Fibroblast-like synoviocytes in inflammatory arthritis pathology: The emerging role of cadherin-11

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease affecting the joint synovium. The normal synovium consists of a lining layer of fibroblast-like synoviocytes (FLS) and macrophages, one to three cells deep that overlies the loose connective tissue of the synovial sublining. During the course of RA, the synovium is the site of inflammation where immune cells are massively infiltrated, and the lining layer becomes hyperplastic and transforms into a pannus tissue that destroys articular cartilage and bone. FLS play an important role in this RA pathogenesis. In this review, we explain that cadherin-11, an adhesion molecule, is selectively expressed on FLS and required for synovial lining formation. In addition, cadherin-11 on FLS contributes to synovial inflammation and mediates cartilage degradation in a mouse model of inflammatory arthritis. Therefore, we suggest that FLS are critical regulators of synovial inflammation and arthritis pathology via mechanisms that are mediated by cadherin-11.