[Molecular and functional characterization of allergens: fundamental and practical aspects].

Well-defined allergens are a prerequisite for the exact diagnosis and immunotherapy of Type I (IgE-mediated) allergic diseases. The allergens have to be available in highly purified form and in sufficient quantities. By applying molecular cloning methods this goal can be achieved with respect to both characterization and reproducibility of allergen preparations. Moreover, this technique leads to the deduction of primary structures of allergens, which allows computer-aided comparisons with already known amino acid sequences. Significant sequence similarities with well-described proteins may point to a biological and biochemical function of the cloned allergen. The major allergen of white birch, Bet v 1, and its close relatives from alder, hazel, and hornbeam belong to a family of pathogenesis-related proteins ubiquitous in angiosperms. Based on these results, a percentage of food intolerance can now be regarded as Type I allergy due to Bet v 1-related proteins. By sequence comparisons, Bet v 2, another birch pollen allergen, was identified as the ubiquitous cytoskeleton-associated protein, profilin. For its high sequence conservation and its ubiquitous appearance in allergenic sources of plant origin, profilin was shown to represent a pan-allergen. Recombinant non-fusion Bet v 1 revealed identical immunological properties with respect to interaction with both antibodies and Bet v 1-specific T cell clones when compared with natural Bet v 1 purified from birch pollen.