MMP13 and arthritic joint disease: IFN-γ-stimulated arthritis induced a marked increase in MMP-3, MMP-12 and MMP-13 mRNA levels in the cartilage layers of both WT controls and p47phox-/- mice, in comparison with the cartilage of naive knee joints (Δ Ct ranging from 3 to 9) (Fig. 6a,b).