Role of TLR2 in immune sensing of gut microbiota in RNA virus induced glomerulonephritis

Abstract

Chronically infected patients with human immune deficiency virus (HIV) are at high risk of developing autoimmune diseases. Despite successful anti-retroviral therapy, autoimmune diseases and renal diseases affect 10–15 % of HIV-infected patients. Due to the lack of appropriate animal models, the pathophysiological mechanisms of HIV-associated glomerulonephritis (GN) remain elusive. <br /> In my thesis, I characterized the murine neoLCMV infection model, which mimics the key hallmarks of HIV infection and allowed me investigating the cellular and molecular mechanisms of HIV-induced GN. Infection of neonatal C57BL/6 mice with the WE-LCMV strain resulted in GN, and reflected most aspects of HIV infection in humans such as, elevated levels of anti-DNA and anti-nucleosome auto-antibodies, cell free circulating DNA and a chronic type I interferons (IFNs) signature. HIV-infected patients suffer from the leaky gut syndrome, which is characterized by the translocation of gut microbiota into the liver, bacterial dissemination and increased inflammation. Clinical investigations in this thesis confirmed elevated levels of leaky gut indicators such as LBP and FABP2, in HIV patients with kidney disease group. These findings were confirmed in the murine neoLCMV infection model. Furthermore, loss of Kupffer cells together with elevated levels of claudin 2 in neoLCMV infected mouse further proved that this mouse model can mimic the leaky gut syndrome found in HIV-infected individuals. <br /> To understand the underlying mechanisms of the leaky gut syndrome, I investigated the role of TLR2 and TLR4, which are known to sense translocated gut microbiota. Loss of TLR2, but not TLR4 resulted in partial protection from GN in neoLCMV-infected mice. TLR2 signaling in neutrophils triggered NETosis which can be the source of self-antigens and might therefore induce autoantibody formation that contributes to LCMV-induced GN. We further provided evidence that neutrophil-recruiting chemokines such as Cxcl2 were produced in a TLR2-dependent manner presumably by macrophages or Kupffer cells in the liver. Cxcl10 expression by hepatocytes, the dominant cell type producing this chemokine, might recruit B cells to the infection site where they encounter NETosis-derived autoantigens, leading to their activation and differentiation to auto-antibody producing plasma cells. Decreased monocyte counts and IL-6 and IL-4 expression in the spleen further indicated the contribution of a Th2 response in LCMV virus-induced GN via TLR2 signaling. <br /> In summary, I could demonstrate how nuclear autoantigens are released by NETosis in the liver of neoLCMV mice and how autoantibodies are induced that can later form deposits in the kidney and thereby contribute to the disease development as a consequence of LCMV infection. Moreover, TLR2 deficiency in the neoLCMV model ameliorated GN and resulted in decreased auto-antibody production. Hence, these findings revealed the importance of TLR2 in the pathogenesis of GN in murine LCMV infection that serves as a model for human HIV infection and its potential contribution to the therapeutic approaches.