[Study on the state of macrophage infiltration in the progression of non-alcoholic fatty liver disease induced by high-fat diet in mice].

Non-alcoholic fatty liver disease (NAFLD) is a common chronic liver disease. Macrophages are an important cell-mediated immune response in the pathogenesis of NAFLD. However, the dynamic changes of intrahepatic infiltration during the pathogenesis of NAFLD remains unclear. Therefore, this study intends to investigate the changes and their correlations with morphological indicators, hepatic histopathological index, and intrahepatic macrophage infiltration in the progression of NAFLD induced by high-fat diet in mice. C57BL/6J mice were fed with 42% high-fat diet, and the morphological data and liver tissue were obtained at 1, 2, 4, 8 and 12 months, respectively. Hepatic histopathological characteristics were evaluated by HE stain. Immunohistochemical staining was used to detect the number of F4/80 positive cells in liver tissue at different stages to evaluate the degree of intrahepatic macrophage infiltration. (1) The body weight, liver weight, and liver weight/body weight of mice fed with high-fat diet had gradually increased. (2) HE staining results showed that mice fed with high-fat diet had mainly developed simple steatosis within 1 to 2 months. In addition, a balloon-like hepatocyte degeneration and intralobular inflammation had begun to appear at 4 months, indicating that non-alcoholic steatohepatitis had started, and can be seen very clearly at 8 to 12 months. (3) Immunohistochemical staining results suggested that in the simple steatosis stage of NAFLD, the intrahepatic macrophage infiltration was not significant. However, after NAFLD activity score > 3, a large amount of infiltration had appeared and cluster-like changes in the later stage. (4) Correlation analysis results indicated that the degree of macrophage infiltration was not related to the mice morphological indicators (body weight, liver weight and liver weight/body weight) and pathological indicators (percentage of hepatic steatotic change, and degree of hepatocyte ballooning and intralobular inflammation), but was significantly related to the NAFLD activity score. High-fat diet can successfully induce NAFLD in mice and progress to the stage of non-alcoholic steatohepatitis. At the same time, high-fat diet can induce macrophage infiltration in liver tissue of mice and the changing trend of infiltration is related to NAFLD activity score.