In contrast to OA, RA is characterized by severe inflammation and synoviocyte infiltration.9 Given that Fap+ synovial fibroblasts are known to play key roles in RA72 and that genetic deletion of Fap significantly ameliorates articular cartilage damage in a mouse model of RA,50 it is intriguing to test whether Fap inhibitors could also be used to treat RA in the future. Here, FAP is linked to rheumatoid arthritis.