Histology. For histological assessment of arthritis, total ankle joints from 15-week-old mice were isolated and fixed for 4 days in 4% formaldehyde, then decalcified in 5% formic acid and embedded in paraffin. Tissue sections of 7 μm were stained using H&E to study the inflammatory cell influx and chondrocyte death or using safranin O to determine proteoglycan depletion and cartilage and bone destruction. Each parameter was scored on a scale from 0 to 3 by 2 independent observers in a blinded manner. At least 4 junctions per tissue section and 4 sections per ankle joint were scored.