E variants found in Japanese and c antigenicity alteration without substitution in the second extracellular loop

BACKGROUND: The molecular basis of E variants in the Japanese population is poorly understood. In this study, molecular analysis of E variants detecte d in Japanese by serologic methods was carried out. STUDY DESIGN AND METHODS: E variants from healthy Japanese blood donors wer e screened by serologic analysis using E MoAbs. Fifteen E variant samples w ere divided into three types-EFM, EKH, and EKK-on the basis of patterns of reactivity with five distinct E antibodies. The entire coding region of the Rh cDNAs from the E variant samples was analyzed by sequencing. RESULTS: Although the Rh cDNA sequences of the three types were different f rom each other, those of the EFM-type variants (RHEFM) had a partial DNA ex change in exon 5 between the RHCE and RHD genes, generating an RHcEvariant (Gln233Glu, Met238Val). The cDNA of EKH-type variants (RHEKH) exhibited a p oint mutation (G461C) in exon 3 of the RHcE allele that resulted in an Arg1 54Thr substitution in the third external loop of the RhcE peptide. The EKK- type variant (RHEKK) carried a hybrid gene structure characterized by repla cement of exons 1-3 (or 2-3) of the RHCE gene with those of the RHD gene, T he RHD gene of a person possessing an E variant of the EKK type was also a hybrid gene, D-cE(2-3)-D or cE(1-3)-D (RHDKK). The E variants of types EKH and EKK showed weak c antigenicity. CONCLUSION: In serologic screening of 140,723 Japanese blood donors, 15 wer e found to possess E variants (0.011%). A new RHCE variant, RHEKH, was iden tified. On the basis of the variants found in this study, the c antigenicit y seemed to be determined not only by Pro-103 but also by the structure of the third extracellular loop or the amino acids contained in it.