Diagnosis of Alternaria alternata sensitization with natural and recombinant Alt a 1 allergens.

BACKGROUND: Diagnosis of Alternaria alternata sensitization is hampered by the variability and complexity of fungal extracts, and thus simplification of the diagnostic procedures with purified allergens should be pursued.
OBJECTIVE: We sought to compare A alternata extract and purified natural Alt a 1 (nAlt a 1) and recombinant Alt a 1 (rAlt a 1) allergens for their diagnostic value.
METHODS: Forty-two patients allergic to A alternata , 10 atopic patients with negative skin prick test responses to A alternata extract, and 10 healthy subjects were investigated. Skin prick tests and determination of specific IgE levels were performed with nAlt a 1 and 2 different types of rAlt a 1: rbAlt a 1, expressed in Escherichia coli , and ryAlt a 1, expressed in the yeast Yarrowia lipolytica .
RESULTS: Prevalence for Alt a 1, Alt a 2, and Alt a 11 by IgE dot-blot testing was 98%, 0%, and 15%, respectively, and therefore Alt a 1 was used as a marker for A alternata sensitization. Immunoblotting and inhibition analysis showed no IgE-binding differences between nAlt a 1 and rAlt a 1. The whole group of patients with allergy to A alternata had positive skin test reactions to purified allergens at 100 microg/mL, whereas no false-positive reactions were detected. Natural or ryAlt a 1 elicited a similar response in skin tests compared with A alternata extract, although a reduced reactivity was observed with rbAlt a 1. Specific IgE levels to nAlt a 1 or rAlt a 1 showed significant correlation and similar sensitivity and specificity.
CONCLUSIONS: Alt a 1, either in its natural or recombinant form, is sufficient for a reliable diagnosis of A alternata sensitization and induces skin prick reactivity comparable with that produced by A alternata extract.