Studies of CD8+ T-cell Mediated Liver Injury and Stellate Cell Activation Using an AAV Model: An Investigation into the Role of Key Cytokines

Thesis (Ph. D.)--University of Rochester. School of Medicine and Dentistry. Dept. of Microbiology and Immunology, 2009.Inflammation in the liver and subsequent dysfunction is a result of many diverse factors. Accumulation of immune cells within the liver, described as hepatitis, and subsequent scarring of liver due to excess collagen deposition, described as fibrosis, can be caused by infectious diseases such as Hepatitis B or C viruses, or toxic factors such as alcohol and carbon tetrachloride. Though many molecules and cell types associated with the immune system have been correlated with induction or exacerbation of liver pathology, insights into how these factors and cells interact and contribute to the diseased state are lacking. Using an Adeno-Associated Virus vector to transfect a specific target antigen into hepatocytes, we studied how recognition of antigen by CD8+ T-cells in the liver results in liver injury and activation of collagen-producing stellate cells. Using TCR transgenic mice and mice that are genetically deficient in key cytokines, or their receptors, we have identified a mechanism of liver injury which requires IFNγ signaling on bone marrow derived cells resulting in TNFα production by activated Kupffer cells. This TNFα production was shown to be dependent on TNFR1 signaling, presumably on the Kupffer cells themselves, in order to facilitate optimal activation. TNFR1 signaling on the liver parenchyma itself did not contribute to liver injury. In parallel, IFNγ signaling on the parenchyma contributed significantly to pathology, but does not appear to be directly cytotoxic. This autocrine TNFR1 signaling on Kupffer cells was required for liver injury and for initial stellate cell activation, as measured by TIMP-1 expression. These data suggest a link between Kupffer cell derived factors and stellate cell activation. By generating chimeras that have IL-6 deficient bone marrow, we found that production of IL-6 by bone marrow derived cells is not required for TIMP-1 expression. This was also seen in intact IL-6 deficient mice. We propose a mechanism of CD8+ T-cell mediated liver injury that is initiated by IFNγ driven Kupffer cell activation and results in subsequent stellate cell activation. While Kupffer cell activation appears to contribute to stellate cell expression of TIMP-1, we found no role for IL-6 despite previous in vitro reports. These data reveal previously unknown mechanistic details about the central role of TNFα and IFNγ in promoting liver injury and the initiation of the wound-healing response in the liver. Therapies targeted toward suppression of these pathways could decrease pathology while simultaneously promoting clearance of liver infections