Basophil-derived IL-6 regulates T17 cell differentiation and CD4 T cell immunity.

Basophils are rare, circulating granulocytes proposed to be involved in T helper (T) type 2 immunity, mainly through secretion of interleukin (IL)-4. In addition to IL-4, basophils produce IL-6 and tumor necrosis factor (TNF)-α in response to immunoglobulin E (IgE) crosslinking. Differentiation of T17 cells requires IL-6 and transforming growth factor (TGF)-β, but whether basophils play a significant role in T17 induction is unknown. Here we show a role for basophils in T17 cell development by using in vitro T cell differentiation and in vivo T17-mediated inflammation models. Bone marrow derived-basophils (BMBs) and splenic basophils produce significant amounts of IL-6 as well as IL-4 following stimulation with IgE crosslink or cholera toxin (CT). In addition, through IL-6 secretion, BMBs cooperate with dendritic cells to promote T17 cell differentiation. In the T17 lung inflammation model, basophils are recruited to the inflamed lungs following CT challenge, and T17 responses are significantly reduced in the absence of basophils or IL-6. Furthermore, reconstitution with wild-type, but not IL-6-deficient, basophils restored CT-mediated lung inflammation. Lastly, basophil-deficient mice showed reduced phenotypes of T17-dependent experimental autoimmune encephalomyelitis. Therefore, our results indicate that basophils are an important inducer of T17 cell differentiation, which is dependent on IL-6 secretion.