TIMP-1-/- mice are more susceptible to CCl4-induced chronic liver injury. Wild-type and TIMP-1-/- mice were treated with CCl4 for 4 weeks, and euthanized at various time points after the last injection. A, Serum ALT levels were assayed. B, The liver sections were stained with H&E and representative pictures are shown (original magnification × 100). C, D, TUNEL positive hepatocytes were counted (C) and representative pictures of TUNEL staining are shown (D). *P < 0.05.