Depletion of CD4+ CD25+ T cells switches the whey-allergic response from immunoglobulin E- to immunoglobulin free light chain-dependent

Background Symptoms of allergy are largely attributed to an IgE-mediated hypersensitivity response. However, a considerable number of patients also exhibit clinical features of allergy without detectable systemic IgE. Previous work showed that Ig-free light chains (IgLC) may act as an alternate mechanism to induce allergic responses. CD4(+) CD25(+) T cells are crucial in the initiation and regulation of allergic responses and compromised function might affect the response to allergens. Objective To examine the contribution of CD4(+) CD25(+) T cells and IgLC towards the whey-allergic response. Methods Mice were sensitized orally with whey using cholera toxin as an adjuvant. CD25(+) T cells were depleted in vivo using a CD25 mAb. The acute allergic skin response to whey and ex vivo colon reactivity was measured in the presence or absence of F991, a specific inhibitor of IgLC. Serum whey-specific antibodies and IgLC in serum and mesenteric lymph node (MLN) supernatants were measured. Depletion of CD4(+) CD25(+) T cells was confirmed in the spleen. Results Anti-CD25 treatment strongly reduced whey-specific antibody levels and resulted in a partial depletion of effector T cells and a major depletion of Foxp3(+) regulatory T cells. Surprisingly, despite the abolished specific IgE response, the acute allergic skin response to whey was not affected. IgLC levels were enhanced in the serum and MLN supernatants of CD25-depleted sensitized mice. F991 inhibited the acute skin response and colon hyperreactivity in anti-CD25-treated mice, indicating that these responses were mainly IgLC dependent. Conclusions Depletion of CD4(+) CD25(+) T cells resulted in a switch from an IgE- to an IgLC-dependent acute skin response and functional hyperresponsiveness of the colon. Our data suggest that CD25(+) T cells play a crucial role in balancing cow's milk allergy between IgE and IgE- independent responses and both mechanisms might play a role in allergic responses to the same allergen.