Molecular, serologic, and functional evidence for an apparent HLA-DR triplet.

During routine typing procedures the individual GER was demonstrated to possess an unusual class II phenotype exhibiting three DR serotypes (DR1, DR2, DRw6). Closer serologic examination on this person's family showed that the DR1 and DR2 antigens segregated together on one haplotype. Biochemical evidence will be presented that the B cell line derived from the individual GER expresses five distinct types of DR molecules. Antigen presentation studies proved that the DR molecules carrying either DR1, DR2, or DRw6 (DRw13) allodeterminants are not only coordinately expressed but also are functional. No evidence could be found for altered DQ expression. The implications of these findings for the evolutionary aspects of the MHC class II region will be discussed.