Preparation and isolation of antibodies to human MHC class II alpha chains by aid of synthetic peptides.

Antibodies against HLA Class II alpha chains were prepared by using as immunogens synthetic peptides selected from the HLA-DQ1 alpha chains sequence. Antibodies raised against peptide E2, a 15-residue fragment of the polymorphic first domain, reacted preferentially with cells with the DQ1 phenotype; however, despite the low sequence homology of this fragment with corresponding segments in DQw2 and DQw3 alpha chains, a partial crossreactivity with cells not expressing the DQw1 specificity was detected. Antibodies to peptide H, selected from the monomorphic frame, might be specific for DQ alloantigens, and presumably do not react with DR antigens. The two peptides, in addition, bind anti-Class II antibodies from the serum of a rabbit immunized with human cells, and appear to represent immunogenic linear determinants in the native glycoprotein molecule.