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

Molecular genetic analysis of Mia -positive hybrid glycophorins revealed two novel alleles of GP.Vw and multiple variant transcripts of GYPB existing in both the homozygous GP.Mur and wild-type GPB individuals

BACKGROUND

The hybrid glycophorins of MNS blood group system express a series of low incidence antigens including Mi^a , which are commonly found in Southeast Asian populations. In this study, the molecular basis of Mi^a -positive hybrid glycophorins was firstly clarified in the Chinese Southern Han population. RNA transcripts of GYPB gene in the homozygous GP.Mur individuals were also analyzed.

STUDY DESIGN AND METHODS

DNAs were extracted from the whole blood samples of 111 Mi^a -positive donors. Then, high-resolution melting (HRM) analysis for GYP(B-A-B) was used to analyze the genotypes. Sequencing of GYPB pseudoexon 3 was conducted in the samples with variant melting curves. TA-cloning and subsequent sequencing of GYPA exons 2-4 were performed in the Mi^a -positive samples with normal GYPB/GYPB genotype by HRM. The transcript analysis of GYPB was conducted in homozygous GP.Mur and wild-type glycophorin B (GPB) individuals using RNA extracted from the cultured erythroblast.

RESULTS

The heterozygous GYP*Mur/GYPB (n = 101), homozygous GYP*Mur/GYP*Mur (n = 7) including one novel GYP*Mur allele with an extra GYPA/GYPE specific nucleotide substitution (c.229+110A>T), heterozygous GYP*Bun/GYPB (n = 1) and GYP*Vw/GYPA (n = 2) with two novel GYP*Vw alleles were identified. RNA transcript analysis revealed multiple transcripts of GYPB existing in both homozygous GP.Mur and normal GPB individuals.

CONCLUSION

The results showed the genetic diversity of hybrid glycophorins in the Chinese population. Besides, the successful analysis of GYPB transcripts indicates that the cultured erythroblast is a good source for RNA transcript analysis for the protein only expressed on the red blood cells.

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.

Transfusion support with RBCs from an Mk homozygote in a case of autoimmune hemolytic anemia following diphtheria-pertussis-tetanus vaccination

BACKGROUND

Autoimmune hemolytic anemia (AIHA) in children, although unusual, is often associated with recent infection. Several reports have identified the diphtheria-pertussis-tetanus (DPT) vaccination as a possible trigger for AIHA.

STUDY DESIGN AND METHODS

Life-threatening AIHA was diagnosed in a 6-week-old infant 5 days after receiving a DPT vaccination. The patient required daily transfusion and/or exchange transfusion for 3 weeks. RBCs from an Mk homozygote were found compatible with the patient's autoantibody. Transfusion of RBCs from an Mk homozygote and later RBCs from an individual (K.T.) with a variant glycophorin, Mi.VII, were required to sustain the patient's Hb level until autoantibody production ceased, as evidenced by a fall in antibody titer and the patient's Hct returning to normal.

RESULTS

The DAT was positive (3+) with only anti-C3 on presentation. An IgM cold reactive autoantibody with probable anti-Pr specificity and high thermal amplitude (37 degrees C) was identified in the serum. The DAT was no longer positive after transfusion with compatible blood.

CONCLUSION

This case represents life-threatening AIHA in an infant, temporally related to a DPT injection and responsive to a combination of immunosuppression and transfusion of rare compatible blood.

Genomic typing of human red cell miltenberger glycophorins in a Taiwanese population

BACKGROUND

Antigens in the human red cell Miltenberger series are glycophorin variants of the MN (MNS) blood group system that are due to the rearrangement of glycophorin A (GPA) and glycophorin B (GPB) genes.

STUDY DESIGN AND METHODS

Taking advantage of the differences between the GPA and GPB genes, a polymerase chain reaction-based method was developed to detect all the Miltenberger glycophorin variants and St(a) subtype. GPA- and GPB-specific primers were used to amplify the GPA or GPB gene, and the amplified products were used to recognize the different hybrid genes after restriction enzyme digestions.

RESULTS

Among 264 Taiwanese subjects studied, Mi.III and St(a) are the most common types of Miltenberger variants found. Mi.III was present in 13 (4.92%) of 264, and St(a) was found in 8 (3. 03%) of 264; 1 case (0.4%) of Mi.V was also identified from the study group.

CONCLUSION

This is the first polymerase chain reaction-based method of detecting most of the Miltenberger variants and St(a). The genomic typing results were confirmed by control DNA of identified Miltenberger phenotypes. The prevalence rates of Mi. III and St(a) in this study were also consistent with other previous reports using different methods.

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.

Biochemistry and molecular biology of MNSs blood group antigens

This chapter has reviewed the nature of antigens of the MNSs blood group system. The structures of the proteins and the molecular features and organization of glycophorin genes were described, emphasizing their domain arrangement and the extensive sequence homology that indicates that their common and variant alleles belong to a single gene family. Methods currently used to examine these antigens are immunoblotting and DNA typing. The majority of variant genes are hybrids of parent glycophorin genes in a variety of arrangements; they contain no other sequences but those of the parent genes. The structures of the hybrids are summarized in Figure 8. Several hybrids appear to have arisen by unequal homologous recombination but others appear to have occurred through gene conversion. In this system the molecular genetic basis for a single variant phenotype may differ, as documented by gene rearrangements that appear to have occurred, as separate events, at different sites in the same intron; this has resulted in protein structures (hence phenotypes) that are identical. For example, unequal homologous recombination occurring within intron 3 can have given rise to only a limited number of phenotypes, namely alpha M-delta S, alpha N-delta S, alpha M-delta S, alpha N-delta S and delta-alpha. In addition, different sites of an exon may have been involved in gene rearrangements through gene conversion leading to nearly identical protein structures, yet different serological phenotypes. Thus, gene conversion could be more significant for generation of antigenic diversification as the number of possible new alleles is quite large. The participation of the HGpE gene in these rearrangements would make this number even larger. New sites and the expressed pseudoexon have created the epitopes of the variant phenotypes, and sequences specific for several variant antisera have been identified. Thus, the molecular basis for several serological reactions involving this system is now better understood.

The cytolytic toxin aerolysin must aggregate to disrupt erythrocytes, and aggregation is stimulated by human glycophorin

The hole-forming toxin aerolysin was shown to aggregate after binding to erythrocytes at 37 degrees C. Although the protein also bound and aggregated at 4 degrees C, hole formation was not observed, indicating that aggregation preceded penetration of the lipid bilayer. Aggregation, but not binding, could be blocked by pretreatment of the toxin with diethyl pyrocarbonate, a histidine-reactive reagent. This resulted in inactivation of the toxin. Incubation of aerolysin with glycophorin purified from human erythrocytes caused aggregation and complete inactivation. Erythrocytes which lacked glycophorin were less sensitive to the toxin. Proaerolysin, the inactive precursor of aerolysin, also bound to erythrocytes; however, it did not aggregate, nor did it aggregate when preincubated with glycophorin. The protoxin could be activated by treatment with trypsin even after it had bound to erythrocytes. Activation could also be achieved by reaction of proaerolysin with a variety of other proteases, each of which brought about a similar reduction in protein molecular weight. The activated protein was resistant to further proteolysis. These results indicate that aggregation is a necessary step in hole formation and that the sites on aerolysin required for binding and for aggregation and hole formation are separate.