M1/M2

d-galactosamine (d-GalN) is a well-known hepatotoxic agent that causes liver injury. Conversely, hepatic macrophages play a crucial role in maintaining liver tissue integrity. Macrophage functions were investigated in hepatic lesions induced by a single intraperitoneal injection of d-GalN (800 mg/kg body weight [BW]) in 6-week-old F344 rats. Blood and liver samples were examined at 8 hr and on 1, 2, 3, and 5 days postsingle injection (PSI). Hepatic lesions consisting of degeneration/sporadic foci of coagulation necrosis, inflammatory cell reaction, and reparative fibrosis were seen on PSI days 1 and 2, reflected by significantly increased serum levels of aspartate transaminase and alanine transaminase and upregulation of CD68 M1 (tumor necrosis factor-α, interleukin [IL]-6, and interferon-γ) and CD163 M2 (transforming growth factor-β1, IL-10, monocyte chemoattractant protein-1, and IL-4) macrophage-related factors. Double immunofluorescence staining on PSI day 2 demonstrated that 82% of hepatic macrophages expressed of CD163/CD68 simultaneously; 65–75% of MHC class II macrophages showed co-expression of CD163 or CD68 and 95% CD204-expressing macrophages reacted to CD163 or CD68. These findings showed that both M1- and M2-macrophages contributed to the development of hepatic lesions induced by d-GalN and provided information about macrophage activation, indicating the importance of analysis of macrophage phenotypes for hepatotoxicity based on M1/M2-polarization