Purification and characterization of an 18-kd allergen of birch (Betula verrucosa) pollen: Identification as a cyclophilin

Background: Five birch pollen allergens have been identified so far. In a p revious study we detected new birch pollen allergens with an isoelectric po int in the range 9.0 to 9.3, present only in extracts prepared at controlle d basic pH. Objective: The purpose of the current study was to purify and characterize those allergens. Methods: The target allergens were purified by ion exchange and hydrophobic interaction chromatography. Analyses were carried out by SDS-PAGE, isoelec tric focusing, immunoblotting, and amino acid sequencing. The in vivo react ivity of the allergens was evaluated by skin testing. Results: An 18-kd protein, which we named Bet v 7, was purified. This 18-kd protein corresponded to 3 bands on isoelectric-focusing immunoblots that p robably represent isoforms. On immunoblots up to 20.8 % of birch pollen-all ergic patients recognized those allergens. The clinical relevance of Bet v 7 was demonstrated by positive immediate-type skin testing on a patient all ergic to birch pollen. Sequencing of an internal peptide yielded an amino a cid sequence showing high homology with various plant cyclophilins. The rot amase activity of the protein, inhibited by cyclosporin A, further confirme d that Bet v 7 belongs to the group of cyclophilins. Conclusion: We have purified a novel allergen of birch pollen, Bet v 7, bel onging to the cyclophilin family. Because cyclophilins are highly conserved proteins over the phylogeny, we may postulate that Bet v 7 is a member of a new family of panallergens.