Characterization of GYP*Mur and novel GYP*Bun-like hybrids in Thai blood donors reveals a qualitatively altered s antigen.

Background and objectives The Mi(a+) GP(B-A-B) hybrid phenotypes occur with a prevalence of 2%-23% across Southeast Asia. While the s antigen is alleged to be altered, no evidence for specific variants is known. Screening using a monoclonal IgM anti-s mistyped six S-s+ RBC units as S-s-. Further, alloanti-s was identified in an S+s+ patient. Our objective was to investigate the s antigen further. Materials and methods DNA from 63 Thai blood donor samples PCR-positive for aGYP(B-A-B)hybrid was sequenced with primers spanningGYPBexons 3-4. Flow cytometry was used for semiquantitative analysis of s expression and correlated with the glycophorin genotype. Results DNA sequencing showed thatGYP*Murwas carried by 56/63 samples (88 center dot 9%) of which 5/56 lacked normalGYPB: three of these wereGYP*Murhomozygotes, one was a compound heterozygote carryingGYP*Murand aGYP*Bun-like allele (designatedGYP*Thai), and the fifth sample carriedGYP*Murand anotherGYP*Bun-like allele. Seven samples (7/63) wereGYP*Thaiheterozygotes. IgM monoclonal anti-s (P3BER) did not react with the s antigen carried by GP.Mur or GP.Bun, whereas two IgG anti-s showed enhanced reactivity. Conclusions We confirmed thatGYP*Muris the most frequent variant in Thai blood donors and also identifiedGYP*Thaiwith a frequency of 1 center dot 1%. We showed that s antigen on Mi(a+) GP(B-A-B) hybrids is qualitatively altered and should be considered when selecting reagents for phenotyping where such hybrids are prevalent, endemically and in blood centres worldwide.