CHARACTERIZATION OF A DOMINANT ANTIGENIC DETERMINANT OF PAR-O-I ENCODED BY RECOMBINANT-DNA

Background The pollens from Parietaria judaica and Parietaria officina lis are a major cause of pollinosis in Europe. Pai o I (13.5 kDa) and Par j I (12 kDa), the major allergens from these species, are highly c rossreactive. Methods We have immunoscreened a P. judaica pollen cDNA expression library with a rabbit antiserum specific for Par j I and wi th a serum pool from allergic patients. An immunopositive clone contai ning a 26 bp insert was further characterized. The insert sequence was determined and the beta-galactosidase fusion protein was partially pu rified by electroelution from sodium dodecyl sulfate-polyacrylamide ge l electrophoresis (SDS-PAGE) gels. Results This fusion protein specifi cally and extensively inhibited Par o I and Par j I binding of a rabbi t antiserum and of a serum pool obtained from allergic patients. The a ntifusion-protein antiserum obtained in a rabbit (anti 6a) specificall y precipitated radioiodinated purified Par o I in the double antibody radioimmunoassay (DARIA) and competed with antibodies of sera from all ergic patients for the binding to Parietaria pollen extract allergens by enzyme linked immunosorbent assay (ELISA). We investigated the prev alence of antibody response towards the 6a epitope in patients natural ly sensitized to Parietaria. The presence of 6a specific IgE antibodie s was assessed in the sera of 33 patients using inhibition assays. All sera had antibodies with this specificity: the extensive percentage o f inhibition reached suggested that they dominated individual ab respo nse. Conclusion In conclusion, the antibody response induced by natura l exposure to the pollen of Parietaria appears to be higly focused on a single linear antigenic determinant of the major allergens which may play a relevant role in the development of clinical allergy. This rep ort is, to our knowledge, the first description of a dominant linear e pitope of a major allergen.