Evidence for the association of I-A and I-E molecules in d-haplotype mice.

Previous studies using sequential immunoprecipitation indicated the existence of two I-E molecules in d-haplotype mice. Using N-terminal amino acid radiosequence analysis, we have shown that the sequence of the alpha- and beta-chains from the I-E molecule, which is immunoprecipitated by a monoclonal antibody (14.4.4S), is consistent with that determined for the gene of the I-Ed molecule. The material, which is immunoprecipitated by an anti-I-Ed alloantiserum [(B10 X D2.GD)F1 anti-B10.D2] after preclearing with 14.4.4S, has a N-terminal amino acid sequence consistent with it being a mixture of the I-Ed and I-Ad alpha- and beta-chains. The amount of I-Ad varied with each preparation, ranging from 15 to 40% of the total. Nonequilibrium pH gradient gel electrophoresis fractionation of the beta-chain pool precipitated by the alloantiserum yielded two molecules. One molecule had an Ad beta N-terminal amino acid sequence and the other had an Ed beta N-terminal sequence. The existence of antibodies cross-reactive with I-A in the anti-I-E alloantiserum were ruled out because this antiserum could not immunoprecipitate any I-Ad molecules from a D2.GD spleen cell lysate. Therefore, we conclude that the alloantiserum is recognizing determinants that are formed by an interaction between I-Ad and I-Ed molecules or their subunits.