Blood group A(1) and A(2) revisited: an immunochemical analysis

The increasing need for ABO blood group genotyping and quality assurance implications for laboratory implementation

ABO blood group antigens are critical determinants of immunologic self and non-self and are ubiquitously expressed on all cellular tissues. Antibodies against non-self ABO antigens are naturally present and can mediate pathologic reactions against incompatible transfused blood cells and transplanted tissues. Laboratory testing for ABO antigens and isoagglutinins is essential for safe and effective transfusion and transplantation. Testing for ABO antigens has traditionally depended on serologic testing. However, there is increasing need for evaluation of genetic analysis of ABO antigens, to enable evaluation of ABO blood group in cases where serologic testing may be ambiguous or impossible to accurately perform. The clinical need for ABO genotyping is being addressed by the development of multiple molecular diagnostic approaches. Recent data have clearly demonstrated the potential utility of ABO genotyping in solid organ transplantation, yet widespread implementation has been slow. We propose that this lag is related to practical considerations in laboratory testing, including limited regulatory guidance on the performance and reporting of these assays and the absence of widely available external proficiency testing programs for quality assurance. Here we describe approaches to ABO genotyping, current initiatives in developing ABO genotyping proficiency testing programs, and laboratory quality assurance considerations for ABO genotyping.

ABO blood group antigens and differential glycan expression: Perspective on the evolution of common human enzyme deficiencies

Enzymes catalyze biochemical reactions and play critical roles in human health and disease. Enzyme variants and deficiencies can lead to variable expression of glycans, which can affect physiology, influence predilection for disease, and/or directly contribute to disease pathogenesis. Although certain well-characterized enzyme deficiencies result in overt disease, some of the most common enzyme deficiencies in humans form the basis of blood groups. These carbohydrate blood groups impact fundamental areas of clinical medicine, including the risk of infection and severity of infectious disease, bleeding risk, transfusion medicine, and tissue/organ transplantation. In this review, we examine the enzymes responsible for carbohydrate-based blood group antigen biosynthesis and their expression within the human population. We also consider the evolutionary selective pressures, e.g. malaria, that may account for the variation in carbohydrate structures and the implications of this biology for human disease.

Red Blood Cells Oligosaccharides as Targets for Plasmodium Invasion

The key element in developing a successful malaria treatment is a good understanding of molecular mechanisms engaged in human host infection. It is assumed that oligosaccharides play a significant role in Plasmodium parasites binding to RBCs at different steps of host infection. The formation of a tight junction between EBL merozoite ligands and glycophorin receptors is the crucial interaction in ensuring merozoite entry into RBCs. It was proposed that sialic acid residues of O/N-linked glycans form clusters on a human glycophorins polypeptide chain, which facilitates the binding. Therefore, specific carbohydrate drugs have been suggested as possible malaria treatments. It was shown that the sugar moieties of N-acetylneuraminyl-N-acetate-lactosamine and 2,3-didehydro-2-deoxy-N-acetylneuraminic acid (DANA), which is its structural analog, can inhibit P. falciparum EBA-175-GPA interaction. Moreover, heparin-like molecules might be used as antimalarial drugs with some modifications to overcome their anticoagulant properties. Assuming that the principal interactions of Plasmodium merozoites and host cells are mediated by carbohydrates or glycan moieties, glycobiology-based approaches may lead to new malaria therapeutic targets.

AB0-incompatibility of mother and fetus: the role of anti-glycan alloantibodies in the hemolytic disease of newborns

The mother and fetus incompatibility due to Rh-factor, blood group or other blood factors can lead to hemolytic disease of the fetus and newborn (HDN). HDN is a clinical disease condition of the fetus and newborn as a result of hemolysis, when maternal IgG alloantibodies cross the placenta and destroy the red blood cells of the fetus and newborn. The child disease begins in utero and can dramatically increase immediately after birth. As a result, hyperbilirubinemia and anemia develop, that can lead to abortions, serious complications, or death of the neonates in the absence of proper therapy. The range of HDN has changed significantly now compared to previous decades. Half a century ago, HDN was considered an almost complete synonym of RhD-alloimmunization, and this was a frequent problem for newborns. By now due to the high effective of Rh-conflict prevention, immunological AB0-conflicts have become the most common cause of HDN. The review aimes to one of the main causes of jaundice and anemia in neonates at present, i.e. HDN due to immunological AB0-conflict of mother and newborn (AB0-HDN). The main participants of the AВ0- incompatibility mother and child are considered, namely A- and B-glycans, as well as the corresponding anti-glycan alloantibodies. Close attention is paid to the structure features of glycan alloantigens on the red blood cells of the fetus and adult. The possible correlation of the frequency and severity of HDN with the blood group of mother and child, as well as with the titer of maternal alloantibodies, has been considered. The influence of immunoglobulin G subclasses on the AB0-HDN development has been evaluated. In most cases, AB0-HDN appear when the mother has the blood group 0, and the fetus has the group A (subgroup A1) or the group B. Other rare incidences of AB0-incompatibility with severe course are occurred. As a whole the etiology of AB0-HDN is complex and the HDN severity is influenced by many factors. The authors have analyzed statistical data, as well as the prevalence of AB0-incompatibility and AB0-HDN in various regions of the world. Current approaches to the diagnosis of AB0-HDN are discussed in addition. By now the problems of AB0- HDN occurrence and developing of ways to overcome this disease remain relevant.

Group O plasma as a media supplement for CAR-T cells and other adoptive T-cell therapies

BACKGROUND

Most chimeric antigen receptor T (CAR-T) cells and other adoptive T-cell therapies (ACTs) are currently manufactured by ex vivo expansion of patient lymphocytes in culture media supplemented with human plasma from group AB donors. As lymphocytes do not express A or B antigens, the isoagglutinins of non-AB plasmas are unlikely to cause deleterious effects on lymphocytes in culture.

STUDY DESIGN AND METHODS

Seeding cultures with peripheral blood mononuclear cell (PBMNC) concentrates from group A₁ donors and using a CAR-T culture protocol, parallel cultures were performed, each with unique donor plasmas as media supplements (including group O plasmas with high-titer anti-A and group AB plasmas as control). An additional variable, a 3% group A₁ red blood cell (RBC) spike, was added to simulate a RBC-contaminated PBMNC collection. Cultures were monitored by cell count, viability, flow cytometric phenotype, gene expression analysis, and supernatant chemokine analysis.

RESULTS

There was no difference in lymphocyte expansion or phenotype when cultured with AB plasma or O plasma with high-titer anti-A. Compared to controls, the presence of contaminating RBCs in lymphocyte culture led to poor lymphocyte expansion and a less desirable phenotype-irrespective of the isoagglutinin titer of the plasma supplement used.

CONCLUSIONS

This study suggests that ABO incompatible plasma may be used as a media supplement when culturing cell types that do not express ABO antigens-such as lymphocytes for CAR-T or other ACT. The presence of contaminating RBCs in culture was disadvantageous independent of isoagglutinin titer.

GBGT1 is allelically diverse but dispensable in humans and naturally occurring anti-FORS1 shows an ABO-restricted pattern

BACKGROUND

The FORS histo-blood group system was described in 2013 and much remains to be investigated regarding its genetic and immunohematologic characteristics, as well as its clinical importance. While presence of the c.887G>A-mutated GBGT1 gene, which results in FORS1 glycosphingolipid expression on human red blood cells (RBCs), is rare in the populations tested so far, naturally occurring anti-FORS1 in plasma appears common.

STUDY DESIGN AND METHODS

The Erythrogene database was utilized to probe genetic variation in GBGT1 among 2504 individuals in the 1000 Genomes Project. We screened 1108 Swedish blood donors for three principally important single-nucleotide polymorphisms (c.363C>A, c.886C>T, and c.887G>A) and selected samples were analyzed further. Screening for naturally occurring anti-FORS1 in plasma from 100 donors was performed using antigen-positive RBCs.

RESULTS

We identified 68 GBGT1 alleles, of which three were previously listed blood group alleles. Eight potential null alleles were observed, based on three different nonsense mutations. Four healthy donors were found homozygous for c.363C>A, which truncates the GBGT1-encoded Fs synthase prematurely. This is the first description of human knock-outs for GBGT1. The c.886C>T mutation that alters the same codon (p.Arg296Trp) changed by c.887G>A (p.Arg296Gln) was overexpressed to investigate if it induces the FORS1+ phenotype. However, c.886C>T did not result in synthesis of FORS1. We detected anti-FORS1 in 10% of all donors tested but none in the A₁ or A₁B groups.

CONCLUSION

We have extended the knowledge of GBGT1 variants, allele frequencies, and the characteristics of naturally occurring antibodies in our newest carbohydrate blood group system, FORS. The finding of c.363C>A-homozygous donors indicates that GBGT1 is dispensable.

Position of human blood group O(H) and phenotype-determining enzymes in growth and infectious disease

The human ABO(H) blood group phenotypes arise from the evolutionarily oldest genetic system found in primate populations. While the blood group antigen A is considered the ancestral primordial structure, under the selective pressure of life‐threatening diseases blood group O(H) came to dominate as the most frequently occurring blood group worldwide. Non‐O(H) phenotypes demonstrate impaired formation of adaptive and innate immunoglobulin specificities due to clonal selection and phenotype formation in plasma proteins. Compared with individuals with blood group O(H), blood group A individuals not only have a significantly higher risk of developing certain types of cancer but also exhibit high susceptibility to malaria tropica or infection by Plasmodium falciparum. The phenotype‐determining blood group A glycotransferase(s), which affect the levels of anti‐A/Tn cross‐reactive immunoglobulins in phenotypic glycosidic accommodation, might also mediate adhesion and entry of the parasite to host cells via trans‐species O‐GalNAc glycosylation of abundantly expressed serine residues that arise throughout the parasite's life cycle, while excluding the possibility of antibody formation against the resulting hybrid Tn antigen. In contrast, human blood group O(H), lacking this enzyme, is indicated to confer a survival advantage regarding the overall risk of developing cancer, and individuals with this blood group rarely develop life‐threatening infections involving evolutionarily selective malaria strains.

Structural diversity and biological importance of ABO, H, Lewis and secretor histo-blood group carbohydrates

ABO, H, secretor and Lewis histo-blood system genes control the expression of part of the carbohydrate repertoire present in areas of the body occupied by microorganisms. These carbohydrates, besides having great structural diversity, act as potential receptors for pathogenic and non-pathogenic microorganisms influencing susceptibility and resistance to infection and illness. Despite the knowledge of some structural variability of these carbohydrate antigens and their polymorphic levels of expression in tissue and exocrine secretions, little is known about their biological importance and potential applications in medicine. This review highlights the structural diversity, the biological importance and potential applications of ABO, H, Lewis and secretor histo-blood carbohydrates.

Comprehensive red blood cell and platelet antigen prediction from whole genome sequencing: proof of principle

BACKGROUND

There are 346 serologically defined red blood cell (RBC) antigens and 33 serologically defined platelet (PLT) antigens, most of which have known genetic changes in 45 RBC or six PLT genes that correlate with antigen expression. Polymorphic sites associated with antigen expression in the primary literature and reference databases are annotated according to nucleotide positions in cDNA. This makes antigen prediction from next-generation sequencing data challenging, since it uses genomic coordinates.

STUDY DESIGN AND METHODS

The conventional cDNA reference sequences for all known RBC and PLT genes that correlate with antigen expression were aligned to the human reference genome. The alignments allowed conversion of conventional cDNA nucleotide positions to the corresponding genomic coordinates. RBC and PLT antigen prediction was then performed using the human reference genome and whole genome sequencing (WGS) data with serologic confirmation.

RESULTS

Some major differences and alignment issues were found when attempting to convert the conventional cDNA to human reference genome sequences for the following genes: ABO, A4GALT, RHD, RHCE, FUT3, ACKR1 (previously DARC), ACHE, FUT2, CR1, GCNT2, and RHAG. However, it was possible to create usable alignments, which facilitated the prediction of all RBC and PLT antigens with a known molecular basis from WGS data. Traditional serologic typing for 18 RBC antigens were in agreement with the WGS-based antigen predictions, providing proof of principle for this approach.

CONCLUSION

Detailed mapping of conventional cDNA annotated RBC and PLT alleles can enable accurate prediction of RBC and PLT antigens from whole genomic sequencing data.

Chemical Basis for Qualitative and Quantitative Differences Between ABO Blood Groups and Subgroups: Implications for Organ Transplantation

Blood group ABH(O) carbohydrate antigens are carried by precursor structures denoted type I-IV chains, creating unique antigen epitopes that may differ in expression between circulating erythrocytes and vascular endothelial cells. Characterization of such differences is invaluable in many clinical settings including transplantation. Monoclonal antibodies were generated and epitope specificities were characterized against chemically synthesized type I-IV ABH and related glycans. Antigen expression was detected on endomyocardial biopsies (n = 50) and spleen (n = 11) by immunohistochemical staining and on erythrocytes by flow cytometry. On vascular endothelial cells of heart and spleen, only type II-based ABH antigens were expressed; type III/IV structures were not detected. Type II-based ABH were expressed on erythrocytes of all blood groups. Group A1 and A2 erythrocytes additionally expressed type III/IV precursors, whereas group B and O erythrocytes did not. Intensity of A/B antigen expression differed among group A1 , A2 , A1 B, A2 B and B erythrocytes. On group A2 erythrocytes, type III H structures were largely un-glycosylated with the terminal "A" sugar α-GalNAc. Together, these studies define qualitative and quantitative differences in ABH antigen expression between erythrocytes and vascular tissues. These expression profiles have important implications that must be considered in clinical settings of ABO-incompatible transplantation when interpreting anti-ABO antibodies measured by hemagglutination assays with reagent erythrocytes.

Pathogenesis and mechanisms of antibody-mediated hemolysis

BACKGROUND

The clinical consequences of antibodies to red blood cells (RBCs) have been studied for a century. Most clinically relevant antibodies can be detected by sensitive in vitro assays. Several mechanisms of antibody-mediated hemolysis are well understood. Such hemolysis after transfusion is reliably avoided in a donor-recipient pair, if one individual is negative for the cognate antigen to which the other has the antibody.

STUDY DESIGN AND RESULTS

Mechanisms of antibody-mediated hemolysis were reviewed based on a presentation at the Strategies to Address Hemolytic Complications of Immune Globulin Infusions Workshop addressing intravenous immunoglobulin (IVIG) and ABO antibodies. The presented topics included the rates of intravascular and extravascular hemolysis; immunoglobulin (Ig)M and IgG isoagglutinins; auto- and alloantibodies; antibody specificity; A, B, A,B, and A1 antigens; A1 versus A2 phenotypes; monocytes-macrophages, other immune cells, and complement; monocyte monolayer assay; antibody-dependent cell-mediated cytotoxicity; and transfusion reactions due to ABO and other antibodies.

CONCLUSION

Several clinically relevant questions remained unresolved, and diagnostic tools were lacking to routinely and reliably predict the clinical consequences of RBC antibodies. Most hemolytic transfusion reactions associated with IVIG were due to ABO antibodies. Reducing the titers of such antibodies in IVIG may lower the frequency of this kind of adverse event. The only way to stop these events is to have no anti-A or anti-B in the IVIG products.

Structural basis for the ABO blood-group dependence of Plasmodium falciparum rosetting

The ABO blood group influences susceptibility to severe Plasmodium falciparum malaria. Recent evidence indicates that the protective effect of group O operates by virtue of reduced rosetting of infected red blood cells (iRBCs) with uninfected RBCs. Rosetting is mediated by a subgroup of PfEMP1 adhesins, with RBC binding being assigned to the N-terminal DBL1α₁ domain. Here, we identify the ABO blood group as the main receptor for VarO rosetting, with a marked preference for group A over group B, which in turn is preferred to group O RBCs. We show that recombinant NTS-DBL1α₁ and NTS-DBL1α₁-CIDR1γ reproduce the VarO-iRBC blood group preference and document direct binding to blood group trisaccharides by surface plasmon resonance. More detailed RBC subgroup analysis showed preferred binding to group A₁, weaker binding to groups A₂ and B, and least binding to groups A_x and O. The 2.8 Å resolution crystal structure of the PfEMP1-VarO Head region, NTS-DBL1α₁-CIDR1γ, reveals extensive contacts between the DBL1α₁ and CIDR1γ and shows that the NTS-DBL1α₁ hinge region is essential for RBC binding. Computer docking of the blood group trisaccharides and subsequent site-directed mutagenesis localized the RBC-binding site to the face opposite to the heparin-binding site of NTS-DBLα₁. RBC binding involves residues that are conserved between rosette-forming PfEMP1 adhesins, opening novel opportunities for intervention against severe malaria. By deciphering the structural basis of blood group preferences in rosetting, we provide a link between ABO blood grouppolymorphisms and rosette-forming adhesins, consistent with the selective role of falciparum malaria on human genetic makeup.

Rosetting, the capacity of infected red blood cells (RBCs) to bind uninfected RBCs, is a Plasmodium falciparum virulence factor. Rosetting is influenced by the ABO blood group, being less efficient with O RBCs. Although this preference may account for protection against severe malaria afforded by the O blood group, its understanding is fragmentary. We identify the ABO blood group as the main receptor for the rosetting Palo Alto VarO parasites, which display a marked preference for blood group A. Rosetting is caused by a sub-group of PfEMP1 adhesins. PfEMP1-VarO shares with other rosetting lines a specific NTS-DBL1α₁-CIDR1γ Head region. We show that the Head region binds RBCs more efficiently than NTS-DBL1α₁ and that ABO blood group polymorphisms influence binding of both domains. The 2.8 Å resolution crystal structure of the Head region reveals extensive contacts between the DBL1α₁ and CIDR1γ domains, and shows structural features of the NTS-DBL1α₁ hinge region essential for RBC binding. We localize the RBC-binding site to the face opposite to the heparin-binding site of NTS-DBL1α₁ and document direct binding of the Head region to A and B trisaccharides These findings provide novel insights into the interactions established by malaria parasites with a prominent human blood group.

Apparent expression of varicella-zoster virus proteins in latency resulting from reactivity of murine and rabbit antibodies with human blood group a determinants in sensory neurons

Analyses of varicella-zoster virus (VZV) protein expression during latency have been discordant, with rare to many positive neurons detected. We show that ascites-derived murine and rabbit antibodies specific for VZV proteins in vitro contain endogenous antibodies that react with human blood type A antigens in neurons. Apparent VZV neuronal staining and blood type A were strongly associated (by a χ² test, α = 0.0003). Adsorption of ascites-derived monoclonal antibodies or antiserum with type A erythrocytes or the use of in vitro-derived VZV monoclonal antibodies eliminated apparent VZV staining. Animal-derived antibodies must be screened for anti-blood type A reactivity to avoid misidentification of viral proteins in the neurons of the 30 to 40% of individuals who are blood type A.

The structural basis of blood group A-related glycolipids in an A3 red cell phenotype and a potential explanation to a serological phenomenon

Glycolipids from the red cells of a rare blood group A subgroup individual, expressing the blood group A(3) phenotype with the classical mixed-field agglutination phenomenon, A(2(539G>A))/O(1) genotype, and an unusual blood group A glycolipid profile, were submitted to a comprehensive biochemical and structural analysis. To determine the nature of blood group A glycolipids in this A(3) phenotype, structural determination was carried out with complementary techniques including proton nuclear magnetic resonance (1D and 2D), mass spectrometry (MS) (nano-electrospray ionization/quadrupole time-of-flight and tandem mass spectrometry) and thin layer chromatography with immunostaining detection. As expected, total blood group A structures were of low abundance, but contrary to expectations extended-A type 2 and A type 3 glycolipids were more dominant than A hexaglycosylceramides based on type 2 chain (A-6-2 glycolipids), which normally is the major A glycolipid. Several para-Forssman (GalNAcβ3GbO(4)) structures, including extended forms, were identified but surmised not to contribute to the classic mixed-field agglutination of the A(3) phenotype. It is proposed that the low level of A antigen combined with an absence of extended branched glycolipids may be the factor determining the mixed-field agglutination phenomenon in this individual.