MONOCLONAL-ANTIBODIES AGAINST DERMATOPHAGOIDES GROUP-I ALLERGENS AS PSEUDO-CYSTATINS BLOCKING THE CATALYTIC SITE OF CYSTEINE PROTEINASES

The enzyme allergens Der p I and Der f I produced by the house dust mi tes Dermatophagoides pteronyssinus and D. farinae display partial sequ ence homology with other members of the cysteine proteinase superfamil y. We report that certain widely used mouse mAbs against these Group I allergens indeed crossreact with the plant enzymes papain, bromelain and ficin. The recognition sites of these anti Group I mAbs comprise c onformational and thermolabile epitopes involved in molding the cataly tic center of the proteinases. Thus, the mAbs inhibit the enzymatic hy drolysis of specific chromogenic substrates by the Group I allergens, while specific cysteine proteinase inhibitors abolish the recognition of the enzymes by the mAbs. Similarly, activation of the thiol-proteas es with L-cysteine abrogates their binding in the two-site mAb system, indicating that the mAbs recognize a proenzyme conformational peptide epitope. It follows that mAb-based assays for mite Group I components can neither detect the allergens after inactivation, nor in their ful ly activated forms.