DNA-like class R inhibitory oligonucleotides (INH-ODNs) preferentially block autoantigen-induced B-cell and dendritic cell activation in vitro and autoantibody production in lupus-prone MRL-Fas(lpr/lpr) mice in vivo

Host-pathogen protein-nucleic acid interactions: A comprehensive review

Recognition of pathogen-derived nucleic acids by host cells is an effective host strategy to detect pathogenic invasion and trigger immune responses. In the context of pathogen-specific pharmacology, there is a growing interest in mapping the interactions between pathogen-derived nucleic acids and host proteins. Insight into the principles of the structural and immunological mechanisms underlying such interactions and their roles in host defense is necessary to guide therapeutic intervention. Here, we discuss the newest advances in studies of molecular interactions involving pathogen nucleic acids and host factors, including their drug design, molecular structure and specific patterns. We observed that two groups of nucleic acid recognizing molecules, Toll-like receptors (TLRs) and the cytoplasmic retinoic acid-inducible gene (RIG)-I-like receptors (RLRs) form the backbone of host responses to pathogen nucleic acids, with additional support provided by absent in melanoma 2 (AIM2) and DNA-dependent activator of Interferons (IFNs)-regulatory factors (DAI) like cytosolic activity. We review the structural, immunological, and other biological aspects of these representative groups of molecules, especially in terms of their target specificity and affinity and challenges in leveraging host-pathogen protein-nucleic acid interactions (HP-PNI) in drug discovery.

A TLR7 antagonist restricts interferon-dependent and -independent immunopathology in a mouse model of severe influenza

Cytokine-mediated immune-cell recruitment and inflammation contribute to protection in respiratory virus infection. However, uncontrolled inflammation and the "cytokine storm" are hallmarks of immunopathology in severe infection. Cytokine storm is a broad term for a phenomenon with diverse characteristics and drivers, depending on host genetics, age, and other factors. Taking advantage of the differential use of virus-sensing systems by different cell types, we test the hypothesis that specifically blocking TLR7-dependent, immune cell-produced cytokines reduces influenza-related immunopathology. In a mouse model of severe influenza characterized by a type I interferon (IFN-I)-driven cytokine storm, TLR7 antagonist treatment leaves epithelial antiviral responses unaltered but acts through pDCs and monocytes to reduce IFN-I and other cytokines in the lung, thus ameliorating inflammation and severity. Moreover, even in the absence of IFN-I signaling, TLR7 antagonism reduces inflammation and mortality driven by monocyte-produced chemoattractants and neutrophil recruitment into the infected lung. Hence, TLR7 antagonism reduces diverse types of cytokine storm in severe influenza.

Role of nucleic acid sensing in the pathogenesis of type 1 diabetes

During infections, nucleic acids of pathogens are also engaged in recognition via several exogenous and cytosolic pattern recognition receptors, such as the toll-like receptors, retinoic acid inducible gene-I-like receptors, and nucleotide-binding and oligomerization domain-like receptors. The binding of the pathogen-derived nucleic acids to their corresponding sensors initiates certain downstream signaling cascades culminating in the release of type-I interferons (IFNs), especially IFN-α and other cytokines to induce proinflammatory responses towards invading pathogens leading to their clearance from the host. Although these sensors are hardwired to recognize pathogen associated molecular patterns, like viral and bacterial nucleic acids, under unusual physiological conditions, such as excessive cellular stress and increased apoptosis, endogenous self-nucleic acids like DNA, RNA, and mitochondrial DNA are also released. The presence of these self-nucleic acids in extranuclear compartments or extracellular spaces or their association with certain proteins sometimes leads to the failure of discriminating mechanisms of nucleic acid sensors leading to proinflammatory responses as seen in autoimmune disorders, like systemic lupus erythematosus, psoriasis and to some extent in type 1 diabetes (T1D). This review discusses the involvement of various nucleic acid sensors in autoimmunity and discusses how aberrant recognition of self-nucleic acids by their sensors activates the innate immune responses during the pathogenesis of T1D.

Cross-Reactive Antigen Expressed by B6 Splenocytes Drives Receptor Editing and Marginal Zone Differentiation of IgG2a-Reactive AM14 Vκ8 B Cells

The AM14 BCR, derived from an autoimmune MRL/lpr mouse, binds autologous IgG2aa/j with low affinity, and as a result, AM14 B cells only proliferate in response to IgG2a immune complexes that incorporate DNA, RNA, or nucleic acid-binding proteins that serve as autoadjuvants. As such, AM14 B cells have served as a useful model for demonstrating the importance of BCR/TLR coengagement in the activation of autoreactive B cells. We now show that the same receptor recognizes an additional murine-encoded Ag, expressed by B6 splenocytes, with sufficient avidity to induce a TLR-independent proliferative response of BALB/c AM14 Vκ8 B cells both in vivo and in vitro. Moreover, detection of this cross-reactive Ag by B6 AM14 Vκ8 B cells promotes an anergic phenotype as reflected by suboptimal responses to BCR cross-linking and the absence of mature B cells in the bone marrow. The B6 Ag further impacts B cell development as shown by a dramatically expanded marginal zone compartment and extensive receptor editing in B6 AM14 Vκ8 mice but not BALB/c AM14 Vκ8 mice. Despite their anergic phenotypes, B6 AM14 Vκ8 B cells can respond robustly to autoantigen/autoadjuvant immune complexes and could therefore participate in both autoimmune responses and host defense.

Pharmacological modulation of nucleic acid sensors - therapeutic potential and persisting obstacles

Nucleic acid sensors, primarily TLR and RLR family members, as well as cGAS-STING signalling, play a critical role in the preservation of cellular and organismal homeostasis. Accordingly, deregulated nucleic acid sensing contributes to the origin of a diverse range of disorders, including infectious diseases, as well as cardiovascular, autoimmune and neoplastic conditions. Accumulating evidence indicates that normalizing aberrant nucleic acid sensing can mediate robust therapeutic effects. However, targeting nucleic acid sensors with pharmacological agents, such as STING agonists, presents multiple obstacles, including drug-, target-, disease- and host-related issues. Here, we discuss preclinical and clinical data supporting the potential of this therapeutic paradigm and highlight key limitations and possible strategies to overcome them.

DNA-Based Biomaterials for Immunoengineering

Man-made DNA materials hold the potential to modulate specific immune pathways toward immunoactivating or immunosuppressive cascades. DNA-based biomaterials introduce DNA into the extracellular environment during implantation or delivery, and subsequently intracellularly upon phagocytosis or degradation of the material. Therefore, the immunogenic functionality of biological and synthetic extracellular DNA should be considered to achieve desired immune responses. In vivo, extracellular DNA from both endogenous and exogenous sources holds immunoactivating functions which can be traced back to the molecular features of DNA, such as sequence and length. Extracellular DNA is recognized as damage-associated molecular patterns (DAMPs), or pathogen-associated molecular patterns (PAMPs), by immune cell receptors, activating either proinflammatory signaling pathways or immunosuppressive cell functions. Although extracellular DNA promotes protective immune responses during early inflammation such as bacterial killing, recent advances demonstrate that unresolved and elevated DNA concentrations may contribute to the pathogenesis of autoimmune diseases, cancer, and fibrosis. Therefore, addressing the immunogenicity of DNA enables immune responses to be engineered by optimizing their activating and suppressive performance per application. To this end, emerging biology relevant to the generation of extracellular DNA, DNA sensors, and its role concerning existing and future synthetic DNA biomaterials are reviewed.

Lupus-Associated Immune Complexes Activate Human Neutrophils in an FcγRIIA-Dependent but TLR-Independent Response

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of autoantibodies against nucleic acids and nucleoproteins. Anti-dsDNA Abs are considered a hallmark of SLE, and previous studies have indicated that nucleic acid-containing immune complexes (ICs) induce B cell and dendritic cell activation in a TLR-dependent process. How ICs containing nucleic acids affect neutrophil function has not been well investigated. In this study, we report that nucleic acid-containing ICs derived from the sera of SLE patients induce human and mouse neutrophil activation through TLR-independent mechanisms. Soluble ICs containing Sm/RNP, an RNA Ag, activate human neutrophils to produce reactive oxygen species (ROS) and IL-8. In contrast, ICs containing DNA have to be immobilized to efficiently activate neutrophils. We found that deleting TLR7 or TLR9, the receptors for RNA and DNA, had no effect on mouse neutrophil activation induced by RNA-containing and immobilized DNA-containing ICs. Binding of ICs are mediated through FcγRIIA and FcγRIIIB. However, neutrophil activation induced by RNA- and DNA-containing ICs requires FcγRIIA, as blocking FcγRIIA inhibited ROS release from neutrophils. RNA-containing ICs induce calcium flux, whereas TLR7/8 ligand R848 do not. Surprisingly, chloroquine inhibits calcium flux induced by RNA-containing ICs, suggesting that this lesser known function of chloroquine is involved in the neutrophil activation induced by ICs. These data indicate the SLE-derived ICs activate neutrophils to release ROS and chemokines in an FcγRIIA-dependent and TLR7- and TLR9-independent manner that likely contributes to local tissue inflammation and damage.

Patent highlights August-September 2016

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Abnormal thymic maturation and lymphoproliferation in MRL-Fas lpr/lpr mice can be partially reversed by synthetic oligonucleotides: implications for systemic lupus erythematosus and autoimmune lymphoproliferative syndrome

MRL-Fas ^lpr/lpr mice represent an excellent animal model for studying non-malignant lymphoproliferation, regeneration and systemic autoimmunity. Retro-transposon insertion into the second intron of the pro-apoptotic Fas gene appears to be responsible for both lymphoproliferation and autoimmunity, while other genes are more likely to contribute to the regenerative healing characteristic of this mouse strain. Previous studies have shown that neonatal thymectomy can halt the development of abnormal lymphoproliferation. Whereas at four weeks of age primary and secondary lymphoid organs appear to be grossly intact, vigorous lymphoproliferation and autoantibody production subsequently ensues. This is first noticeable at six weeks of age, at which time lymph nodes, spleens and thymuses, but not the bone marrow, become infiltrated with abnormal B220⁺CD3⁺CD4^-CD8^- T cells. Around the same time, thymuses show a significant drop in CD4⁺CD8⁺double-positive T cells generating an abnormal ratio between double-positive and single-positive thymocytes. The objective of current study was to evaluate the effect of synthetic oligonucleotides-toll-like receptor antagonists on early lymphoid development in this strain of mice. Herein, we demonstrate the ability of synthetic oligonucleotides made with the nuclease-resistant phosphorothioate backbone to partially reverse abnormal lymphoproliferation and thymic involution in pre-diseased MRL-Fas ^lpr/lpr mice when administered intraperitoneally starting from week four of age. This curative effect of oligonucleotides was primary sequence/secondary oligonucleotide structure-independent, suggesting an effect through the toll-like receptor 7. A similar approach may potentially benefit patients with autoimmune lymphoproliferative syndrome who, like MRL-Fas ^lpr/lpr mice, carry a mutation in the Fas gene.

Interfering with baffled B cells at the lupus tollway: Promises, successes, and failed expectations

B cells play an important role in systemic lupus erythematosus by acting not only as precursors of autoantibody-producing cells but also as antigen-presenting, cytokine-secreting, and regulatory cells. Unopposed activation of B cells through their B-cell receptor for antigen, as seen in B cells lacking Lyn kinase, results in systemic autoimmunity. The B-cell activating factor of the TNF family (BAFF), nucleic acid-sensing Toll-like receptors (TLRs), and type I interferon can affect B-cell survival and decrease their threshold for activation. Herein we discuss both direct and indirect strategies aimed at targeting B cells in patients with lupus by blocking BAFF, type I interferon, or TLR7 to TLR9. Although BAFF-depleting therapy with belimumab achieved approval for lupus, other BAFF inhibitors were much less beneficial in clinical trials. Inhibitors of the B-cell receptor for antigen signaling and antibodies against type I interferon are in the pipeline. The TLR7 to TLR9 blocker hydroxychloroquine has been in use in patients with lupus for more than 50 years, but oligonucleotide-based inhibitors of TLR7 to TLR9, despite showing promise in animal models of lupus, have not reached the primary end point in a recent phase 1 trial. These data point toward possible redundancies in B-cell signaling/survival pathways, which must be better understood before future clinical trials are executed.

Breakdown of Immune Tolerance in Systemic Lupus Erythematosus by Dendritic Cells

Dendritic cells (DC) play an important role in the pathogenesis of systemic lupus erythematosus (SLE), an autoimmune disease with multiple tissue manifestations. In this review, we summarize recent studies on the roles of conventional DC and plasmacytoid DC in the development of both murine lupus and human SLE. In the past decade, studies using selective DC depletions have demonstrated critical roles of DC in lupus progression. Comprehensive in vitro and in vivo studies suggest activation of DC by self-antigens in lupus pathogenesis, followed by breakdown of immune tolerance to self. Potential treatment strategies targeting DC have been developed. However, many questions remain regarding the mechanisms by which DC modulate lupus pathogenesis that require further investigations.

Structure, mechanism and therapeutic utility of immunosuppressive oligonucleotides

Synthetic oligodeoxynucleotides that can down-regulate cellular elements of the immune system have been developed and are being widely studied in preclinical models. These agents vary in sequence, mechanism of action, and cellular target(s) but share the ability to suppress a plethora of inflammatory responses. This work reviews the types of immunosuppressive oligodeoxynucleotide (Sup ODN) and compares their therapeutic activity against diseases characterized by pathologic levels of immune stimulation ranging from autoimmunity to septic shock to cancer (see graphical abstract). The mechanism(s) underlying the efficacy of Sup ODN and the influence size, sequence and nucleotide backbone on function are considered.

Oligodeoxynucleotide inhibition of Toll-like receptors 3, 7, 8, and 9 suppresses cytokine production in a human rheumatoid arthritis model

Toll-like receptors (TLRs) are innate immune receptors that respond to both exogenous and endogenous stimuli and are suggested to contribute to the perpetuation of chronic inflammation associated with rheumatoid arthritis (RA). In particular, the endosomal TLRs 3, 7, 8, and 9 have more recently been postulated to be of importance in RA pathogenesis. In this study, pan inhibition of the endosomal TLRs by a phosphorothioate-modified inhibitory oligodeoxynucleotide (ODN) is demonstrated in primary human B cells, macrophages, and RA fibroblasts. Inhibition of TLR8 was of particular interest as TLR8 has been associated with RA pathogenesis in both human and murine arthritis models. ODN1411 competitively inhibited TLR8 signaling and was observed to directly bind to a purified TLR8 ectodomain, suggesting inhibition was through a direct interaction with the receptor. Addition of ODN1411 to human RA synovial membrane cultures significantly inhibited spontaneous cytokine production from these cultures, suggesting a potential role for one or more of the endosomal TLRs in inflammatory cytokine production in RA and the potential for inhibitory ODNs as novel therapies.

Immunomodulatory spherical nucleic acids

Immunomodulatory nucleic acids have extraordinary promise for treating disease, yet clinical progress has been limited by a lack of tools to safely increase activity in patients. Immunomodulatory nucleic acids act by agonizing or antagonizing endosomal toll-like receptors (TLR3, TLR7/8, and TLR9), proteins involved in innate immune signaling. Immunomodulatory spherical nucleic acids (SNAs) that stimulate (immunostimulatory, IS-SNA) or regulate (immunoregulatory, IR-SNA) immunity by engaging TLRs have been designed, synthesized, and characterized. Compared with free oligonucleotides, IS-SNAs exhibit up to 80-fold increases in potency, 700-fold higher antibody titers, 400-fold higher cellular responses to a model antigen, and improved treatment of mice with lymphomas. IR-SNAs exhibit up to eightfold increases in potency and 30% greater reduction in fibrosis score in mice with nonalcoholic steatohepatitis (NASH). Given the clinical potential of SNAs due to their potency, defined chemical nature, and good tolerability, SNAs are attractive new modalities for developing immunotherapies.

Guanine-modified inhibitory oligonucleotides efficiently impair TLR7- and TLR9-mediated immune responses of human immune cells

Activation of TLR7 and TLR9 by endogenous RNA- or DNA-containing ligands, respectively, is thought to contribute to the complicated pathophysiology of systemic lupus erythematosus (SLE). These ligands induce the release of type-I interferons by plasmacytoid dendritic cells and autoreactive antibodies by B-cells, both responses being key events in perpetuating SLE. We recently described the development of inhibitory oligonucleotides (INH-ODN), which are characterized by a phosphorothioate backbone, a CC(T)XXX3-5GGG motif and a chemical modification of the G-quartet to avoid the formation of higher order structures via intermolecular G-tetrads. These INH-ODNs were equally or significantly more efficient to impair TLR7- and TLR9-stimulated murine B-cells, macrophages, conventional and plasmacytoid dendritic cells than the parent INH-ODN 2088, which lacks G-modification. Here, we evaluate the inhibitory/therapeutic potential of our set of G-modified INH-ODN on human immune cells. We report the novel finding that G-modified INH-ODNs efficiently inhibited the release of IFN-α by PBMC stimulated either with the TLR7-ligand oligoribonucleotide (ORN) 22075 or the TLR9-ligand CpG-ODN 2216. G-modification of INH-ODNs significantly improved inhibition of IL-6 release by PBMCs and purified human B-cells stimulated with the TLR7-ligand imiquimod or the TLR9-ligand CpG-ODN 2006. Furthermore, inhibition of B-cell activation analyzed by expression of activation markers and intracellular ATP content was significantly improved by G-modification. As observed with murine B-cells, high concentrations of INH-ODN 2088 but not of G-modified INH-ODNs stimulated IL-6 secretion by PBMCs in the absence of TLR-ligands thus limiting its blocking efficacy. In summary, G-modification of INH-ODNs improved their ability to impair TLR7- and TLR9-mediated signaling in those human immune cells which are considered as crucial in the pathophysiology of SLE.

Cell-intrinsic expression of TLR9 in autoreactive B cells constrains BCR/TLR7-dependent responses

Endosomal TLRs play an important role in systemic autoimmune diseases, such as systemic erythematosus lupus, in which DNA- and RNA-associated autoantigens activate autoreactive B cells through TLR9- and TLR7-dependent pathways. Nevertheless, TLR9-deficient autoimmune-prone mice develop more severe clinical disease, whereas TLR7-deficient and TLR7/9-double deficient autoimmune-prone mice develop less severe disease. To determine whether the regulatory activity of TLR9 is B cell intrinsic, we directly compared the functional properties of autoantigen-activated wild-type, TLR9-deficient, and TLR7-deficient B cells in an experimental system in which proliferation depends on BCR/TLR coengagement. In vitro, TLR9-deficient cells are less dependent on survival factors for a sustained proliferative response than are either wild-type or TLR7-deficient cells. The TLR9-deficient cells also preferentially differentiate toward the plasma cell lineage, as indicated by expression of CD138, sustained expression of IRF4, and other molecular markers of plasma cells. In vivo, autoantigen-activated TLR9-deficient cells give rise to greater numbers of autoantibody-producing cells. Our results identify distinct roles for TLR7 and TLR9 in the differentiation of autoreactive B cells that explain the capacity of TLR9 to limit, as well as TLR7 to promote, the clinical features of systemic erythematosus lupus.

Synthetic oligodeoxynucleotides containing suppressive TTAGGG motifs inhibit AIM2 inflammasome activation

Synthetic oligodeoxynucleotides (ODNs) comprised of the immunosuppressive motif TTAGGG block TLR9 signaling, prevent STAT1 and STAT4 phosphorylation and attenuate a variety of inflammatory responses in vivo. In this study, we demonstrate that such suppressive ODN abrogate activation of cytosolic nucleic acid-sensing pathways. Pretreatment of dendritic cells and macrophages with the suppressive ODN-A151 abrogated type I IFN, TNF-α, and ISG induction in response to cytosolic dsDNA. In addition, A151 abrogated caspase-1-dependent IL-1β and IL-18 maturation in dendritic cells stimulated with dsDNA and murine CMV. Inhibition was dependent on A151's phosphorothioate backbone, whereas substitution of the guanosine residues for adenosine negatively affected potency. A151 mediates these effects by binding to AIM2 in a manner that is competitive with immune-stimulatory DNA and as a consequence prevents AIM2 inflammasome complex formation. Collectively, these findings reveal a new route by which suppressive ODNs modulate the immune system and unveil novel applications for suppressive ODNs in the treatment of infectious and autoimmune diseases.

Guanine modification of inhibitory oligonucleotides potentiates their suppressive function

Inhibitory TLR7 and/or TLR9 oligonucleotides (inhibitory oligonucleotide [INH-ODN]) are characterized by a phosphorothioate backbone and a CC(T)XXX₃₋₅GGG motif, respectively. INH-ODN 2088 is a prototypic member of this class of INH-ODN and acts as a TLR7 and TLR9 antagonist. It contains a G quadruple that leads to higher order structures by the formation of G tetrads. These structures are unfavorable for the prediction of their pharmacological and immunological behavior. We show in this study that modification of Gs within the G quadruple by 7-deaza-guanine or 7-deaza-2'-O-methyl-guanine avoids higher order structures and improves their inhibitory potential. Whereas TLR9-induced TNF-α secretion of bone marrow-derived macrophages and conventional dendritic cells was equally inhibited by INH-ODN 2088 and G-modified INH-ODNs such as INH-ODN 24888, TLR7-induced TNF-α release and TLR7- and TLR9-induced IL-12p40 release were significantly more impaired by G-modified INH-ODNs. Similarly, the IL-6 release of B cells from wild-type and autoimmune MRL/Mp-lpr/lpr mice was more efficiently impaired by G-modified INH-ODNs. Surprisingly, INH-ODN 2088 stimulated B cells to proliferate when used in higher doses. Finally, in vivo, in wild-type and autoimmune MRL/Mp-lpr/lpr mice, G-modified INH-ODN 24888 was significantly more efficient than unmodified INH-ODN 2088. In summary, G modification allows the development of INH-ODNs with superior inhibitory potency for inflammatory diseases with high medical need such as systemic lupus erythematosus.

A novel antagonist of Toll-like receptors 7, 8 and 9 suppresses lupus disease-associated parameters in NZBW/F1 mice

Systemic Lupus Erythematosus is an autoimmune disease characterized by production of autoantibodies against nucleic acid-associated antigens. Endogenous DNA and RNA associated with these antigens stimulate inflammatory responses through Toll-like receptors (TLRs) and exacerbate lupus disease pathology. We have evaluated an antagonist of TLR7, 8 and 9 as a therapeutic agent in lupus-prone NZBW/F1 mice. NZBW/F1 mice treated with the antagonist had lower serum levels of autoantibodies targeting DNA, RNP, Smith antigen, SSA and SSB than did untreated mice. Reduction in blood urea nitrogen and proteinuria and improvements in kidney histopathology were observed in antagonist-treated mice. The antagonist treatment also reduced serum IL-12 and IL-1β and increased IL-10 levels. Levels of mRNA for IL-6, iNOS and IL-1β were lower in the kidneys and spleen of antagonist-treated mice than in those of untreated mice. Levels of mRNA for IP-10, TNFRSF9 and FASL were lower and IL-4 mRNA were higher in spleens of antagonist-treated mice than in spleens of untreated mice. mRNA for the inflammasome component NLRP3 was lower and mRNA for the antioxidant enzymes, catalase and glutathione peroxidase 1 was higher in the kidneys of antagonist-treated mice than in those of untreated mice. These results show that the antagonist of TLR7, 8 and 9 effectively inhibits inflammatory pathways involved in the development of lupus in NZBW/F1 mice and constitutes a potential therapeutic approach for the treatment of lupus and other autoimmune diseases.

Modulating toll-like receptor 7 and 9 responses as therapy for allergy and autoimmunity

Type I allergic diseases, such as allergic rhinitis and asthma, depend on allergen-induced T-helper type 2 (Th2) cells and IgE-secreting plasma cells. Fortunately, this harmful immune response can be modified by engaging Toll-like receptor (TLR)7 and TLR9, offering hopes to allergy sufferers. While clinical trials employing synthetic ligands for TLR7 or TLR9 are under way, one can wonder whether TLR7 or TLR9 engagements may trigger inadvertent autoreactivity and/or Th1-/Th17-mediated tissue pathology. To neutralize such danger, we have pioneered the development of potent TLR9 pathway antagonists, inhibitory oligonucleotides (INH-ODNs), which work in a sequence-specific manner. Interestingly, INH-ODNs also have TLR7-inhibitory properties; however, these effects appear to be sequence independent and phosphorothioate backbone dependent. In B cells, co-engagement of the B-cell receptor for antigen and TLR7 or TLR9 may influence how INH-ODNs impose their regulatory effects. INH-ODNs block TLR9 activation by competitively antagonizing ligand binding to proteolytically cleaved C-terminal TLR9 fragment. One may envision future use of INH-ODNs in systemic autoimmune diseases, DNA-mediated sepsis, or other situations in which chronic inflammation results from abnormal TLR7- and/or TLR9-mediated immune activation.

Design, synthesis and biological evaluation of novel antagonist compounds of Toll-like receptors 7, 8 and 9

Oligonucleotides containing an immune-stimulatory motif and an immune-regulatory motif act as antagonists of Toll-like receptor (TLR)7 and TLR9. In the present study, we designed and synthesized oligonucleotide-based antagonists of TLR7, 8 and 9 containing a 7-deaza-dG or arabino-G modification in the immune-stimulatory motif and 2′-O-methylribonucleotides as the immune-regulatory motif. We evaluated the biological properties of these novel synthetic oligoribonucleotides as antagonists of TLRs 7, 8 and 9 in murine and human cell-based assays and in vivo in mice and non-human primates. In HEK293, mouse and human cell-based assays, the antagonist compounds inhibited signaling pathways and production of a broad range of cytokines, including tumour necrosis factor alpha (TNF-α), interleukin (IL)-12, IL-6, interferon (IFN)-α, IL-1β and interferon gamma-induced protein (IP)-10, mediated by TLR7, 8 and 9. In vivo in mice, the antagonist compounds inhibited TLR7- and TLR9-mediated cytokine induction in a dose- and time-dependent fashion. Peripheral blood mononuclear cells (PBMCs) obtained from antagonist compound-treated monkeys secreted lower levels of TLR7-, 8- and 9-mediated cytokines than did PBMCs taken before antagonist administration. The antagonist compounds described herein provide novel agents for the potential treatment of autoimmune and inflammatory diseases.

B cell TLR7 expression drives anti-RNA autoantibody production and exacerbates disease in systemic lupus erythematosus-prone mice

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disease characterized by the production of antinuclear autoantibodies. Antinuclear autoantibody development is recognized as one of the initial stages of disease that often results in systemic inflammation, kidney disease, and death. The etiology is complex, but it is clear that innate pathways may play an important role in disease progression. Recent data have highlighted an important role for the TLR family, particularly TLR7, in both human disease and murine models. In this study, we have presented a low copy conditional TLR7 transgenic (Tg7) mouse strain that does not develop spontaneous autoimmunity. When we combine Tg7 with the Sle1 lupus susceptibility locus, the mice develop severe disease. Using the CD19(Cre) recombinase system, we normalized expression of TLR7 solely within the B cells. Using this method we demonstrated that overexpression of TLR7 within the B cell compartment reduces the marginal zone B cell compartment and increases B and T cell activation but not T follicular helper cell development. Moreover, this enhanced B cell TLR7 expression permits the specific development of Abs to RNA/protein complexes and exacerbates SLE disease.

Structure-activity relationship of a guanine-free oligodeoxynucleotide as immunopotent inhibitor

Excessive innate immune response could contribute to the pathogenesis of inflammatory and autoimmune diseases. It is required to develop agents to inhibit the overwhelming innate immune response. SAT05f, an inhibitory ODN with CCT repeat sequence found in human microsatellite DNA, has been demonstrated to down-regulate TLR7/9-mediated innate immune response, protect mice from D-GalN/CpG ODN induced lethal shock, and reduce anti-ssDNA antibody level in the lupus-prone mice induced by chronic graft versus host disease (cGVHD). In this article, to explore the structure-activity relationship of SAT05f, we designed and synthesized a series of ODNs based on the sequence of SAT05f by changing repeat number of the CCT unit, substituting CCT unit with AAG at 3' end or 5' end or in the middle and by forming hairpin at 5' or 3' end, and tested their inhibitory effect on the CpG ODN induced proliferation and TNF-α production in murine immune cells. The results indicated that 1) at least 8 CCT units were required for a CCT repeat ODN to display its inhibitory activity; 2) CCT unit at 3' end of SAT05f was necessary for its full inhibitory activity; and 3) 5' end of SAT05f could be modified to design a more potent SAT05f derived inhibitory ODN. The data provided here would be helpful for finding a potent inhibitory ODN as a candidate medicament for the treatment of diseases associated with over-activated innate immune response.

Myeloid dendritic cells from B6.NZM Sle1/Sle2/Sle3 lupus-prone mice express an IFN signature that precedes disease onset

Patients with systemic lupus erythematosus show an overexpression of type I IFN-responsive genes that is referred to as "IFN signature." We found that B6.NZMSle1/Sle2/Sle3 (Sle1,2,3) lupus-prone mice also express an IFN signature compared with non-autoimmune C57BL/6 mice. In vitro, myeloid dendritic cells (mDCs) (GM-CSF bone marrow-derived dendritic cells; BMDCs) from Sle1,2,3 mice constitutively overexpressed IFN-responsive genes such as IFN-β, Oas-3, Mx-1, ISG-15, and CXCL10 and members of the IFN signaling pathway STAT1, STAT2, and IRF7. The IFN signature was similar in Sle1,2,3 BMDCs from young, pre-autoimmune mice and from mice with high titers of autoantibodies, suggesting that the IFN signature in mDCs precedes disease onset and is independent from the autoantibodies. Sle1,2,3 BMDCs hyperresponded to stimulation with IFN-α and the TLR7 and TLR9 agonists R848 and CpGs. We propose that this hyperresponse is induced by the IFN signature and only partially contributes to the signature, as oligonucleotides inhibitory for TLR7 and TLR9 only partially suppressed the constitutive IFN signature, and pre-exposure to IFN-α induced the same hyperresponse in wild-type BMDCs as in Sle1,2,3 BMDCs. In vivo, mDCs and to a lesser extent T and B cells from young prediseased Sle1,2,3 mice also expressed the IFN signature, although they lacked the strength that BMDCs showed in vitro. Sle1,2,3 plasmacytoid DCs expressed the IFN signature in vitro but not in vivo, suggesting that mDCs may be more relevant before disease onset. We propose that Sle1,2,3 mice are useful tools to study the role of the IFN signature in lupus pathogenesis.

A novel pathogenetic concept-antiviral immunity in lupus nephritis

Lupus nephritis is a complication of systemic lupus erythematosus, a heterogeneous autoimmune syndrome involving multiple pathways. Accumulating data from the fields of genetics, clinical science, transcriptomics and basic immunology indicate that antiviral immunity has relevance in the pathogenesis of lupus nephritis. This idea is based on the existence of genetic variants that promote the persistence of nuclear particles in the extracellular space or inside lysosomes. Such nuclear particles mimic viral particles and their RNA or DNA components activate viral nucleic acid recognition receptors in antigen-presenting cells. These autoadjuvant effects of endogenous nucleic acids promote an inappropriate immune interpretation of the nuclear particles during antigen presentation. This process fosters the expansion of autoreactive T cells and B cells, which promotes autoantibody production and immune complex glomerulonephritis. The release of interferon α sets off an antiviral immune response with a coordinated induction of hundreds of antiviral genes both inside and outside the kidney. In this article we summarize the available data indicating that innate immunity triggers antiviral immunity in systemic lupus erythematosus. We also discuss the related implications for innovative therapeutic strategies.

The potential importance of Toll-like receptors in ankylosing spondylitis

Cells involved in innate immunity scan for pathogens via extracellular and intracellular (endosomal) pattern recognition receptors (PRRs). Engagement of PRRs by a specific ligand results in downstream activation of intracellular inflammatory cascades. There is emerging evidence indicating that one class of PRR, the Toll-like receptor (TLR) plays a potential role in the pathogenesis of spondyloarthropathies. Since certain Gram-negative bacteria are known to act as triggers for reactive arthritis, there has been much interest in studying the role of TLRs in spondyloarthropathies. In this article, we introduce the immunology of TLRs followed by a discussion of their potential role in ankylosing spondylitis.

Mdm2 promotes systemic lupus erythematosus and lupus nephritis

Systemic lupus erythematosus (SLE) is a polyclonal autoimmune syndrome directed against multiple nuclear autoantigens. Although RNA and DNA seem to have identical immunostimulatory effects on systemic and intrarenal inflammation, each seems to differ with regard to the propensity to induce mitogenic effects such as lymphoproliferation. To identify potential mechanisms by which DNA specifically contributes to the pathogenesis of lupus nephritis, we stimulated cells with immunostimulatory DNA or RNA in vitro and used microarray to compare the transcriptomes of RNA- and DNA-induced genes. Immunostimulatory DNA, but not RNA, induced Mdm2, which is a negative regulator of p53. In vivo, we observed greater expression and activation of Mdm2 in the spleen and kidneys in a mouse model of lupus (MRL-Fas(lpr) mice) than healthy controls. Treatment of MRL-Fas(lpr) mice with the Mdm2 inhibitor nutlin-3a prevented nephritis and lung disease and significantly prolonged survival. Inhibition of Mdm2 reduced systemic inflammation and abrogated immune complex disease by suppressing plasma cells and the production of lupus autoantibodies. In addition, nutlin-3a suppressed the abnormal expansion of all T cell subsets, including CD3(+)CD4(-)CD8(-) T cells, which associated with attenuated systemic inflammation. However, inhibiting Mdm2 did not cause myelosuppression or affect splenic regulatory T cells, neutrophils, dendritic cells, or monocytes. Taken together, these data suggest that the induction of Mdm2 promotes the expansion of plasma cells and CD3(+)CD4(-)CD8(-) T cells, which cause autoantibody production and immune complex disease in MRL-Fas(lpr) mice. Antagonizing Mdm2 may have therapeutic potential in lupus nephritis.

The TLR7/8 ligand resiquimod targets monocyte-derived dendritic cell differentiation via TLR8 and augments functional dendritic cell generation

Imidazoquinolone compounds, such as resiquimod are Toll-like receptor (TLR) 7/8 ligands representing novel immune response modifiers undergoing clinical testing. Resiquimod has been reported to modulate conventional human monocyte-derived DC (moDC) differentiation, but the role of TLR7 and TLR8 is unclear. We directly dissected the TLR7- and TLR8-dependency by employing selective TLR7 ligands and resiquimod-coculture experiments with inhibitory oligonucleotides (iODN) suppressing TLR7, TLR7+8 or TLR7+8+9. Selective TLR7 ligands did not affect conventional moDC differentiation as analyzed by CD14/CD1a expression. iODN experiments confirmed that resiquimod's effects during DC differentiation were antagonized only with TLR8 iODNs. Direct comparison of resiquimod DC with TLR7- and control-DC revealed significantly higher T-cell costimulatory molecule and MHC class II expression. Resiquimod DC promoted significantly stronger allogeneic T-cell proliferation and stronger naïve CD4(+) T-cell proliferation. These results indicate the relevance of TLR8 for human monocyte-derived DC differentiation and maturation and may be relevant for clinical trials employing resiquimod.

Nucleic acid-binding polymers as anti-inflammatory agents

Dead and dying cells release nucleic acids. These extracellular RNAs and DNAs can be taken up by inflammatory cells and activate multiple nucleic acid-sensing toll-like receptors (TLR3, 7, 8, and 9). The inappropriate activation of these TLRs can engender a variety of inflammatory and autoimmune diseases. The redundancy of the TLR family encouraged us to seek materials that can neutralize the proinflammatory effects of any nucleic acid regardless of its sequence, structure or chemistry. Herein we demonstrate that certain nucleic acid-binding polymers can inhibit activation of all nucleic acid-sensing TLRs irrespective of whether they recognize ssRNA, dsRNA or hypomethylated DNA. Furthermore, systemic administration of such polymers can prevent fatal liver injury engendered by proinflammatory nucleic acids in an acute toxic shock model in mice. Therefore these polymers represent a novel class of anti-inflammatory agent that can act as molecular scavengers to neutralize the proinflammatory effects of various nucleic acids.

Optimal oligonucleotide sequences for TLR9 inhibitory activity in human cells: lack of correlation with TLR9 binding

Toll-like receptor (TLR)9 performs our innate response to bacterial DNA, warning us of the presence of infection. Inhibitory oligodeoxyribonucleotides (INH-ODN) have been developed that selectively block activation of mouse TLR9. Their inhibitory motif consisting of CCx(not-C)(not-C)xxGGG (x = any base) also reduces anti-DNA antibodies in lupus mice. The current study demonstrates that this motif also provides the sequences required to block TLR9 in human B cells and human embryonic kidney (HEK) cells transfected with human TLR9. However, extending the sequence by four to five bases at the 5' end enhanced activity and this enhancement was greater when a phosphorothioate (pS) backbone replaced the native phosphodiester (pO) backbone. A series of pO-backbone INH-ODN representing a 500-fold range of activity in biologic assays was shown to cover less than a 2.5-fold range of avidity for binding human TLR9-Ig fusion protein, eliminating TLR9 ectodomain binding as the explanation for sequence-specific differences in biologic activity. With few exceptions, the relative activity of INH-ODN in Namalwa cells and HEK/human TLR9 cells was similar to that seen in mouse B cells. INH-ODN activity in human peripheral blood B cells correlated significantly with the cell line data. These results favor the conclusion that although the backbone determines strength of TLR9 binding, critical recognition of the INH-ODN sequence necessary for biologic activity is performed by a molecule that is not TLR9. These studies also identify the strongest INH-ODN for human B cells, helping to guide the selection of INH-ODN sequences for therapeutics in any situation where inflammation is enhanced by TLR9.

Toll-like receptor driven B cell activation in the induction of systemic autoimmunity

Studies over the past decade have demonstrated a key role for pattern recognition receptors in the activation of autoreactive B cells. Self reactive B cells that manage to escape negative selection often express relatively low affinity receptors for self antigens (ignorant B cells), and can only be activated by integrating a relatively weak BCR signal with signals from additional receptors. Members of the toll-like receptor (TLR) gene family, and especially the nucleic acid binding receptors TLR 7, 8 and 9, appear to play a key role in this regard and promote the production of autoantibodies reactive with DNA- or RNA-associated autoantigens. These autoantibodies are able to form immune complexes with soluble or cell-bound ligands, and these immune complexes can in turn activate a second round of proinflammatory cells that further contribute to the autoimmune disease process. Recent data have emerged showing a pathogenic role for TLR7, with an opposing, protective role for TLR9. Targeting these disregulated pathways offers a therapeutic opportunity to treat autoimmune diseases without crippling the entire immune system. Further understanding of the role of specific receptors, cell subsets, and inhibitory signals that govern these TLR-associated pathways will enable future therapeutics to be tailored to specific categories of autoimmune disease.

Aggregation and secondary loop structure of oligonucleotides do not determine their ability to inhibit TLR9

Toll-like receptor 9 (TLR9) is an endosomal DNA sensor that warns us of the presence of infectious danger and triggers a rapid pro-inflammatory response in dendritic cells, macrophages, and B cells. The consequences of uncontrolled TLR9 activation can be detrimental for the host, contributing to the pathogenesis of bacterial septic shock or autoimmune diseases, such as systemic lupus erythematosus. Therefore, we need to develop TLR9 antagonists. We and others have created inhibitory oligonucleotides (INH-ODN) that are capable of sequence-dependent inhibition of TLR9-induced activation in both human and mouse cells. However, it is not clear whether marked differences in INH-ODN activity related to base sequence derived from polymerization of INH-ODNs or their ability to complex with stimulatory CpG-oligonucleotides (ST-ODN). Furthermore, the 5' end of INH-ODNs may assume a particular loop configuration that may be needed for binding to a critical site on TLR9. Here, we show that 1) G-tetrads required for ODN stacking were compatible with INH-ODN activity but were not necessary; 2) there was no relationship between activity and self-association at endosomal pH; 3) there was no evidence for direct binding between ST-ODNs and INH-ODNs; 4) when a 3G sequence was disrupted, despite a preserved stem-loop formation, INH-ODN activity was abolished. These results support the conclusion that certain features of the primary linear sequence are critical for TLR9 inhibition, but changes in secondary structure or in ODN aggregation are irrelevant.

Engagement of the B cell receptor for antigen differentially affects B cell responses to Toll-like receptor-7 agonists and antagonists in BXSB mice

Nucleic acid sensors of the Toll-like receptor (TLR) family play a well-established role in the pathogenesis of lupus. This is particularly true for a single-stranded RNA-sensing TLR-7 receptor, as lupus mice lacking TLR-7 show ameliorated disease. Cytosine-guanosine dinucleotide (CpG)-DNA-sensing TLR-9, conversely, has a complex regulatory role in systemic lupus erythematosus (SLE). Much less is known about whether signals through the B cell receptor for antigen (BCR) may affect the ability of B cells to respond to suboptimal TLR-7 agonists and antagonists. We studied this question in prediseased BXSB male and female B cells. We found that male B cells responded more vigorously to numerous TLR-7 ligands and this responsiveness was enhanced further upon co-engagement of the BCR. This synergy was seen primarily with the interleukin (IL)-6 secretion. A number of 32-mer inhibitory oligonucleotides (INH-ODNs) with a nuclease-resistant phosphorothioate backbone were capable of blocking TLR-7, but not BCR-induced B cell activation, with an inhibitory concentration (IC)(50) of approximately 100 nm. Surprisingly, while the presence of a single TGC motif at the 5' end of an ODN did not increase its inhibitory capacity, INH-ODNs containing multiple TGC motifs had greater inhibitory potency. When BCR and TLR-7 were co-engaged, INH-ODNs showed a differential effect on B cell activation. Whereas apoptosis protection and G1-M entry completely escaped suppression, IL-6 secretion remained sensitive to inhibition, although with a 10-fold lower potency. Our results suggest that while TLR-7 antagonists may be considered as lupus therapeutics, simultaneous co-engagement of the TLR-7 and BCR might favour autoreactive B cell survival. This hypothesis needs further experimental validation.

5'-Phosphate oligodeoxynucleotides enhance the phosphodiester-CpG DNA-induced inflammatory response in macrophages

Dying cells release genomic DNA into the surroundings where the DNA is first degraded to oligodeoxynucleotides, then to nucleotides, nucleosides and so on. Given that the unmethylated CpG dinucleotide (CpG motif), which is characteristic of bacterial DNA, is also contained in mammalian DNA and has been reported to be involved in the exacerbation of DNA-associated autoimmune diseases, we investigated whether nucleotides and nucleosides affect immune responses to phosphodiester (PO)-CpG DNA. Addition of non-CpG DNA to RAW264.7, murine macrophage-like cells, induced no significant TNF-α production irrespective of treatment with DNase I; however, DNase I-treated, but not untreated, non-CpG DNA increased the PO-CpG DNA-mediated TNF-α production. This increase was not observed with phosphorothioate-CpG DNA or ligands for TLR3, TLR4 or TLR7. Deoxynucleotides with a 5'-phosphate showed similar effects to those of DNase I-treated non-CpG DNA, but DNase II-treated DNA or deoxynucleosides did not. Subcutaneous injection of PO-CpG DNA into the mouse footpad induced little swelling of the paw; however, significant swelling was observed when DNase I-treated DNA was co-injected with PO-CpG DNA. These results imply that PO-CpG DNA-dependent inflammatory responses are increased by DNA molecules with a 5'-phosphate; such molecules could therefore be considered as exacerbating factors for CpG motif-related inflammation.

FcγRIIB regulation of BCR/TLR-dependent autoreactive B-cell responses

Crosslinking of Fc γ receptor II B (FcγRIIB) and the BCR by immune complexes (IC) can downregulate antigen-specific B-cell responses. Accordingly, FcγRIIB deficiencies have been associated with B-cell hyperactivity in patients with systemic lupus erythematosus and mouse models of lupus. However, we have previously shown that murine IgG2a-autoreactive AM14 B cells respond robustly to chromatin-associated IC through a mechanism dependent on both the BCR and the endosomal TLR9, despite FcγRIIB coexpression. To further evaluate the potential contribution of FcγRIIB to the regulation of autoreactive B cells, we have now compared the IC-triggered responses of FcγRIIB-deficient and FcγRIIB-sufficient AM14 B cells. We find that FcγRIIB-deficient cells respond significantly better than FcγRIIB-sufficient cells when stimulated with DNA IC that incorporate low-affinity TLR9 ligand (CG-poor dsDNA fragments). AM14 B cells also respond to RNA-associated IC through BCR/TLR7 coengagement, but such BCR/TLR7-dependent responses are normally highly dependent on IFN-α costimulation. However, we now show that AM14 FcγRIIB(-/-) B cells are very effectively activated by RNA IC without supplemental IFN-α priming. These results demonstrate that FcγRIIB can effectively modulate both BCR/TLR9 and BCR/TLR7 endosomal-dependent activation of autoreactive B cells.

Cytokine induction by immunostimulatory DNA in porcine PBMC is impaired by a hairpin forming sequence motif from the genome of Porcine Circovirus type 2 (PCV2)

Porcine Circovirus type 2 (PCV2) can cause postweaning multisystemic wasting syndrome (PMWS) in young pigs with severe immunosuppression as a major characteristic of the disease complex. Despite the dramatic involvement of the immune system, the interaction between PCV2 and the host is until date not well understood. The DNA genome of PCV2 contains sequences that in synthetic form (oligodeoxyribonucleotides; ODNs) can act immunomodulatory on porcine peripheral blood mononuclear cells (poPBMCs) in vitro. One such sequence (ODN PCV2/1) acts inhibitory on interferon (IFN)-α production induced by immunostimulatory DNA but not that induced by RNA, and the inhibitory activity is dependent on secondary structure formation. In the present study, the characteristic of ODN PCV2/1 was examined further by altering the nucleotide sequence to disrupt hairpin structure formation but still enable multimer structures through G-tetrads. This modification resulted in loss of IFN-α-inhibitory activity of the ODN and thus indicated the importance of hairpin structures. In addition, ODN PCV2/1 was compared to another inhibitory ODN (IRS 869) previously used in human and murine cells. In contrast to ODN PCV2/1, ODN IRS 869 did not inhibit IFN-α production induced by class A ODN 2216 but was a more efficient inhibitor of IFN-α production induced by plasmid DNA than ODN PCV2/1. In cultures induced by the RNA stimulator Poly I:C, however, a strong synergistic IFN-α stimulatory effect was seen in combination with ODN IRS 869. These results indicate that ODN PCV2/1 and ODN IRS 869 function through separate mechanisms to affect cytokine production by immune cells. The effect of ODN PCV2/1 was studied further by monitoring the expression of mRNA for IFN-α, IL-12p40, IL-10, IL-6, IFN-γ, IL-1β, TGF-β, and TNF-α in cultures of poPBMC stimulated with ODN 2216 or Poly I:C. Results from qPCR analyses showed that ODN PCV2/1 clearly inhibited the expression of IFN-α, IL-12p40, IL-10 and IL-6 when induced by ODN 2216, but did not seem to affect any of the cytokines examined when induced by Poly I:C. Initial studies using confocal microscopy and fluorochrome labelled ODNs indicate that ODN 2216 and ODN PCV2/1 co-localize in subpopulations of poPBMC.

B-cell receptor for antigen modulates B-cell responses to complex TLR9 agonists and antagonists: implications for systemic lupus erythematosus

The capacity to make secondary structures significantly affects the ability of Toll-like receptor 9 (TLR9) agonists and antagonists to either induce or block TLR9-dependent activation in B cells. However, it has a minor impact on TLR9-induced activation in interferon alpha (IFNα)-producing dendritic cells. Based on the ability of inhibitory oligodeoxynucleotides to form predictable secondary structures, we have classified TLR9-antagonists into Class R ('restricted', palindromic) and Class B ('broadly reactive', linear) oligodeoxynucleotides. In non-autoreactive B cells, Class R oligodeoxynucleotides are at least 10-fold less potent TLR9-inhibitors. We wanted to determine whether engagement of the B-cell receptor for antigen could overcome this restriction. Here we show that in non-autoreactive mouse B cells, B-cell receptor for antigen engagement increased the potency of Class R oligodeoxynucleotides for TLR9 activation at least 10-fold, making it equal in potency to linear oligodeoxynucleotides. However, this enhanced potency was selective for TLR9-induced B-cell cycling and apoptosis protection while TLR9-induced IL-6, an event that strongly depends on signaling via late endosomes, still required 10 times more Class R oligodeoxynucleotides. Thus, pathway-specific effects of Class R oligodeoxynucleotides for TLR9/B-cell receptor for antigen co-stimulated B cells may have therapeutic advantages over non-selective targeting of B cells, a strategy that may be seen as a potential therapy for human systemic lupus erythematosus.

Nuclease deficiencies promote end-stage lupus nephritis but not nephritogenic autoimmunity in (NZB × NZW) F1 mice

New information has profoundly improved our insight into the processes that account for lupus nephritis. This review summarizes the data proving that secondary necrotic chromatin fragments are generated and retained in kidneys at time-points when the major renal nuclease Dnase-1 is selectively and severely downregulated. Second, we discuss data, which may indicate that nuclease deficiencies are not associated with autoimmunity to chromatin. Secondary to downregulation of renal Dnase-1, large chromatin fragment-immunoglobulin G complexes are accumulated in glomerular basement membranes of patients producing anti-chromatin autoantibodies. Exposure of chromatin in situ in glomeruli is the factor that renders anti-chromatin (anti-dsDNA and anti-nucleosome) antibodies nephritogenic. Without exposed chromatin, they circulate as non-pathogenic antibodies. This shows that acquired loss of renal Dnase-1 enzyme activity is a dominant event responsible for the progression of lupus nephritis into end-stage disease. Before the loss of Dnase-1, lupus-prone (NZB × NZW) F1 mice develop mild or silent nephritis with mesangial immune complex deposits, which correlates solely with onset of anti-dsDNA antibody production. The principal cellular and molecular requirements needed to produce these autoantibodies have been explained experimentally, but the mechanism(s) accounting for them in vivo in context of lupus nephritis have not yet been determined. However, published data show that defects in nucleases operational in apoptotic or necrotic cell death are not associated with the induction of nephritogenic anti-dsDNA autoantibodies. The data discussed in this study explain how an unusual exposure of chromatin may be a central factor in the evolution of lupus nephritis in (NZB x NZW) F1 mice, but not in promoting nephritogenic chromatin-specific autoimmunity.

Classification, mechanisms of action, and therapeutic applications of inhibitory oligonucleotides for Toll-like receptors (TLR) 7 and 9

Our immune defense depends on two specialized armed forces. The innate force acts as an alarm mechanism that senses changes in the microenvironment through the recognition of common microbial patterns by Toll-like receptors (TLR) and NOD proteins. It rapidly generates an inflammatory response aimed at neutralizing the intruder at the mucosal checkpoint. The innate arm also communicates this message with more specialized adaptive forces represented by pathogen-specific B cells and T cells. Interestingly, B cells also express some innate sensors, like TLR7 and TLR9, and may respond to bacterial hypomethylated CpG motifs and single-stranded RNA viruses. Intracellular nucleic acid sensing TLRs play an important role in the pathogenesis of Systemic Lupus Erythematosus (SLE). In this review, we describe recent achievements in the development of oligonucleotide—(ODN)-based inhibitors of TLR9 and/or TLR7 signaling. We categorize these novel therapeutics into Classes G, R, and B based on their cellular and molecular targets. Several short ODNs have already shown promise as pathway-specific therapeutics for animal lupus. We envision their future use in human SLE, microbial DNA-dependent sepsis, and in other autoinflammatory diseases.

Nucleic acid sensing receptors in systemic lupus erythematosus: development of novel DNA- and/or RNA-like analogues for treating lupus

Double-stranded (ds) DNA, DNA- or RNA-associated nucleoproteins are the primary autoimmune targets in SLE, yet their relative inability to trigger similar autoimmune responses in experimental animals has fascinated scientists for decades. While many cellular proteins bind non-specifically negatively charged nucleic acids, it was discovered only recently that several intracellular proteins are involved directly in innate recognition of exogenous DNA or RNA, or cytosol-residing DNA or RNA viruses. Thus, endosomal Toll-like receptors (TLR) mediate responses to double-stranded RNA (TLR-3), single-stranded RNA (TLR-7/8) or unmethylated bacterial cytosine (phosphodiester) guanine (CpG)-DNA (TLR-9), while DNA-dependent activator of IRFs/Z-DNA binding protein 1 (DAI/ZBP1), haematopoietic IFN-inducible nuclear protein-200 (p202), absent in melanoma 2 (AIM2), RNA polymerase III, retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) mediate responses to cytosolic dsDNA or dsRNA, respectively. TLR-induced responses are more robust than those induced by cytosolic DNA- or RNA- sensors, the later usually being limited to interferon regulatory factor 3 (IRF3)-dependent type I interferon (IFN) induction and nuclear factor (NF)-kappaB activation. Interestingly, AIM2 is not capable of inducing type I IFN, but rather plays a role in caspase I activation. DNA- or RNA-like synthetic inhibitory oligonucleotides (INH-ODN) have been developed that antagonize TLR-7- and/or TLR-9-induced activation in autoimmune B cells and in type I IFN-producing dendritic cells at low nanomolar concentrations. It is not known whether these INH-ODNs have any agonistic or antagonistic effects on cytosolic DNA or RNA sensors. While this remains to be determined in the future, in vivo studies have already shown their potential for preventing spontaneous lupus in various animal models of lupus. Several groups are exploring the possibility of translating these INH-ODNs into human therapeutics for treating SLE and bacterial DNA-induced sepsis.

Interferon-alpha and -beta in kidney inflammation

Type I interferons, interferon-alpha and interferon-beta, are central regulators of antiviral immunity and autoimmunity, but little is known about their role in renal inflammation. Recent work documents that viral nucleic acids are potent inducers of interferon-alpha and interferon-beta in mesangial cells and glomerular endothelial cells. This review discusses the available evidence on the role of interferon-alpha and interferon-beta in viral nephropathies, in kidney diseases triggered by extrarenal infections, in lupus nephritis, and in other kidney disease entities. Finally, we propose areas of research that may help unravel the roles of type I interferons and interferon-related genes in the renal field.

Pseudoviral immunity - a novel concept for lupus

Systemic lupus erythematosus (SLE or lupus) is a polygenic syndrome of immunity against nuclear autoantigens. Recent data from several fields now suggest 'pseudoviral' immunity as a novel disease concept. Known lupus risk factors commonly compromise those mechanisms that protect chromatin and ribonucleoprotein particles from activating viral nucleic acid sensors. This process activates antigen-presenting cells and induces type I interferons. These central mediators of antiviral immunity have similar proinflammatory roles in lupus, explaining overlapping clinical manifestations, immunopathology and ultrastructural abnormalities in systemic viral infection and lupus. Structurally, chromatin and ribonucleoprotein particles resemble viral particles and have a similar potency to trigger antigen-specific B- and T-cell responses. Therefore, self nucleic acid-driven 'pseudoviral' immunity is evolving as another concept in understanding the pathogenesis of lupus and may offer novel targets for therapy.

Inhibitory short synthetic oligodeoxynucleotides and lupus

B cells and antigen-presenting cells express a group of intracellular Toll-like receptors (TLRs) that recognize nucleic acids and can be accessed only when apoptotic debris or immune complexes are internalized by B-cell receptors or Fc receptors. This results in rapid cell activation and release of inflammatory mediators that perpetuate the autoantibody response. TLR-7 and TLR-9 are required to generate autoantibodies to RNA and DNA, respectively. Synthetic oligodeoxynucleotides that inhibit the activity of these intracellular TLRs attenuate systemic lupus erythematosus in mouse models and may be of therapeutic benefit in human systemic lupus erythematosus.