The pro-inflammatory cytokine IL-23, composed of IL-23p19 and IL-12p40 (ref. 6), has been shown to be a key driver of pathology in various murine models of autoimmune and chronic inflammatory disease such as experimental autoimmune encephalomyelitis (EAE)7, collagen induced arthritis8 and intestinal inflammation9, 10, 11, 12. Here, IL23A is linked to experimental autoimmune encephalomyelitis.