A comparative analysis of the cross‐reactivity in the polcalcin family including Syr v 3, a new member from lilac pollen

Background: Polcalcins are pollen‐specific allergens with two EF‐hand calcium‐binding sites that exhibit strong cross‐reactivity. Our objective was to isolate and express the cDNA coding of the EF‐hand calcium‐binding allergen from lilac pollen and to study cross‐reactivity with other polcalcins from related and nonrelated pollen sources with different specific antibodies and sera from two different populations. Methods: Specific cDNA was amplified by PCR, cloned and expressed in Escherichia coli. Purification was achieved by gel permeation and ion exchange chromatographies. ELISA titration and inhibition assays were performed using the recombinant forms of Syr v 3, Ole e 3, Che a 3 and Phl p 7 with sera from two Spanish regions with different sensitization profiles, as well as Phl p 7‐ and Ole e 3‐specific polyclonal rabbit antisera, and an Ole e 3‐specific monoclonal antibody. Results: Syr v 3 displays two EF‐hand consensus sites and 8863 Da of theoretical molecular mass. The allergen consists of 80 residues with identities ranging from 66 to 87% with polcalcins included in this study. Syr v 3, Ole e 3, Che a 3 and Phl p 7 showed a similar IgG‐ and IgE‐binding capacity although differences at quantitative level were observed depending on the population of patients’ sera. Conclusion: Syr v 3 is a polcalcin with structural and antigenic similarities to the members of this family. Diagnosis of polcalcin‐sensitized patients could be performed whatever polcalcin used, whereas for immunotherapy, primary sensitization to a particular allergenic source should be considered.