Bro p 3, an nsLTP1: The first major allergen identified in Broussonetia papyrifera pollen.

BACKGROUND

Broussonetia papyrifera pollen is an important cause of allergy worldwide, yet its key allergenic components remain unclear. This study aims to identify and characterize the major allergen of B.papyrifera pollen.

METHODS

Patients with allergic rhinitis (AR) symptoms in B.papyrifera pollen season and positive skin prick test (SPT) to B.papyrifera pollen extract were enrolled. Serum sIgE was measured by ImmunoCAP. The pollen crude extract was immunoblotted with patients' sera. The major allergen was purified and subjected to mass spectrometry analysis. The cDNA of the allergen was cloned from a pollen cDNA library. The antigenicity of recombinant allergen was measured by ELISA. Overlapping peptides spanning the allergen were synthesized. Type 2 T cell epitopes were screened using patients' PBMC by IL-4 ELISpot. Cross-reactivity of the allergen was evaluated.

RESULTS

B. papyrifera-sIgE was confirmed in 194 of 201 patients by ImmunoCAP. Bro p 3 was identified as major allergen by immunoblot. We purified, cloned the cDNA of, and determined the full-protein sequence of Bro p 3, an nsLTP1 with an average mass of 10264 Da. Recombinant Bro p 3 (rBro p 3) exhibited identical antigenicity as natural Bro p 3, with sensitization rates of 74.53 % and 78.89 %, respectively. Peptides Pep 7-21, Pep 10-24 and Pep 13-27 stimulated IL-4 secretion by T cells from 8, 9 and 8 out of 11 patients. Bro p 3-sIgE sensitization was significantly correlated to elevated sIgE of B. papyrifera, Morus alba, Morus. rubra, and Humulus scandens. It was also associated with the concurrence of conjunctivitis and conjunctivitis plus asthma. No IgE binding was found to the other two B.papyrifera nsLTPs. Bro p 3 inhibited the IgE binding to M. alba and H. scandens pollen extracts.

CONCLUSIONS

We demonstrated that Bro p 3 is the major allergen of B. papyrifera pollen and the first allergen from this species with its full sequence determined. The I7-R27 peptides of Bro p 3 represent its immunodominant type 2 T cell epitopes. Bro p 3 sensitization is relevant to clinical phenotypes and the cross-reactivity between M. alba, H. scandens and B.papyrifera pollen.