Although they are mainly characterized by the secretion of interleukin-17 (IL-17), Th17 cells display differential plasticity and can shift towards a Th1-like phenotype co-producing IL-17 and interferon-γ (IFN-γ) in chronic inflammatory settings.1-3 Importantly, these IFN-γ co-producing Th17 cells are emerging as key players in multiple sclerosis (MS), a chronic autoimmune inflammatory disease of the CNS. The gene discussed is IFNG; the disease is multiple sclerosis.