Isolation and partial characterization of Fes p 4 allergen.

More than 75% of grass pollen-allergic patients produce specific IgE antibodies against group-4 allergens. Purification and characterization of different grass group-4 allergens should help to further understand their allergenicity. In this study, an attempt was made to isolate and characterize Fes p 4 allergen by several biochemical and immunochemical methods. Fes p 4 was purified by a combination of chromatographic techniques (gel permeation and ion exchange chromatography). Isolated protein revealed four main spots at a molecular weight of 60 kDa and a pI ranging from 8.7 to 9.1. Eight sera were selected from patients with positive result of skin prick test to the mixture of grass pollen extracts. ELISA inhibition technique was used to study Fes p 4-specific IgE in the patients' sera. ELISA to Festuca pratensis was inhibited up to 80% by F. pratensis pollen extract and up to 48% by Fes p 4. 2D-PAGE-immunoblot was used to identify allergenic and antigenic components of Fes p 4 with patients' IgE and monoclonal antibodies (MABs). Three components of purified protein expressed IgE binding ability. Two MABs which recognized unrelated regions on Phl p 4, bound three components of Fes p 4. The role of the carbohydrate moiety in allergenicity was examined with individual patient sera by using periodate-treated Fes p 4. Six out of eight patients reduced IgE binding to periodate-treated allergen. Isolated Fes R 4 glycoprotein consisted of four components, three of which were allergenic, and share common epitopes specific for grass group-4 homologs. The results of periodate oxidation of Fes p 4 suggest that the carbohydrate moiety is involved in IgE binding.