The antibodies were found to react with the N and "N' antigens on the MN and Ss glycoprotein, respectively. The NH2-terminal leucine and the side chain(s) of sialic acid(s) in oligosaccharide(s) linked to the second, third and/or fourth position(s) of the glycoproteins represent parts of the binding site for the anti-N antibodies. Formaldehyde reacts with the amino group of the NH2-terminal leucine, presumably leading to the formation of the hydroxy-methylene-derivative. These modified N antigens represent the structures triggering the formation of anti-N antibodies in dialysis patients, which cross-react with the native N receptors.

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.