Objective: Many pathogenesis-related (PR) proteins from plants are allergenic. We review the evidence that PR proteins represent an increasingly important group of plant-derived allergens.
Data sources: A detailed literature search was conducted through PubMed and GenBank databases.
Study selection: All reports in PubMed and GenBank related to PR protein allergens for which at least partial amino acid sequence is known were included.
Results: Production of PR proteins by plants is induced in plants by stress. Members of PR-protein groups 2, 3, 4, 5, 8, 10, and 14 have demonstrated allergenicity. PR2-, 3-, 4-, and 8-homologous allergens are represented by the latex allergens. Cross-reactivity of PR3 latex allergen, Hev b 6.02, with some fruit allergens may be a reflection of the representation of homologous PR proteins among varied plants. The expression of one of the representative PR5-homologous cedar pollen allergens, Jun a 3, is highly variable across years and geographic areas, possibly because of variable induction of this PR protein by environmental factors. PR10-homologous birch pollen allergen, Bet v 1, is structurally similar to and cross-reacts with PR10 proteins from fruits (eg, Mal d 1) which cause oral allergy syndrome. PR14 allergens (eg, Zea m 14) consist of lipid transfer proteins found in grains and fruits and are inducers of anaphylaxis.
Conclusions: PR-homologous allergens are pervasive in nature. Similarity in the amino acid sequences among members of PR proteins may be responsible for cross-reactivity among allergens from diverse plants. Induced expression of PR-homologous allergens by environmental factors may explain varying degrees of allergenicity. Man-made environmental pollutants may also alter the expression of some PR protein allergens.