Studies on Alternaria allergens. IV. Biologic activity of a purified Alternaria fraction (Alt-I).

We have previously isolated a purified Alternaria fraction (Alt-I) by means of immunochemical (RAST) assays to document allergenicity. In the present study we investigated the allergenicity of Alt-I by in vivo and in vitro biologic tests in a selected group of 16 nonimmunized Alternaria-sensitive patients, all of whom had positive skin tests to crude Alternaria extract; a control group of eight nonallergic individuals was also studied. Intradermal skin-test titration endpoints to Alt-I ranged from 60 pg/ml to 60 ng/ml in the Alternaria-sensitive patients. Alt-I induced greater than 30% in vitro leukocyte histamine in all Alternaria-sensitive patients at submicrogram concentrations. Alt-I did not produce positive skin tests or induce significant leukocyte histamine release in nonallergic individuals. In 14 of 16 Alternaria-sensitive patients bronchoprovocation testing produced greater than 20% fall in forced expiratory volume in one second at Alt-I test concentrations of 0.6 to 60 micrograms/ml. In a separate prospective study of 100 unselected individuals, concordant skin-test reactions were noted to crude Alternaria extract and Alt-I in 96 instances. These results confirm that the Alt-I fraction is a biologically active, major allergenic component of crude Alternaria extract.