Characterization of Api g 1.0201, a new member of the Api g 1 family of celery allergens

Background: The association of pollinosis with allergy to plant foods occur s in up to 70% of tree pollen-allergic patients. In recent years, some of t he relevant crossreacting proteins have been characterized at the molecular and immunological level. Api g 1 has been identified as the celery homolog ue of the major birch pollen allergen, Bet v 1. Although a number of Bet v 1 isoforms have been characterized from birch pollen, little is known about isoforms of food allergens and their allergenic features. Methods: Api g 1 .0201, an isoform of Api g 1, was isolated from a cDNA library, cloned and sequenced. The cDNA was expressed in Escherichia coli and the purified reco mbinant protein was tested in immunoblots. Results: Api g 1.0201 displays 7 2% sequence similarity to the previously identified Api g 1.0101 and consis ts of 159 amino acid residues. The sequence of Api g 1.0201 has five additi onal amino acid residues at the carboxy-terminus as compared to Api g 1.010 1. Purified recombinant Api g 1.0201 is recognized by IgE from the sera of celery-allergic patients, as well as by the murine monoclonal anti-Bet v 1 antibody. In general, this isoform displays a weaker IgE-binding capacity t han Api g 1.0101, as concluded from immunoblotting experiments. Results fro m inhibition assays revealed that IgE-binding to Api g 1.0201 is only sligh tly reduced by preincubation with either purified recombinant Api g 1.0101 or purified recombinant Bet v 1 a. Total inhibition was only achieved when using purified natural Bet v 1. Conclusions: At present, little is known ab out the IgE-binding capacity of isoforms of Bet v 1 homologues of food alle rgens. Identification and characterization of such isoforms may help to con tribute to a better understanding of food allergy and the observed cross-re activity to pollen allergy. Copyright (C) 2000 S. Karger AG. Basel.