ISOLATION AND CHARACTERIZATION OF A NOVEL 98-KD DERMATOPHAGOIDES-FARINAE MITE ALLERGEN

Background: Exposure to allergens from house dust mites is a significa nt cause of immediate hypersensitivity. Thus far, the active mite alle rgens defined are low molecular weight (MW) proteins or glycoproteins. However, other important mite allergens remain to be investigated. In this study a high MW mite antigen with a high IgE-binding activity wa s characterized. Methods: An Anti-Dermatophagoides farinae (Df) monocl onal antibody, mAb642, which recognized a 98-kd allergenic mite protei n, was used for affinity chromatography, The purified Df642 was charac terized biochemically and immunologically. Results: Competitive ELISA demonstrated that mAb642 was inhibited by the interaction between seru m IgE from allergic patients and Df642 antigen in a dose-dependent fas hion. The IgE reactivity to both 98-kd and 92-kd components was remove d or diminished by preincubation of asthmatic sera with Df642-coated C NBr-activated cellulose-4B gel. Two-dimensional immunoblot analysis re vealed that there are at least 4 isoforms of Df642 that represent a mi nor component in the crude mite extract. The allergenicity of Df642 wa s assayed by IgE immunoassay with a large panel of 67 sera from asthma tic patients with positive skin reactions, and Df 642 showed positive IgE reactivity with more than 80% of the sera tested. Thus it should b e classified as an important allergen. In addition, amino acid sequenc e analysis revealed that Df642 shares more than 50% homology,vith para myosin from invertebrates. Conclusion: We have identified and characte rized a 98-kd house dust mite allergen that showed greater than 80% Ig E reactivity with sera from patients allergic to mites. This is the fi rst high MW allergen characterized to date, and it shares high sequenc e homology with paramyosins in invertebrates.