The Dendritic Cell Response to Exogenous and Endogenous Danger Signals

Abstract

Systemic lupus erythematosus (SLE) is complex autoimmune disease in which autoantibodies form against double stranded DNA (dsDNA) and nuclear antigens. Autoantigen immune complexes form, deposit in the vasculature, and cause multisystem organ damage. Both genetic and environmental factors contribute to the development of SLE. This thesis will explore three major themes found in the study of SLE: 1) Bacterial infection as an environmental trigger, 2) cytokine dysregulation in immune cells, and 3) the treatment of end organ damage in the form of lupus nephritis. Viral infections have long been associated with the development of systemic autoimmune disease, but the mechanisms by which chronic bacterial infections may promote autoimmunity remain unclear. In chapter three we show that a component of bacterial biofilms, the amyloid-like protein “curli”, irreversibly forms fibers with bacterial or eukaryotic DNA during biofilm formation. This interaction accelerates amyloid polymerization and creates potent immunogenic complexes that activate immune cells, including dendritic cells, to produce cytokines such as type I interferons, which are pathogenic in SLE. When given systemically, curli/DNA composites trigger immune activation and production of autoantibodies in lupus-prone and wild type mice. We also found that infection with curli-producing bacteria triggered higher autoantibody titers in lupus-prone mice compared to curli-deficient bacteria. These data provide a mechanism by which the microbiome and biofilm-producing enteric infections may contribute to the progression of SLE and point to a potential molecular target for treatment of autoimmunity. Cytokine dysregulation is also common in SLE patients. Serum cytokines are often elevated during active disease, including type I IFNs and IL-10. In chapter four we demonstrate that Il10 is a type I IFN response gene and has increased basal expression in dendritic cells (DCs) derived from pre-disease lupus-prone Sle1,2,3 mice. We show that Sle1,2,3-derived DCs overproduce IL-10 in response to TLR ligands and that this is the result of autocrine signaling though the type I IFN receptor (IFNAR). These results suggest that dysregulation of cytokine signaling in the myeloid compartment may contribute to IL-10 dysregulation in SLE. Renal disease remains a major cause of morbidity and mortality in SLE. A number of mouse models of chronic kidney disease have implicated the EGFR-family receptors in the progression of renal fibrosis and dysfunction. In chapter five we show that renal expression of ErbB2 is increased in murine lupus. We therefore asked if EGFR-family inhibition could prevent murine lupus nephritis. To test this possibility we used lapatinib, an EGFR-ErbB2 dual kinase inhibitor, in an IFN-accelerated model of murine lupus. We found that lapatinib administration lowered autoantibody levels but worsened renal disease. Lapatinib failure to treat murine lupus nephritis despite lowered autoantibody levels suggests EGFR-family signaling is required for tissue repair in the acute phase of kidney injury. Together this thesis clearly demonstrates the complexity of systemic autoimmune disease – bringing us to the crossroads of immunity and tolerance. The combination of both environmental triggers (e.g. bacterial infection) and genetic susceptibility (e.g. intrinsic cytokine dysregulation) leads to end organ damage (e.g. lupus nephritis). Here we sought to explore each aspect of disease progression in the hopes to develop better interventions for systemic autoimmune disease.