LU21: a new high-frequency antigen in the Lutheran blood group system.

Background and Objectives  The Lutheran blood group system comprises 18 antigens numbered LU1 to LU20, with two numbers obsolete. Thirteen antigens are of high frequency. Materials and Methods  Serological tests were performed by conventional methods. The monoclonal antibody-specific immobilization of erythrocyte antigens (MAIEA) assay was carried out with monoclonal antibodies to Lutheran glycoprotein. All exons of the LU gene were amplified by the polymerase chain reaction (PCR) and directly sequenced from genomic DNA. Results  A patient was found to have an antibody to a high-frequency red cell antigen during her second pregnancy. The antibody was shown to be Lutheran-related and was distinguished from all reported Lutheran antibodies. MAIEA suggested the antibody was defining a novel epitope in domain 1 of the Lu-glycoprotein. Sequencing of the LU gene revealed a new homozygous single-point mutation, C282G, in exon 3, encoding an Asp94Glu change in the first domain of the Lu-glycoprotein. Conclusions  The antibody detected a new high-frequency Lutheran antigen, numbered LU21, that appears to result from an Asp94Glu substitution in the first, N-terminal domain of the Lu-glycoprotein.