FN1 and Arthritis: To be sure that this discrepancy was not related to the difference in species, type of arthritis or source of synovial fibroblasts (synovial fluid versus synovial tissue), we treated murine arthritic synovial fibroblasts with DMSO, PF-562,271 or PF-573,228 (as described above) and then allowed them to migrate across fibronectin-coated transwells for 4 hours.