Background: While it is well known that there is significant intraspecific variation in the content and potency of Alternaria alternata allergens, little data has been published on intraspecific variability for individual allergens from moulds.

Objective: To assess the variability of Alt a 1 expression in different strains of A alternata.

Methods: Eleven strains of A alternata were cultured in a Czapek broth medium and culture filtrate extracts were obtained. A sensitive two-site enzyme-linked immunosorbent assay was used to measure Alt a 1 concentrations in medium following 3 weeks of culture and in culture filtrate extracts.

Results: Expression of Alt a 1 was highly variable in different strains of A alternata (coefficient of variation > 135 %). A good correlation was found between Alt a 1 concentrations at the beginning of the process and measurements at the end of extract production (r = 0.940).

Conclusions: The high variability of Alt a 1 expression in different A alternata strains makes it necessary to measure Alt a 1 concentrations during the first stage of allergenic extract production in order to be able to choose a suitable strain for producing extracts or purifying Alt a 1.

Key words: Alternaria alternata. Alt a 1. Major allergen. Variability.