DETECTION OF A COMMON POLYPEPTIDE-CHAIN IN I-A AND I-E SUB-REGION IMMUNOPRECIPITATES

Two-dimensional polyacrylamide gel electrophoresis of I-A and I-E sub-region antigens has indicated that all Ia antigen immunoprecipitates contain three distinct polypeptide chains. Two of these molecules show haplotype-specific differences in electrophoretic mobility, while the mobility of the third chain (mol. wt 31,000 daltons) is the same as for I-A or I-E sub-region precipitates from all six H-2 haplotypes tested. The mobility of this invariant la-associated chain (provisionally called Ii) is also not affected by different genetic backgrounds. Ii is found uniquely in Ia antigen immunoprecipitates; its lack of detectable polymorphism suggest that it is precipitated because it binds specifically to the polymorphic I-region products. Ii does not label with 125I using lactoperoxidase, and it is not yet known whether Ii is part of the native Ia molecule on the cell surface, or whether it binds to Ia antigens during extraction. © 1979.