Direct evidence for the existence of Miltenberger antigen

Characterization of alternatively spliced transcript variants of glycophorin A and glycophorin B genes in Chinese blood donors

BACKGROUND AND OBJECTIVES

The molecular basis of MNS blood group variants is not fully clear yet. In this study, we have characterized mRNA variants of GYPA and GYPB genes to reveal whether alternative RNA splicing may cause antigenic diversity of the MNS system.

MATERIALS AND METHODS

Total RNA was extracted from peripheral blood of Chinese blood donors and full-length cDNA products were generated. A nested polymerase chain reaction (PCR)-based method was established for fragment amplification and Sanger sequencing. Resulted full-length mRNA sequences were aligned with GYPA or GYPB genomic sequences respectively for exon identification. Amino acid (AA) sequences of GPA and GPB proteins were extrapolated and GYPA-EGFP, GYPB-EGFP fusion genes were generated to monitor subcellular distribution of the encoded glycophorin (GP) proteins.

RESULTS

Totally 10 blood samples were analysed. GYPB mRNAs of all the subjects demonstrated frequent exon insertion or deletion whereas this kind of variation was only observed in 3 of 10 GYPA mRNA samples. None of the reported Miltenberger hybrids was detected in any of the mRNA samples. The alternative splicing resulted in changes of AA sequences in N-terminal domains where the MNS antigenic motifs resided; however, subcellular localizations of GP-EGFP fusion proteins showed that the above-mentioned AA changes did not affect cell surface distribution of the encoded GP proteins.

CONCLUSIONS

Alternative RNA splicing may influence the antigenic features of GP proteins but not their cell surface distribution. Therefore, GYPA and GYPB mRNA characterization might be an invaluable supplement to serological phenotyping and DNA-based genotyping in MNS blood grouping.

Universal Detection of Mia Antigen and Frequencies of Glycophorin Hybrids among Blood Donors in Taiwan by Human Monoclonal Antibodies against Mia (MNS7), Mur (MNS10), and MUT (MNS35) Antigens

Glycophorin hybrids such as GP.Mur are common in Southeast Asians. In Taiwan, clinically significant alloantibodies to the GP.Mur phenotype are the most important issue in blood banks. A large-scale screening of glycophorin hybrids in the Taiwanese population is urgently needed to ensure transfusion safety. Four clones of human hybridomas that secrete anti-Mi^a, anti-MUT, and anti-Mur were established by fusing human B-lymphocytes and myeloma cells (JMS-3). The specificity of each monoclonal antibody (MoAb) was characterized. Three MoAbs were applied on an Automated Pretransfusion Blood Testing Analyzer (PK7300/PK7400) for donor screening. Genotyping was performed to determine the detailed subgrouping of glycophorin hybrids. Four MoAbs are IgM antibodies. Anti-Mi^a (377T) binds to ⁴⁶DXHKRDTYA⁵⁴, ⁴⁸HKRDTYAAHT⁵⁷ peptides, and anti-Mi^a (367T) binds to ⁴³QTNDXHKRD⁵¹ peptides (X indicates T, M, or K). Anti-Mur is reactive with ⁴⁹KRDTYPAHTA⁵⁸ peptides. Anti-MUT is reactive with ⁴⁷KHKRDTYA⁵⁴. A total of 78,327 donors were screened using three MoAbs, and 3690 (4.71%) were GP.Mur, 20 (0.025%) were GP.Hut, and 18 (0.022%) were GP.Vw. When the Mi^a antigen was introduced as routine screening, the frequency of Mi(a+) among blood donors in Taiwan was 4.66% (67,348/1,444,541). Mi^a antigen was implemented as a routine blood testing, and the results were labeled on all red blood cell (RBC) units.

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.

Molecular Detection of Glycophorins A and B Variant Phenotypes and their Clinical Relevance

Crossover or conversion between the homologous regions of glycophorin A (GYPA) and glycophorin B (GYPB) gives rise to several different hybrid glycophorin genes encoding a number of different glycophorin variant phenotypes which bear low prevalence antigens in the MNS blood group system. GP.Mur is the main glycophorin variant phenotype which causes hemolytic transfusion reaction (HTR) and hemolytic disease of the fetus and newborn (HDFN) in East and Southeast Asians. The detection of glycophorin variant phenotypes using serological methods is limited to phenotyping reagents that are not commercially available. Moreover, the red blood cells used for antibody identification are usually of the GP.Mur phenotype. The current Polymerase Chain Reaction (PCR)-based methods and loop-mediated isothermal amplification (LAMP) are available alternatives to phenotyping that allow for the specific detection of glycophorin variant phenotypes. This review highlights the molecular detection method for glycophorins A and B variant phenotypes and their clinical relevance.

The prevalence, immunogenicity, and evanescence of alloantibodies to MUT and Mur antigens of GP.Mur red blood cells in a Southeast Asian patient cohort

BACKGROUND

Antibodies to Mi^a , MUT, and Mur are among the most frequently identified alloantibodies in Southeast Asia. Understanding the characteristics of these antibodies in terms of induction and evanescence would aid in optimizing methods for their detection.

STUDY DESIGN AND METHODS

Antibody testing results between the years 2013 and 2015 with relevant patient demographic data and red blood cell (RBC) transfusion history were retrieved. Cumulative alloimmunization incidence and evanescence to MUT and Mur were estimated by Kaplan-Meier analysis in relation to the number of RBC units transfused and time.

RESULTS

Of 70,543 selected patients, 6186 nonalloimmunized subjects with available antibody testing results posttransfusion were identified. Cumulative alloimmunization incidence for MUT increased from 0.12% (95% confidence interval [CI], 0.03-0.21) to 0.63% (95% CI, 0.25-1.01), while for Mur it increased from 0.04% (95% CI, 0-0.09) to 0.42% (95% CI, 0.05-0.79) when a patient was transfused 2 RBC units as compared to 12. Both antibodies had high evanescence rates and at 1 year, anti-MUT and -Mur will be detected in only 45% (95% CI, 35%-57%) and 27% (95% CI, 17%-43%), respectively, of previously positive patients. MUT and Mur immunogenicity was estimated to be 1.7 and 1.2 times higher than E when their rate of evanescence was taken into account.

CONCLUSION

Antibodies to MUT and Mur develop following multiple RBC exposures. Immunogenicity of MUT/Mur and evanescence rates of the corresponding antibodies is higher compared to anti-E. Appropriate selection of antibody screening cells is needed in view of the high prevalence, immunogenicity, and evanescence of the antibodies.

Frequency of Mi(a) antigen: A pilot study among blood donors

The Miltenberger (Mi) classes represent a group of phenotypes for red cells that carry low frequency antigens associated with the MNSs blood group system. This pilot study was aimed at determining the Mia antigen positivity in the blood donor population in a tertiary care hospital in New Delhi, India. The study was performed between June to August 2014 on eligible blood donors willing to participate. Antigen typing was performed using monoclonal anti-Mia antiserum by tube technique. Only one of the 1000 blood donors (0.1%) tested was found to be Mia antigen positive. the Mia antigen can, therefore, be considered as being rare in the Indian blood donor population.

A direct blood polymerase chain reaction approach for the determination of GP.Mur (Mi.III) and other Hil+ Miltenberger glycophorin variants

BACKGROUND

GP.Mur (Mi.III) is a glycophorin B-A-B hybrid sialoglycoprotein expressing several potent immunogens, including Mi(a), Mur, and Hil. GP.Mur is considered one of the most important red blood cell (RBC) phenotypes in blood banking in Southeast Asia. However, there are no antibodies commercially available for the screening of GP.Mur RBCs.

STUDY DESIGN AND METHODS

To develop a direct blood polymerase chain reaction (PCR) approach for the screening of GP.Mur cells, we first confirmed the genomic sequence differences among four GP.Mur and three Mi(a-) samples by sequencing their GYP.Mur and GYPB genes. With these data, we designed PCR primers that best discriminate GYPB and GYP.Mur. Our primer design also allows the detection of other Hil+ glycophorin variants. We also constructed two plasmids--pGBi2i3 and pMiIIIi2i3--which serve as the negative and positive control DNA, respectively, for the PCR procedure. Additionally, we designed a control PCR to be run side by side with the typing PCR.

RESULTS

Because of the high specificity of our primers, we found it unnecessary to extract DNA from blood samples for PCR. We have tested this PCR method on 379 fresh and frozen blood samples. The results were further validated by serology and DNA sequencing and were shown to be completely accurate in our hand. We also found that the rapid genotyping method--high-resolution melting--can be a timesaving alternative for DNA sequencing.

CONCLUSION

This direct blood PCR approach for determination of GP.Mur and related Hil+ phenotypes is reliable and economical and is expected to be useful for blood banking in Southeast Asia.

Molecular basis of blood group expression

Antigen diversity arises from changes at the gene level that range from single nucleotide polymorphisms (SNPs) to intra- and inter-genic exchanges, inversions, insertions, and deletions. Nucleotide changes often result in amino acid difference from the wild-type gene product and with those changes new blood group antigens arise. Alternatively, there is loss of expression altogether, which is deemed the 'null' phenotype. Near complete knowledge of the genetic changes underlying the expression of blood group antigens will lead to the reality that red cell genotyping as a test-of-record. The importance of molecular testing in immunohematology necessitates appropriate training and competency programs to ensure that the highly skilled staff has the appropriate knowledge background. This review summarizes the core mechanisms for gene expression and provides a compilation of the molecular basis for blood group expression.

Anti-"Mi(a)" immunization is associated with HLA-DRB1*0901

BACKGROUND

Anti-"Mi(a)" is one of the most important irregular red blood cell antibodies found in Taiwan. The aim of this study was to investigate whether specific HLA-DRB1 alleles are associated with anti-"Mi(a)" production.

STUDY DESIGN AND METHODS

A case-control retrospective study was performed on 68 patients showing presence of anti-"Mi(a)" and 219 unrelated control subjects from the Mackay Memorial Hospital. HLA-DRB1 genotyping was carried out using sequence-based typing method. Fisher's exact test using 2 x 2 contingency tables was used to analyze significance of the association between DRB1 polymorphisms and presence of anti-"Mi(a)" in patients.

RESULTS

HLA-DRB1*0901 allele frequency in the anti-"Mi(a)" group (30%) was significantly higher than in the control group (16%) with an odds ratio of 2.27 (95% confidence interval, 1.44-3.55; p = 0.0005; p(c) = 0.016).

CONCLUSION

HLA-DRB1*0901 is significantly more prevalent in the anti-"Mi(a)" patients group than in the control group. It is suggested that cells from DR9 individuals might present processed "Mi(a)" antigen-allospecific peptides more effectively than cells from individuals carrying other DR phenotypes. Finally, it was predicted that two epitopes, derived from the MiIII glycophorin amino acid sequence, were likely to bind preferentially with the DR9 molecule. Further work will be necessary to determine if these epitopes are responsible for anti-"Mi(a)" alloimmunization.

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.

Detection of MNS hybrid molecules in the Thai population using PCR-SSP technique

We developed a polymerase chain reaction-sequence-specific primer (PCR-SSP) technique to screen for hybrid molecules in the MNS blood group in the Thai population using two sets of newly designed primers specific for four GYP(B-A-B) hybrids, GP.Mur, GP.Hop, GP.Bun and GP.HF, and two GYP(A-B-A) hybrids, GP.Vw and GP.Hut. One thousand and forty-one blood samples were tested with human anti-Mi(a) by conventional tube technique, and 598 samples of these were tested by the PCR-SSP technique. Ninety-four samples (9.03%) were strongly positive with human antisera by conventional tube technique. For PCR-SSP test results, the GP.Hut, GP.Mur, GP.Hop, GP.Bun and GP.HF genotypes were amplified with the first set of primers, whereas GP.Vw genotype was amplified with a second set of primers. The GYP(A-B) hybrids (GP. Hil and GP.JL), GYP(A-B-A) hybrids (GP.Nob, GP.Joh and GP.Dane), GYPA, GYPB and GYPE were not amplified by either set of primers. Results of testing 94 Mi(a+) and 504 Mi(a-) by conventional tube technique and PCR-SSP were concordant. This study shows that analysis by PCR-SSP is simple and convenient; therefore, it can be used as an alternative to conventional tube technique for mass screening for MNS hybrids, especially when specific antisera are not available.

Immunological characterization of anti-Mi(a), a red blood cell alloantibody, in Taiwan

BACKGROUND AND OBJECTIVES

The red blood cell Mi III phenotype is prevalent in Asia, and its corresponding alloantibody, anti-Mi(a), has been reported to cause haemolytic transfusion reactions and haemolytic disease of the newborn. However, a complete picture of the immunological characteristics of anti-Mi(a) is still lacking. We therefore conducted a systematic study to evaluate the potential clinical significance of this antibody.

MATERIALS AND METHODS

From April 1999 to March 2000, we identified 60 sera containing anti-Mi(a) among pretransfusion samples at a teaching hospital in Taiwan. These antibodies were tested for immunoglobulin class, thermal range and activity in a monocyte monolayer assay.

RESULTS

Thirty-four (57%) of the antibodies were immunoglobulin M (IgM), and 15 retained their activity at 37 degrees C. Of those that were immunoglobulin G (IgG), 96% were of subclasses IgG1 and/or IgG3. Monocyte monolayer assay studies showed that 69% (18/26) of the IgG anti-Mi(a) sera were reactive.

CONCLUSIONS

Our study justifies the implementation of anti-Mi(a) screening in Taiwan.