Background: English plantain (Plantago lanceolata L.) and olive (Olea europaea L.) pollens are important causes of pollinosis in large areas of North America, Australia, and the Mediterranean basin. The major pollen allergens of both plants, Pla l 1 and Ole e 1, share 38.7% of their amino acid sequences.

Objective: To analyze putative cross-reactivity between these 2 proteins.

Methods: Several antibodies and patients’ sera were used in immunoblot and immunocytochemistry experiments.

Results: Two anti-Pla l 1antibodies were able to bind to 3 polypeptides from olive pollen protein extracts, which correspond to the 3 glycosylation isoforms of Ole e 1 (18-22 kDa) previously described. Moreover, Pla l 1 protein was found in the cytoplasm of both the
vegetative and the generative cells of P lanceolata mature pollen. On olive pollen sections, these anti-Pla l 1 antibodies displayed signifi cant labeling in the cytoplasm of the vegetative cell and in both the exine and the material adhering to this outer layer of the pollen wall.
In addition, the anti-Ole e 1 antibody 10H1 was found to cross-react with proteins of similar masses (16-20 kDa) to Pla l 1 variants. In Plantago pollen sections, the 10H1 antibody recognized proteins located in the cytoplasm of both the vegetative and generative cells. Cross-reaction was confirmed using sera from patients allergic to either plant pollen.

Conclusion: Both allergens share common epitopes, which can be cross-recognized by different antibodies and sera from different patients, although this antigenic similarity seems to have little clinical relevance.

Key words: Cross-reactivity. Localization. Ole e 1. Pla l 1. Pollen.