A recombinant Sal k 1 isoform as an alternative to the polymorphic allergen from Salsola kali pollen for allergy diagnosis.

BACKGROUND: The incidence of Amaranthaceae pollen allergy has increased due to the desertification occurring in many countries. In some regions of Spain, Salsola kali is the main cause of pollinosis, at almost the same level as olive and grass pollen. Sal k 1 - the sensitization marker of S. kali pollinosis - is used in clinical diagnosis, but is purified at a low yield from pollen. We aimed to produce a recombinant (r)Sal k 1 able to span the structural and immunological properties of the natural isoforms from pollen, and validate its potential use for diagnosis. METHODS: Specific cDNA was amplified by PCR, cloned into the pET41b vector and used to transform BL21 (DE3) Escherichia coli cells. Immunoblotting, ELISA, basophil activation and skin-prick tests were used to validate the recombinant protein against Sal k 1 isolated from pollen. Sera and blood cells from S. kali pollen-sensitized patients and specific monoclonal and polyclonal antisera were used. RESULTS: rSal k 1 was produced in bacteria with a yield of 7.5 mg/l of cell culture. The protein was purified to homogeneity and structural and immunologically validated against the natural form. rSal k 1 exhibited a higher IgE cross-reactivity with plant-derived food extracts such as peanut, almond or tomato than with pollen sources such as Platanus acerifolia and Oleaceae members. CONCLUSIONS: rSal k 1 expressed in bacteria retains intact structural and immunological properties in comparison to the pollen-derived allergen. It spans the immunological properties of most of the isoforms found in pollen, and it might substitute natural Sal k 1 in clinical diagnosis.

A pectin methylesterase as an allergenic marker for the sensitization to Russian thistle (Salsola kali) pollen.

BACKGROUND: Chenopodiaceae pollen is considered the main cause of pollen allergy in desert countries and its incidence is world-wide increasing by the desertization of extensive zones. Although the correlation between the sensitization to Chenopodium album and Salsola kali pollens of patients suffering from allergy to Chenopodiaceae pollens is high, a significant number of patients exhibited IgE sensitivity exclusively towards S. kali. OBJECTIVE: To analyse this differential reactivity and to purify, clone and characterize the putative responsible allergen. METHODS: Immunoblotting was used to analyse the IgE binding to pollen extract for S. kali and C. album. The protein was isolated by two chromatographic steps and characterized by Edman degradation, mass spectrometry, finger print analysis and Concanavalin A lectin staining. Specific cDNA was amplified by polymerase chain reaction, cloned in Escherichia coli and sequenced. Immunologic characterization was performed by immunoblotting, enzyme-linked immunoassay detection and inhibition experiments using sera from 11 patients allergic to S. kali pollen. RESULTS: cDNA codifies for a mature protein of 339 amino acids plus a putative signal peptide of 23 residues and it belongs to the plant pectin methylesterase (PME) family. It is a mildly basic and polymorphic protein and was recognized by the IgE from all the patients allergic to S. kali included in the study, and was called Sal k 1. The protein was not recognized in the C. album pollen extract using the sera of these patients. CONCLUSION: Sal k 1 is a protein from the PME family with a high allergenic relevance. Considering this allergen as responsible for the different sensitization between S. kali and C. album pollen, it may be a useful marker to classify patients allergic to Chenopodiaceae allowing a safer and more specific immunotherapy.