Standardization of Alternaria alternata:: Extraction and quantification of Alt a 1 by using an mAb-based 2-site binding assay

Background: Alternaria alternata is recognized as an important cause of allergic disease. As with other molds, the extracts of A alternata used for diagnosis and therapy are highly heterogeneous, and there is a need for improved standardization. The major allergen Alt a 1 is well characterized and has been produced as a recombinant protein, but very few data are available on the Alt a 1 content in extracts. Objective: An assay for the quantification of Alt a 1 was developed and used for monitoring batch-to-batch consistency of A alternata extracts, and the correlation between skin prick test responses and Alt a 1 concentrations was studied. Methods: A 2-site binding assay based on an Alt a 1-specific mAb was developed and used for the quantification of Alt a 1 in allergen extracts. Quantitative skin prick tests were performed on 16 A alternata-sensitive patients and correlated with the Alt a 1 concentration. Results: The Alt a 1-specific mAb was found to be suitable for affinity purification, as well as for a 2-site binding quantification assay. In allergen extracts the Alt a 1 content was estimated as 2% to 4.7% of total protein. Quantitative skin prick tests showed an Alt a 1 concentration-dependent response. Conclusion: Quantification of Alt a 1 in A alternata extracts reflects their batch-to-batch consistency Skin prick test responses to a standardized A alternata extract correlate with the Alt a 1 contents. An extract containing 3.7 mu g/mL Alt a 1 caused a response equal to that of a 1% histamine dihydrochloride solution.