Two monoclonal antibodies highly specific for the blood group N determinant

The structures of glycophorin C N-glycans, a putative component of the GPC receptor site for Plasmodium falciparum EBA-140 ligand

Glycophorins C and D are highly glycosylated integral sialoglycoproteins of human red blood cell membranes carrying the Gerbich blood group antigens. The O- and N-glycosidic chains of the major erythrocyte glycoprotein (Lisowska E. 2001, Antigenic properties of human glycophorins - an update. Adv Exp Med Biol, 491:155-169; Tomita M and Marchesi VT. 1975, Amino-acid sequence and oligosaccharide attachment sites of human erythrocyte glycophorin. Proc Natl Acad Sci USA, 72:2964-2968.) are well characterized but the structure of GPC N-glycans has remained unknown. This problem became important since it was reported that GPC N-glycans play an essential role in the interaction with Plasmodium falciparum EBA-140 merozoite ligand. The elucidation of these structures seems essential for full characterization of the GPC binding site for the EBA-140 ligand. We have employed detailed structural analysis using sequential mass spectrometry to show that many GPC N-glycans contain H2 antigen structures and several contain polylactosamine structures capped with fucose. The results obtained indicate structural heterogeneity of the GPC N-glycans and show the existence of structural elements not found in glycophorin A N-glycans. Our results also open a possibility of new interpretation of the data concerning the binding of P. falciparum EBA-140 ligand to GPC. We hypothesize that preferable terminal fucosylation of N-glycosidic chains containing repeating lactosamine units of the GPC Gerbich variant could be an explanation for why the EBA-140 ligand does not react with GPC Gerbich and an indication that the EBA-140 interaction with GPC is distinctly dependent on the GPC N-glycan structure.

Identification of an erythrocyte binding peptide from the erythrocyte binding antigen, EBA-175, which blocks parasite multiplication and induces peptide-blocking antibodies

A biotinylated peptide covering a sequence of 21 amino acids (aa) from the erythrocyte binding antigen (EBA-175) of Plasmodium falciparum bound to human glycophorin A, an erythrocyte receptor for merozoites, as demonstrated by enzyme-linked immunosorbent assay (ELISA) and to erythrocytes as demonstrated by flow cytometry analysis. The peptide, EBA(aa1076-96), also bound to desialylated glycophorin A and glycophorin B when tested by ELISA. The peptide blocked parasite multiplication in vitro. The glycophorin A binding sequence was further delineated to a 12-aa sequence, EBA(aa1085-96), by testing the binding of a range of truncated peptides to immobilized glycophorin A. Our data indicate that EBA(aa1085-96) is part of a ligand on the merozoite for binding to erythrocyte receptors. This binding suggests that the EBA(aa1085-96) peptide is involved in a second binding step, independent of sialic acid. Antibody recognition of this peptide sequence may protect against merozoite invasion, but only a small proportion of sera from adults from different areas of malaria transmission showed antibody reactivities to the EBA(aa1076-96) peptide, indicating that this sequence is only weakly immunogenic during P. falciparum infections in humans. However, Tanzanian children with acute clinical malaria showed high immunoglobulin G reactivity to the EBA(aa1076-96) peptide compared to children with asymptomatic P. falciparum infections. The EBA(aa1076-96) peptide sequence from EBA-175 induced antibody formation in mice after conjugation of the peptide with purified protein derivative. These murine sera inhibited EBA(aa1076-96) peptide binding to glycophorin A.

Five monoclonal antibodies against glycophorin A of human erythrocyte recognize glycoprotein of bovine erythrocyte

To study heterophile blood antigens on erythrocytes between human and experimental or domestic animals, we have produced 295 monoclonal antibodies (MAbs) to human erythrocyte membrane protein. According to the affinity, reactivity, and titre of the MAbs, we selected 40 clones to study the heterophile blood antigens between human and bovine, chicken, guinea pig, horse, rabbit, sheep, and swine. Five MAbs commonly reacted with human type A, type B, and type O erythrocytes and reacted with bovine erythrocytes as well but did not react with erythrocytes from other species. Other MAbs did not react with erythrocytes from all the tested animals. These five MAbs reacted with the same erythrocyte membrane protein, 90 KD glycophorin A (GPA) of human or 200 KD major glycoprotein and other two components of bovine by immunoblotting and GPA competitive inhibition assay. Furthermore, by enzyme treatment and monosaccharide competitive inhibition assay, it was confirmed that these five MAbs recognized antigen epitope of glycosylation free amino acid portion but not glycosylation portion of GPA of erythrocyte membrane.

Blood group MN-dependent difference in degree of galactosylation of O-glycans of glycophorin A is restricted to the GalNAc residues located on amino acid residues 2-4 of the glycophorin polypeptide chain

Glycophorin A (GPA) of human erythrocytes contains a minor number of unsubstituted GalNAc residues (Tn receptors) which are recognized by Moluccella laevis lectin (MLL). The lectin reacts better with blood group N- than M-type of GPA which suggests a higher number of Tn receptors in GPA-N than in GPA-M. To find out whether this difference is restricted to a defined domain of GPA, the N-terminal tryptic glycopeptides of GPA-M and GPA-N (a.a. residues 1-39) and their fragments obtained by degradation with CNBr (a.a. residues 1-8 and 9-39) were analyzed. The untreated and desialylated glycopeptides were tested as inhibitors of MLL in ELISA, and the content of GalNAc-ol was determined in the products of beta-elimination of the asialoglycopeptides by gas-liquid chromatography/mass spectrometry. The asialoglycopeptides 1-39 and 1-8 derived from GPA-N showed about 2 and 4 times higher content of non-galactosylated GalNAc residues, respectively, and higher reactivity with MLL than their counterparts derived from GPA-M, while asialoglycopeptides 9-39 of GPA-M and GPA-N did not show such differences. These results demonstrate that higher expression of non-galactosylated GalNAc in GPA-N than in GPA-M is confined to GalNAc residues located in the amino-terminal portion of GPA polypeptide chain, between the blood group M- and N-specific amino acid residues 1 and 5.

Receptor and ligand domains for invasion of erythrocytes by Plasmodium falciparum

A 175-kilodalton erythrocyte binding protein, EBA-175, of the parasite Plasmodium falciparum mediates the invasion of erythrocytes. The erythrocyte receptor for EBA-175 is dependent on sialic acid. The domain of EBA-175 that binds erythrocytes was identified as region II with the use of truncated portions of EBA-175 expressed on COS cells. Region II, which contains a cysteine-rich motif, and native EBA-175 bind specifically to glycophorin A, but not to glycophorin B, on the erythrocyte membrane. Erythrocyte recognition of EBA-175 requires both sialic acid and the peptide backbone of glycophorin A. The identification of both the receptor and ligand domains may suggest rational designs for receptor blockade and vaccines.

Carbohydrate antigen expression in murine embryonic stem cells and embryos. II. Sialylated antigens and glycolipid analysis

A mouse embryonic stem (ES) cell line E14 and early mouse embryos were stained with a panel of 15 monoclonal antibodies recognizing sialylated or potentially sialylated carbohydrate determinants. Sialyl Le-x and sialyl Le-a were detected on the pre-implantation embryo from the 8-cell stage, and sialyl Le-a weakly on undifferentiated ES cells. Changes in cell surface carbohydrates occurred after induction of ES cell differentiation with retinoic acid (RA) and dibutyryl cAMP. Qualitative analysis of the neutral glycolipids of untreated and RA-treated ES cells using high-performance thin-layer chromatography (HPTLC) revealed few differences between the two types of culture. The major gangliosides in both cultures were indicative of an active 'a' ganglioside synthesis pathway. GD3, a precursor of the 'b' synthesis pathway, previously reported to be characteristic of embryonal carcinoma (EC) cells, was absent. RA-induced differentiation caused a shift in the spectrum to more complex gangliosides. Application of fast atom bombardment mass spectrometry (FAB-MS) to permethylated derivatives of individual bands permitted partial characterization of an unusual sialylated glycolipid and a rare ganglioside with the suggested structure of GalNAc-GD1a.

Degradation of human erythrocyte surface components by human neutrophil elastase and cathepsin G: preferential digestion of glycophorins

Human erythrocytes treated with purified human neutrophil elastase (HNE) or cathepsin G (CathG) were analysed by serological methods and by SDS-polyacrylamide gel electrophoresis followed by staining or immunoblotting with monoclonal antibodies. Both enzymes digested exhaustively glycophorins A, B and C, and HNE caused a partial digestion of band 3 protein. The degradation of other membrane proteins was not detectable by the methods used. Immunoblotting with the use of monoclonal antibodies against the defined epitopes of glycophorin A showed that HNE and CathG hydrolysed distinct peptide bonds in this antigen. The antibody PEP80, specific for the epitope in the cytoplasmic fragment of glycophorin A, gave patterns of bands which were characteristic for each of the two proteases. These bands could be distinctly identified in erythrocyte membrane samples containing only few percent of digested glycophorins. Therefore, the immunoblotting with this antibody may be useful as a sensitive assay for detecting the action of neutrophil proteases on red blood cells.

An immunoblotting procedure for screening glycophorins and band 3 protein in the same blots. Identification of glycophorin and band 3 variant forms

An immunoblotting procedure is described which makes it possible to screen multiple blood samples for the presence of glycophorin and band 3 variant forms with altered electrophoretic mobility. The procedure can be simplified by using whole red blood cell hemolysates instead of membranes for SDS-polyacrylamide gel electrophoresis. The use of hemolysates also has the advantage that antigens sensitive to proteolysis are not degraded in vitro. The same nitrocellulose blots were used for immunoenzymatic detection of glycophorins with a set of anti-glycophorin monoclonal antibodies, and for autoradiographic detection of band 3-derived bands with 125I-labeled anti-band 3 monoclonal antibody. The screening of 157 Caucasian blood samples revealed the presence of a slower-migrating form of band 3 in seven cases and variant glycophorin in one case. The variant glycophorin exhibited the features of hybrid glycophorin of B-A type.

Immunochemical studies on the combining site of the A + N blood type specific Moluccella laevis lectin

The specificity of the anti A+N lectin of Moluccella laevis (MLL) was examined by hemagglutination experiments with enzyme-modified human erythrocytes and by inhibition of hemagglutination. In addition, binding to various glycoproteins and inhibition by different sugars and glycoproteins were examined by enzyme immunoassay with antibodies to the lectin. Treatment of AMM erythrocytes with proteolytic enzymes increased their agglutinability by MLL 4-16-fold; similar treatment of ONN cells decreased their agglutinability 8-16-fold. This is in line with the known location and enzyme sensitivity of A and N specificity determinants. Treatment of the erythrocytes with sialidase increased their agglutinability and abolished the distinction between N and M cells. Hapten inhibition of hemagglutination of AMM and ONN erythrocytes by the lectin, and its binding to glycoproteins measured by enzyme immunoassay, confirmed the high specificity of MLL for N-acetyl-D-galactosamine (200-500 times more than for D-galactose) and suggested the presence of hydrophobic interactions around HO-2 of the D-galactose unit. The methyl alpha-glycosides of D-galactose and of N-acetyl-D-galactosamine were better inhibitors than the corresponding beta-glycosides; this preference was abolished, and sometimes reversed, when the p-nitrophenyl glycosides of the same monosaccharides were tested, stressing again the importance of hydrophobic interactions in the binding of carbohydrates to MLL. The lectin reacted well with ONN substance and with glycophorin A of the N phenotype (GPAN), but did not react with OMM substance or GPAM. The strongest inhibitor was asialo ovine submaxillary mucin, which contains many unsubstituted alpha-D-GalpNAc-(1-->3)-Ser/Thr residues; calculated per N-acetyl-D-galactosamine residue, it was 1500 stronger than free N-acetyl-D-galactosamine. In accordance with this result, it was found that the lectin strongly agglutinates Tn cells. The specificity of MLL can, thus, be defined as anti-Tn, crossreactive with blood types A and N, and with sialosyl-Tn. The N-specificity can best be explained by assuming that GPAN contains a small number of unsubstituted or partially sialylated alpha-D-GalpNAc-(1-->3)-Ser/Thr residues, which are present in smaller proportions, if at all, in GPAM.

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.

Application of chemically desialylated and degalactosylated human glycophorin for induction and characterization of anti-Tn monoclonal antibodies

Human erythrocyte glycophorin was desialylated by mild acid hydrolysis and degalactosylated by Smith degradation. Two monoclonal antibodies (Tn5 and Tn56) obtained by immunization of mice with this 'artificial' Tn antigen were characterized and compared in some experiments with two antibodies (BRIC111 and LM225) obtained in other laboratories by immunization with Tn erythrocytes. The specific binding of the antibodies to glycophorins desialylated and degalactosylated on the nitrocellulose blot and to asialo-agalactoglycophorin-coated ELISA plates, and reactions with authentic Tn antigen served for identification of their anti-Tn specificity. The antibodies were further characterized in inhibition assay with various glycoproteins. The antibody Tn5 (similar to BRIC111) was shown to be specific for human erythrocyte Tn antigen, whereas Tn56 reacted strongly with different glycoproteins carrying O-linked GalNAc alpha- residues, and was strongly bound to the murine adenocarcinoma cell line Ta3-Ha. The antibodies Tn5, Tn56 and BRIC111 were similarly inhibited by ovine submaxillary mucin (OSM) and asialoOSM, but the antibody LM225 showed a distinct preference in reaction with OSM (sialosyl-Tn antigen). The results show that Tn antigen, obtained by chemical modifications of human glycophorin, enables the preparation and characterization of anti-Tn monoclonal antibodies, without using rare Tn erythrocytes.

Identification of an epitope recognized by the monoclonal antibody PEP80 in the C-terminal cytoplasmic fragment of glycophorin A

The monoclonal antibody PEP80 (IgG1) was raised by immunization of BALB/c mice with asialo-agalacto-glycophorin from human erythrocytes. The antibody is specific for glycophorin A (GPA) and reacts strongly with the GPA-derived tryptic peptide which is the C-terminal cytoplasmic portion of GPA, containing amino acid residues 102-131. Using the smaller chymotryptic fragments of this peptide and a set of solid phase-synthesized peptides allowed to establish that the MAb PEP80 is directed against an epitope comprising amino acid residues 112-121 of GPA. The peptides terminated with 120th or 119th amino acid residue were slightly less active, and the minimal structure which still gave a weak reaction with the antibody was the sequence of amino acid residues 112-118. The MAb PEP80 did not bind to live human erythroleukemic K562 cells, but showed a strong binding to the cells permeabilized with methanol.

Antibody binding to blood group antigens in relation to temperature: scanning electron microscopy of immunogold-labelled erythrocytes

Binding patterns of mouse monoclonal antibodies (mAb) to P1, Pk, N, I, H, Y or A antigens were visualized in the backscatter electron imaging mode of a scanning electron microscope by indirect immunogold labelling. Experiments were performed at room temperature (RT) and at 4 degrees C. In experiments with anti-P1 and anti-Pk, clusters of immunolabelling particles dominated the immunolabelling pattern much more at RT than at 4 degrees C. By contrast, no clustering was seen with anti-N, even at RT. Clustering was also observed at RT with anti-I, anti-H and anti-Y, and on some Ax and A3 cells with anti-A, but was much reduced at 4 degrees C. Immunolabelling was stronger at 4 degrees C than at RT with all mAb except anti-N and anti-A. The results indicate that glycolipid blood group antigens are more mobile in the membrane of intact erythrocytes at RT than at 4 degrees C, and that the cells bind more antibodies to such antigens at 4 degrees C than at RT. We suggest that antigen immobilization in the cold will reduce cross-linking of antigens and hence increase the number of antibody molecules needed for epitope saturation, leading to increased binding of antibody in the cold. This may be the main reason for cold-enhanced agglutination with human blood group antibodies.

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)

A new technique using an aggregating antibody against glycophorin-A for purging Ficoll-Paque-separated leucocytes of contaminating erythroid lineage cells

Ficoll-separated leucocytes used for phenotyping may be contaminated with erythroblasts or erythrocytes, which can cause problems in cytofluorography, especially if erythroid lineage cells outnumber leucocytes in the preparation. Different means have been described for removing erythroid cells from leucocyte preparations, such as BD-FACS lysing solution, hypotonic shock and ammonium chloride, but none of these is entirely satisfactory. In my hands all these techniques damaged the leucocytes to a greater or lesser extent and did not adequately eliminate the erythroblasts, sometimes not even the reticulocytes and erythrocytes. To obtain pure leucocyte suspensions, I developed a new technique based on an aggregating antibody (alpha-Gly-A, 733/8F7, from BioCarb, Sweden) directed against glycophorin-A which is found on the cell surface of erythroid lineage cells. Agglutinated erythroid cells could be removed by filtration or low-speed centrifugation. With the new technique there was no loss or damage of the leucocytes.

Degradation of the human erythrocyte membrane band 3 studied with monoclonal antibody directed against an epitope on the cytoplasmic fragment of band 3

The mouse hybridoma monoclonal antibody BIII.136 of the IgG2a class is specific for human erythrocyte band-3 protein. It was shown by means of immunoblotting and immunoprecipitation assays that the antibody recognized an epitope located in the cytoplasmic pole of the band-3 molecule within approximately 20 kDa from the N-terminal end. The N-terminal fragments of band-3 protein, migrating in SDS/polyacrylamide gel electrophoresis in the 60-kDa, 40-kDa and 20-kDa regions, were detected with the antibody in untreated red-cell membranes as products of autolysis of band-3 protein. A correlation was found between the amount of these fragments and erythrocyte age, which suggests that partial degradation of band 3 proceeds in vivo during senescence of erythrocytes. The further degradation of band-3 protein in vitro was not observed in intact erythrocytes stored at 4 degrees C, but progressed distinctly after hemolysis of red cells, during washing and storing the membranes.

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.

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.