Monoclonal antibody 1a3 recognizes a monomorphic epitope unique to DQ molecules.

Monoclonal antibody 1a3 reacts with a unique monomorphic epitope present only on DQ molecules as determined by immunoprecipitation, two-dimensional gel analysis and partial N-terminal amino acid sequencing. This monomorphic epitope is found on DQ molecules of all homozygous B lymphoblastoid cell lines tested, including those that type as either DQw1, DQw2, DQw3, or DQ "blank." Analysis of the predicted secondary structure of class II molecules indicates that the regions most likely to constitute an antigenic determinant are variable in DQ molecules, possibly accounting for the rarity of antibodies to monomorphic DQ epitopes.