FN1 and rheumatoid arthritis: Fibronectin fragments have been detected in cartilage and synovial fluid samples from patients with RA or OA [15] and are thought to play a role in cartilage destruction in arthritis by stimulating chondrocytes to produce matrix metalloproteinases (MMPs) as well as multiple cytokines and chemokines, including IL-1, IL-6, IL-8, monocyte chemotactic protein-1, and growth-related oncogene family members [5,16,17].