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 were tested with 10-fold increasing concentrations (0.01 to 10.0 microg/mL) of recombinant (r) Bet v 1a and rBet v 1d 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 microg/mL of rBet v 1a was observed in 21 of 48 by SPT, in 48 of 48 by IDT, and in 33 of 48 by CPT. In contrast, the IDT response to 10 microg/mL of rBet v 1d was reduced by a factor of 100 because it was equivalent to the response to 0.1 microg/mL of rBet v 1a. rBet v 1d 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 1a and 6 of 21 to rBet v 1d. Only 1 subject had a positive reaction to rBet v 1d alone.


CONCLUSIONS
The natural isoforms rBet v 1a and rBet v 1d differ in their ability to bind IgE but are similar in their immunogenicity for T cells. Thus rBet v 1d might be a promising candidate for use in immunotherapy of birch pollen-allergic individuals.
Arquint
O
O
Division of Allergology, Inselspital, Bern, Switzerland.
Helbling
A
A
Crameri
R
R
Ferreira
F
F
Breitenbach
M
M
Pichler
W J
WJ
D000328:Adult; D000485:Allergens / Q000276:immunology; D052179:Antigens, Plant; D003228:Conjunctiva; D003233:Conjunctivitis, Allergic / Q000175:diagnosis; D003941:Diagnostic Techniques, Ophthalmological; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000175:diagnosis; D010940:Plant Proteins / Q000737:chemistry / Q000276:immunology*; D011058:Pollen / Q000276:immunology*; D020033:Protein Isoforms / Q000276:immunology; D012882:Skin Tests
D000485:Allergens; D052179:Antigens, Plant; D010940:Plant Proteins; D020033:Protein Isoforms; C061312:Bet v 1 allergen, Betula