Higher pH level, corresponding to that on the skin of patients with atopic eczema, stimulates the release of Malassezia sympodialis allergens

Background: The opportunistic yeast Malassezia is a trigger factor in atopic eczema (AE). Around 30-80% of patients with AE have an IgE and/or T-cell reactivity to the yeast. Several IgE-binding components have been identified in Malassezia extracts and 11 allergens have been cloned and sequenced. The pH of the skin surface in patients with AE is higher than that of normal healthy skin. We here investigate whether different pH conditions mimicking those of AE skin and healthy skin can influence the production and release of Malassezia allergens. Methods: Malassezia sympodialis (ATCC strain 42132) was cultured in Dixon broth at pH 6.1 to 5.0 for 1-15 days. Culture supernatants were analysed for the presence of IgE-binding components by immunoblotting. The M. sympodialis cells were analysed for allergen expression and production with immunocytochemistry and quantitative polymerase chain reaction. Results: We found that M. sympodialis cells produce, express and release allergens to a greater extent when cultured at the higher pH. This was particularly true of a 67-kDa major allergen designated Mala s 12. Conclusions: The data suggest that the skin barrier in AE patients provides an environment that can enhance the release of allergens from M. sympodialis, which can contribute to the inflammation.