Physico-chemical and biologic properties of the Ascaris allergen.

Ascaris species and their soluble extracts are exceptionally active in inducing atopic sensitization in a very high proportion of exposed individuals and stimulate high levels of reaginic (IgE) antibodies in many experimental animal models. A component responsible for both stimulating reaginic antibodies and eliciting skin reactions in previously sensitized animals was isolated and purified from the crude extract by associating Sephadex gel filtration and polyvinyl chloride block electrophoresis. The allergen (Asc-1) had a molecular weight of 17,000-18,000, had an isoelectric point of 5.0-5.2, contained 8.5% carbohydrate and dissociated in polyacrylamide gel electrophoresis in SDS as a subunit with a molecular weight of 8.400. A single injection of 10 mug protein Asc-1 could stimulate reagin production in rats. Experimental A.suum infections in rats determine reaginic antibody titers ranging from 1:160 after a single infection to 1:4000 after a second infection. The reagins could be detected using Asc-1 as challenge, indicating that the allergen obtained from the crude extract was present in all stages of the parasite life cycle and was directly involved in stimulating reagin production during the migratory phase of the infection. Immunization of rats with Asc-1 in complete Freund's adjuvant completely suppressed the reagin response expected to follow after either one or two infections. Asc-1 did not act as an adjuvant for reagin production nor did an A.suum infection potentiate the reagin response to irrelevant antigens.