Nizzoli and colleagues recently demonstrated that pathogenicity of IL-17-secreting cells isolated from Crohn’s disease (CD) patients and from colitic animals were directly dependent on Interferon-γ (IFN-γ) secretion, as demonstrated by the reduced colitogenic activity of Th17 cells isolated from IFN-γ-/- mice [22]. The gene discussed is IL17A; the disease is Crohn disease.