Representative histological sections from murine collagen-induced arthritis study 1. In all figures, the arrowheads point to the femoral condyle (top) and tibial plateau (bottom) articular cartilages and the asterisks highlight the inflammatory cells in the soft tissue surrounding the joint. Panel (a) is from a naïve control containing no damage to the articular cartilage and few cells in the soft tissue surrounding the joint. Panel (b) is from a vehicle treated animal, demonstrating significant influx of inflammatory cells into the synovial tissue and cavity as well as significant proteoglycan loss and erosion of the articular cartilage. Panels (c) and (d) are from animals that have been dosed with CP-690550 at 15 and 1.5 mg/kg/day, respectively. At both dose levels, CP-690550 decreased cell influx, synovial hypertrophy, articular cartilage damage and proteoglycan loss. The knees from animals dosed with CP-690550 15 mg/kg/day were very similar to the knees from the naïve animals. Bar = 500 μm.