Regulation of type 2 immunity by basophils.

The immune response against helminths and allergens is generally characterized by high levels of IgE and increased numbers of Th2 cells, eosinophils, and basophils. Basophils represent a relatively rare population of effector cells and their in vivo functions are incompletely understood. Recent studies with basophil-depleting antibodies revealed that these cells might play an important role during the early and late stages of type 2 immune responses. To further characterize the relevance of basophils for protective immunity and orchestration of allergic inflammation, we generated constitutively basophil-deficient mice. We observed a normal Th2 response induced by helminth infections or immunization with alum/OVA or papain/OVA. However, basophils contributed to worm expulsion during secondary helminth infection and mediated an IgE-dependent inflammatory response of the skin. These results argue against a critical role of basophils as antigen-presenting cells for induction of Th2 polarization and highlight their effector cell potential during later stages of a type 2 immune response.