Reduced in vivo allergenicity of Bet v 1d isoform, a natural component of birch pollen

Background: The major allergen of birch pollen, Bet v 1, is present in structurally slightly different isoforms, It has been postulated that certain isoforms show a distinct ability to bind birch pollen-specific IgE, although the T-cell response remains similar. Objective: We verified the hypothesis of a distinct allergenicity but similar T-cell immunogenicity of 2 isoforms in birch pollen-allergic subjects by in vivo tests and an in vitro assay for T-cell stimulation. Methods: Forty-eight birch pollen-allergic, 11 grass pollen-allergic, and 10 nonatopic control individuals n ere tested with 10-fold increasing concentrations (0.01 to 10.0 mu g/mL) of recombinant (r) Bet v la and rBet v Id by skin prick test (SPT), intradermal test (IDT), and conjunctival provocation test (CPT), An allergen-specific proliferation assay was performed on 21 patients with the 2 recombinant and the natural birch pollen allergens. Results: In each test system only birch pollen-allergic subjects but no controls reacted to the recombinant allergens. A positive in vivo response to 10 mu g/mL of rBet v la was observed in 21 of 48 by SPT, in 48 of 38 by IDT, and in 33 of 48 by CPT. In contrast, the IDT response to 10 mu g/mL of rBet v Id was reduced by a factor of 100 because it was equivalent to the response to 0.1 mu g/mL of rBet v la, rBet v Id failed to elicit a positive reaction in SPT and CPT The proliferative response of T cells was similar for both recombinant isoforms because 8 of 21 individuals reacted to rBet v Ia and 6 of 21 to rBet v Id. Only I subject had a positive reaction to rBet v Id alone. Conclusion: The natural isoforms rBet v la and rBet v Id differ in their ability to bind IgE but are similar in their immunogenicity for T cells. Thus rBet v Id might be a promising candidate for use in immunotherapy of birch pollen-allergic individuals.