And some groups identified FSTL1 as a new proinflammatory mediator that contributes to rheumatoid arthritis by promoting the expression of TNFα, IL-1β, IL-6 and IL-8, as well as by enhancing the interferon-γ (IFN-γ) signaling pathway in a mouse model [22,31,32]. Here, FSTL1 is linked to rheumatoid arthritis.