Novel RHD alleles with weak hemagglutination and genetic Exon 9 diversity: weak D Types 45.1, 75, and 76

Characterization of Novel RHD Allele Variants and Their Implications for Routine Blood Group Diagnostics

The Rh system, including the highly immunogenic D antigen, is one of the clinically most important blood group systems in transfusion medicine. Numerous alleles of the RHD gene are associated with variant RhD phenotypes. In case of Rh incompatibility, some of them can induce hemolytic transfusion reactions and hemolytic disease of the fetus and newborn. Thus, accurate blood group diagnostics are critical for safe transfusion therapy. We characterized phenotypes of four individuals revealing weakened D expression during routine pre-transfusion testing. Standard gel card matrix techniques with monoclonal and polyclonal anti-D antibodies were used for serological typing, complemented using D epitope and antigen density analysis. Genotyping employing PCR with sequence-specific primers, genomic and allele-specific Sanger sequencing and in silico protein analysis were performed. Four novel RHD alleles associated with weak D or partial D phenotypes were identified. One of the mutations is predicted to disrupt the terminal stop codon and result in an elongated translation of the mutant D protein that phenotypically exhibits a loss of D epitopes. Furthermore, a hybrid gene formed with the homologue RHCE gene is described. The presented data enhances the understanding of the Rh system and may contribute to continued advances in blood group diagnostics.

Rh flow cytometry: An updated methodology for D antigen density applied to weak D types 164 and 165

BACKGROUND

An original methodology for determining the D antigen density on red cells was published in 2000 and has been applied in many publications since. This flow cytometry-based assay remained largely unrevised utilizing monoclonal anti-Ds that are not readily available anymore. We updated the methodology to quantify erythrocyte D antigen sites using microspheres and monoclonal anti-Ds that are commercially available today.

METHODS

The absolute D antigen density of a frozen standard CcDEe cell, drawn in 2003, a fresh blood donation from the same individual, drawn in 2022, and an internal control CcDEe cell, was quantified by flow cytometry using fluorescence-labeled microspheres. The internal control CcDEe cell was used in conjunction with 9 commercial anti-Ds to determine D antigen densities of 7 normal D, 4 partial D, and 11 weak D type samples, including 2 novel alleles.

RESULTS

The reproducibility of the updated assay was evaluated with red cells of published D antigen densities. The current results matched the known ones closely. The new weak D types 164 and 165 carried 4500 and 1505 D antigens/red cell, respectively. The absolute D antigen density decreased from 27,231 to 26,037 in an individual over 19 years.

DISCUSSION

The updated assay gave highly reproducible results for the D antigen densities of Rh phenotypes. Readily available anti-Ds allowed for the determination of the D antigen densities of 7 weak D types. The assay is suitable to evaluate the effects of distinct amino acid substitutions on the RhD phenotype.

Aberrant ABO B Phenotype with Irregular Anti-B Caused by a Para-Bombay FUT1 Mutation

Background

Routine ABO blood group typing for pre-transfusion testing of a male Austrian patient of Far Eastern origin showed discrepant results with an apparently weak blood group B phenotype and irregular anti-B.

Materials and Methods

ABH phenotyping and cross-matching was done by standard serologic techniques and levels of H expression were determined by flow cytometry. ABO gene sequencing including regulatory regions as well as analysis of FUT1 (H), FUT2 (Secretor), and FUT3 (Lewis) were carried out.

Results

While monoclonal ABO antigen typing indicated blood group O, weak agglutination reactions using polyclonal human anti-B and anti-AB were seen. In reverse typing at room temperature, the plasma was reactive with A1 and A2 RBCs and negative with B and O cells, whereas at 4°C, anti-B reactivity was found. The indirect anti-globulin cross-match of the patient's plasma was positive with group B RBCs and negative with group O RBCs. Sequencing analysis showed the presence of ABO*B.01 (B114) allele and homozygosity for the FUT1 mutation c.551_552delAG. Flow cytometry demonstrated trace amounts of H antigen on the patient's RBCs.

Conclusion

While a functional B allele was found, analysis of FUT1 and FUT2 genes revealed the presence of a rare para-Bombay genotype O_h^B. Interestingly, no anti-H but irregular anti-B was found in the patient's plasma, responsible for the positive cross-match with group B RBCs. Even though very rare and not reported for the European population, the presence of an H-deficient phenotype should be considered when investigating individuals with an unusual ABO blood group type.