Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease caused by environmental factors and loss of key proteins. One such protein is a serum endonuclease secreted by macrophages and dendritic cells, Dnase1L3. Loss of Dnase1L3 causes pediatric-onset lupus in humans is Dnase1L3. Reduction in Dnase1L3 activity occurs in adult-onset human SLE. However, the amount of Dnase1L3 necessary to prevent lupus onset, if the impact is continuous or requires a threshold, and which phenotypes are most impacted by Dnase1L3 remain unknown. To reduce Dnase1L3 protein levels, we developed a genetic mouse model with reduced Dnase1L3 activity by deletingDnase1L3from macrophages (cKO). Serum Dnase1L3 levels were reduced 67%, though Dnase1 activity remained constant. Sera were collected weekly from cKO and littermate controls until 50 weeks of age. Homogeneous and peripheral anti-nuclear antibodies were detected by immunofluorescence, consistent with anti-dsDNA antibodies. Total IgM, total IgG, and anti-dsDNA antibody levels increased in cKO mice with increasing age. In contrast to global Dnase1L3-/-mice, anti-dsDNA antibodies were not elevated until 30 weeks of age. The cKO mice had minimal kidney pathology, except for deposition of immune complexes and C3. Based on these findings, we conclude that an intermediate reduction in serum Dnase1L3 causes mild lupus phenotypes. This suggest that macrophage-derived DnaselL3 is critical to limiting lupus.

One leading cause of death in women is autoimmunity. One prominent autoimmune disease is Systemic Lupus Erythematosus (lupus). During lupus, inflammation is driven by autoantibodies that target cell-free DNA. Cell-free DNA is degraded by two serum endonucleases, Dnase1 and Dnase1L3. The loss of Dnase1L3 causes lupus in humans and mice, but the amount of Dnase1L3 necessary to prevent lupus onset is unknown. Since DnaselL3 is secreted by macrophages and dendritic cells, we hypothesized that loss of macrophage-derived DnaselL3 is sufficient to cause lupus-like phenotypes in mice. We generated conditional knockout (cKO) mice lacking DnaselL3 expression in macrophages. Sera was collected weekly from these mice until 50 weeks of age. To measure autoantibody induction, total IgG, total IgM, anti-dsDNA and anti-nuclear antibody levels were analyzed at 4, 20, 30 and 50 weeks. Sandwich ELISA was used to quantitate antibody levels in control and cKO mice. Homogeneous and peripheral anti-nuclear antibodies were detected by immunofluorescence, consistent with anti-dsDNA antibodies. Total IgG, anti-ds DNA antibody levels increased in cKO mice. We conclude that SLE-like phenotypes arise in mice due to the loss of macrophage Dnase1L3. This suggest that macrophage derived DnaselL3 is critical to controlling lupus. Plains Bridges to the Baccalaureate Program (PBB) (NIH 2R25GM83730-B)