Three Ia species with different structures and alloantigenic determinants in an HLA-homozygous cell line.

Abstract

Three distinct molecular subsets with different structures and alloantigenic determinants were identified in human Ia antigens from cells of an HLA-Dw7 homozygous cell line. The subsets carried DR7 specificity, BR4X7 supertypic specificity and MB2 supertypic specificity, respectively, and were immunospecifically separated by the use of operationally monospecific alloantisera. These specificities showed HLA-linked segregation in families, and they were distributed in the population according to different but partially overlapping patterns. On peptide mapping analysis, the 3 subsets showed marked differences in the .beta.-chains. The .alpha.-chains of the DR7 and BR4X7 subsets were very similar to each other; the .alpha.-chains of the MB2 subset were distinguishable from those of DR7 and BR4X7. The presence of a minimum of 3 HLA-linked loci is indicated: DR locus, a locus that encodes BR4X7 and a locus that encodes MB2 and the 3-loci concept for the genetic control of human Ia antigens is substantiated.