High frequency antigens of human erythrocyte membrane sialoglycoproteins. I. Ena receptors in the glycosylated domain of the MN sialoglycoprotein

Immunochemical characterisation of monoclonal antibodies directed to glycophorins A and/or B

Among sixty-nine monoclonal antibodies submitted to the workshop, 28 antibodies directed to glycophorins A and/or B but without blood group specificity were investigated by a series of methods involving agglutination, flow cytometry with CHO transfected cells expressing glycophorin A, ELISA with a carbohydrate-free peptide (residues 1-72) of glycophorin A, and immunoblotting. These MAbs were subdivided in several groups according to their specificity: N-terminal portion of GPA and GPB; N-terminal trypsin-sensitive portion of GPA; extracellular ficin-sensitive portion of GPA; intracellular domain of GPA; undetermined. Both flow cytometry with transfectant cells and ELISA with the synthetic peptide prove to be of value in order to determine subspecificities within these groups.

Fine characterization of a series of new monoclonal antibodies directed against glycophorin A

OBJECTIVES

Glycophorins A (GPA) and B (GPB) are the major sialoglycoproteins of the human erythrocyte (RBC) membrane. To prepare tools for the analysis of GPA and GPB, we produced a series of new monoclonal antibodies (mAbs) that identified epitopes of GPA.

METHODS

Seven murine monoclonal antibodies directed to glycophorin A (GPA) were fully characterized by agglutination of untreated and enzyme-treated human erythrocytes, inhibition of agglutination using chemically modified glycophorins and peptides from GPA, immunoblotting, and binding to synthetic peptides on plastic pins.

RESULTS

The antibodies identify epitopes located on four different portions of GPA. (1) NaM13-6D2 binds to the N-terminal portion of GPA and GPB carrying the N blood group antigen; (2) NaM26-3F4 recognizes the homologous portion of GPA and GPB corresponding to their amino acids 6-26; (3) NaM10-2H12, NaM16-IB10 and NaM10-6G4 are specific for the amino acid sequence 38-45 of GPA; and (4) NaM37-5F4 and NaM13-4E4 bind to the amino acid residues 119-124 located on the intracellular ponion of GPA.

CONCLUSION

These antibodies represent precise tools to investigate GPA and related molecules in different cells and tissues.

Partial characterization of the human erythrocyte receptor for rabbit haemorrhagic disease virus

An important, well known property of the rabbit haemorrhagic disease virus is its ability to agglutinate human red blood cells. Accordingly, red cells from human adult donors were agglutinated despite their blood group ABO status, and treatments with proteases or glycosidases did not prevent agglutination. However, we discovered that the cells from human umbilical cords or foetuses were not agglutinated. In order to identify the viral receptor on human erythrocytes, glycolipids and glycoproteins from adult red cells were separated and tested for their potency in inhibiting agglutination. The bulk of the biological activity was associated with the highly glycosylated glycolipids (polyglycosylceramides), whereas a lower but significant activity was also associated with neutral glycolipids. No activity was found in the lipid-free sialoglycoprotein fractions. All these data strongly suggest that the RHDV receptor on human red cells corresponds to a development antigen which is not expressed on foetal cells and is mainly carried by glycolipids. Faint activity was also found in membranes from sheep red cells, suggesting that a similar glycolipid component is carried by these animal cells.

Characterization of new murine monoclonal antibodies directed against glycophorins C and D

Six new murine monoclonal antibodies (mAbs) directed to the erythrocyte membrane glycophorins C (GPC) and D (GPD) were obtained from splenocytes of different BALB/c mice immunized with human red blood cells, and fully characterized. The mAbs were selected by agglutination tests with control and Gerbich-negative cells, and by immunoblotting analysis. They showed specificity for the N-terminal domain(s) of GPC (and GPD) and were classified into three categories by competitive analysis using 125I-labelled antibodies and real-time biospecific interaction. The first group (NaM10-7G11, NaM70-1G4 and NaM77-7B6) compete for epitope(s) located at the N-terminal portion of GPC. Agglutination-inhibition tests revealed that the 7G11 epitope involves the amino group of Met1 and sialic acid residue(s) whereas the 1G4 and 7B6 epitopes contain O-glycans. NaM89-2G11 belongs to a second group; its epitope is located in a region including Glu17, Asp19 and (an) O-glycan(s). The third group comprises mAbs NaM19-3C4 and NaM98-3C1 which bind to both GPC and GPD in proximity of the binding site of human anti-Ge:3 antibodies. In addition, mAb 3C4 (anti-GPC/GPD) was found to bind to approximately 125,000 sites per red cell. Considering that the ratio of the GPC to GPD is about 3-4 to 1, the number of GPC and GPD molecules was estimated as 95,000 and 35,000, respectively.

Evidence for expression of the Joa blood group antigen on the Gya/Hy-active glycoprotein

The phenotypic association between the non-assigned high-incidence antigen Joa and the Gya collection antigens Gya and Hy was investigated by haemagglutination studies, flow cytometric analysis, immune precipitation and immunoblotting experiments. In haemagglutination tests anti-Joa gave the same pattern of reactivity with erythrocytes pre-treated with pronase, trypsin, alpha-chymotrypsin and thiol reducing agents as did anti-Gya and anti-Hy. In addition, similar to that found for anti-Gya and anti-Hy, anti Joa also showed reduced binding, as determined by haemagglutination and flow cytometric analysis, to erythrocytes from patients with paroxysmal nocturnal haemoglobinuria. Immune precipitates prepared from radio-iodinated antigen-positive red cells with anti-Joa, anti-Gya and anti-Hy gave similar results--a major component of M(r) 49,000-60,000 (the Gya/Hy-active glycoprotein) and a second component of M(r) 85,000-92,000 (this may be a dimer of the Gya/Hy-active glycoprotein, or a coprecipitated protein). These immune precipitates, when probed with both anti-Gya and anti-Hy under non-reducing conditions, gave a positive immunoblotting reaction to both the M(r) 49,000-60,000 and the M(r) 85,000-92,000 components. These results strongly suggest that the Joa antigen is expressed on the same glycoprotein that carries the Gya and Hy antigens.

Production of a new murine monoclonal antibody with Fy6 specificity and characterization of the immunopurified N-glycosylated Duffy-active molecule

A murine monoclonal antibody (mAb i3A; IgG1, kappa light chain) was obtained using human red blood cells as immunogen. The antibody showed Fy6 specificity since it agglutinated all but Fy(a-b-)-untreated red cells and failed to agglutinate chymotrypsin-treated cells. An erythrocyte membrane protein of 42-46 kD was revealed as the major component recognized by the antibody on immunoblots. The antibody also bound to 92- to 95- and 200-kD proteins, tentatively identified as oligomers of the 42- to 46-kD monomeric form. The affinity-purified Fy6-active protein was converted to a sharp band of 35 kD after N-glycanase treatment. The molecule appeared as a slightly broadly band after neuraminidase treatment but was not further altered by O-glycanase. The i3A mAb bound to 6,000 +/- 1,000 receptor sites on either Fy(a-b+), Fy (a+b+) and Fy(a+b-) red cells with an affinity constant in the range of 3-6 x 10(8) M-1. No binding was observed to other blood cells nor to several cells (B, T, myelomonocytic and erythro-leukemia cell lines). Also, the bulk of i3A-Fy6 immune complexes could be dissociated from the red cell membrane with as low as 0.2% Triton X-100, showing that the Fy6-active glycoprotein is not tightly associated with the membrane skeleton. Our data obtained with a new monoclonal antibody directed to the Fy6 antigen demonstrate that the blood group Duffy-active component is a red cell-specific glycoprotein carrying one or more N-linked oligosaccharides.

[Characterization of murine monoclonal antibodies against fetal erythrocytes]

Balb/c mice were immunized against papain-treated fetal erythrocytes and splenocytes were fused with Sp2/0-Ag-14 myeloma cells. Several hybrids secreting antibodies directed against antigenic determinants predominantly exposed on fetal and cord cells were selected and cloned twice. Antibodies NaM61-1A2 and NaM61-768 (IgM class) were shown to be specific for an endo-beta-galactosidase-sensitive oligosaccharide chain. The antigen, strongly expressed on fetal and cord cells, was identified as the i blood group antigen. The antibodies represent powerful blood group reagents to be use in conventional agglutination techniques as well as in the gel typing system and in indirect flow cytometry. The antibody NaM46-4A8 (IgG class) is specific for an antigenic structure expressed on fetal cells and accessible only after papain, ficin, bromelin and endo-beta galactosidase treatment. The antigen was not identified.

Analysis of peptidic epitopes recognized by the three monoclonal antibodies specific for the same region of glycophorin A but showing different properties

Analysis of epitopes for the three monoclonal antibodies (GPA105, GPA33, OSK4-1) against glycophorin A (GPA) was performed with the use of proteolytic fragments of GPA, the synthetic nonapeptide with the sequence of amino acid residues 35-43 of GPA, and a series of peptides synthesized on plastic pins. The antibodies were specific for a short peptide sequence RAHE (a.a. 39-42 of GPA, MAbs GPA105 and OSK4-1) or RAHEV (a.a. 39-43 of GPA, MAb GPA33). Despite recognizing the same fragment of GPA, the three antibodies showed differences in fine specificity and in response to antigen desialylation. Reactions with single replacement analogs of the RAHEV sequence showed that immunodominant (unreplaceable) residues for the MAbs GPA33 and OSK4-1 were His and Glu, respectively, whereas no such residue was found for the MAb GPA105. Desialylation of the antigen gave strong enhancement of reactivity with the MAb GPA33, moderate--with the MAb GPA105, and weak or no enhancement of reaction with the MAb OSK4-1. The results showed that monoclonal antibodies directed against the same fragment of the polypeptide chain of densely glycosylated antigen may recognize different subsites which are masked at different degree by sialic acid residues.

Miltenberger subsystem of the MNSs blood group system. Review and outlook

The Miltenberger (Mi) classes represent a group of phenotypes for red cells that carry low frequency antigens associated with the MNSs blood group system. The antigens of this system are known to be located on two sialoglycoproteins denoted as glycophorin A (GP A) and GP B. The structural alterations of seven (classes I, II, III, V, VI, VII, VIII) Mi variants and a related variant (J.L.) have been elucidated. Based on these data and yet incomplete studies of the Mi antigens, the approximate structural alterations in class IV and IX may be predicted. In addition, knowledge of the various structures and partial characterization of the Mi antigens allows one to propose detailed hypotheses concerning the epitopes recognized by the various antibodies that define the Mi subsystem. The understanding of the Mi subsystem at the molecular level paves the way for future studies aimed at a more detailed elucidation of epitopes of Mi-related antibodies, the characterization of novel Mi variants and a search for hypothetical, hitherto unknown Mi-related antibodies.

Miltenberger class IX of the MNS blood group system

Mi.IX is a new phenotype in the Miltenberger series of the MNS blood group system with a frequency of 0.43% in Denmark. Mi.IX red cells are Mur+ but do not express any of the other established Miltenberger determinants. They react with a new antibody, anti-DANE, which defines a determinant present on Mi.IX cells but not on cells of other Miltenberger phenotypes. Four Mi.IX propositi have been found. Their families show that MiIX is inherited with a MS complex (lod score 3.69 at theta = 0.00) which produces a trypsin-resistant M antigen. DANE has been allotted the ISBT number 002032 (MNS32). Serological and immunochemical studies with human and monoclonal antibodies to various determinants on glycophorin A (GPA) suggest that Mi.IX is associated with an aberrant GPA molecule that lacks the trypsin cleavage site at amino-acid residue 39, retains the chymotrypsin cleavage site at residue 34 and has an apparent Mr of about 1,000 less than normal GPA. It is proposed that this Mi.IX molecule has an amino acid and possibly also a glycosylation change in the region of amino-acid residues 35-39.

A mouse monoclonal antibody against glycophorin A produced by in vitro stimulation with human red cell membranes

Human erythrocyte membranes were used as antigen for production of mouse monoclonal antibodies against blood group related structures by in vitro immunization. Culture medium supernatant of PHA and PMA stimulated mouse thymus cells was used as source of cytokines. The selected antibody designated 124,D-7 (isotype IgM) was found to directly agglutinate all human red cells, except the rare erythrocytes En(a-) which lack glycophorin A. Immunoblotting showed faint bands in the positions of glycophorin A, whereas no binding occurred to glycophorin B. Inhibition of agglutination with purified glycophorin A and peptides suggests that the epitope is located within the amino acid residues 35-40. Rat and chicken erythrocytes also reacted with the antibody, whereas mouse erythrocytes were only agglutinated at very low dilutions of ascitic fluid.

Studies on the structures of the Tm, Sj, M1, Can, Sext and Hu blood group antigens

The Glycophorins (GPs = sialoglycoproteins) in erythrocyte membranes from various Black individuals, some of which exhibit the M1, Can, Sj, Tm, Sext and/or Hu antigens, and several Caucasian donors, including pooled fetal red cells, were studied. Using agglutination inhibition assays with GP fractions, GP fragments and chemically modified GPs as well as trypsin treatment of intact red cells, the antigens defined by anti-M1, anti-M+M1, anti-Can and anti-Tm sera were found to be located on the N-terminal tryptic peptide (T2, residues 1-31) of the major GP (GP A = MN sialoglycoprotein). Evidence was obtained that the N-terminal amino-acid residue, NeuNAc and/or (a) different sugar residue(s) are involved in the antigens. Amino-acid sequence and composition analyses excluded an amino-acid exchange within the N-terminal region (residues 1-31) of GP A. Carbohydrate analyses revealed the attachment of GlcNAc residues (up to about five, dependent on the strength of the above-mentioned antigens) to O-glycosidically linked oligosaccharides within the N-terminal portion (residues 1-31) of GP A. As judged from the carbohydrate compositions of peptides, the alteration of the O-glycosidic oligosaccharides is associated with a slight increase of the Gal and Fuc contents and a slight decrease of the NeuNAc level. Analyses of small, secondary cyanogen bromide and V8 proteinase peptides from the N-terminal region of GP A from Blacks, Caucasians and Caucasian fetal cells suggest that the variable attachment of small quantities of GlcNAc (about 0.03 to about 0.2 residues per peptide molecule) accounts, at least in part, for the polymorphisms detected by anti-Can and the original anti-Tm (serum Sheerin). Remarkably, the GlcNAc-containing O-glycosidic oligosaccharides occur only in small quantities, or not all at, within the positions 32-61 of GP A and the glycosylated domains of GP B and GP C.(ABSTRACT TRUNCATED AT 400 WORDS)

The nature and abundance of human red cell surface glycoproteins

Available evidence suggests that there are at least 30 different proteins at the red cell surface. These proteins vary in abundance from a few hundred copies/cell to more than a million copies/cell. Recently, a new Glycophorin gene (Glycophorin E) has been identified and sequenced. In this paper evidence is presented that a monoclonal anti-M detects the product of the Glycophorin E gene in normal red cells.

The Mz variety of the St(a+) phenotype--a variant of glycophorin A exhibiting a deletion

The NeuNAc level of erythrocyte membranes from two related donors exhibiting the Mz variety of St(a+) phenotype within the MNSs blood group system was found to be decreased by about 16%. The quantity of glycophorin A was decreased by about 38%, whereas that of glycophorin B was not significantly different from normal. Mz erythrocyte membranes were also found to contain an abnormal component (molar ratio to glycophorin A about 0.89:1.0) with an apparent molecular mass of about 24,000 Da. Immunoblotting experiments and amino-acid sequence analysis revealed that the novel component (and glycophorin A in one of the donors) carries blood group M activity. Blood group N activity was demonstrable for glycophorin A and glycophorin B from both donors. Amino-acid sequence analysis of chymotryptic, tryptic and cyanogen bromide peptides demonstrated that the novel molecule exhibits the typical structure of a Sta-active molecule. However, since it exhibits blood group M activity, it appears to represent a variant of glycophorin A lacking the residues 27-58 (encoded by exon three of the glycophorin A gene) rather than a glycophorin B-glycophorin A-hybrid molecule of the anti-Lepore type. Since one of the Mz heterozygotes was found to exhibit both M- and N activity on glycophorin A, the Mz gene complex appears to encode a blood group N-active glycophorin A apart from the novel component and a blood group s-active glycophorin B, although the level of glycophorin A in the erythrocyte membranes is decreased by about half.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood group-active surface molecules of the human red blood cell

The surface of the human red blood cell is dominated by a small number of abundant blood group active proteins. The major proteins are the anion transport protein (band 3) which has AB(H) activity, and Glycophorin A which has MN activity. Band 3 and Glycophorin A are of equal abundance in the normal red cell membrane (approximately 10(6) copies of each) and the two proteins may associate together as a complex. The glucose transporter (band 4.5) had AB(H) activity and there are about 5 x 10(5) copies/red cell. Several polypeptides associate together to form the Rh complex. The major components of this complex (abundance 1-2 x 10(5) copies/red cell) are polypeptides of Mr 30,000, polypeptides of Mr 45,000-100,000 and Glycophorin B. The antigens of the Rh blood group system appear to be associated with the polypeptides of Mr 30,000 and those of Mr 45,000-100,000 (the latter also express AB(H) activity). Glycophorin B expresses the blood group 'N' antigen and the Ss antigens. Glycophorins C and D carry the Gerbich antigens and, together, these polypeptides comprise approximately 10(5) copies/red cell. The complete protein sequence of all the above-mentioned proteins is known, except for the Mr 30,000 and Mr 45,000-100,000 polypeptides of the Rh complex for which only partial sequences are available, and Glycophorin D, the sequence of which can be inferred from that of Glycophorin C. Several of the minor blood group active proteins at the red cell surface (abundance less than 1.2 x 10(4)/red cell) have been the subject of recent studies. The polypeptide expressing Cromer-related blood group antigens has been identified as decay-accelerating factor and that carrying the Ina/Inb antigens as CD44. The protein sequence of both of these proteins has been deduced form nucleotide sequencing. The polypeptides expressing Kell antigens, Lutheran antigens, Fy antigens, and LW antigens have also been identified and partially characterised.

Structural analysis of glycophorin A from Miltenberger class VIII erythrocytes

The major human erythrocyte membrane sialoglycoprotein (glycophorin A or MN glycoprotein) was purified from the erythrocytes of two individuals heterozygous for the Mi-VIII gene in the Miltenberger subsystem of the MNSs blood-group system. The complete structure of a tryptic glycopetide from glycophorin A comprising the residues 40-61 was deduced from automated and manual sequence analyses. The Mi-VIII-specific glycophorin A was found to exhibit an arginine----threonine exchange at position 49. The threonine residue was found to be glycosylated. Hemagglutination and hemagglutination inhibition assays demonstrated that one of the Mi-VIII-characteristic antigenic determinants (Anek) is located within the residues 40-61 of glycophorin A. Furthermore, erythrocytes from the two Mi-VIII heterozygotes reacted only weakly with anti-EnaKTsera, suggesting that the Mi-VIII-specific glycophorin A does not express the EnaKT antigen that is located within the positions 46-56 of normal glycophorin A. Our data suggest that the Mi-VIII-specific glycophorin A represents the evolutionary link between normal glycophorin A and the Mi-VIII-specific molecule which exhibits arginine----threonine and tyrosine----serine exchanges at the positions 49 and 52, respectively. Our data also provide an explanation for the close serological similarity between Mi-VII and Mi-VIII erythrocytes.

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.

Structural analysis of the major human erythrocyte membrane sialoglycoprotein from Miltenberger class VII cells

The major human erythrocyte membrane sialoglycoprotein (glycophorin A or MN glycoprotein) was purified from the red blood cells of an individual, homozygous for the Mi-VII gene in the Miltenberger subsystem of the MNSs blood-group system. The complete structure of a tryptic peptide comprising the residues 40-61 of glycophorin A was deduced from manual sequence analyses. The Mi-VII-specific glycophorin A was shown to exhibit an arginine----threonine and a tyrosine----serine exchange at the positions 49 and 52 respectively. The threonine-49 residue was found to be glycosylated. Inhibition assays demonstrated that one of the Mi-VII-specific antigen determinants (Anek) is located within the residues 40-61 of glycophorin A and comprises sialic acid residue(s) attached to O-glycosidically linked oligosaccharide(s). Our data contribute to an understanding of the Miltenberger system and provide an explanation at the molecular level for the previous finding that the erythrocytes from the Mi-VII homozygote lack a high-frequency antigen (EnaKT), located within the residues 46-56 of normal glycophorin A.

Hybrid glycophorins from human erythrocyte membranes. I. Isolation and complete structural analysis of the hybrid sialoglycoprotein from Dantu-positive red cells of the N.E. variety

The hybrid glycophorin in Dantu-positive human erythrocytes of the N.E. variety was not cleaved by treatment of intact cells with various proteases, in contrast to normal glycophorins. Therefore, it could be purified by phenol/saline extraction of membranes from trypsin-treated and chymotrypsin-treated red cells and subsequent gel filtration in the presence of Ammonyx-LO. The complete structure of the hybrid molecule, comprising 99 amino acid residues, was elucidated by sequence analyses of peptides prepared by chymotrypsin, trypsin, cyanogen bromide or V8 proteinase treatment. The N-terminal 39 residues and the glycosylation of the molecule were found to be indistinguishable from those of blood-group-s-specific glycophorin B. Conversely, the residues 39-99 were shown to be identical with the residues 71-131 of the major blood-group M-active or N-active sialoglycoprotein (glycophorin A). Hemagglutination inhibition assays revealed that the Dantu antigen represents a labile structure. The receptor might be located within the residues approximately 28-40 of the hybrid glycophorin, as judged from the effects of modifications of membranes. Our data provide an explanation for the previous findings that Dantu-positive cells (N.E. type) exhibit a protease-resistant N antigen and a qualitatively altered s antigen.

High-frequency antigens of human erythrocyte membrane sialoglycoproteins, IV. Molecular properties of the U antigen

The nature of the common erythrocyte antigen U, that is absent from S-s-U-cells, which lack glycophorin B (Ss sialoglycoprotein), was investigated using six different antisera. The molecular features of a U-like antigen (Duclos), detected by a hitherto unique serum, were also studied. The U and Duclos antigens are complex in that they exhibit relationships with the MNSs and Rh blood group systems. Various fractionation, cleavage, or modification products of normal erythrocyte membranes were used in hemagglutination inhibition assays. Both, the U and Duclos antigens were found to represent labile structures that require lipids, at least for optimum expression of antigen activity. The antigens could be solubilized using conditions of Triton X-100 extraction that release glycophorin B, but solubilize the Rh antigens only to a small extent. Anti-U and anti-Duclos were also inhibited, albeit weakly, by glycophorin B-containing fractions obtained by chromatographic separation of Triton X-100 extracts. The residues approx. 33-39 of glycophorin B represent essential parts of the U antigen, as judged from proteolytic digestion and chemical modification. Conversely, the expression of Duclos activity seems to require a region of glycophorin B (C-terminal of the positions approx. 34-36) that could not be cleaved by various proteinases. Data obtained with anti-Duclos have to be interpreted with caution, since there is evidence that this serum might contain a mixture of antibodies.

High frequency antigens of human erythrocyte membrane sialoglycoproteins, III. Studies on the EnaFR, Wrb and Wra antigens

The nature of the common erythrocyte antigens EnaFR and Wrb, that are both absent from En(a-) cells, and the rare Wra receptor, apparently encoded by an allele of Wrb, was investigated. Various modification, fractionation or cleavage products of erythrocyte membranes were used in hemagglutination inhibition assays. The EnaFR and Wrb antigens were shown to represent labile structures within the residues approx. 62-72 of the major (MN) sialoglycoprotein that require lipids, at least for complete expression of antigenic activity. During the course of these experiments, the arrangement of the MN glycoprotein's peptide chain with respect to the lipid bi-layer was also studied, using various proteinases. Furthermore, the MN glycoprotein was found to aggregate with the major membrane protein (band 3) in the presence of Triton X-100. The Wra antigen was shown to exhibit properties that differ considerably from those of the Wrb receptor. Analyses on the MN glycoprotein, isolated from the red cells of the only known Wra homozygote and two WraWrb individuals, did not reveal any amino-acid exchange within the residues 40-96 of the molecule. Therefore, the Wr locus that determines the presence or absence of the Wrb antigen on the MN glycoprotein might influence the post-translational modification of amino-acid residues, the structure of tightly bound lipids or the aggregation of the MN glycoprotein with a different protein such as band 3.

Altered membrane sialoglycoproteins in human erythrocytes lacking the Gerbich blood group antigens

The sialoglycoproteins (glycophorins) in human red cell membranes of rare individuals lacking totally (Ge-1,-2,-3 phenotype) or partially (Ge-1,-2,3 phenotype) the Gerbich (Ge) blood group antigens and two Ge-1,-2,-3 heterozygotes were studied by dodecylsulfate polyacrylamide gel electrophoretic techniques. Two sialoglycoproteins (components D and E) were not detectable in the membranes from the homozygotes and found to be decreased by about 50% in those from the heterozygotes. Ge--1,-2,-3 and Ge-1,-2,3 cells were found to contain a 'new' component (mol. masses about 29 and 30 kDa, respectively) possibly representing a D/E hybrid molecule. This sialoglycoprotein was not detectable in membranes from the Ge-1,-2,-3 heterozygotes, suggesting that the Ge-1,-2,-3 phenotype may be caused by at least two different alleles at the Ge blood group antigen locus. Hemagglutination or hemagglutination inhibition tests involving anti-Ge 1,2,3 and -Ge 1,2 as well as native and enzyme-treated normal red cells (phenotype Ge 1,2,3) or membrane and sialoglycoprotein fractions from normal erythrocytes indicate that the receptors of these sera are located within the glycosylated domain(s) of the D and/or E sialoglycoprotein(s). Our data suggest that the Ge locus encodes the polypeptide sequences of the D and E sialoglycoproteins.