Role of the spleen in liver fibrosis in rats may be mediated by transforming growth factor beta-1

BACKGROUND: The effect of the spleen on the cirrhotic liver is unknown. Transforming growth factor-beta 1 (TGF-beta 1), which plays a crucial role in the matrix production during liver fibrosis, is an inhibitory factor regarding the regeneration of hepatocytes. In this study, we investigated the TGF-beta 1 production in the spleen of cirrhotic rats and the effects of a splenectomy on the healing process from liver fibrosis. METHODS: Thirty-six Wistar male rats were used. Thioacetamide (TAA) was administered intraperitoneally for 24 weeks. The rats underwent either a sham operation (TAA + Sham) or a splenectomy (TAA + SPL). The improvements in liver fibrosis and liver regeneration were investigated 10, 30 and 60 days after the operations in each group. The effect of a splenectomy on the plasma concentration of TGF-beta 1 in the portal vein was investigated by ELISA. The TGF-beta 1 expressions in the spleen were measured using immunohistochemical staining and the degree of such expression was measured using RT-PCR. The activity of TGF-beta 1 in the portal vein of TAA + Sham and TAA + SPL was assessed by the inhibiting effect of rat parenchymal hepatocyte proliferation in primary culture. RESULTS: Liver regeneration (PCNA-labeling index) in the TAA + SPL rats was stimulated more at 10 and 30 days after the operation (P < 0.05) than in the TAA + Sham rats, and the improvement of liver fibrosis (fibrosis rate) in the TAA + SPL rats was higher at 60 days (P < 0.05) than in the TAA + Sham rats. The plasma concentration of TGF-beta1 of the portal vein in TAA + SPL rats was significantly lower than in the TAA + Sham rats for each period. Immunohistochemically, TGF-beta1-positive stained cells were recognized in the spleen macrophages in the red pulp of cirrhotic rats. The plasma of the TAA + Sham rats at 10 and 30 days after the operation was significantly stronger than that of the TAA + SPL rats in inhibiting the proliferation of rat hepatocytes of primary culture. Inhibitory effects were then dose-dependently neutralized by monoclonal TGF-beta 1 antibody. CONCLUSION: Spleen-derived TGF-beta 1 may thus play an inhibitory role in the healing of liver cirrhosis by inhibiting the regeneration of the damaged liver.