An unusual variant glycophorin expressing protease-resistant M antigen encoded by the GYPB-E(2-4)-B hybrid gene.

Background And Objectives: MNS is a highly polymorphic blood group comprising 49 antigens recognized by International Society of Blood Transfusion, some of which may have been generated by genomic recombination among the closely linked genes GYPA, GYPB and GYPE. The GYPE gene has an almost identical sequence to GYPA*01 allele in exon 2 (99% homology), which accounts for M antigen. We investigated an unusual glycophorin molecule with protease-resistant M antigen.

Methods: Blood samples were screened by an automated blood typing system (PK7300) using bromelain-treated red blood cells (RBCs) and murine monoclonal anti-M. The M-positive RBC samples were analysed by immunoblotting using anti-M as the primary antibody. GYPA, GYPB and GYPE genes were analysed by polymerase chain reaction (PCR), cloning and sequencing using reticulocyte mRNA and genomic DNA.

Results: Serological tests and immunoblotting revealed that 103 of the 193 009 individuals (0·0534%) expressed protease-resistant M-active glycophorin having a molecular weight of 20 kDa. All the 103 individuals were S+ s- or S- s+. When reticulocyte mRNA from the individuals with M-active glycophorin (20 kDa) was examined by PCR and cloning followed by sequencing, a novel GYPE-B hybrid transcript was identified. Long-range PCR and sequencing using genomic DNA revealed that the individuals had a GYPB-E(2-4)-B hybrid gene. This hybrid gene was predicted to encode a 59-amino-acid mature glycoprotein that expresses no S or s antigens CONCLUSIONS: The prevalence of the M-active glycophorin (20 kDa) in the Japanese population is 0·0534%. This glycophorin is predicted to be a 59 amino acids polypeptide encoded by the novel GYPB-E(2-4)-B hybrid gene.