MMP9 and Chronic colitis: In accordance with a concept viewing MMP13 as a proteolytic activator of proinflammatory non-matrix substrates such as CCL2, CCL7, TNFα and pro-MMP9 (15–17, 26), Mmp13-/- mice in our study showed endoscopic signs of reduced chronic colitis which was confirmed by histopathological analysis demonstrating lower numbers of CD45+ immune cells.