Differences in the intrinsic immunogenicity and allergenicity of Bet v 1 and related food allergens revealed by site-directed mutagenesis.
BACKGROUND
Birch pollen allergies are frequently associated with adverse reactions to various fruits, nuts, or vegetables, described as pollen-food syndrome (PFS) and caused by cross-reactive IgE antibodies primarily directed against Bet v 1. Specific immunotherapy (SIT) represents an effective treatment for inhalant allergies; however, successful birch pollen SIT does not correlate well with the amelioration of concomitant food allergies.


METHODS
As vaccine candidates, apple Mal d 1 as well as hazelnut Cor a 1 derivatives were designed by in silico backbone analyses of the respective allergens. The proteins were produced by site-directed mutagenesis as fold variants of their parental allergens. Because Mal d 1 and Cor a 1 form cysteine-mediated aggregates, nonaggregative cysteine to serine mutants were also generated. The proteins were characterized physicochemically, immunologically, and in in vivo models with or without adjuvant.


RESULTS
The structurally modified proteins showed significantly decreased IgE binding capacity. Notably, both in vivo models revealed reduced immunogenicity of the hypoallergenic fold variants. When formulated with alum, the monomeric cysteine mutants induced a similar immune response as the aggregated parental allergens, which is in contrast with data published on Bet v 1.


CONCLUSIONS
These findings lead to the suggestion that the Bet v 1 structure has unique intrinsic properties, which could account for its high allergenicity. Obviously, these characteristics are not entirely shared with its food homologues from apple and hazelnut. Thus, it is important to tackle pollen-related food allergies from different angles for the generation of effective vaccine candidates to treat birch PFS.
Department of Molecular Biology, University of Salzburg, Salzburg, Austria.
A
A
Roulias
U
U
Pichler
M
M
Hauser
M
M
Himly
H
H
Hofer
P
P
Lackner
C
C
Ebner
P
P
Briza
B
B
Bohle
M
M
Egger
M
M
Wallner
F
F
Ferreira
D000485:Allergens / Q000737:chemistry* / Q000276:immunology*; D000818:Animals; D052179:Antigens, Plant / Q000737:chemistry / Q000276:immunology*; D003429:Cross Reactions / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005512:Food Hypersensitivity / Q000276:immunology*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000737:chemistry / Q000276:immunology; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000276:immunology
D000485:Allergens; D052179:Antigens, Plant; C562011:Cor a 11 allergen, hazelnut; C095551:MALD1 protein, Malus domestica; D010940:Plant Proteins; D011994:Recombinant Proteins; C061312:Bet v 1 allergen, Betula
apple allergy; birch pollen-associated food allergies; hazelnut allergy; pollen-food syndrome; protein remodeling