CHARACTERIZATION OF AN HLA-DQ2-SPECIFIC MONOCLONAL-ANTIBODY - INFLUENCE OF AMINO-ACID SUBSTITUTIONS IN DQ-BETA-1(ASTERISK)0202

The HLA-DQ(alpha 1()0501,beta 1(*)0201) and -DQ(alpha 1(*)0501,beta 1 ()0202) (i.e., DQ2) heterodimers are probably involved in the pathoge nesis of celiac disease and several other HLA-DQ-associated diseases. To obtain a tool for studies of these molecules, a mAb of the IgG1 iso type, 2.12.E11, was produced by immunization with purified DQ(alpha 1( )0501,beta 1(*)0201) molecules and murine NIH 3T3 cells transfected w ith both DQA1()05011 and DQB1(*)0202. Panel cell studies with HLA hom ozygous B-lymphoblastoid cells and HLA-transfected murine cells demons trated that 2.12.E11 bound only to cells expressing HLA-DQ beta 1()02 01 or 0202, irrespective of the accompanying DQ or chain (i.e., DQ alp ha 1()0501 or DQ alpha 1(*)0201). Another DQ2-specific mAb (XIII 358. 4) and the broadly HLA class-II-reactive mAb Tu39 strongly inhibited b inding of 2.12.E11. Epitope mapping employing mutants with single aa s ubstitutions of DQ beta 1()0202 indicated that position 37 may be of some importance for 2.12.E11 binding. A triple mutant (45G-->E, 46E--> V, 47F-->Y) failed to bind 2.12.E11, suggesting a crucial role for one or more of these residues in the epitope. However, the expression of the mutant beta chain could not be formally proved, as none of the DQ2 -reactive mAbs recognized this transfectant.