Activation of c-Kit in dendritic cells regulates T helper cell differentiation and allergic asthma

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Abstract
Dendritic cells (DCs) are integral to the differentiation of T helper cells into T helper type 1 TH1, TH2 and TH17 subsets. Interleukin-6 (IL-6) plays an important part in regulating these three arms of the immune response by limiting the TH1 response and promoting the TH2 and TH17 responses. In this study, we investigated pathways in DCs that promote IL-6 production. We show that the allergen house dust mite (HDM) or the mucosal adjuvant cholera toxin promotes cell surface expression of c-Kit and its ligand, stem cell factor (SCF), on DCs. This dual upregulation of c-Kit and SCF results in sustained signaling downstream of c-Kit, promoting IL-6 secretion. Intranasal administration of antigen into c-Kit–mutant mice or neutralization of IL-6 in cultures established from the lung-draining lymph nodes of immunized wild-type mice blunted the TH2 and TH17 responses. DCs lacking functional c-Kit or those unable to express membrane-bound SCF secreted lower amounts of IL-6 in response to HDM or cholera toxin. DCs expressing nonfunctional c-Kit were unable to induce a robust TH2 or TH17 response and elicited diminished allergic airway inflammation when adoptively transferred into mice. Expression of the Notch ligand Jagged-2, which has been associated with TH2 differentiation, was blunted in DCs from c-Kit–mutant mice. c-Kit upregulation was specifically induced by TH2- and TH17-skewing stimuli, as the TH1-inducing adjuvant, CpG oligodeoxynucleotide, did not promote either c-Kit or Jagged-2 expression. DCs generated from mice expressing a catalytically inactive form of the p110δ subunit of phosphatidylinositol-3 (PI3) kinase (p110D910A) secreted lower amounts of IL-6 upon stimulation with cholera toxin. Collectively, these results highlight the importance of the c-Kit–PI3 kinase–IL-6 signaling axis in DCs in regulating T cell responses.

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