Molecular characterization of weak D phenotypes by site-directed mutagenesis and expression of mutant Rh–green fluorescence protein fusions in K562 cells.

Background and Objectives Mutations detected in 161 weak D samples from Caucasians have been classified into 16 types. Because flow cytometry using monoclonal anti-D antibodies (mAbs) has shown that weak D red cells display type-specific antigen density, these mutations in transmembranous regions have been assigned weak D phenotypes. The present study attempts to confirm or refute this assignment. Materials and Methods We amplified DNA from four Japanese weak D samples using the polymerase chain reaction (PCR), and directly sequenced the amplified DNA. Using site-directed mutagenesis, we constructed three vectors expressing mutant RHD s – G212C, V270G (weak D type 1) and G358A (type 2) – in K562 cells. The expression of RhD antigens was examined by flow cytometry using mAbs. Results A new mutation resulting in a conversion at amino acid residue 212 (Gly to Cys) was detected in a Japanese weak D sample. K562 cells transduced with mutant RhD cDNA reacted weakly in a type-specific manner with mAbs. Conclusions The mutations – G212C (new weak D type), V270G (weak D type 1) and G358A (type 2) – in transmembranous regions had obvious effects on the D epitopes recognized by mAbs. The results of this study provide direct evidence that these mutations can account for weak D phenotypes. [ABSTRACT FROM AUTHOR]