A novel blood group B subgroup: serological and genetic studies

Abstract

A discrepancy in the ABO blood groups between a newborn child and her parents was identified. Serological and DNA investigative techniques were performed. A weak variant of B (B(w)) was detected on the erythrocytes of the child, her grandmother and great-uncle. Adsorption-elution studies showed that their erythrocytes adsorb and yield anti-B on elution. The B(w) antigenic strength of the A(1)B(w) cells of her mother and maternal aunt was reduced when compared to that of the A(2)B(w) from another family member. Only one of 15 different anti-B sera agglutinated the A(1)B(w) erythrocytes. Agglutinin anti-B that reacted strongly with normal B erythrocytes and did not agglutinate the B(w) cells, was found in the sera of the A(1)B(w) individuals. The B(w) serum glycosyltransferase could not convert O cells into B cells and no B substance was found in saliva. All family members with the B(w)/AB(w) phenotypes were heterozygous for a B allele and DNA sequencing revealed a novel missense mutation in exon 7 of the B allele (556A > G), resulting in M186V. This substitution changes a highly conserved region of the enzyme, proposed to be a disordered loop near the enzyme cleft, and is expected to diminish the enzyme's activity, leading to this B(w) phenotype.

ABO reverse grouping: effect of varying concentrations of the enzyme bromelain

“…The density of B epitopes on the cell surface and the structure of the various glycoconjugates to which they are attached affects the ability of anti-B antibodies to interact with normal B and B subgroup red cells. 20 At 0.5% bromelain, the reagent A cells appeared to be over-sensitised by the enzyme as there were two falsepositive reactions at this concentration. Although antibody detection increases with increased bromelain concentration, false-positive reactions are also increased.…”

“…However, other research indicates that there is a relationship between the ABO antigen-antibody reaction and the concentration of enzyme (bromelain) used. 20,21 As there are a greater number of antigen sites on A 1 cells (~0.81-1.17 x 10 6 ) than on B cells (0.75 x 10 6 ), reagent B cells tend to generate more ABO failures during ABO reverse grouping. 11 From the failure rates obtained at varying bromelain concentrations (Table 2), as concentration increases generally reagent B cell reactions are improved (fewer false negatives in this category).…”

“…20 In the same way, the avidity of anti-A, anti-B and anti-A,B in the immune system varies between individuals, thus affecting reagent red cell agglutination and making some ABO failures inevitable.…”

“…This proved that a weak variant of B existed on either the mother's or the father's erythrocytes (originally thought to be blood group A and blood group O, respectively) and thus confirmed parenthood. 20 Another study showed that bromelain has a significant effect on ABO reverse-grouping reactions when a microplate agglutination method was devised for blood grouping and reverse typing without the need for centrifugation. 21 From the mean SPC values obtained at varying bromelain concentrations (Table 3), it can be seen that the reaction between reagent cells and donor plasma is improved and cell agglutination is improved as bromelain concentration increases.…”

Structural basis for red cell phenotypic changes in newly identified, naturally occurring subgroup mutants of the human blood group B glycosyltransferase

“…The molecular basis underlying many of these B subgroup alleles has been studied and more than 20 B weak (B w ) alleles have been reported so far. [12][13][14][15][16][17][18][19][20][21][22][23] Typically, these phenotypes result from missense mutations at the ABO locus resulting in single amino acid changes in the B-enzyme. Variant glycosyltransferases associated with weak A or B subgroups, however, have not yet undergone structural analysis to resolve the conformational basis for these phenotypes.…”