Molecular genetics of the ABO histo-blood group system

Six splice site variations, three of them novel, in the ABO gene occurring in nine individuals with ABO subtypes

Background

Nucleotide mutations in the ABO gene may reduce the activity of glycosyltransferase, resulting in lower levels of A or B antigen expression in red blood cells. Six known splice sites have been identified according to the database of red cell immunogenetics and the blood group terminology of the International Society of Blood Transfusion. Here, we describe six distinct splice site variants in individuals with ABO subtypes.

Methods

The ABO phenotype was examined using a conventional serological method. A polymerase chain reaction sequence-based typing method was used to examine the whole coding sequence of the ABO gene. The ABO gene haplotypes were studied using allele-specific primer amplification or cloning technology. In silico analytic tools were used to assess the functional effect of splice site variations.

Results

Six distinct variants in the ABO gene splice sites were identified in nine individuals with ABO subtypes, including c.28 + 1_2delGT, c.28 + 5G > A, c.28 + 5G > C, c.155 + 5G > A, c.204-1G > A and c.374 + 5G > A. c.28 + 1_2delGT was detected in an A_w individual, while c.28 + 5G > A, c.28 + 5G > C, and c.204-1G > A were detected in B_el individuals. c.155 + 5G > A was detected in one B₃ and two AB₃ individuals, whereas c.374 + 5G > A was identified in two A_el individuals. Three novel splice site variants (c.28 + 1_2delGT, c.28 + 5G > A and c.28 + 5G > C) in the ABO gene were discovered, all of which resulted in low antigen expression. In silico analysis revealed that all variants had the potential to alter splice transcripts.

Conclusions

Three novel splice site variations in the ABO gene were identified in Chinese individuals, resulting in decreased A or B antigen expression and the formation of ABO subtypes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03141-5.

A historical overview of advances in molecular genetic/genomic studies of the ABO blood group system

In 1990, 90 years after the discovery of ABO blood groups by Karl Landsteiner, my research team at the Molecular Biology Laboratory of the now-defunct Biomembrane Institute elucidated the molecular genetic basis of the ABO polymorphism. Henrik Clausen, Head of the Immunology Laboratory, initiated the project by isolating human group A transferase (AT), whose partial amino acid sequence was key to its success. Sen-itiroh Hakomori, the Scientific Director, provided all the institutional support. The characterization started from the 3 major alleles (A1, B, and O), and proceeded to the alleles of A2, A3, Ax and B3 subgroups and also to the cis-AB and B(A) alleles, which specify the expression of A and B antigens by single alleles. In addition to the identification of allele-specific single nucleotide polymorphism (SNP) variations, we also experimentally demonstrated their functional significance in glycosyltransferase activity and sugar specificity of the encoded proteins. Other scientists interested in blood group genes later characterized more than 250 ABO alleles. However, recent developments in next-generation sequencing have enabled the sequencing of millions of human genomes, transitioning from the era of genetics to the era of genomics. As a result, numerous SNP variations have been identified in the coding and noncoding regions of the ABO gene, making ABO one of the most studied loci for human polymorphism. As a tribute to Dr. Hakomori's scientific legacy, a historical overview in molecular genetic/genomic studies of the human ABO gene polymorphism is presented, with an emphasis on early discoveries made at his institute.

Patients of Myelodysplastic Syndrome with Mild/Moderate Myelofibrosis and a Monosomal Karyotype are Independently Associated with an Adverse Prognosis: Long-Term Follow-Up Data

Purpose

The aim of our study was to evaluate the clinical characteristics of myelodysplastic syndrome (MDS) patients with concomitant mild-to-moderate myelofibrosis (MF), and to assess its independent prognostic role in MDS patients diagnosed by World Health Organization 2016 classification (WHO2016C) with long-term follow-up.

Patients and Methods

A total of 157 patients with primary MDS associated with or without MF were examined retrospectively with long-term follow-up. MF graded as MF-1/MF-2 was defined as "mild/moderate". Cytogenetics testing and fluorescence in situ hybridization (FISH) were also conducted in all MDS patients.

Results

Thirty-four (21.7%) of 157 MDS patients had MF. Also, 24 (15.3%) MDS patients based on WHO2016 criteria were defined as MF-1 and 10 (6.4%) as MF-2. MDS patients with MF-1/2 had a higher prevalence of death (p=0.002), leukemic progression (p=0.013), O blood type (p=0.039) as well as less hypercellular proliferation (p<0.001) and less supportive treatment (p=0.003) compared with those without mild/moderate MF. Cytogenetics testing did not show a significant difference between MDS patients with and without MF. Multivariate analyses showed that MF (mild/moderate), a monosomal karyotype (MK) and % bone-marrow blasts were independently associated with shorter overall survival (OS) and progression-free survival (PFS). Age was an independent indicator of the adverse OS of MDS patients. Compared with those without MF, MDS patients with mild/moderate MF were significantly associated with worse OS and PFS in MK-negative subgroups and relatively low-risk Revised International Prognostic Scoring System for Myelodysplastic Syndromes (IPSS-R) stratification in long-term follow-up.

Conclusion

Mild/moderate myelofibrosis and monosomal karyotype are independent indicators of a poor clinical outcome in MDS patients. In long-term follow-up, MDS with mild/moderate MF can be a prognostic marker for MDS patients with a specific MK stratification and IPSS-R stratification.

ABO blood type, smoking status, other risk factors and prognosis of pancreatic ductal adenocarcinoma

The aim of this observational study was to test whether ABO blood type was a prognostic factor for pancreatic ductal adenocarcinoma (PDAC) patients and whether other risk factors could influence pancreatic cancer patients' survival. This study included 610 patients who were diagnosed as pancreatic cancer and had undergone radical surgery. Patients' characteristics included age, gender, tumor stage, tumor grade, adenosquamous carcinoma (ASC) status, preoperative serum carbohydrate antigen 19-9 (CA19-9) levels, preoperative serum carcinoembryonic antigen (CEA) levels, ABO blood type, smoking status, and drinking status were analyzed in this study. Cox proportional hazards regression model and Kaplan-Meier method were used to evaluate the role of prognostic factors. For pancreatic cancer patients undergoing radical surgery, the overall survival was worse for ASC patients than PDAC patients (Log-rank = 11.315, P < .001). Compared with ASC patients (Log-rank < 0.001, P = .996), PDAC patients can benefit from chemotherapy (Log-rank = 17.665, P < .001). For PDAC patients, O blood type had better overall survival than non-O blood type (Log-rank = 4.153, P = .042). Moreover, the group with higher serum levels of CA19-9 had poor prognosis compared to another group with low serum CA19-9 (Log-rank = 4.122, P = .042). Higher CEA levels indicated poor prognosis (Log-rank = 13.618, P < .001). In conclusion, ASC status was associated with overall survival of pancreatic cancer patients and cannot benefit from postoperative chemotherapy. Non-O blood type was a prognostic factor for PDAC patients.

Determination of complete sequence information of the human ABO blood group orthologous gene in pigs and breed difference in blood type frequencies

The sequence information of the genomic form of the human ABO blood group orthologous gene (erythrocyte antigen A, EAA) is not complete in pigs. Therefore, we cloned and characterized the nucleotide sequence of EAA intron 7, which is critical to understand genetic difference between A and 0 blood groups in pigs, covering complete genomic sequence information of EAA excluding a ~560bp unsequencible gap. We also analyzed genetic polymorphisms within EAA intron 7 and exon 8. We found difference in A0 blood group frequencies among pig breeds. In addition, we designed a new genomic DNA-based A0 blood group typing method and improved the accuracy and simplicity of the typing.

Blood type B antigen modulates cell migration through regulating cdc42 expression and activity in HaCaT cells

ABO blood group is determined by carbohydrate antigens, called ABH antigens. It has been known that the change of carbohydrate antigen expression, including ABH antigens, has correlation with the tumor metastasis and survival; however, the exact mechanism remains to be elucidated. ABH antigens are expressed not only in blood cells but also in several tissues. In epidermis, ABH antigen is expressed in the uppermost spinous and granular layer. We investigated the role of ABH antigens on the cell migration of HaCaT keratinocytes, which express B antigen. Knock-down of B antigen expression by small interference RNA of FUT1 inhibited HaCaT cell migration. At that time, we found that lamellipodia and actin fiber were also reduced by knock-down of B antigen expression. The transcription of cdc42, a kind of Rho GTPase which plays a key role in actin polymerization, was reduced by down-regulated B antigen expression. Furthermore, the reduced B antigen expression also inhibited the interaction of cdc42 and N-WASP. Collectively, our data provide a clue how ABH antigens regulate the cell migration mechanism.

[Phenotype characteristics of humoral immunity parameters in patients with chronic generalized periodontitis with different blood groups]

Interrelationships between parameters of humoral immunity with AB0 blood groups have been investigated. The highest content of IgA to transglutaminase was found in A(II) patients, while the lowest content was found in AB(IV) patients. The blood content on anti-gliadin IgA was higher in healthy donors. The oral liquid of periodontic patients contained anti-gliadin IgA and IgB lacking in healthy donors. It have been found that 47% of healthy people and 52.7% of patients are infcted with Helicobacter pylori. In the group of periodontic patients A(II) individually predominated; they were characterized by the presence of antibodies to H. pylori in the oral liquid, these antibodies were absent in healthy donors. The pepsinogen level was higher in blood of periodontic patients than in healthy donors. B(III) patients had the lowest level of blood pepsinogen.

Expression of histo-blood group antigens in vertebrate gonads

The tissue expression of human histo-blood group antigens (HBGA) in vertebrates, as well as their evolutionary tendencies and relation to histogenesis, especially in the reproductive system, are not entirely understood.The present research comprises a large-scale immunohistochemical study of HBGA A and B expression in ovaries and testicles of 14 species belonging to six classes of free-living vertebrates from Chondrichtyes to Mammalia .We present novel data for ABH antigen reactivity in reproductive organs of vertebrates which have not been studied so far. Our results suggest that HBGA are evolutionary stable structures, most possibly related to vitellogenesis in oocytes with high yolk content. The tendency observed in A and B antigen expression is mostly associated with the processes of gamete differentiation and vitellogenesis, rather than with the evolutionary development of vertebrate species.

ABO blood groups and genetic risk factors for thrombosis in Croatian population

AIM

To assess the association between ABO blood group genotypes and genetic risk factors for thrombosis (FV Leiden, prothrombin G20210A, and methylenetetrahydrofolate reductase C677T mutations) in the Croatian population and to determine whether genetic predisposition to thrombotic risk is higher in non-OO blood group genotypes than in OO blood group genotypes.

METHODS

The study included 154 patients with thrombosis and 200 asymptomatic blood donors as a control group. Genotyping to 5 common alleles of ABO blood groups was performed by polymerase chain reaction with sequence specific primers (PCR-SSP). FV Leiden was determined by PCR-SSP, while prothrombin and methylenetetrahydrofolate reductase were determined by PCR and restriction fragment length polymorphism (PCR-RFLP).

RESULTS

There was an association between non-OO blood group genotypes and the risk of thrombosis (odds ratio [OR] 2.08, 95% confidence interval [CI], 1.32-3.27). The strongest association with thrombotic risk was recorded for A1B/A2B blood group genotypes (OR, 2.73; 95% CI, 1.10-6.74), followed by BB/O1B/O2B (OR, 2.29; 95% CI, 1.25-4.21) and O1A1/O2A1 (OR, 1.95; 95% CI, 1.15-3.31). FV Leiden increased the risk of thrombosis 31-fold in the group of OO carriers and fourfold in the group of non-OO carriers. There was no significant difference in the risk of thrombosis between OO and non-OO blood groups associated with prothrombin mutation. Non-OO carriers positive for methylenetetrahydrofolate reductase had a 5.7 times greater risk of thrombosis than that recorded in OO carriers negative for methylenetetrahydrofolate reductase.

CONCLUSION

Study results confirmed the association of non-OO blood group genotypes with an increased risk of thrombosis in Croatia.

Biological and clinical aspects of ABO blood group system

The ABO blood group was discovered in 1900 by Austrian scientist, Karl Landsteiner. At present, the International Society of Blood Transfusion (ISBT) approves as 29 human blood group systems. The ABO blood group system consists of four antigens (A, B, O and AB). These antigens are known as oligosaccharide antigens, and widely expressed on the membranes of red cell and tissue cells as well as, in the saliva and body fluid. The ABO blood group antigens are one of the most important issues in transfusion medicine to evaluate the adaptability of donor blood cells with bone marrow transplantations, and lifespan of the hemocytes.This article reviews the serology, biochemistry and genetic characteristics, and clinical application of ABO antigens.

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

BACKGROUND AND OBJECTIVE

The basis of blood group A(1) and A(2) phenotypes has been debated for many decades, and still the chemical basis is unresolved. The literature generally identifies the glycolipid chemical differences between blood group A(1) and A(2) phenotypes as being poor or no expression of A type 3 and A type 4 structures on A(2) red cells, although this assertion is not unanimous.

MATERIALS AND METHODS

Using purified glycolipids and specific monoclonal antibodies, we revisited the glycolipid basis of the A(1) and A(2) phenotypes. Purified glycolipids were extracted from four individual A(1) and four individual A(2) blood units. One blood unit from an A weak subgroup was also included. Monoclonal anti-A reagents including those originally used to define the basis of A(1) and A(2) phenotypes were used in a thin layer chromatography - enzyme immunoassay to identify the presence of specific glycolipids.

RESULTS

A type 3 glycolipid structures were found to be present in large amounts in all phenotypes. In contrast, the A type 4 glycolipid structure was virtually undetectable in the A(2) phenotype, but was present in the A(1) and A subgroup samples.

CONCLUSION

The major glycolipid difference between the A(1) and A(2) phenotypes is the dominance of A type 4 glycolipids in the A(1) phenotype.

Molecular genotyping and frequencies of A1, A2, B, O1 and O2 alleles of the ABO blood group system in a Kuwaiti population

Expression of the highly polymorphic ABO gene cluster is commonly investigated for blood transfusion and analysis, but little information is available for Middle Eastern populations. This study determined the major ABO allele frequency in a Kuwaiti Arab cohort using a multiplex PCR-RFLP technique; 355 unrelated blood donors of phenotype A1 (46), A2 (31), A1B (6), A2B (4), B (97) and O (171) were genotyped. DNA fragments of 252 (251 for O1) and 843 (842 for A2) bp spanning the two major exons, 6 and 7, of the ABO gene were amplified and digested with HpaII and KpnI. Thirteen different genotypes could be identified when combining the A1, A2, B, O1 and O2 alleles from the digestion patterns: 1 A1 A1 (0.28%), 6 A1 A2 (1.69%), 38 A1 O1 (10.71%), 1 A1 O2 (0.28%), 1 A2 A2 (0.28%), 30 A2 O1 (8.45%), 6 A1 B (1.69%), 4 A2 B (1.13%), 12 BB (3.38%), 79 BO1 (22.25%), 6 BO2 (1.69%), 167 O1 O1 (47.04%) and 4 O1 O2 (1.13%). Two of the combinations (A2 O2, O2 O2) were not found. All genotypes determined were consistent with the serotypes. The frequencies of the five alleles in the Kuwaiti sample population were ABO*A1 = 0.0746, ABO*A2 = 0.0592, ABO*B = 0.1676, ABO*O1 = 0.6831 and ABO*O2 = 0.0155. These results are discussed with reference to gene frequencies reported for other ethnic groups.

Use of maternal plasma for non-invasive prenatal diagnosis of fetal ABO genotypes

BACKGROUND

Measurement of free fetal DNA in maternal plasma opened a door for non-invasive prenatal diagnosis. Prenatal diagnosis of fetal ABO genotypes can provide a basis for the prevention and therapy of maternal-fetal incompatibility. We identified fetal ABO genotypes using fetal DNA in plasma from pregnant women with blood group O. The aim of the study was to investigate the accuracy and feasibility of this method.

METHODS

A total of 105 blood group O women in middle or late pregnancy were enrolled. Fetal DNA in maternal plasma and genomic DNA in umbilical vein blood from newborns were extracted using a QIAamp DNA Blood Kit. DNA was amplified to identify ABO genotypes by PCR with sequence-specific primers (PCR-SSP). The genotype results were evaluated using serologic tests for ABO phenotyping.

RESULTS

Using DNA from umbilical vein blood, ABO genotypes of 105 newborns were successfully identified by PCR-SSP. Using fetal DNA from maternal plasma, 88.6% (93/105) fetal ABO genotypes was correct; 12 false results were from 66 pregnant women with fetuses of type non-O. The accuracy in middle pregnancy was lower than that in late pregnancy, although the difference was not significant (0.05<p<0.10).

CONCLUSIONS

It is feasible to use measurement of fetal DNA in plasma from pregnant women with blood group O for prenatal diagnosis of fetal ABO genotypes. The method is useful for the diagnosis and therapy of ABO maternal-fetal incompatibility and hemolytic disease of the newborn.

Expression of the histo-blood group B gene predominates in AB-genotype cells

BACKGROUND

It has been demonstrated that the 43-bp minisatellite sequence in the 5' region of the ABO gene plays an important role in its transcriptional regulation. It was determined in previous investigations that the structure of the minisatellite enhancer was specific to A, B, and O alleles.

STUDY DESIGN AND METHODS

Real-time polymerase chain reaction (PCR) detection and a PCR-restriction fragment length polymorphism (RFLP) strategy were used to compare the quantities of the A and B transcripts in AB-genotype cells, including peripheral blood cells and cancer cell line with the group AB phenotype. The 5' 3.7-kb regions of the A and B genes were cloned and the sequences compared. The transcriptional activities of the 5' segments of the A and B genes were compared with luciferase reporter assay.

RESULTS

Both real-time PCR and PCR-RFLP analyses show that there is evidently more of the B transcript in the AB-genotype cells. It was demonstrated that the 5' segment of the B gene had a markedly higher transcription-activation activity relative to the A gene. This difference in transcription capability appears to result from the variation in minisatellite-enhancer structures in the A and B genes, which contain one and four repeats of the 43-bp enhancer unit, respectively.

CONCLUSION

Our study indicates that the majority of steady-state mRNA within AB-genotype cells is composed of the B transcript and that this phenomenon is due to the predominant expression of the B gene relative to the A gene.

A modified PCR-SSP method for the identification of ABO blood group antigens

The ABO blood group antigens are carbohydrate molecules synthesized by the glycosyltransferases encoded by the ABO gene on chromosome 9. Kidney transplantation across the ABO barrier generally leads to rapid humoral graft rejection due to the presence of naturally occurring antibodies to the A and B antigens. We have developed a method for ABO typing our cadaveric organ donors by the polymerase chain reaction using sequence-specific primers (PCR-SSP). The method uses 12 primers in eight PCR mixtures and is performed under the same conditions as our routine HLA-A, B, C PCR-SSP typing. The PCR-SSP-based types of 166 regular blood donors and 148 cadaveric organ donors all showed total concordance with their serologically assigned ABO groups. Six individuals possessing the ABO A subgroups (A3, Ax and Aend) all typed as A1 by PCR-SSP, as expected. PCR-SSP is an appropriate method for ABO typing of cadaveric organ donors and, importantly, enables both ABO and HLA typing to be performed on the same DNA material.

Mapping of the bovine blood group systems J, N', R', and Z show evidence for oligo-genetic inheritance

Genes determining the bovine erythrocyte antigens were mapped by linkage analysis. In total 9591 genotypes of 20 grandsire families with 1074 sires from a grand-daughter design were elucidated for the genes determining the erythrocyte antigens EAA, EAB, EAC, EAF, EAJ, EAL, EAM, EAN', EAR', EAS, EAT', and EAZ according to standard paternity testing procedures in the blood typing laboratories. Linkage analyses were performed with 248 microsatellite markers, eight SSCP markers and four polymorphic proteins and enzymes covering the 29 autosomes and the pseudoautosomal region of the sex chromosomes. The number of informative meioses for the blood group systems ranged from 76 to 947. Blood group systems EAM and EAT' were non-informative. Most of the erythrocyte antigen loci showed significant linkage to a single chromosome and were mapped unequivocally. The genes determining erythrocyte antigen EAA, EAB, EAC, EAL, and EAS were mapped to chromosomes 15, 12, 18, 3, and 21, respectively. Lod-score values ranged from 11.43 to 107.83. Moreover, the EAF system could be mapped to chromosome 17. However, the EAN' system previously known as part of the EAF system could be mapped to chromosome 5. In addition, the blood group systems EAJ, the new EAN', EAR', and EAZ, showed significant linkage to microsatellite markers on various chromosomes and also to other blood groups. The appearance of a single blood group system might be therefore either dependent on the existence of other blood group systems or because of an interaction between different loci on various chromosomes as is known in humans and in pigs.

Allele frequencies and molecular genotyping of the ABO blood group system in a Kuwaiti population

The phenotypic distributions of observed numbers of ABO blood groups in a Kuwaiti sample population of 18,558 subjects are 4962 (26.7%) with A, 4,462 (24.1%) with B, 858 (4.6%) with AB, and 8,276 (44.6%) with 0. The calculated gene frequencies are 0.6678 for ABO*O, 0.1768 for ABO*A, and 0.1554 for ABO*B. Molecular genotyping of the ABO blood group system in a Kuwaiti sample population was determined using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. The positions of nucleotides 258 and 700 of cDNA from A transferase were amplified by PCR. The amplified DNA was subjected to RFLP analysis to distinguish A, B, and O alleles. Blood samples of known ABO phenotype from 101 healthy unrelated Kuwaiti individuals (A, 29; B, 23; AB, 14; O,35) were used. Two DNA fragments of the ABO locus were designed to be amplified by 2 pairs of primers. To identify the 258th nucleotide, a 199- or 200-bp DNA fragment was amplified by PCR and digested with KpnI. For the 700th nucleotide, a 128-bp DNA fragment was amplified by PCR and digested with AluI. By analyzing the electrophoresis patterns,ABO genotypes were conclusively determined by examining the DNA fragments. The ABO genotypes of the known 101 samples were as follows: AA, 4.30%; AO, 24.41%; BB, 4.16%; BO, 24.2%; AB, 8.46%; and 00, 34.65%. These results were confirmed statistically using the calculated frequencies of IA, IB, and IO alleles.

Structural and functional diversity of blood group antigens

Biochemical and molecular genetic studies have revealed that blood group antigens are present on cell surface molecules of wide structural diversity, including carbohydrate epitopes on glycoproteins and/or glycolipids, and peptide antigens on proteins inserted within the membrane via single or multi-pass transmembrane domains, or via glycosylphosphatidylinositol linkages. These studies have also shown that some blood group antigens are carried by complexes consisting of several membrane components which may be lacking or severely deficient in rare blood group 'null' phenotypes. In addition, although all blood group antigens are serologically detectable on red blood cells (RBCs), most of them are also expressed in non-erythroid tissues, raising further questions on their physiological function under normal and pathological conditions. In addition to their structural diversity, blood group antigens also possess wide functional diversity, and can be schematically subdivided into five classes: i) transporters and channels; ii) receptors for ligands, viruses, bacteria and parasites; iii) adhesion molecules; iv) enzymes; and v) structural proteins. The purpose of this review is to summarize recent findings on these molecules, and in particular to illustrate the existing structure-function relationships.

A case of DNA analysis of ABO blood group variant allele A2

The ABO phenotype of a bloodstain (B) on a knife that was used as a weapon in an attempted murder case was found to be different from that of the Peruvian victim's blood (AB). Serological analysis showed that the A-antigenicity was much weaker than B antigenicity, suggesting that the victim's phenotype was A(2)B or A(3)B. So, the ABO genotypes of the knife bloodstain and the victim's blood were determined by DNA analysis. The 261st G deletion, specific to the O(1) allele, was not detected in the specimens by restriction fragment length polymorphism analysis. Also, the 871st A, specific to the A(3) allele, was not found by the allele-specific amplification method. Amplified product length polymorphism and direct sequencing methods finally demonstrated that the typical B sequence was found in one allele and a single C deletion in the 1,059th-1,061st C stretch in the other allele, indicating that the ABO phenotype of the bloodstain and victim's blood were A(2)B.

Evolution of the ABO blood group gene in Japanese macaque

We determined 5 sequences of Japanese macaque ABO blood group gene exon 7 (ca. 0.5 kb) and 2 sequences for exon 5 and intron 6 (ca. 1.7 kb). We compared those data with published sequences of other Old World monkey species, and the results suggest that alleles A and B were polymorphic in the ancestral species of macaques, and that B type allele evolved independently in macaque and baboon lineages.

Applications of molecular biology techniques to transfusion medicine

Other articles in this issue of Seminars in Hematology have reviewed the results of basic research in relation to the understanding of the genes, the molecular basis of blood group variants, and structural and functional aspects of the proteins carrying blood group antigens. Although molecular techniques are currently being used in a limited fashion in clinical laboratories, their application has far-reaching possibilities and undoubtedly will be soon applied more generally. We focus on two general areas: molecular genotyping for blood group antigens and their expression analysis in heterologous systems.

Progress in the study of ABO blood group system

Progress in the study of ABO blood group system during the last three decades was reviewed according to following 5 items. 1. Structure of H-, A- and B-active saccharides isolated from the globoside fractions from human erythrocytes. 2. Enzyme characterization of a blood group A-gene specified alpha-N-acetyl-galactosaminyltransferase (A-enzyme), and a blood group B-gene specified alpha-galactosyltransferase (B-enzyme). 3. Immunological properties of the A- and B-enzyme. 4. The cDNA structures of human blood group ABO genes. 5. Transcriptional regulation of the human blood group ABO genes.

Genomic analysis of ABO chimeras and mosaics using hematopoietic colony-derived DNA

BACKGROUND

While there are many case reports dealing with ABO mosaicism and chimerism, there have been few attempts to determine the patient's genotype.

STUDY DESIGN AND METHODS

Peripheral blood and buccal mucosa were obtained from three persons with ABO mosaicism or chimerism. DNA extracted from hematopoietic progenitor cell-derived colonies and from peripheral blood and buccal mucosa were analyzed by polymerase chain reaction-restriction fragment length polymorphism methods. In addition, analyses of short tandem repeat markers were carried out.

RESULTS

Hematopoietic progenitor cell-derived DNA analysis revealed that, in two of the three persons there were 2 apparently distinct progenitor cell lineages whose percentages were close to those in the peripheral blood of the patients, as analyzed by flow cytometry; the exception was Subject 3, who had myelodysplastic syndrome (MDS). Short tandem repeat analysis showed that the former two subjects had two pairs of ABO alleles and the latter subject, with MDS, had loss of heterozygosity in some colony-derived DNA as well as blood DNA.

CONCLUSION

The subjects without MDS had two distinct hematopoietic cell lineages that led to their ABO chimeric status. The subject with MDS was assumed to have an ABO mosaicism caused by the somatic deletion of the ABO gene in the hematopoietic progenitor cells.

Insights into the structure and function of membrane polypeptides carrying blood group antigens

In recent years, advances in biochemistry and molecular genetics have contributed to establishing the structure of the genes and proteins from most of the 23 blood group systems presently known. Current investigations are focusing on genetic polymorphism analysis, tissue-specific expression, biological properties and structure-function relationships. On the basis of this information, the blood group antigens were tentatively classified into five functional categories: (i) transporters and channels, (ii) receptors for exogenous ligands, viruses, bacteria and parasites, (iii) adhesion molecules, (iv) enzymes and, (v) structural proteins. This review will focus on selected blood groups systems (RH, JK, FY, LU, LW, KEL and XK) which are representative of these classes of molecules, in order to illustrate how these studies may bring new information on common and variant phenotypes and for understanding both the mechanisms of tissue specific expression and the potential function of these antigens, particularly those expressed in nonerythroid lineage.

Characterization of the ABO blood group genes in macaques: evidence for convergent evolution

The ABO blood group system is known to act as a major transplantation barrier in primates. Different primate species share the presence of A and B antigens. The polymorphism of the macaque ABO blood group genes was analyzed by cloning and sequencing the exon 7 region. In the case of the rhesus macaque (Macaca mulatta) and cynomolgus monkey (Macaca fascicularis) we were able to identify ABO blood group gene segments which cluster into two lineages, namely: *A/*O1 and *B. In addition allelic variation was observed. The 2 amino acid replacements at positions 266 and 268, which are thought to be crucial for A or B transferase activity, could be confirmed for both macaque species. Comparison of primate sequences shows that A and B reactivity was generated independently from each other in the hominoids and Old World monkey lineages. Hence, the primate A and B blood group genes are subject to convergent evolution.

[Blood groups and structure-activity relations]

In the recent years, advances in biochemistry and molecular genetics have contributed to establish the structure of the genes and proteins from most of the 23 blood group systems presently known. From these findings, five functional classes of molecules can be schematically distinguished: (i) transporters and channels, (ii) receptors for ligands, viruses, bacteria and parasites, (iii) adhesion molecules, (iv) enzymes, and (v) structural proteins. Recent advances on these molecules will be reviewed, particularly by illustrating available structure-function relationships.

A(1,2)BO(1,2) genotyping by multiplexed allele-specific PCR

The ABO blood group is the most clinically important human alloantigen system in transfusion medicine. The system involves three antigens A, B and H. H antigen is converted to either A or B by the activity of alpha1-->3-N-acetyl-galactosaminyl transferase (A transferase) or alpha1-->3 galactosyl transferase (B transferase). The O phenotype is the result of an inactive glycosyltransferase, which is unable to glycosylate the H antigen. The immunological properties of the ABO system were identified at the turn of the century; however, the genetic basis of the ABO system has only recently been characterized. This has enabled the development of a number of molecular ABO typing methods. Described here is a two-reaction multiplex allele-specific PCR (ASPCR) genotyping assay for the A1, A2, B, O1 and O2 subtypes. 11 different allele-specific oligonucleotide primers were selected to detect the presence or absence of the O1 associated G--> (-) deletion at base 261, the O2 associated G --> A substitution at base 802, the B associated G --> A substitution at base 803, and finally the A2 associated C --> (-) deletion at base 1059. A total of 122 peripheral blood samples were genotyped and serologically forward and reverse typed. A concordance rate of 98.4% (120/122 samples) was observed between the actual genotype and the serologically-based predicted genotype. These results indicate that this assay provides a rapid, accurate, and simple method for A(1,2)BO(1,2) genotyping that serves as a useful supplement to standard serological ABO typing.

A rapid molecular method (polymerase chain reaction with sequence-specific primers) to genotype for ABO blood group and secretor status and its potential for organ transplants

We hypothesize that kidneys from non-secretor blood group A2 donors may be used for transplant into non-A recipients. In addition, we believe that organs from A2 donors may be used in non-A recipients where the anti-A titer is low. In order to reliably identify non-secretor A2 kidneys from cadaver donors, we have developed a rapid molecular method. The PCR-SSP-based method was developed to genotype ABO blood group and secretor status. Samples of known blood group ABO and Lewis phenotype determined by standard serological methods were used to appraise the method. A retrospective renal cadaver donor study was conducted to assess the potential of using A2 non-secretor organs for transplantation into non-A recipients. Phenotype frequencies of blood group A donors were 76% and 24% for A1 and A2 subgroups respectively, whereas 27% of the donor sample population were non-secretors. Three donors were identified as A2 non-secretors, and analysis was performed to theoretically place the organs by considering them as blood group O. These results coupled with a detailed analysis of HLA type and antibody status of our panel suggests that using A2 donors would be a useful adjunct to strategies for transplanting highly sensitized patients and redressing the donor-recipient imbalance in terms of blood group.

Sequence comparison of baboon ABO histo-blood group alleles: lesions found in O alleles differ between human and baboon

Histo-blood group O has only rarely been observed in baboon. Recent discovery of such an animal has provided use the opportunity to investigate the molecular genetics of the ABO locus in baboons. The major baboon prototype O allele, observed in two homozygous and several heterozygous animals, is related to the A allele as is the case in humans. Additional apparent prototype O alleles have been observed in heterozygotes, one of which is related to the B allele. The nucleotide changes conferring the O phenotype in the two known human O alleles have not been observed in any baboon allele. This information will aid the identification of baboons useful for the development of xenotransplantation in humans.

Advances in molecular genetics of alpha-2- and alpha-3/4-fucosyltransferases

Fucosyltransferases are involved in the last steps of the biosynthesis of ABH and Lewis oligosaccharide antigens. Seven human genes (FUT1 to FUT7) and one pseudogene (Sec 1) have been cloned and localized on different chromosomes (9q34.3; 11q21; 19p13.3 and 19q13.3). Their locations and their high degree of primary sequence identity, suggest that they have appeared by successive duplications followed by translocation and divergent evolution. Their expression is tissue specific and they present a switch during human embryo-foetal development similar to that of hemoglobins. Polymorphic genes FUT1-FUT2 and FUT3-FUT5-FUT6 are organized in two clusters and each gene is partially or totally inactivated by different types of point mutations (nonsense, missense and frame shift), complete gene deletion or a fusion gene. The products of the monomorphic genes FUT4 and FUT7 seem implicated in cell-cell interactions during embryo-foetal development and in the leukocyte adhesion phenomena to endothelial cells in the adult. A phylogenetic tree of the 28 available nucleotide coding sequences of fucosyltransferases has allowed us to situate the duplication events with respect to the separation of species from the main evolutionary path (nematods, birds, mammals, primates and humans). Recently, using a computer approach a general structure of fucosyltransferases has been proposed, inspired from the crystalline structure of the beta-glucosyltransferase of bacteriophage T4. This folding contains two domains with an alternate succession alpha and beta chains. In this model the GDP-fucose binding site would be located between the two domains.

Evidence for a new type of O allele at the ABO locus, due to a combination of the A2 nucleotide deletion and the Ael nucleotide insertion

Using a recently introduced multiplex polymerase chain reaction and restriction fragment length polymorphism ABO genotype screening method we have found an anomalous ABO genotype (A2O1variant) not correlating with the serological phenotype (blood group O). The blood group was confirmed by absorption/elution and detection of blood group substances in saliva. Sequencing of exons 6 and 7 in the ABO genes of the propositus indicated an A2 gene (C467T and C1060-) apparently inactivated by the same single nucleotide insertion recently reported in individuals with the ABO subgroup Ael. Investigation of relatives confirmed the inheritance of this new inactive hybrid allele.

Amino acid residue at codon 268 determines both activity and nucleotide-sugar donor substrate specificity of human histo-blood group A and B transferases. In vitro mutagenesis study

Histo-blood group A transferase produces A antigens and transfers GalNAc to the acceptor substrate, H structures of glycolipids and glycoproteins. B transferase transfers galactose in place of GalNAc to the same acceptor substrate to synthesize B antigens. We have previously identified four amino acid substitutions between human A and B transferases. Out of these four, substitutions at the last two positions (codons 266 and 268) were found to be crucial for the different donor nucleotide-sugar specificities between A and B transferases as analyzed by gene transfer of chimeric A-B transferase genes. In the present study, we have in vitro mutagenized codon 268 of these two transferase cDNA expression constructs (glycine and alanine in A and B transferases, respectively) and produced substitution constructs with every possible amino acid residue at this position. We examined the activity and specificity of each construct by gene transfer followed by immunodetection of A and B antigens and in vitro enzymatic assay. Amino acid substitution constructs on the A transferase backbone with alanine, serine, and cysteine expressed enzymes with A and B transferase activities. Weak A activity was detected with histidine and phenylalanine constructs while weak B activity was detected with asparagine and threonine constructs. All the other amino acid substitutions at codon 268 on the A transferase backbone showed neither A nor B activity. The glycine construct on the B transferase backbone expressed both A and B transferase activities. Some substitution constructs on the B transferase backbone maintained B activity while some other substitutions abolished the activity. These results show that the side chain of the amino acid residue at 268 of the human A and B transferases is responsible for determining both activity and nucleotide-sugar donor substrate specificity and strongly suggest its direct involvement in the recognition of and binding to the sugar moiety of the nucleotide-sugars.

[A molecular approach to the structure, polymorphism and function of blood groups]

Biochemical and molecular genetic studies have contributed to our molecular knowledge of blood group-associated molecules in the past few years. Among the 23 blood group systems presently identified, almost all have a molecular basis and present investigations are oriented towards the analysis of genetic polymorphisms, tissue-specific expression and structure-function relationships. Antigens defined by carbohydrate structures, among which ABO, Hh, Lewis and Secretor are the main representative species, are indirect gene products. They are synthesized by Golgi-resident glycosyltransferases, which are the direct products of the blood group genes. Many of these enzymes have been cloned and the molecular basis of the silent phenotypes, for instance 0, Bombay/paraBombay, Le(a-b-) and non-secretor, has been elucidated. However, the glycosyltransferases involved in the biosynthesis of Pk, P and P1 antigens are not yet characterized. A large number of blood group antigens carried by red cell polypeptides expressed at the cell surface are not related to a carbohydrate structure, and these proteins are direct blood group gene products. Most have been cloned and characterized recently, for instance MN antigens (glycophorin A), Ss antigens (glycophorin B), Gerbich antigens (glycophorins C and D) and antigens encoded by the RH, LW, KEL, FY, JK, XG, LU and XK loci. Other antigens have been located on proteins already identified, for instance the Cromer antigens on DAF, Knops antigens on CR1, Indian and AnWj antigens on CD44, Yt antigens on AChE, Diego, Wr, Rga and Warr on Band 3, Colton antigens on AQP-1 (water channel). The SC (Scianna) et DO (Dombrock) systems, however, still resist to molecular cloning. On the basis of this information, a tentative classification of blood group antigens into five functional categories is emerging: - Transporters and channels, - Receptors and ligands, - Adhesion molecules, - Enzymes, - Structural proteins. This review will focus on these recent findings and will illustrate how these studies may bring new information for analysis of normal and abnormal phenotypes and for understanding both the mechanisms of tissue specific expression and the potential function of these antigens, particularly those expressed in non-erythroid lineage. In addition, since our knowledge of the molecular basis of blood group polymorphisms has significantly increased, new genotyping techniques potentially useful in clinical applications will become available.