Effects of gadolinium chloride (GdCl(3)) on the appearance of macrophage populations and fibrogenesis in thioacetamide-induced rat hepatic lesions.

Macrophages infiltrating injured tissue play an important part in fibrogenesis. To shed light on the functional roles of macrophages, we investigated the appearance of macrophage populations in thioacetamide (TAA)-induced rat hepatic lesions, with or without pretreatment with GdCl(3), a chemical capable of inhibiting Kupffer cell functions. In the GdCl(3)+TAA group rats received a single intraperitoneal injection of GdCl(3) (7.5mg/kg body weight) and, after 24h, a single intravenous injection of TAA (300mg/kg body weight). Rats in the TAA group received TAA only. Rats in both groups were examined on post-TAA injection (PTI) days 3, 5, and 7. In the TAA group, on PTI day 3, when TAA-induced hepatocyte injury was particularly prominent, the number of macrophages peaked, subsequently decreasing until PTI day 7. As compared with the TAA group, the GdCl(3)+TAA group showed significantly decreased numbers of ED1-immunolabelled cells (exudate macrophages) and ED2-immunolabelled cells (Kupffer cells) on PTI days 3, 5, and 7, and OX6-immunolabelled cells (antigen-presenting macrophages) on PTI days 3 and 5. Although less strikingly, the numbers of alpha-smooth muscle actin-positive myofibroblasts and fibrotic areas were decreased in the GdCl(3)+TAA group. By RT-PCR, the expression of TGF-beta1 mRNA was suppressed on PTI days 3 and 7 in the GdCl(3)+TAA group, and the suppressed expression was confirmed in vitro by treating rat macrophage-like cells (HS-P) with 1% GdCl(3). The study showed that GdCl(3) treatment decreased the numbers of macrophages appearing in hepatic lesions and inhibited TGF-beta1 mRNA expression in macrophages. Decreased numbers of macrophages may contribute to improvement of hepatic fibrosis.