Novel glycolipid variations revealed by monoclonal antibody immunochemical analysis of weak ABO subgroups of A

Identification of a novel A2 allele through nt543 substitution

BACKGROUND

ABO blood system has many subgroups. In A group, A₁ phenotype and A₂ phenotype are more common, and A₂ is caused by deletion or substitution in A¹ allele (ABO*A1.01).

METHODS

Based on standard ABO serological test, the subject was identified as A₂ phenotype. Direct sequencing and ABO gene cloning were performed to analyze the allele.

RESULTS

The subject had one A^1v allele (ABO*A1.02) and one O allele. The haplotype sequencing analysis of each allelic clone demonstrated that allele 1 was A^1v (ABO*A1.02) allele with nt543 variation (543 G > C) and allele 2 was O^1v allele (ABO*O.01.02) with nt261 deletion and nt220 variation.

CONCLUSION

The 543 G > C nucleotide substitution of the present A^1v allele (ABO*A1.02) shares the same sequence variation site with A^x allele (ABO*AW.33) (543 G > T), and both 543 G > C and 543 G > T nucleotide substitutions encode the same amino acid change of tryptophan to cysteine. Mechanism, such as allelic enhancement, has been proposed to explain this controversial phenotype-genotype relationship. But in present case, there has been no B allele to enhance the expression of A_x to that expected of A₂, so there could be another novel underlying mechanism to be investigated.

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.

Genetic Sequencing Analysis of A307 Subgroup of ABO Blood Group

BACKGROUND The aim of this study was to investigate the serology and gene sequence characteristics of the A307 subgroup of the ABO blood group. MATERIAL AND METHODS Monoclonal anti-A and anti-B antibodies were used to detect the ABO antigens of a proband whose positive blood type was not consistent with the negative blood type of the ABO blood group. Standard A-, B-, and O-negative typing cells were used to test for ABO antibodies in the serum. Additionally, polymerase chain reaction with sequence-specific primer (PCR-SSP) was used to confirm the genotype, and subsequently, exons 6 and 7 of the ABO gene were detected by gene sequencing. Samples from the wife and daughters of the proband were also used for serological and genetic testing. RESULTS Red blood cells of the proband showed weak agglutination reaction with anti-A antibody, while anti-B antibody was detected in the serum. Moreover, PCR-SSP detected A307 and O02 alleles, while gene sequencing revealed mutation of c.745C>T in exon 7, which produced a polypeptide chain p.R249W. The A307 gene of the proband was not inherited by his daughters. CONCLUSIONS A mutation (c.745 C>T) in exon 7 of the ABO blood group gene resulted in low activity of a-1,3-N-acetyl-galactosaminyl transferase, producing A3 phenotype.

Forssman expression on human erythrocytes: biochemical and genetic evidence of a new histo-blood group system

In analogy with histo-blood group A antigen, Forssman (Fs) antigen terminates with α3-N-acetylgalactosamine and can be used by pathogens as a host receptor in many mammals. However, primates including humans lack Fs synthase activity and have naturally occurring Fs antibodies in plasma. We investigated individuals with the enigmatic ABO subgroup A(pae) and found them to be homozygous for common O alleles. Their erythrocytes had no A antigens but instead expressed Fs glycolipids. The unexpected Fs antigen was confirmed in structural, serologic, and flow-cytometric studies. The Fs synthase gene, GBGT1, in A(pae) individuals encoded an arginine to glutamine change at residue 296. Gln296 is present in lower mammals, whereas Arg296 was found in 6 other primates, > 250 blood donors and A(pae) family relatives without the A(pae) phenotype. Transfection experiments and molecular modeling showed that Agr296Gln reactivates the human Fs synthase. Uropathogenic E coli containing prsG-adhesin-encoding plasmids agglutinated A(pae) but not group O cells, suggesting biologic implications. Predictive tests for intravascular hemolysis with crossmatch-incompatible sera indicated complement-mediated destruction of Fs-positive erythrocytes. Taken together, we provide the first conclusive description of Fs expression in normal human hematopoietic tissue and the basis of a new histo-blood group system in man, FORS.

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.

Modification of red blood cells for laboratory quality control use

PURPOSE OF REVIEW

This review describes the current state-of-the-art with respect to the modification of red blood cells for creating quality controls for use in immunohaematology.

RECENT FINDINGS

The author has identified five technologies able to create modified red blood cells potentially suitable for use in quality control. Two of the technologies use enzymes, glycosidases or glycosyltransferases, to modify red blood cells and create ABO quality control cells. A third technology uses polyethylene glycol to reduce antigen expression by masking epitopes, whereas a fourth technology is speculative and involves the in-vitro generation of genetically modified erythroid cells. None of these four technologies are in routine use to make commercially available quality controls. A fifth commercially available technology creates quality controls by adding synthetic blood group A and B antigens (FSLs) to group O red blood cells, creating what are referred to as 'kodecytes'. This technology is also being used to add blood group peptides onto red cells for use in the future in a range of diagnostic applications.

SUMMARY

Transducing cell-derived erythroid populations with blood group encoding or silencing vectors, and the use of FSLs to create kodecytes, are two technologies with the potential to provide quality controls for laboratory use.

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.

An extensive polymerase chain reaction-allele-specific polymorphism strategy for clinical ABO blood group genotyping that avoids potential errors caused by null, subgroup, and hybrid alleles

BACKGROUND

ABO genotyping is complicated by the remarkable diversity at the ABO locus. Recombination or gene conversion between common alleles may lead to hybrids resulting in unexpected ABO phenotypes. Furthermore, numerous mutations associated with weak subgroups and nondeletional null alleles should be considered. All known ABO genotyping methods, however, risk incorrect phenotype predictions if any such alleles are present.

STUDY DESIGN AND METHODS

An extensive set of allele-specific primers was designed to accomplish hybrid-proof multiplex polymerase chain reaction (PCR) amplification of DNA fragments for detection of ABO alleles. Results were compared with serologic findings and ABO genotypes defined by previously published PCR-restriction fragment length polymorphism/PCR-allele-specific polymorphism (ASP) methods or DNA sequencing.

RESULTS

Phenotypically well-characterized samples from blood donors with common blood groups and rare-subgroup families were analyzed. In addition to the commonly encountered alleles (A1, A1(467C>T), A2, B, O1, O1v, and O2), the new method can detect hybrid alleles thanks to long-range amplification across intron 6. Four of 12 PCR-ASP procedures are used to screen for multiple infrequent subgroup and null alleles. This concept allows for a low-resolution typing format in which the presence of, for example, a weak subgroup or cis-AB/B(A) is indicated but not further defined. In an optional high-resolution step, more detailed genotype information is obtained.

CONCLUSION

A new genotyping approach has been developed and evaluated that can correctly identify ABO alleles including nondeletional null alleles, subgroups, and hybrids resulting from recombinational crossing-over events between exons 6 and 7. This approach is clinically applicable and decreases the risk for erroneous ABO phenotype prediction compared to previously published methods.