Immunization with Ascaris suum extract impairs T cell functions in mice.

The effect of an Ascaris suum extract (Asc) on several T cell functions was studied in mice immunized with Asc and ovalbumin (OA) in complete Freund's adjuvant. Delayed-type hypersensitivity reactions following challenge with aggregated OA were markedly diminished in mice injected with OA plus a high dose of Asc compared to OA-immunized animals. Proliferation and IL-2, IFN-gamma, IL-4, and IL-10 production in OA-stimulated lymph node cells from the OA + Asc-immunized group were also inhibited. Titration of anti-OA antibodies also showed suppression of IgG1, IgG2a, and IgE isotypes in the animals injected simultaneously with the extract. The degree of suppression induced by Asc on OA-specific cell-mediated responses was dose dependent. The profile of cytokines synthesized in response to Asc also changed depending on the injected dose. IL-4 and IL-10 were mainly produced in response to high doses, whereas IL-2 and IFN-gamma were greatly enhanced at a low dose of Asc. These findings indicate that the A. suum extract may impair crucial T cell functions for cell-mediated as well as humoral immune responses to other antigens through the induction of a predominantly Th2-like response.