The kinase Itk is normally required for differentiation of IL-17-producing CD4 T-helper (Th)17 cells however, Elmore, Carter et al. now report that Itk can be bypassed during Th17 differentiation in Saccharopolyspora rectivirgula induced hypersensitivity pneumonitis. The gene discussed is CD4; the disease is hypersensitivity pneumonitis.