The mechanisms of chronic HBV infection and immunopathogenesis are poorly understood due to a lack of a robust small animal model. Here we report the development of a humanized mouse model with both human immune system and human liver cells by reconstituting the immunodeficient A2/NSG (NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ mice with human HLA-A2 transgene) with human hematopoietic stem cells and liver progenitor cells (A2/NSG-hu HSC/Hep mice). The A2/NSG-hu HSC/Hep mouse supported HBV infection and approximately 75% of HBV infected mice established persistent infection for at least 4 months. We detected human immune responses, albeit impaired in the liver, chronic liver inflammation and liver fibrosis in infected animals. An HBV neutralizing antibody efficiently inhibited HBV infection and associated liver diseases in humanized mice. In addition, we found that the HBV mediated liver disease was associated with high level of infiltrated human macrophages with M2-like activation phenotype. Importantly, similar M2-like macrophage accumulation was confirmed in chronic hepatitis B patients with liver diseases. Furthermore, gene expression analysis showed that induction of M2-like macrophage in the liver is associated with accelerated liver fibrosis and necrosis in patients with acute HBV-induced liver failure. Lastly, we demonstrate that HBV promotes M2-like activation in both M1 and M2 macrophages in cell culture studies. Our study demonstrates that the A2/NSG-hu HSC/Hep mouse model is valuable in studying HBV infection, human immune responses and associated liver diseases. Furthermore, results from this study suggest a critical role for macrophage polarization in hepatitis B virus-induced immune impairment and liver pathology. Over 350 million people worldwide are chronically infected with the hepatitis B virus (HBV), which leads to severe liver diseases including fibrosis and cancer. The mechanisms of chronic HBV infection and disease are poorly understood due to a lack of a robust small animal model. Here we report a novel animal model that can be efficiently repopulated with both human immune and liver cells. The A2/NSG-hu HSC/Hep humanized mouse model supported persistent HBV infection, human immune responses, albeit impaired in the liver, chronic liver inflammation and liver fibrosis. In addition, we found that the HBV mediated liver immune impairment and liver disease was associated with high level of infiltrated human immuno-suppressive/pro-fibrogenic macrophages; this result was confirmed in chronic HBV-induced liver disease patients and acute HBV – induced liver failure patients. Importantly, we demonstrate that HBV promotes immuno-suppressive/pro-fibrogenic macrophage polarization in human macrophages using cell culture models. The humanized mouse model is a valuable platform in studying HBV infection, human immune response and liver diseases. Furthermore, results from this study suggest a critical role for macrophage activation in hepatitis B induced liver diseases, thus providing a novel therapeutic target.

Administration of phthalates is known to cause toxicity and liver cancer in rodents through the activation of peroxisome proliferator-activated receptors (PPARs), and the monoesters appear to be the active metabolites that function as ligands of PPARs. There is evidence that PPARs exhibit significant species differences in response to ligand activation. In this study, the activation of mouse and human PPARα, PPARβ, and PPARγ by a broad class of phthalate monoesters was investigated using a trans-activation assay, functional analysis of PPARα target gene expression, and a PPARγ-mediated differentiation assay. These studies demonstrated a range in the ability of various phthalate monoesters to activate PPARα, with the mouse PPARα generally being activated at lower concentrations and exhibiting a greater response than human PPARα. Similarly, a range in the trans-activation of mouse PPARβ by phthalate monoesters was also observed, but this effect was not found with human PPARβ. A number of phthalate monoesters activated both mouse and human PPARγ, with similar sensitivity being exhibited by both receptors. These studies show that the potency and efficacy of phthalate monoesters for the activation of PPARα and PPARγ increase with increasing side-chain length. These studies also show that mouse PPARα and PPARβ are generally activated at lower concentrations of phthalate monoesters than human PPARα and PPARβ, and that both mouse and human PPARγ exhibit similar sensitivity to phthalate monoesters. Lastly, there is a good relationship between the relative ability of phthalate monoesters to trans-activate PPARα and PPARγ, and the relative induction of PPARα target gene mRNA and PPARγ-mediated adipocyte differentiation, respectively.

Potential functional roles for the peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) in skeletal muscle fatty acid catabolism and epithelial carcinogenesis have recently been described. Whereas PPARβ/δ is expressed in liver, its function in this tissue is less clear. To determine the role of PPARβ/δ in chemically induced liver toxicity, wild-type and PPARβ/δ-null mice were treated with azoxymethane (AOM) and markers of liver toxicity examined. Bile duct hyperplasia, regenerative hyperplasia, and increased serum alanine aminotransferase (ALT) were found in AOM-treated PPARβ/δ-null mice, and these effects were not observed in similarly treated wild-type mice. Exacerbated carbon tetrachloride (CCl4) hepatoxicity was also observed in PPARβ/δ-null as compared with wild-type mice. No differences in messenger RNAs (mRNAs) encoding cytochrome2E1 required for the metabolic activation of AOM and CCl4 were observed between wild-type or PPARβ/δ-null mice in response to CCl4. Significant differences in the expression of genes reflecting enhanced nuclear factor kappa B (NF-κB) activity were noted in PPARβ/δ-null mice. Conclusion: Results from these studies show that PPARβ/δ is protective against liver toxicity induced by AOM and CCl4, suggesting that this receptor is hepatoprotective against environmental chemicals that are metabolized in this tissue. (Hepatology 2007.)