The Russian Thistle (Salsola kali) pollen major allergen, Sal k 1, can be quantified in allergenic extracts and airborne pollen.

BACKGROUND

Russian thistle (Salsola kali) pollen is an important cause of pollinosis in areas where rainfall is not abundant. Our aim was to develop an ELISA for quantification of the major allergen of S. kali extracts, Sal k 1, and to assess the correlation of this allergen content with the allergenic activity of extracts.

METHODS

Sal k 1 was purified by ion exchange and gel permeation chromatography and identified by mass spectrometry. Monoclonal antibody 4C11 was used for capture at 5 microg/ml and biotin-labeled specific antiserum at 0.25 microg/ml served for detection. The allergenic activity of the pollen extracts was measured by enzyme allergosorbent test inhibition.

RESULTS

Sal k 1 reacted to 85% of sera from 40 S. kali-allergic patients and was able to inhibit 92% of the IgE-binding capacity of patients' serum pool to the whole extract. The ELISA had a lineal range between 1.25 and 20 ng/ml of purified Sal k 1. The intra- and interassay coefficients of variation were lower than 5 and 10%, respectively. The assay was very sensitive since it had a detection limit of 0.08 ng/ml. No reactivity was found outside the Amaranthaceae family where only Kochia and Salicornia sp. gave significant reactivity. A good correlation (Spearman's rho = 0.92) was obtained between Sal k 1 content of different S. kali extracts and their IgE-binding activity.

CONCLUSIONS

The results proved the usefulness of the two-site sandwich ELISA for aeroallergen control and for the standardization of S. kali pollen extracts intended for clinical use.