Background No efficient therapy for liver fibrosis has been available. This study was aimed to provide evidence that the introduction of a plasmid expressing antisense tissue inhibitor of metalloproteinase-1 (TIMP-1) into a rat model of immunologically induced liver fibrosis can result in the increased activity of interstitial collagenase, thus enhancing the degradation of collagen.Methods Real-time nested polymerase chain reaction (RT-Nested-PCR) and gene recombination techniques were used to construct a rat antisense TIMP-1 recombinant plasmid that can be expressed in eukaryotic cells. Both the recombinant plasmid and an empty vector (pcDNA3) were encapsulated with glycosyl-poly-L-lysine and injected into rats suffering from pig serum-induced liver fibrosis. The expression of exogenous transfected plasmid was assessed by Northern blot, RT-PCR, and Western blot. Hepatic interstitial collagenase activity was detected using fluorescinisothiocyanate (FITC)-labeled type Ⅰ collagen. In addition to hepatic hydroxyproline content, hepatic collagen types Ⅰ and Ⅲ were detected by immunohistochemical staining, and the stages of liver fibrosis by Van Gieson staining.Results Exogenous antisense TIMP-1 was successfully expressed in vivo and could block the gene and protein expression of TIMP-1. Active and latent hepatic interstitial collagenase activities were elevated (P