Identification of the amino acid residues contributing to monoclonal antibody-defined DQw1 epitopes.

The reactivity of monoclonal antibodies (mAbs) R1, S1, and S5, shown previously to recognize polymorphic epitopes on HLA-DQ molecules, have been found to correlate with the presence of certain DQB1 alleles. mAb S5 reacts with cells expressing DQB1*0503, 0601, 0602, 0603, or 0604 alleles while R1 and S1 react with all DQB1 alleles except *0201 and 0301. In the case of R1 and S1, sequence comparison of these chains suggests the involvement of residues 45-47 (GVY) in formation of the epitopes. This prediction has been confirmed by showing that a G----E mutation in position 45 of the DQB1*0302 gene eliminates binding of both mAbs.