Severe hemolytic disease of the newborn due to anti-Vw and detection of glycophorin A antigens on the Miltenberger I sialoglycoprotein by Western blotting

Fetal inheritance of GP*Mur causing severe HDFN in an unrecognized case of maternal alloimmunization

BACKGROUND

The clinical and laboratory features of hemolytic disease of the newborn can be challenging to diagnose during pregnancy in the apparent absence of a blood group antibody. Low-frequency antibodies go undetected due to the lack of appropriate antigen-positive reagent red blood cells (RBCs).

CASE REPORT

A pregnant woman of Southeast Asian descent was referred to a maternal-fetal medicine outpatient clinic due to a complicated obstetric history and a negative antibody screen. This initial visit at 29 weeks and 0 days' gestational age (GA) was unremarkable. A hydropic infant, born at 29 weeks and 5 days' GA, succumbed on the seventh day of life. Comprehensive laboratory testing was performed after birth. The hospital blood bank performed a maternal antibody identification. Direct antiglobulin test was performed on the cord blood. A reference laboratory confirmed an anti-Mi^a , performed paternal Mi^a phenotyping, and identified a hybrid glycophorin B-A-B GP*Mur allele.

DISCUSSION

Maternal alloimmunization to low-frequency antigens remains a challenge. Southeast Asians make up a significant percentage in some US locations. Worldwide reports on the frequency of maternal alloimmunization of the MNS system can be used to guide the use of specific reagent RBCs for testing. Such strategies rely on the identification of blood donor units for reagent manufacture and use in perinatal antibody screens.

CONCLUSION

The incidence of Mi^a and related antibodies is significant among Southeast Asians. In North America, prenatal antibody screening cells are not routinely chosen to match this population. The clinical and societal implications are discussed.

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.

SARA: a "new" low-frequency MNS antigen (MNS47) provides further evidence of the extreme diversity of the MNS blood group system

BACKGROUND

Until recently, SARAH (SARA) was a low-frequency antigen within the 700 series (700.052). SARA was discovered in Australia and subsequently described in Canada where anti-SARA was implicated in severe hemolytic disease of the fetus and newborn (HDFN). This study investigated whether SARA could be recategorized into an existing, or novel, blood group system.

STUDY DESIGN AND METHODS

Serologically typed Australian SARA family members (n = 9) were exome sequenced followed by bioinformatics analysis. Sanger sequencing of Exon 3 of GYPA of Australian (n = 9) and Canadian (n = 9) family members was then performed, as were peptide inhibition studies.

RESULTS

Exome sequencing identified 499,329 single-nucleotide variants (SNVs) within the nine individuals. Filtering excluded SNVs with an NCBI dbSNP ID (n = 482,177) and non-protein coding SNVs (n = 14,008); for the remaining 3144 SNVs, only one, c.240G>T of GYPA encoding p.Arg80Ser, was present in all six SARA-positive individuals. Sanger sequencing confirmed the presence of c.240G>T in the Australian SARA-positive individuals and demonstrated the same genetic basis in the Canadian SARA family. For a peptide representing the SARA sequence, inhibition of anti-SARA against SARA-positive cells was 84.6% at a concentration of 1.0 mg/mL.

CONCLUSION

We provide evidence that the SARA antigen is encoded by a SNV on GYPA and SARA has been reassigned to the MNS blood group system, now MNS47. This discovery provides a basis for application of genetic approaches in SARA typing when clinically indicated, for example, in HDFN.

Sixty years of antibodies to MNS system hybrid glycophorins: what have we learned?

The MNS system was the second blood group system discovered and at least 16 of the 46 antigens in the MNS system result from genetic recombination, producing a hybrid glycophorin. The incidence of these hybrid glycophorins is highest in East Asian populations. MNS system antigens defined by hybrid glycophorins are immunogenic with alloimmune IgG responses developing after transfusion or pregnancy; with reports originating from Asia, Europe, the Americas, and Australia. This demonstrates the global nature of problems associated with these antibodies. Since the initial report that production of anti-Mi(a) was a cause of hemolytic disease of the fetus and newborn (HDFN), antibodies to antigens defined by hybrid glycophorins have been reported in 27 cases of HDFN (1 fatal) and 8 cases of hemolytic transfusion reaction (HTR) (1 fatal). In at least 40% of these clinical cases, the disease was reported as severe. Hyporegenerative fetal anemia is a common feature of the reported HDFN cases. In all published cases, the causative antibodies were identified by reference laboratory investigative tests following clinical presentation. The failure to detect these antibodies by routine testing highlights the need for consideration of the medical importance of these antibodies when defining antibody screening practices and reagents. The aim of this review is to raise awareness of severe disease caused by antibodies to MNS antigens defined by hybrid glycophorins and, thus, to improve diagnosis and patient management.

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.

Red cell antigens on band 3 and glycophorin A

Band 3 and glycophorin A (GPA) are the two most abundant integral proteins of the red cell membrane, being present in approximately 10(6) copies per cell. The main functions of band 3 are membrane anion transport and maintenance of red cell membrane stability through interaction with the cytoskeleton. GPA plays an important role in prevention of red cell aggregation in the circulation and contribution to the glycocalyx. The extracellular domains of both proteins are highly polymorphic. Band 3 carries the antigens (currently 19) of the Diego blood group system and GPA and glycophorin B the antigens (currently 43) of the MNS system. There is substantial evidence that band 3 and GPA associate in the red cell membrane and the Wr(b) antigen, although a product of the band 3 gene, is known to require a complex of GPA and band 3 for normal expression. The discovery of a novel GPA mutation (Ala65-->Pro) giving rise to aberrant Wr(b) expression has been informative with regard to the site of interaction of the two proteins. The extensive array of GPA-related antigens is largely due to genetic events between two closely linked genes and different genetic mechanisms can give rise to the same antigen. This is in contrast to the antigens on band 3 which are exclusively due to single nucleotide mutations in the band 3 gene.

Glycophorin A mutation Ala65 --> Pro gives rise to a novel pair of MNS alleles ENEP (MNS39) and HAG (MNS41) and altered Wrb expression: direct evidence for GPA/band 3 interaction necessary for normal Wrb expression

We report here a novel Glycophorin A (GPA) mutation Ala65 --> Pro which gives rise to a low-incidence antigen HAG, lack of a high-incidence antigen ENEP and aberrant expression of the high-incidence Wrb antigen. Anti-ENEP was identified in the serum of a transfused male patient (E.H.) who was homozygous for a GPA Ala65 --> Pro mutation and possessed a novel low-incidence antigen which we have called HAG. An unrelated HAG-positive individual, heterozygous for the Ala65 --> Pro mutation, has also been identified. Anti-HAG was present in several multispecific antisera to low-incidence antigens and in one monospecific serum. Normal expression of the Wrb antigen depends on the presence of amino acid Glu658 of band 3 and on the presence of GPA. However, a specific epitope on GPA has not previously been implicated. DNA sequence analysis of band 3 from patient E.H. was normal in the region of Wra/Wrb polymorphism with homozygous presence of Glu658 and therefore the abnormal Wrb expression results from the Ala65 --> Pro mutation in GPA. The ENEP and HAG antigens have been assigned the MNS blood group system numbers 002.039 and 002.041, respectively, by the ISBT Working Party on Terminology for Red Cell Surface Antigens.

Biochemical characterization of the O-glycans on recombinant glycophorin A expressed in Chinese hamster ovary cells

Alterations in N- and O-linked glycosylation affect cell surface expression and antigenicity of recombinant glycophorin A expressed in transfected Chinese hamster ovary (CHO) cells. To understand these effects further, glycophorin A was purified by immunoaffinity chromatography from transfected wild type and glycosylation deficient CHO cells. The O-glycans were characterized both biochemically, using gel filtration and high performance anion exchange chromatography, and immunologically, using carbohydrate specific monoclonal antibodies to probe Western blots. The O-glycans of human erythrocyte glycophorin A consist mainly of short oligosaccharides with one, two, or three sialic acid residues linked to a common disaccharide core, Gal beta 1-3GalNAc alpha 1-Ser/Thr, with the disialylated structure being the most abundant. With the exception of the trisialylated derivative, the same structures were found on recombinant glycophorin A expressed by wild type CHO cells. However, in contrast to human erythrocyte glycophorin A, the monosialylated oligosaccharide was the most abundant structure on the recombinant protein. Furthermore, recombinant glycophorin A was shown to express a small amount of the Tn antigen (GalNAc alpha 1-Ser/Thr). Recombinant glycophorin A had the same O-glycan composition, whether purified from clones expressing high or moderate levels of the recombinant glycoprotein. This indicates that the level of expression of the transfected glycoprotein did not affect its O-glycan composition. Deletion of the N-linked glycosylation site at Asn26, by introducing the Mi.I mutation (Thr28-->Met) by site-directed mutagenesis, did not markedly affect the O-glycan composition of the resulting recombinant glycoprotein expressed in wild type CHO cells.(ABSTRACT TRUNCATED AT 250 WORDS)