Shared allergenic and antigenic determinants in Alternaria and Stemphylium extracts

Alternaria and Stemphylium extracts were compared by means of various immunochemical and biologic methods. Skin-test responses to Alternaria and Stemphylium in allergic patients were positively correlated, and RAST binding values with the sera of 30 patients utilizing solid-phase Alt-I, Alternaria (70% ammonium sulfate-precipitable fraction), and Stemphylium allergens showed significant correlation, giving evidence for the presence of common allergenic determinants among these three extracts. In RAST inhibition assays, Alternaria and Stemphylium extracts exhibited dose-related inhibition with solid-phase Stemphylium, Alternaria, and Alt-I, confirming the presence of Alt-I as the major shared allergenic fraction in the two extracts. In repetitive absorption experiments, both Alt-I and Alternaria solid-phase allergens absorbed Stemphylium-specific IgE antibodies from a 12-person serum pool. Similarly, Stemphylium solid-phase allergen absorbed both Alternaria- and Alt-I -specific IgE antibodies. Double-antibody radioimmunoassay for Alt-I showed higher Alt-I activity in Stemphylium than in Alternaria extract. In double-immunodiffusion experiments with rabbit anti-Alt-I antibodies, both Stemphylium and Alternaria extracts produced precipitin lines of identity with Alt-I. The antigenic relationship of the two crude extracts was further confirmed by crossed and crossed-line immunoelectrophoresis experiments. Our results showed that Alternaria and Stemphylium extracts contain multiple shared allergenic and antigenic determinants, including Alt-I.