MOLECULAR MAPPING OF THE CROMER BLOOD-GROUP CR-A AND TC-A EPITOPES OFDECAY-ACCELERATING FACTOR - TOWARD THE USE OF RECOMBINANT ANTIGENS INIMMUNOHEMATOLOGY

Cromer blood group antigens reside on the complement regulatory protei n decay accelerating factor (DAF, CD55). Th is glycosyl-phosphatidylin ositol-anchored glycoprotein is widely distributed, especially among c ell types in contact with plasma. Numerous Cromer blood group antigens have been defined using alloantibodies induced by transfusion or preg nancy. However, few pairs of antithetical antigens have been described in this system, presumably because of the rarity of the low-frequency alleles. Analysis of polymerase chain reaction-amplified genomic DNA showed that the Cr(a-) phenotype has a Ala(193) --> Pro substitution i n short consensus repeat 4 (SCR4) of DAF, and the Tc(a-b+) phenotype h as a Arg(18) --> Leu substitution in SCR1 of DAF. The locations of Cra and Tca epitopes were confirmed by analysis of Chinese hamster ovary cell transfectants expressing a Cr(a-) allele-specific transfectant an d a chimeric protein containing only SCR1 of DAF, respectively. Overal l, these studies further show the usefulness of an approach based on r ecombinant proteins in mapping blood group antigen epitopes and identi fying blood group antibodies. (C) 1994 by The American Society of Hema tology.