We found that combining both isotypes at a 1:1 ratio formed complexes that triggered much greater secretion of IFN- than the complexes containing a single immunoglobulin isotype (Fig. self-destructive autoimmune responses. == Introduction == Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the loss of immune tolerance to nucleic acids, activation of autoreactive lymphocytes, and the production of large quantities of self-reactive antibodies that induce tissue damage1. Renal autoantibody deposition and lymphocyte infiltration lead to nephritis, a serious complication of lupus that presents in the clinical course of up to 60% of patients2. A hallmark of SLE is the production of type I interferons (IFN-I) in response to immune complexes (ICs) made up of self-DNA from lifeless cells and DNA-specific IgG3. There is now a mounting body of evidence pointing to plasmacytoid dendritic cells (pDCs) as the main pathogenic IFN-I suppliers in SLE4. pDCs are immune cells that specialize in antiviral responses5. Upon sensing viral nucleic acids through TLR7 (RNA) and TLR9 (DNA), pDCs release up to 1000 occasions more IFN-I than any other cell type6, promoting the cellular expression of IFN-stimulated genes and the apoptosis of infected cells. Although TLR9 binds indiscriminately to both viral and host endogenous DNA, its intracellular localization within endo-lysosomal compartments prevents the acknowledgement of self-DNA. In SLE, DNA-specific Cardiolipin autoantibodies bind to endogenous DNA (released from damaged cells) forming DNA-ICs, which are then internalized by pDCs via the Fc-gamma receptor IIa (FcRIIa)7, a process that allows delivery of self-DNA to TLR9 within pDCs, triggering an aberrant antiviral response. Acknowledgement of self-DNA by TLR9 prospects to the recruitment of the adaptor protein myeloid differentiation main response gene 88 (MyD88) and then to the activation of nuclear factor B (NF-B), and interferon regulatory factor 7 (IRF7), which Cardiolipin induce the secretion of proinflammatory cytokines (such as TNF) and the secretion of large amounts of IFN-I respectively8,9. TLR9 activation also induces cell migration and their ability to activate T cell and B cells, which positions pDCs at the crossroads of both innate and adaptive immune responses10. Recent evidence demonstrates that double-stranded DNA (dsDNA)-specific antibodies of the IgE immunoglobulin class are also found in some SLE patients11,12,13and although they have been associated with basophil activation12,14, their role in disease pathogenesis remains unclear. Found only in mammals, IgE is the least abundant immunoglobulin isotype and signals through two types of Fc-epsilon receptor (FcR), the high-affinity receptor FcRI and the low-affinity receptor FcRII. IgE provides protection against parasitic worms (helminths), but also triggers vigorous harmful, even deadly, allergic reactions against innocuous foreign proteins (allergens)15,16. In both of these cases, IgE recognizes exogenous antigens and triggers an immunological response that is associated with mast cell degranulation and the subsequent ZCYTOR7 release of biogenic amines, lipid mediators, the production of Th2 cytokines (such as IL-4, IL-5, and IL-13), and eosinophilia15. Paradoxically, none of these inflammatory responses are key drivers of SLE pathogenesis11,17,18and SLE patients do not appear to be more prone to IgE-driven environmental allergies than the general populace19,20,21. Thus, it is plausible that self-reactive IgE in autoimmunity may present with different functions than those explained for IgE in helminth defense and allergy. To explore this, we investigated the potential functions of DNA-specific IgE in SLE pathogenesis. == Results == == IgE triggers IFN- secretion in SLE == In the SLE cohort we analyzed, 98 out of 180 (54.4%) of patients exhibited detectable concentrations of dsDNA-specific IgE, while healthy individuals, as well as patients with atopic dermatitis (a disease associated with elevated serum IgE concentrations) were all negative for this autoantibody (Fig. 1a). Amounts of circulating dsDNA-specific IgEs were particularly increased Cardiolipin in active disease (Fig. 1b), and correlated with low amounts of match component 3 (C3), a marker of serologic disease activity13,22(Fig. 1c). To investigate the role of dsDNA-specific IgE role in SLE, we explored whether these autoantibodies could modulate the IFN-I response. Activation of FcR on pDCs by heat-aggregated IgEs inhibited influenza-induced secretion of IFN- (Supplementary Fig. 1), a mechanism.
We found that combining both isotypes at a 1:1 ratio formed complexes that triggered much greater secretion of IFN- than the complexes containing a single immunoglobulin isotype (Fig
