Regulatory Role of Toll-like receptor signaling in lupus development

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Systemic lupus erythematosus (SLE) is a chronic, life threatening autoimmune disorder of unknown etiology, leading to multiple organ pathologies and kidney destruction. Loss of self tolerance is accompanied by the emergence of autoreactive B-cell clones producing anti-DNA and other anti-self antibodies with subsequent formation of pathogenic immune complexes (IC). These ICs can activate immune cells via endosomal nucleic acid sensing Toll-like receptors (TLRs), TLR3, TLR7 and TLR9 to produce type I interferons. A murine model which is dependent on type I Interferon and TLR signaling is the so-called pristane-induced model of systemic autoimmunity. We have recently characterized cells and tissues from these mice and identified an interferon stimulated gene (ISG) signature comparable to the ISG signature found in human lupus patients. Since TLR9 is an important endosomal nucleic acid sensor of bacterial but also mammalian self-DNA, it was thought, that deficiency of TLR9 would be protective in murine lupus models. Surprisingly, however TLR9 KO mice showed exacerbated lupus pathology and kidney disease, indicating a protective role for TLR9 signaling in lupus and likely other systemic autoimmune diseases. Different hypotheses have been proposed to explain this protection, however the exact mechanism is not understood. Using the well-established model of pristane-induced autoimmune disease in the lab we propose to study the effect of TLR9 deficiency in the initiation and the later stages of the disease in more detail. Specifically we want to study the underlying mechanism of the increased recruitment of potentially pathogenic inflammatory monocytes in TLR9 deficient pristane injected mice. Further, we want to understand the factors that cause accelerated and more severe kidney disease in the absence of TLR9 in this model. We plan to generate mixed bone marrow chimeras, produced by reconstituting normal mice with allotype- and CD45-disparate TLR7 KO and TLR9 KO mice. These will then be challenged with pristane and the contribution of B cells, DCs, macrophages and neutrophils, derived from the 2 parental strains to various aspects of the disease process will be determined. Furthermore, we wish to identify a subset of lupus patients in which a shift towards increased TLR7 compared to TLR9 induced Interferon alpha production in plasmacytoid dendritic cells is accompanied by a cytoplasmic staining pattern on HEp-2 cells and a loss of protective anti-DNA antibodies of IgM isotype. We hope that in this subset we might enrich patients with defects in the TLR9 signaling cascade, which predispose them to lupus development. Lastly, we propose to stimulate patient derived monocytes with nucleic acids transfected into the cytosol and wish to establish an assay to identify patients with defects in the cytosolic nucleic acid degradation/sensing pathways.