Rh alloimmunization in chronically transfused patients with thalassemia receiving RhD, C, E, and K matched transfusions.

Chronically transfused patients with thalassemia are at risk for red cell alloimmunization. No studies have specifically examined alloimmunization after implementation of prophylactic Rh (D, C, E) and K matched red cells in a racially diverse population of thalassemia patients and donors. This retrospective study examined Rh antibodies among 40 chronically transfused patients (Asian, White, Black, Indian, Middle Eastern) with thalassemia receiving a mean of 174 serologic prophylactic RhD, C, E, and K matched red cell units. We examined the patients' RH genotype, as well as donor race and Rh phenotypes over 3 transfusion events preceding antibody detection. Eighteen alloantibodies were detected in 13 of 40 patients (32.5%), with an alloimmunization rate of 0.26 antibodies per 100 units transfused. Thirteen antibodies (72.2%) were directed against Rh (5 anti-D, 4 anti-C, 2 anti-E, 1 anti-e, 1 anti-V), despite donor phenotypes that confirmed lack of transfusion of D, C, or E antigens to patients lacking the corresponding antigen(s). Ten of 40 patients had an altered RH genotype, but the Rh antibodies were not associated with patients with variant RH. Black donors with a known high frequency of RH variants provided 63% of the units transfused in the 3 visits preceding unexplained anti-Rh detection. Rh alloimmunization not explained by the thalassemia patients' RH genotype or the donors' serologic phenotype suggests more precise matching is needed, and the role of donor RH genotypes on alloimmunization should be explored. Extending Rh D, C, and E matching to include c and e would result in better-matched units and further minimize Rh alloimmunization.

A DOB allele encoding an amino acid substitution (Phe62Ser) resulting in a Dombrock null phenotype.

BACKGROUND: The gene polymorphisms responsible for the antigens Doa, Dob, Hy, and Joa in the Dombrock (Do) blood group system have been identified. Four different mutations have been reported to cause the Dombrock null [Gy(a-)] phenotype. These include splice mutations, an eight-nucleotide deletion, and insertion of a stop codon. Here a Dombrock null caused by a single-amino-acid substitution in the full-length protein is reported. STUDY DESIGN AND METHODS: DOA and DOB were determined by polymerase chain reaction-restriction fragment length polymorphism, and DO (ART4) exons and flanking regions were sequenced from genomic DNA. Expression analysis was performed by transfection of wild-type and mutant cDNAs into HEK 293T cells followed by flow cytometry and immunoblotting. Homology modeling was used to map the mutation on the protein structure. RESULTS: The patient's sample carried nt 793G/G, indicating a DOB/DOB background. Exon 2 sequencing showed the sample carried a new mutation, nt 185T>C, causing a Phe62Ser substitution. This variant Do was not expressed on the surface of transfected HEK 293T cells. The mutation maps to a highly conserved FDDQY motif located between the beta1-strand and alpha1-helix near the COOH terminus in the native molecule. CONCLUSIONS: The Dombrock null reported here is due to a single Phe62Ser mutation. The expression data confirmed that 62Ser is responsible for lack of cell surface Do, and protein modeling suggests the mutation disrupts important aromatic side chain interactions between Phe62 and His160. Production of an antibody to a high prevalence Dombrock antigen (anti-Gya) in this patient was consistent with complete absence of Dombrock/ART4 protein.

Anti-Vel reactivity diminished by adsorption with rabbit RBC stroma.

BACKGROUND: An anti-Vel, nearly missed in antibody identification studies, and the effect of a commercially available rabbit RBC stroma (RESt, Immucor) adsorptions on eight anti-Vel sera are reported. Anti-Vel is an antibody to an antigen of high prevalence. CASE REPORT: A 48-year-old woman with chronic vaginal bleeding presented with a Hct of 14.7 percent. The transfusion service was not informed of her history of anti-Vel when she was transferred from another institution. Studies performed on an emergency request for transfusion were interpreted as a cold autoantibody as adsorption with a commercial source of RESt eliminated the reactivity. Stored anti-Vel sera were tested by titration studies before and after adsorption with commercial RESt. RESULTS: Serum from the index case did not react after adsorption with RESt at the transfusion service. Studies with the stored anti-Vel indicated antibody adsorption with four of four samples at immediate spin (IS) and room temperature (RT) phases, four of eight samples at 37 degrees C in albumin (ALB) phase, and four of eight samples at ALB-IgG-AGT phase. Variations in antibody reactivity were observed in the samples tested, but RESt adsorption diminished antibody reactivity in most samples. All eight stored sera demonstrated some reactivity in at least one phase after adsorption with RESt. CONCLUSION: Anti-Vel was completely or partially adsorbed by RESt. Caution should be used when interpreting cold agglutinins with this method. The manufacturer warns that uncommon alloantibodies may be adsorbed.