While IL-17A and IL-17F appear to play overlapping, yet distinct roles in host defense against bacterial and fungal infections8–11, IL-17A has attracted much attention owing to its implication in several autoimmune diseases, including psoriasis, psoriatic arthritis, ankylosing spondylitis, rheumatoid arthritis, multiple sclerosis and non-infectious uveitis12–14. Here, IL17A is linked to rheumatoid arthritis.