Asthma is a predominantly TH2 cell–dominated inflammatory disease characterized by airway inflammation and a major public health concern affecting millions of persons. The Tec family tyrosine kinase IL-2–inducible T-cell kinase (Itk) is primarily expressed in T cells and critical for the function and differentiation of TH cells. Itk−/− mice have a defective TH2 response and are not susceptible to allergic asthma.
We sought to better understand the role of Itk signaling in TH differentiation programs and in the development and molecular pathology of allergic asthma.
Using a murine model of allergic airway inflammation, we dissected the role of Itk in regulating TH cell differentiation through genetic ablation of critical genes, chromatin immunoprecipitation assays, and house dust mite–driven allergic airway inflammation.
Peripheral naive Itk−/− CD4+ T cells have substantially increased transcripts and expression of the prototypic TH1 genes Eomesodermin, IFN-γ, T-box transcription factor (T-bet), and IL-12Rβ1. Removal of IFN-γ on the Itk−/− background rescues expression of TH2-related genes in TH cells and allergic airway inflammation in Itk−/− mice. Furthermore, small hairpin RNA–mediated knockdown of Itk in human peripheral blood T cells results in increased expression of mRNA for IFN-γ and T-bet and reduction in expression of IL-4.
Our results indicate that Itk signals suppress the expression of IFN-γ in naive CD4+ T cells, which in a positive feed-forward loop regulates the expression of TH1 factors, such as T-bet and Eomesodermin, and suppress development of TH2 cells and allergic airway inflammation.