Molecular and biochemical classification of plant-derived food allergens.

Molecular biology and biochemical techniques have significantly advanced the knowledge of allergens derived from plant foods. Surprisingly, many of the known plant food allergens are homologous to pathogenesis-related proteins (PRs), proteins that are induced by pathogens, wounding, or certain environmental stresses. PRs have been classified into 14 families. Examples of allergens homologous to PRs include chitinases (PR-3 family) from avocado, banana, and chestnut; antifungal proteins such as the thaumatin-like proteins (PR-5) from cherry and apple; proteins homologous to the major birch pollen allergen Bet v 1 (PR-10) from vegetables and fruits; and lipid transfer proteins (PR-14) from fruits and cereals. Allergens other than PR homologs can be allotted to other well-known protein families such as inhibitors of alpha-amylases and trypsin from cereal seeds, profilins from fruits and vegetables, seed storage proteins from nuts and mustard seeds, and proteases from fruits. As more clinical data and structural information on allergenic molecules becomes available, we may finally be able to answer what characteristics of a molecule are responsible for its allergenicity.