Several studies have found an inverse correlation between helminth infection and allergic response. Our goal was to determine if the specific Th2 immune response to helminth infection would protect animals from subsequent responses to allergens.

To ascertain whether the chronicity of helminth infection had any effect on the allergic response, we infected mice either with Ascaris suum concurrent with allergen (ragweed-RW) sensitization (Ascaris/RW, Acute model), or prior to RW sensitization (Ascaris/RW, Chronic model). In both models, mice were examined for changes in ocular response after allergen challenge.

Acute infection significantly increased clinical symptoms and eosinophilia, and resulted in significant increases in antigen-specific IL-2, IFN-gamma, IL-5, and IL-6 in in vitro recall assays, as well as an increase in total IgE compared with control groups. Perhaps most strikingly, 90% of the Ascaris/RW Acute animals had evidence of eosinophil-induced blepharitis and anterior uveitis (AU). These data indicate that concomitant helminth infection is not protective in allergic eye responses, and may significantly increase the severity of the ocular inflammatory response. We repeated these studies using different infection protocols to mimic chronic infection. Interestingly, chronic Ascaris infection in RW-sensitized animals protected mice from subsequent allergic responses to RW, potentially mediated through an increase in IL-10 production.

The IL-10 induced by chronic Ascaris infection in our RW sensitized mice conferred protection from AU, resulting in reduced eotaxin levels in the blood, and a subsequent reduction in the number of eosinophils in the tissue.