Section 3: Epitope determination of monoclonal antibodies to glycophorin A and glycophorin B. Coordinator's report. Antibodies to antigens located on glycophorins and band 3

Frequencies of glycophorin variants and alloantibodies against Hil and MINY antigens in Japanese

BACKGROUND AND OBJECTIVES

Antigens of the MNS blood group system are expressed on the red blood cell (RBC) membrane on glycophorin A (GPA) and glycophorin B (GPB) or on hybrid molecules of GPA and GPB. This study investigated the distribution of glycophorin variants and alloantibodies against Hil and MINY among Japanese individuals.

METHODS

Mi(a+) or Hil+ RBCs were screened using an automated blood grouping machine (PK7300) with monoclonal anti-Mi^a or polyclonal anti-Hil. Glycophorin variants were defined by serology with monoclonal antibodies against Mi^a , Vw, MUT and Mur, and polyclonal antibodies against Hil, MINY and Hop + Nob (KIPP). The glycophorin variants were further confirmed by immunoblotting and Sanger sequencing. Alloanti-Hil and alloanti-MINY in the plasma were screened using GP.Hil RBCs in an antiglobulin test. The specificity of anti-Hil or anti-MINY was assessed using GP.Hil (Hil+MINY+) and GP.JL (Hil-MINY+) RBCs.

RESULTS

The GP.HF, GP.Mur, GP.Hut, GP.Vw, GP.Kip and GP.Bun frequencies in 1 005 594 individuals were 0·0357%, 0·0256%, 0·0181%, 0·0017%, 0·0009% and 0·0007%, respectively. GP.Hil was found in as four of the 13 546 individuals (0·0295%). Of 137 370 donors, 10 had anti-Hil (0·0073%) and three had anti-MINY (0·0022%).

CONCLUSIONS

Glycophorin variants were relatively rare in Japanese individuals, with the major variants being GP.HF (0·0357%), GP.Hil (0·0295%) and GP.Mur (0·0256%). Only one example of anti-MINY was previously reported, but we found three more in this study.

The Kg-antigen, RhAG with a Lys164Gln mutation, gives rise to haemolytic disease of the newborn

The Kg-antigen was first discovered in an investigation of a mother whose infant had haemolytic disease of the newborn (HDN). The antibody against the Kg-antigen is believed to be responsible for HDN. The Kg-antigen is provisionally registered under the number 700045, according to the Red Cell Immunogenetics and Blood Group Terminology. However, the molecular nature of the Kg-antigen has remained a mystery for over 30 years. In this study, a monoclonal antibody against the Kg-antigen and the recombinant protein were developed that allowed for the immunoprecipitation analysis. Immunoprecipitants from the propositus' red blood cell ghosts were subjected to mass spectrometry analysis, and DNA sequence analysis of the genes was also performed. A candidate for the Kg-antigen was molecularly isolated and confirmed to be a determinant of the Kg-antigen by cell transfection and flow cytometry analyses. The Kg-antigen and the genetic mutation were then screened for in a Japanese population. The molecular nature of the Kg-antigen was shown to be RhAG with a Lys164Gln mutation. Kg phenotyping further clarified that 0.22% of the Japanese population studied was positive for the Kg-antigen. These findings provide important information on the Kg-antigen, which has been clinically presumed to give rise to HDN.

Frequency of Mia (MNS7) and Classification of Mia-Positive Hybrid Glycophorins in an Australian Blood Donor Population

Background

MNS blood group system genes GYPA and GYPB share a high degree of sequence homology and gene structure. Homologous exchanges between GYPA and GYPB form hybrid genes encoding hybrid glycophorins GP(A-B-A) and GP(B-A-B). Over 20 hybrid glycophorins have been characterised. Each has a distinct phenotype defined by the profile of antigens expressed including Mi^a. Seven hybrid glycophorins carry Mi^a and have been reported in Caucasian and Asian population groups. In Australia, the population is diverse; however, the prevalence of hybrid glycophorins in the population has never been determined. The aims of this study were to determine the frequency of Mi^a and to classify Mi^a-positive hybrid glycophorins in an Australian blood donor population.

Method

Blood samples from 5,098 Australian blood donors were randomly selected and screened for Mi^a using anti-Mi^a monoclonal antibody (CBC-172) by standard haemagglutination technique. Mi^a-positive red blood cells (RBCs) were further characterised using a panel of phenotyping reagents. Genotyping by high-resolution melting analysis and DNA sequencing were used to confirm serology.

Result

RBCs from 11/5,098 samples were Mi^a-positive, representing a frequency of 0.22%. Serological and molecular typing identified four types of Mi^a-positive hybrid glycophorins: GP.Hut (n = 2), GP.Vw (n = 3), GP.Mur (n = 5), and 1 GP.Bun (n = 1). GP.Mur was the most common.

Conclusion

This is the first comprehensive study on the frequency of Mi^a and types of hybrid glycophorins present in an Australian blood donor population. The demographics of Australia are diverse and ever-changing. Knowing the blood group profile in a population is essential to manage transfusion needs.

Detection of hereditary pyropoikilocytosis by the eosin-5-maleimide (EMA)-binding test is attributable to a marked reduction in EMA-reactive transmembrane proteins

INTRODUCTION

Hereditary spherocytosis (HS) and hereditary pyropoikilocytosis (HPP, severe form of hereditary elliptocytosis) are unrelated red cell disorders caused by defects in distinct regions of the red cell cytoskeleton. The high predictive value of the eosin-5-maleimide (EMA)-binding test for the diagnosis of HS is because of its interaction with transmembrane proteins band 3, Rh protein, Rh glycoprotein and CD47, which are reduced on HS red cells. Our study was undertaken to determine why EMA-labelled HPP red cells were previously found to give much lower fluorescence readings than HS.

METHODS

Flow cytometry was used to determine the relative amounts of monoclonal antibodies bound to red cells from normal adults, HS and HPP groups. Confocal microscopy was used to visualise the overall staining pattern of the red cells with selected antibodies.

RESULTS

In flow cytometry, HPP red cells gave lower antibody binding to the four EMA-reactive membrane proteins than HS red cells and bound less antibody to glycophorins A and C, and CD59. Confocal images of Rh protein and band 3 immunostaining revealed a greater number of HPP red cells having partial or no fluorescence than in HS and normal controls.

CONCLUSION

Lesser amounts of EMA-reactive membrane proteins were detected in HPP than HS red cells, thus confirming their lower fluorescence readings in the EMA-binding test. The concomitant reduction in glycophorins A and C, and CD59 in HPP could have caused cellular contraction, resulting in poikilocytosis.

A novel series of anti-human glycophorin A (CD235a) antibodies defining five extra- and intracellular epitopes

Glycophorin A (GPA, CD235a) is a major membrane glycoprotein and marker of cells of the erythroid lineage. It is also the target of Plasmodium falciparum and of influenza virus. We describe a novel series of 10 antibodies towards GPA, recognizing four extra- and intracellular peptide epitopes of this molecule (defined by epitope mapping) and one mixed peptide/carbohydrate epitope. All antibodies bind better to the desialylated than to the fully sialylated molecule, including those specific for the intracellular epitope. For some of the antibodies (representing all five epitopes) functional binding constants were determined by Surface Plasmon Resonance. The new panel complements the already known anti-glycophorin antibodies and offers several potential applications for, e.g., differential diagnosis of erythroleukemias, lineage analyses of erythroid cells, isolation of senescent erythrocytes, or a highly sensitive neuraminidase assay.

Novel GYP(A-B-A) hybrid gene in a DANE+ person who made an antibody to a high-prevalence MNS antigen

BACKGROUND

The glycophorin (GP) molecule associated with the GP.Dane phenotype is a GP(A-B-A) hybrid that contains some amino acids encoded by the Pseudoexon 3 of GYPB and Asn(45) of GPA and carries the low-prevalence MNS antigens DANE and Mur. Serum from a woman of English ancestry contained an immunoglobulin M alloantibody to a high-prevalence MNS antigen, and the purpose of this study was to identify the molecular basis of her phenotype.

STUDY DESIGN AND METHODS

Hemagglutination, Western blotting, and DNA analyses were performed by standard methods.

RESULTS

Tests of the proband's RBCs with monoclonal antibodies indicated a change of amino acids between positions 27 and 55 of GPA. Her RBCs expressed M, s, Mur, and DANE antigens and were M(g)-negative. The antigen recognized by her antibody was sensitive to treatment with papain, ficin, and trypsin and resistant to alpha-chymotrypsin and dithiothreitol. Sequencing of DNA from the proband revealed a sequence of nucleotides identical to the GYP(A-B-A) encoding GP.Dane but without the adenyl nucleotide substitution, which has been predicted to change Ile(46) of GPA to Asn(45). Testing of her immediate family revealed the presence of an M(k) gene.

CONCLUSION

The proband had a novel GYP(A-B-A) encoding a DANE+ GP that is in cis to GYPB(s) and in trans to M(k). The high-prevalence antigen lacking from this GP.Dane phenotype and recognized by the proband's serum is called ENDA (ISBT Number MNS44). Our results indicate that the change of Ile(46) of GPA to Asn(45) of GP.Dane is not required for expression of the DANE antigen.

A simple method for quantifying high density antigens in erythrocyte membrane by flow cytometry

RBC flow cytometric analysis is usually used to quantify antigen content. Calibration systems enable antigen content determination by relating mean fluorescence intensity with the number of bound antibody molecules (equivalent to the number of antigen molecules). For that reason, antibodies must be used at saturating concentration, which may lead to agglutination when working with high density antigens. Then, forward scattering, side scattering and fluorescence will be increased, thus obtaining wrong results. In this work, the simple Langmuir adhesion model was applied. Flow cytometry was used to quantify GPA, a transmembrane protein present at high density on RBC. The fluorescence intensity of samples at different anti-GPA sub-saturating concentrations was measured. Sometimes, agglutinates were present and two peaks of fluorescence were observed, the principal one corresponding to isolated cells and the secondary one corresponding to agglutinated cells. In those cases, the principal peak was taken into account for the analysis. The GPA antigen content obtained for nine analyzed samples ranged from 3 to 13 x 10(5) sites per cell, which is similar to those values found in literature. Therefore, the Langmuir adsorption model enables us to determine the antigen content for the anti-GPA/GPA system on RBC membrane. This model could be used to quantify high density antigens in RBC and in other cells.

Recombinant glycophorins C and D as tools for studying Gerbich blood group antigens

BACKGROUND

The Gerbich blood group system antigens are carried on glycophorin C (GPC) and glycophorin D (GPD) and variants thereof. These glycoproteins have been expressed in a heterologous system to study the individual antigens and to determine whether Ana is antithetical to Ge2.

STUDY DESIGN AND METHODS

cDNAs encoding GPC, GPD, GPC.Yus, GPC.Ge, GPC.Lsa, and GPD.Lsa were transfected and stably expressed in a human embryonic kidney cell line (293T). Individual Gerbich antigens were analyzed with MoAbs and human polyclonal antibodies by flow cytometry and immunoblotting. Recombinant GPD and GPD.Ana were expressed transiently and analyzed for expression of Ge2 and Ana antigens.

RESULTS

All recombinant variants were detected with sialidase-resistant and -sensitive anti-Ge2, anti-Ge3, and anti-Ge4. Ge4 antigen expression was depressed in GPC.Ls(a) transfectants as well as on Ls(a+) RBCs. GPD.An(a) recombinant protein expressed Ana and Ge2 antigens.

CONCLUSION

Cell lines stably expressing glycosylated Gerbich proteins were developed in a heterologous system by transfecting individual variant forms of GPC and GPD. Unexpectedly, it was found that Ge4 antigen is reduced in both the GPC.Ls(a) recombinant and the Ls(a+) RBCs. It was also shown that Ana and Ge2 antigens were expressed on a single GPD.An(a) protein and, therefore, they cannot be antithetical.

Quantification of glycophorin A and glycophorin B on normal human RBCs by flow cytometry

BACKGROUND

The quantification of antigens and proteins on RBCs has been achieved by different approaches. Flow cytometry allows the results of the earliest studies to be to reappraised because it offers the possibility of measuring the immunofluorescence intensity of single cells and integrating the individual data of a large number of cells within a very short time.

STUDY DESIGN AND METHODS

Flow cytometry was used in this work to analyze the binding of four MoAbs to glycophorin A (GPA) and glycophorin B (GPB). RBCs in their native state (nonfixed) were utilized. To avoid the agglutination problem, cells were disaggregated before measurements, dates were taken on 20,000 events on the single-cell region, and the fluorescence intensity of the principal peak present in the fluorescence histograms was used for the analysis. The quantification of sites per RBC was estimated by applying the Langmuir adhesion model.

RESULTS

The numbers of GPA and GPB sites obtained for samples from healthy donors were similar to those found in the literature (1.86-4.9) x 10(5) and (0.48-1.61) x 10(5) for GPA and (0.21-1.14) x 10(5) and (0.47-0.88) x 10(5) for GPB. Differences between antibodies were found that depend on the binding site of each one.

CONCLUSION

A simple method to quantify antigen sites on RBCs was developed. It could be applied whenever one antibody is assumed to bind exactly one antigen.

Glycophorin C is the receptor for the Plasmodium falciparum erythrocyte binding ligand PfEBP-2 (baebl)

We report in this paper that glycophorin C (GPC) is the receptor for PfEBP-2 (baebl, EBA-140), the newly identified erythrocyte binding ligand of Plasmodium falciparum. PfEBP-2 is a member of the Duffy binding-like erythrocyte binding protein (DBL-EBP) family. Although several reports have been published characterizing PfEBP-2, the identity of its erythrocytic receptor was still unknown. Using a combination of enzymatically treated red blood cells (RBCs) and rare, variant RBCs lacking different surface proteins, we have shown that PfEBP-2 does not bind to cells lacking GPC. Additionally, we found that PfEBP-2 binds differentially to variants of GPC lacking exon 2 or exon 3, and determined that the binding domain on GPC is potentially restricted to amino acid residues 14 through 22 within exon 2. Thus PfEBP-2 is involved in a sialic acid-dependent pathway of invasion, which does not involve glycophorin A or glycophorin B and represents a novel route of entry into the RBCs.