Quality and potency profile of eight recombinant isoallergens, largely mimicking total Bet v 1-specific IgE binding of birch pollen.

BACKGROUND: To date only limited information on structure, expression levels and IgE binding of Bet v 1 variants, which are simultaneously expressed in birch pollen, is available.

OBJECTIVE: To analyze and compare structure and serum IgE/IgG binding of rBet v 1 variants to Bet v 1.0101.

METHODS: Recombinant Bet v 1 variants were studied with sera of 20 subjects allergic to birch pollen. Folding, aggregation and solubility of the rBet v 1 variants was analyzed to attribute diverging IgE binding to either allergen structure or methodological features. IgE/IgG binding was studied with rBet v 1 in solution or adsorbed to solid phases. Allergen-mediated crosslinking of FcεRI receptors was determined by mediator release of sensitized humanized rat basophil leukemia cells.

RESULTS: All variants, except for rBet v 1.0113, were monomeric and had Bet v 1-type conformation. Serum IgE binding to variants adsorbed to solid phase was reduced to 6.6% - 36.5% compared with Bet v 1.0101. In contrast, inhibition of IgE binding to Bet v 1.0101 by rBet v 1 variants ranged from 62% - 83%. Similarly, mediator release ranged from 30.7% - 55.2% for all variants and was only clearly reduced for rBet v 1.0301 (10.4%). The IgE binding potency of rBet v 1 variants representing their native quantities in birch pollen was only slightly lower compared to extract. IgG binding to variants was between 50.9% - 134.5% compared with rBet v 1.0101 (100%).

CONCLUSION AND CLINICAL RELEVANCE: Bet v 1 variants previously classified as hypoallergenic can exhibit similar functional IgE binding as Bet v 1.0101. Eight rBet v 1 variants largely reproduce total Bet v 1-specific IgE binding of birch pollen extracts. Assay format dependent variation of IgE binding properties needs to be considered in the development of diagnostic or therapeutic products. This article is protected by copyright. All rights reserved.