A mechanism for the initiation of allergen-induced T helper type 2 responses

Both metazoan parasites and simple protein allergens induce T helper type 2 (T(H)2) immune responses, but the mechanisms by which the innate immune system senses these stimuli are unknown. In addition, the cellular source of cytokines that control T(H)2 differentiation in vivo has not been defined. Here we showed that basophils were activated and recruited to the draining lymph nodes specifically in response to T(H)2-inducing allergen challenge. Furthermore, we demonstrate that the basophil was the accessory cell type required for T(H)2 induction in response to protease allergens. Finally, we show that basophils were directly activated by protease allergens and produced T(H)2-inducing cytokines, including interleukin 4 and thymic stromal lymphopoietin, which are involved in T(H)2 differentiation in vivo.