Oxidized mitochondrial DNA sensing by plasmacytoid dendritic cells bypasses self-tolerance to trigger Tfh dependent autoantibody production [scRNA-seq]

Damage associated molecular patterns (DAMP) trigger inflammation and provide co-stimulatory signals to adaptive immune cells, but whether and how recurring innate stimuli circumvent self-tolerance and initiate maladaptive autoimmunity is unknown. We explored if oxidized mitochondrial DNA (Ox-mtDNA), a DAMP released by stressed macrophages, found in higher amounts in diverse metabolic and autoimmune disorders, including systemic lupus erythematosus (SLE), initiates antibody-mediated autoimmunity. Indeed, Ox-mtDNA release induced by repetitive alum challenges elicited germinal center reactions, autoantibody production and nephropathology. These responses were recapitulated by in-vitro generated Ox-mtDNA, while non-oxidized mtDNA was non-pathogenic. Both mtDNA forms, but not nuclear DNA, were internalized by plasmacytoid dendritic cells (pDC), activated NF-kB via TLR9 and induced interferon (IFN)-I. Yet only Ox-mtDNA triggered NLRP3- and gasdermin D-dependent IL-1β secretion, eliciting autocrine production of IL-21 that together with IL-1β, but independently of IFN-I, enabled pDC to convert naïve CD4+ T cells into follicular helper cells. Highlighting Ox-mtDNA as a uniquely immunogenic DAMP that is specifically sensed by pDC and IL-1β as an orchestrator of autoantibody production, these findings explain how chronic inflammation culminates in autoimmunity and unravel new therapeutic targets applicable to SLE, the autoimmune/inflammatory syndrome induced by adjuvants (ASIA) and related diseases.