Exacerbated autoimmunity in the absence of TLR9 in MRL.Fas(lpr) mice depends on Ifnar1

The essential roles of memory B cells in the pathogenesis of systemic lupus erythematosus

Emerging evidence indicates that memory B cells are dysfunctional in systemic lupus erythematosus (SLE). They are hyporesponsive to signalling through the B cell receptor (BCR) but retain responsiveness to Toll-like receptor (TLR) and type I interferon signalling, as well as to T cell-mediated activation via CD40-CD154. Chronic exposure to immune complexes of ribonucleoprotein (RNP)-specific autoantibodies and TLR-engaging or BCR-engaging cargo is likely to contribute to this partially anergic phenotype. TLR7 or TLR8 signalling and the resulting production of type I interferon, as well as the sustained activation by bystander T cells, fuel a positive feedforward loop in memory B cells that can evade negative selection and permit preferential expansion of anti-RNP autoantibodies. Clinical trials of autologous stem cell transplantation or of B cell-targeted monoclonal antibodies and chimeric antigen receptor (CAR) T cells have correlated replenishment of the memory B cell population with relapse of SLE. Moreover, the BCR hyporesponsiveness of memory B cells might explain the failure of non-depleting B cell-targeting approaches in SLE, including BTK inhibitors and anti-CD22 monoclonal antibodies. Thus, targeting of dysfunctional memory B cells might prove effective in SLE, while also avoiding the adverse events of broad-spectrum targeting of B cell and plasma cell subsets that are not directly involved in disease pathogenesis.

Immunometabolic Mechanisms of LANCL2 in CD4+ T Cells and Phagocytes Provide Protection from Systemic Lupus Erythematosus

Lanthionine synthetase C-like 2 (LANCL2) is an immunoregulatory therapeutic target for autoimmune diseases. NIM-1324 is an investigational new drug aimed at addressing the unmet clinical needs of patients with systemic lupus erythematosus (SLE) by targeting the LANCL2 immunometabolic pathway. In R848 and bm12 adoptive transfer models of systemic inflammation that share pathologies with SLE, Lancl2-/- mice experienced greater mortality, increased spleen weight, and reduced CD25hi FOXP3+ CD4+ regulatory T cells compared with the wild type. Conversely, treatment with NIM-1324 in the wild type increased CD25hi FOXP3+ regulatory T cells while reducing inflammatory IL-17+ and IL-21+ CD4+ T cell subsets in the spleen. In traditional mouse models of SLE (NZB/W F1 and MRL/lpr), oral treatment with NIM-1324 protected against weight loss and proteinuria, decreased anti-dsDNA titers, and provided similar changes to the CD4+ T cell compartment in the spleen. The pharmacological activation of LANCL2 by NIM-1324 rescued hypocomplementemia, reduced kidney histopathological scores, and decreased blood IFN response genes and inflammatory cytokines. The loss of LANCL2 in phagocytes impairs phagosome processing, leading to increased uptake of material and inflammatory cytokine production, yet decreased markers of endosomal maturation, phagosome turnover, and lysozyme activity. Treatment with NIM-1324 increases metabolic and lysozyme activity in the phagosome, providing support for increased markers of early phagosome function. This efficacy translated to human PBMCs from patients with SLE, because ex vivo treatment with NIM-1324 resulted in reduced levels of IFN-α, IL-6, and IL-8. Consequently, the activation of LANCL2 effectively modulates CD4+ T cell differentiation and phagocyte activation, supporting immune tolerance in SLE.

EGFR-ErbB2 dual kinase inhibitor lapatinib decreases autoantibody levels and worsens renal disease in Interferon α-accelerated murine lupus

Glomerulonephritis remains a major cause of morbidity and mortality in systemic lupus erythematosus (SLE). We have reported that expression of HER2/ErbB2, a member of the EGFR family, is increased in kidneys of patients and mice with lupus nephritis. We therefore asked if EGFR-family inhibition could ameliorate murine lupus nephritis. We used lapatinib, an EGFR-ErbB2 dual kinase inhibitor in female lupus-prone NZBxW/F1 mice, in which lupus onset was accelerated by injecting an IFN-α-expressing adenovirus. Mice received lapatinib (75 mg/Kg) or vehicle from the beginning of the acceleration or after the mice developed severe proteinuria (>300 mg/dL). Autoantibodies, kidney disease and markers of fibrosis and wound healing were analyzed. Exposure to IFNα induced ErbB2 expression in the kidney of lupus prone mice. Lapatinib, administered before but not after renal disease onset, lowered autoantibody titers and lessened immune complex deposition in the kidney. However, lapatinib increased proteinuria, kidney fibrosis and mouse mortality. Lapatinib also inhibited an in vitro wound healing assay testing renal cells. Our results suggest that EGFR-ErbB2 dual kinase inhibitor lapatinib decreases autoimmunity but worsens renal disease in IFNα-accelerated lupus, by increasing fibrosis and inhibiting wound healing. Type I Interferons are highlighted as important regulators of HER2/ErbB2 expression in the kidney. Further studies are required to parse the beneficial aspects of EGFR inhibition on autoimmunity from its negative effects on wound healing in lupus nephritis.

CD11b suppresses TLR7-driven inflammatory signaling to protect against lupus nephritis

Lupus Nephritis (LN) is a severe complication of systemic lupus erythematosus (SLE) that affects kidney function. Here, we investigated the role of CD11b, a protein encoded by the ITGAM gene, in the development of LN and its functional activation as a therapeutic strategy. Genetic coding variants of ITGAM significantly increase the risk for SLE and LN by producing a less active CD11b and leading to elevated levels of type I interferon (IFN I). However, a molecular mechanism for how these variants increase LN risk has been unclear. Here, we determined that these variants also significantly associate with elevations in soluble urokinase plasminogen activator receptor (suPAR), a known biomarker linked to kidney disease, suggesting a novel molecular connection. Pharmacologic activation of CD11b with a novel, clinical-stage agonist ONT01 significantly suppressed suPAR production in myeloid cells and reduced systemic inflammation and kidney damage in multiple experimental models of LN. Importantly, delaying treatment with ONT01 until after disease onset also significantly reduced serum suPAR and inflammatory cytokines, and decreased immune complex deposition in the glomerulus, glomerulonephritis and albuminuria, suggesting that CD11b activation is therapeutic for LN. Genetic activation of CD11b via a gain-of-function CD11b mutation also showed complete protection from LN, whereas genetic deletion of CD11b worsened the disease in mice, providing further evidence of the role of CD11b activation in regulating LN. Finally, transfer of human LN PBMCs generated human LN like disease in mice that was significantly reduced by ONT01. Together, these data provide strong evidence that ONT01 mediated CD11b activation can therapeutically modulate TLR7-driven inflammation and protect against LN. These findings support clinical development of CD11b agonists as novel therapeutics for treating lupus nephritis in human patients.

NADPH oxidase in B cells and macrophages protects against murine lupus by regulation of TLR7

Loss of NADPH oxidase (NOX2) exacerbates systemic lupus erythematosus (SLE) in mice and humans, but the mechanisms underlying this effect remain unclear. To identify the cell lineages in which NOX2 deficiency drives SLE, we employed conditional KO and chimeric approaches to delete Cybb in several hematopoietic cell lineages of MRL.Faslpr SLE-prone mice. Deletion of Cybb in macrophages/monocytes exacerbated SLE nephritis, though not to the degree observed in the Cybb global KOs. Unexpectedly, the absence of Cybb in B cells resulted in profound glomerulonephritis and interstitial nephritis, rivaling that seen with global deletion. Furthermore, we identified that NOX2 is a key regulator of TLR7, a driver of SLE pathology, both globally and specifically in B cells. This is mediated in part through suppression of TLR7-mediated NF-κB signaling in B cells. Thus, NOX2's immunomodulatory effect in SLE is orchestrated not only by its function in the myeloid compartment, but through a pivotal role in B cells by selectively inhibiting TLR7 signaling.

The interferon-rich skin environment regulates Langerhans cell ADAM17 to promote photosensitivity in lupus

The autoimmune disease lupus erythematosus (lupus) is characterized by photosensitivity, where even ambient ultraviolet radiation (UVR) exposure can lead to development of inflammatory skin lesions. We have previously shown that Langerhans cells (LCs) limit keratinocyte apoptosis and photosensitivity via a disintegrin and metalloprotease 17 (ADAM17)-mediated release of epidermal growth factor receptor (EGFR) ligands and that LC ADAM17 sheddase activity is reduced in lupus. Here, we sought to understand how the lupus skin environment contributes to LC ADAM17 dysfunction and, in the process, differentiate between effects on LC ADAM17 sheddase function, LC ADAM17 expression, and LC numbers. We show through transcriptomic analysis a shared IFN-rich environment in non-lesional skin across human lupus and three murine models: MRL/lpr, B6.Sle1yaa, and imiquimod (IMQ) mice. IFN-I inhibits LC ADAM17 sheddase activity in murine and human LCs, and IFNAR blockade in lupus model mice restores LC ADAM17 sheddase activity, all without consistent effects on LC ADAM17 protein expression or LC numbers. Anti-IFNAR-mediated LC ADAM17 sheddase function restoration is associated with reduced photosensitive responses that are dependent on EGFR signaling and LC ADAM17. Reactive oxygen species (ROS) is a known mediator of ADAM17 activity; we show that UVR-induced LC ROS production is reduced in lupus model mice, restored by anti-IFNAR, and is cytoplasmic in origin. Our findings suggest that IFN-I promotes photosensitivity at least in part by inhibiting UVR-induced LC ADAM17 sheddase function and raise the possibility that anifrolumab ameliorates lupus skin disease in part by restoring this function. This work provides insight into IFN-I-mediated disease mechanisms, LC regulation, and a potential mechanism of action for anifrolumab in lupus.

Th1/17 polarization and potential treatment by an anti-interferon-γ DNA aptamer in Hunner-type interstitial cystitis

Hunner-type interstitial cystitis (HIC) is a rare, enigmatic inflammatory disease of the urinary bladder with no curative treatments. In this study, we aimed to characterize the unique cellular and immunological factors specifically involved in HIC by comparing with cystitis induced by Mycobacterium bovis bacillus Calmette-Guérin, which presents similar clinicopathological features to HIC. Here, we show that T helper 1/17 +polarized immune responses accompanied by prominent overexpression of interferon (IFN)-γ, enhanced cGAS-STING cytosolic DNA sensing pathway, and increased plasma cell infiltration are the characteristic inflammatory features in HIC bladder. Further, we developed a mouse anti-IFN-γ DNA aptamer and observed that the intravesical instillation of the aptamer significantly ameliorated bladder inflammation, pelvic pain and voiding dysfunction in a recently developed murine HIC model with little migration into the blood. Our study provides the plausible basis for the clinical translation of the anti-IFN-γ DNA aptamer in the treatment of human HIC.

mTORC2 contributes to systemic autoimmunity

The development of many systemic autoimmune diseases, including systemic lupus erythematosus, is associated with overactivation of the type I interferon (IFN) pathway, lymphopenia and increased follicular helper T (Tfh)-cell differentiation. However, the cellular and molecular mechanisms underlying these immunological perturbations remain incompletely understood. Here, we show that the mechanistic target of rapamycin complex 2 (mTORC2) promotes Tfh differentiation and disrupts Treg homeostasis. Inactivation of mTORC2 in total T cells, but not in Tregs, greatly ameliorated the immunopathology in a systemic autoimmunity mouse model. This was associated with reduced Tfh differentiation, B-cell activation, and reduced T-cell glucose metabolism. Finally, we show that type I IFN can synergize with TCR ligation to activate mTORC2 in T cells, which partially contributes to T-cell lymphopenia. These data indicate that mTORC2 may act as downstream of type I IFN, TCR and costimulatory receptor ICOS, to promote glucose metabolism, Tfh differentiation, and T-cell lymphopenia, but not to suppress Treg function in systemic autoimmunity. Our results suggest that mTORC2 might be a rational target for systemic autoimmunity treatment.

Genetic dissection of TLR9 reveals complex regulatory and cryptic proinflammatory roles in mouse lupus

In lupus, Toll-like receptor 7 (TLR7) and TLR9 mediate loss of tolerance to RNA and DNA, respectively. Yet, TLR7 promotes disease, while TLR9 protects from disease, implying differences in signaling. To dissect this 'TLR paradox', we generated two TLR9 point mutants (lacking either ligand (TLR9^K51E) or MyD88 (TLR9^P915H) binding) in lupus-prone MRL/lpr mice. Ameliorated disease of Tlr9^K51E mice compared to Tlr9^-/- controls revealed a TLR9 'scaffold' protective function that is ligand and MyD88 independent. Unexpectedly, Tlr9^P915H mice were more protected than both Tlr9^K51E and Tlr9^WT mice, suggesting that TLR9 also possesses ligand-dependent, but MyD88-independent, regulatory signaling and MyD88-mediated proinflammatory signaling. Triple-mixed bone marrow chimeras showed that TLR9-MyD88-independent regulatory roles were B cell intrinsic and restrained differentiation into pathogenic age-associated B cells and plasmablasts. These studies reveal MyD88-independent regulatory roles of TLR9, shedding light on the biology of endosomal TLRs.

Rubicon promotes rather than restricts murine lupus and is not required for LC3-associated phagocytosis

NADPH oxidase deficiency exacerbates lupus in murine models and patients, but the mechanisms remain unknown. It is hypothesized that NADPH oxidase suppresses autoimmunity by facilitating dead cell clearance via LC3-associated phagocytosis (LAP). The absence of LAP reportedly causes an autoinflammatory syndrome in aged, nonautoimmune mice. Prior work implicated cytochrome b-245, β polypeptide (CYBB), a component of the NADPH oxidase complex, and the RUN and cysteine-rich domain-containing Beclin 1-interacting protein (RUBICON) as requisite for LAP. To test the hypothesis that NADPH oxidase deficiency exacerbates lupus via a defect in LAP, we deleted Rubicon in the B6.Sle1.Yaa and MRL.Faslpr lupus mouse models. Under this hypothesis, RUBICON deficiency should phenocopy NADPH oxidase deficiency, as both work in the same pathway. However, we observed the opposite - RUBICON deficiency resulted in reduced mortality, renal disease, and autoantibody titers to RNA-associated autoantigens. Given that our data contradict the published role for LAP in autoimmunity, we assessed whether CYBB and RUBICON are requisite for LAP. We found that LAP is not dependent on either of these 2 pathways. To our knowledge, our data reveal RUBICON as a novel regulator of SLE, possibly by a B cell-intrinsic mechanism, but do not support a role for LAP in lupus.

Toll-like receptor 5 and Toll-like receptor 9 single nucleotide polymorphisms and risk of systemic lupus erythematosus and nephritis in Egyptian patients

Background

Toll-like (TLRs) play a crucial role in both adaptive and innate immunity. The aim of the present study was to assess the association of TLR5-rs5744168, TLR9-rs187084, and TLR9-rs352140 single nucleotide polymorphisms (SNPs) with susceptibility to systemic lupus erythematosus (SLE) and lupus nephritis (LN) in Egyptian patients.

Results

The C allele and homozygous CC genotype of the TLR9-rs352140 in co-dominant and recessive models were more prevalent in SLE patients than controls (P = 0.047, P = 0.017, and P = 0.005 respectively). In contrast, allelic and genotyping distribution of TLR5-rs5744168 and TLR9-rs187084 SNPs showed no association with the risk of SLE. The T allele of the TLR5-rs5744168 was more prevalent in LN patients than controls (P = 0.021). The homozygous TT genotype of TLR5-rs5744168 SNP was more prevalent in LN patients in the co-dominant and the recessive models than controls (P = 0.036 and P = 0.011 respectively). The C allele of the TLR9-rs352140 was more prevalent in LN patients than controls (P = 0.015). The homozygous CC genotype of the TLR9-rs352140 SNP was more prevalent in LN than controls in co-dominant and recessive models (P = 0.002 and P < 0.001). In the recessive model of the TLR5-rs5744168 SNP, the TT genotype was found in 3.2% of the SLE patients while none of the SLE patients without LN or controls had TT genotype (P = 0.036). Also, in the recessive model of the TLR9-rs352140 SNP, the CC genotype was significantly more frequent in SLE patients with LN than without LN (44.4% vs 29.9%, P = 0.045).

Conclusion

Our results support the potential role of TLR5-rs5744168 SNP and TLR9-rs3532140 SNP not only in increasing the risk for development of SLE, but also in increasing the risk of LN in SLE patients among the Egyptian population.

The Type II Anti-CD20 Antibody Obinutuzumab (GA101) Is More Effective Than Rituximab at Depleting B Cells and Treating Disease in a Murine Lupus Model

OBJECTIVE

Depleting pathogenic B cells could treat systemic lupus erythematosus (SLE). However, depleting B cells in an inflammatory setting such as lupus is difficult. This study was undertaken to investigate whether a type II anti-CD20 monoclonal antibody (mAb) with a different mechanism of action, obinutuzumab (GA101), is more effective than a type I anti-CD20 mAb, rituximab (RTX), in B cell depletion in lupus, and whether efficient B cell depletion results in amelioration of disease.

METHODS

We treated lupus-prone MRL/lpr mice expressing human CD20 on B cells (hCD20 MRL/lpr mice) with either RTX or GA101 and measured B cell depletion under various conditions, as well as multiple clinical end points.

RESULTS

A single dose of GA101 was markedly more effective than RTX in depleting B cells in diseased MRL/lpr mice (P < 0.05). RTX overcame resistance to B cell depletion in diseased MRL/lpr mice with continuous treatments. GA101 was more effective in treating hCD20 MRL/lpr mice with early disease, as GA101-treated mice had reduced glomerulonephritis (P < 0.05), lower anti-RNA autoantibody titers (P < 0.05), and fewer activated CD4+ T cells (P < 0.0001) compared to RTX-treated mice. GA101 also treated advanced disease, and continual treatment prolonged survival. Using variants of GA101, we also elucidated B cell depletion mechanisms in vivo in mice with lupus.

CONCLUSION

Albeit both anti-CD20 antibodies ameliorated early disease, GA101 was more effective than RTX in important parameters, such as glomerulonephritis score. GA101 proved beneficial in an advanced disease model, where it prolonged survival. These data support clinical testing of GA101 in SLE and lupus nephritis.

B Cell Aberrance in Lupus: the Ringleader and the Solution

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease with high heterogeneity but the common characterization of numerous autoantibodies and systemic inflammation which lead to the damage of multiple organs. Aberrance of B cells plays a pivotal role in the immunopathogenesis of SLE via both antibody-dependent and antibody-independent manners. Escape of autoreactive B cells from the central and peripheral tolerance checkpoints, over-activation of B cells and their excessive cytokines release which drive T cells and dendritic cells stimulation, and dysregulated surface molecules, as well as intracellular signal pathways involved in B cell biology, are all contributing to B cell aberrance and participating in the pathogenesis of SLE. Based on that rationale, targeting aberrance of B cells and relevant molecules and pathways is expected to be a promising strategy for lupus control. Multiple approaches targeting B cells through different mechanisms have been attempted, including B-cell depletion via monoclonal antibodies against B-cell-specific molecules, blockade of B-cell survival and activation factors, suppressing T-B crosstalk by interrupting costimulatory molecules and inhibiting intracellular activation signaling cascade by targeting pathway molecules in B cells. Though most attempts ended in failure, the efficacy of B-cell targeting has been encouraged by the FDA approval of belimumab that blocks B cell-activating factor (BAFF) and the recommended use of anti-CD20 as a remedial therapy in refractory lupus. Still, quantities of clinical trials targeting B cells or relevant molecules are ongoing and some of them have displayed promising preliminary results. Additionally, advances in multi-omics studies help deepen our understandings of B cell biology in lupus and may promote the discovery of novel potential therapeutic targets. The combination of real-world data with basic research achievements may pave the road to conquering lupus.

Microvesicles in active lupus nephritis show Toll-like receptor 9-dependent co-expression of galectin-3 binding protein and double-stranded DNA

Circulating microvesicles (MVs) from patients with systemic lupus erythematosus (SLE) express the type 1 interferon (IFN)-inducible protein galectin-3 binding protein (G3BP), which may enhance their deposition in the glomerular basement membrane. The release of G3BP-expressing MVs from normal peripheral blood mononuclear cells (PBMCs) is induced by Toll-like receptor 9 (TLR-9) ligands, and these vesicles contain autoantibody-accessible double-stranded DNA (dsDNA). This study compares the release of MVs expressing G3BP and dsDNA from PBMCs derived from SLE patients with or without active lupus nephritis (LN) and from healthy donors, and taps further into the potential dependency on IFN-α for their generation and impacts of TLR-7/TLR-9 co-stimulation. PBMCs from 10 healthy donors and 12 SLE patients, six of whom had active LN at study inclusion, were stimulated in-vitro with recombinant human IFN-α and the TLR-9 agonists oligodeoxynucleotide (ODN)2216 or ODN2395 alone or in combination with the TLR-7 agonist gardiquimod. MVs in the supernatants were subsequently isolated by differential centrifugation and their expression of G3BP and dsDNA was quantified by flow cytometry. Stimulation with ODN2395 significantly increased the release of MVs co-expressing G3BP and dsDNA from PBMCs isolated from healthy donors and SLE patients. The expression of G3BP on individual MVs and the proportion of G3BP and dsDNA double-positive MVs released were increased in active LN patients. Neither co-stimulation with gardiquimod nor with the IFN-α inhibitor IN-1 had any effect on the MV release induced by ODN2395. In conclusion, the TLR-9-mediated inducibility of MVs co-expressing G3BP and dsDNA is increased in SLE patients with active LN.

Age-Associated B Cells

The age-associated B cell subset has been the focus of increasing interest over the last decade. These cells have a unique cell surface phenotype and transcriptional signature, and they rely on TLR7 or TLR9 signals in the context of Th1 cytokines for their formation and activation. Most are antigen-experienced memory B cells that arise during responses to microbial infections and are key to pathogen clearance and control. Their increasing prevalence with age contributes to several well-established features of immunosenescence, including reduced B cell genesis and damped immune responses. In addition, they are elevated in autoimmune and autoinflammatory diseases, and in these settings they are enriched for characteristic autoantibody specificities. Together, these features identify age-associated B cells as a subset with pivotal roles in immunological health, disease, and aging. Accordingly, a detailed understanding of their origins, functions, and physiology should make them tractable translational targets in each of these settings.

Murine lupus is neutrophil elastase-independent in the MRL.Faslpr model

Loss of tolerance to nuclear antigens and multisystem tissue destruction is a hallmark of systemic lupus erythematosus (SLE). Although the source of autoantigen in lupus remains elusive, a compelling hypothetical source is dead cell debris that drives autoimmune activation. Prior reports suggest that neutrophil extracellular traps (NETs) and their associated death pathway, NETosis, are sources of autoantigen in SLE. However, others and we have shown that inhibition of NETs by targeting the NADPH oxidase complex and peptidylarginine deiminase 4 (PADI4) did not ameliorate disease in spontaneous murine models of SLE. Furthermore, myeloperoxidase and PADI4 deletion did not inhibit induced lupus. Since NET formation may occur independently of any one mediator, to address this controversy, we genetically deleted an additional important mediator of NETs and neutrophil effector function, neutrophil elastase (ELANE), in the MRL.Faslpr model of SLE. ELANE deficiency, and by extension ELANE-dependent NETs, had no effect on SLE nephritis, dermatitis, anti-self response, or immune composition in MRL.Faslpr mice. Taken together with prior data from our group and others, these data further challenge the paradigm that NETs and neutrophils are pathogenic in SLE.

Targeting mitochondrial oxidative stress with MitoQ reduces NET formation and kidney disease in lupus-prone MRL-lpr mice

OBJECTIVES

Recent investigations in humans and mouse models with lupus have revealed evidence of mitochondrial dysfunction and production of mitochondrial reactive oxygen species (mROS) in T cells and neutrophils. This can provoke numerous cellular changes including oxidation of nucleic acids, proteins, lipids and even induction of cell death. We have previously observed that in T cells from patients with lupus, the increased mROS is capable of provoking oligomerisation of mitochondrial antiviral stimulator (MAVS) and production of type I interferon (IFN-I). mROS in SLE neutrophils also promotes the formation of neutrophil extracellular traps (NETs), which are increased in lupus and implicated in renal damage. As a result, in addition to traditional immunosuppression, more comprehensive treatments for lupus may also include non-immune therapy, such as antioxidants.

METHODS

Lupus-prone MRL-lpr mice were treated from weaning for 11 weeks with the mitochondria-targeted antioxidant, MitoQ (200 µM) in drinking water. Mice were then assessed for ROS production in neutrophils, NET formation, MAVS oligomerisation, serum IFN-I, autoantibody production and renal function.

RESULTS

MitoQ-treated mice manifested reduced neutrophil ROS and NET formation, decreased MAVS oligomerisation and serum IFN-I, and reduced immune complex formation in kidneys, despite no change in serum autoantibody .

CONCLUSIONS

These findings reveal the potential utility of targeting mROS in addition to traditional immunosuppressive therapy for lupus.

B-Cell-Intrinsic Type 1 Interferon Signaling Is Crucial for Loss of Tolerance and the Development of Autoreactive B Cells

Type 1 interferon (T1IFN) signaling promotes inflammation and lupus pathology, but its role in autoreactive B cell development in the antibody-forming cell (AFC) and germinal center (GC) pathways is unclear. Using a lupus model that allows for focused study of the AFC and GC responses, we show that T1IFN signaling is crucial for autoreactive B cell development in the AFC and GC pathways. Through bone marrow chimeras, DNA-reactive B cell transfer, and GC-specific Cre mice, we confirm that IFNαR signaling in B cells promotes autoreactive B cell development into both pathways. Transcriptomic analysis reveals gene expression alterations in multiple signaling pathways in non-GC and GC B cells in the absence of IFNαR. Finally, we find that T1IFN signaling promotes autoreactive B cell development in the AFC and GC pathways by regulating BCR signaling. These data suggest value for anti-IFNαR therapy in individuals with elevated T1IFN activity before clinical disease onset.

The B-cell-intrinsic mechanisms of type 1 interferon (T1IFN) signaling in regulating B cell tolerance is unclear. Domeier et al. show that T1IFN signaling in B cells causes loss of B cell tolerance, promoting autoreactive B cell development into the antibody-forming cell and germinal center pathways by regulating BCR signaling.

The role of neutrophil extracellular traps in rheumatic diseases

Rheumatic diseases are a collection of disorders defined by the presence of inflammation and destruction of joints and internal organs. A common feature of these diseases is the presence of autoantibodies targeting molecules commonly expressed in neutrophils. These preformed mediators are released by neutrophils but not by other immune cells such as macrophages. Neutrophils, major players in the host innate immune response, initiate a cell death mechanism termed neutrophil extracellular trap (NET) formation as a way to ensnare pathogens. NETs are also a source of released self-molecules found in rheumatic diseases. Subsequently, research on the role of NETs in the onset, progression and resolution of inflammation in rheumatic diseases has intensified. This Review has two aims. First, it aims to highlight the mechanisms required for the generation of NETs, the research landscape of which is rapidly changing. Second, it aims to discuss the role of neutrophils and NETs in systemic lupus erythematosus, vasculitis (specifically anti-neutrophil cytoplasmic autoantibody-associated vasculitis), rheumatoid arthritis and gout. Our goal is to clarify the field of NET research in rheumatic diseases in the hope of improving the therapeutic approaches utilized for these diseases.

Self-DNA at the Epicenter of SLE: Immunogenic Forms, Regulation, and Effects

Self-reactive B cells generated through V(D)J recombination in the bone marrow or through accrual of random mutations in secondary lymphoid tissues are mostly purged or edited to prevent autoimmunity. Yet, 10–20% of all mature naïve B cells in healthy individuals have self-reactive B cell receptors (BCRs). In patients with serologically active systemic lupus erythematosus (SLE) the percentage increases up to 50%, with significant self-DNA reactivity that correlates with disease severity. Endogenous or self-DNA has emerged as a potent antigen in several autoimmune disorders, particularly in SLE. However, the mechanism(s) regulating or preventing anti-DNA antibody production remain elusive. It is likely that in healthy subjects, DNA-reactive B cells avoid activation due to the unavailability of endogenous DNA, which is efficiently degraded through efferocytosis and various DNA-processing proteins. Genetic defects, physiological, and/or pathological conditions can override these protective checkpoints, leading to autoimmunity. Plausibly, increased availability of immunogenic self-DNA may be the key initiating event in the loss of tolerance of otherwise quiescent DNA-reactive B cells. Indeed, mutations impairing apoptotic cell clearance pathways and nucleic acid metabolism-associated genes like DNases, RNases, and their sensors are known to cause autoimmune disorders including SLE. Here we review the literature supporting the idea that increased availability of DNA as an immunogen or adjuvant, or both, may cause the production of pathogenic anti-DNA antibodies and subsequent manifestations of clinical disease such as SLE. We discuss the main cellular players involved in anti-DNA responses; the physical forms and sources of immunogenic DNA in autoimmunity; the DNA-protein complexes that render DNA immunogenic; the regulation of DNA availability by intracellular and extracellular DNases and the autoimmune pathologies associated with their dysfunction; the cytosolic and endosomal sensors of immunogenic DNA; and the cytokines such as interferons that drive auto-inflammatory and autoimmune pathways leading to clinical disease. We propose that prevention of DNA availability by aiding extracellular DNase activity could be a viable therapeutic modality in controlling SLE.

PINK1 attenuates mtDNA release in alveolar epithelial cells and TLR9 mediated profibrotic responses

We have previously shown that endoplasmic reticulum stress (ER stress) represses the PTEN inducible kinase 1 (PINK1) in lung type II alveolar epithelial cells (AECII) reducing mitophagy and increasing the susceptibility to lung fibrosis. Although increased circulating mitochondrial DNA (mtDNA) has been reported in chronic lung diseases, the contribution of mitophagy in the modulation of mitochondrial DAMP release and activation of profibrotic responses is unknown. In this study, we show that ER stress and PINK1 deficiency in AECII led to mitochondrial stress with significant oxidation and damage of mtDNA and subsequent extracellular release. Extracellular mtDNA was recognized by TLR9 in AECII by an endocytic-dependent pathway. PINK1 deficiency-dependent mtDNA release promoted activation of TLR9 and triggered secretion of the profibrotic factor TGF-β which was rescued by PINK1 overexpression. Enhanced mtDNA oxidation and damage were found in aging and IPF human lungs and, in concordance, levels of circulating mtDNA were significantly elevated in plasma and bronchoalveolar lavage (BAL) from patients with IPF. Free mtDNA was found elevated in other ILDs with low expression of PINK1 including hypersensitivity pneumonitis and autoimmune interstitial lung diseases. These results support a role for PINK1 mediated mitophagy in the attenuation of mitochondrial damage associated molecular patterns (DAMP) release and control of TGF-β mediated profibrotic responses.

Fas ligand promotes an inducible TLR-dependent model of cutaneous lupus-like inflammation

Toll-like receptors TLR7 and TLR9 are both implicated in the activation of autoreactive B cells and other cell types associated with systemic lupus erythematosus (SLE) pathogenesis. However, Tlr9-/- autoimmune-prone strains paradoxically develop more severe disease. We have now leveraged the negative regulatory role of TLR9 to develop an inducible rapid-onset murine model of systemic autoimmunity that depends on T cell detection of a membrane-bound OVA fusion protein expressed by MHC class II+ cells, expression of TLR7, expression of the type I IFN receptor, and loss of expression of TLR9. These mice are distinguished by a high frequency of OVA-specific Tbet+, IFN-γ+, and FasL-expressing Th1 cells as well as autoantibody-producing B cells. Unexpectedly, contrary to what occurs in most models of SLE, they also developed skin lesions that are very similar to those of human cutaneous lupus erythematosus (CLE) as far as clinical appearance, histological changes, and gene expression. FasL was a key effector mechanism in the skin, as the transfer of FasL-deficient DO11gld T cells completely failed to elicit overt skin lesions. FasL was also upregulated in human CLE biopsies. Overall, our model provides a relevant system for exploring the pathophysiology of CLE as well as the negative regulatory role of TLR9.

TLR7-Mediated Lupus Nephritis Is Independent of Type I IFN Signaling

Systemic lupus erythematosus is an autoimmune disease characterized by increased type I IFNs, autoantibodies, and inflammatory-mediated multiorgan damage. TLR7 activation is an important contributor to systemic lupus erythematosus pathogenesis, but the mechanisms by which type I IFNs participate in TLR7-driven pathologic conditions remain uncertain. In this study, we examined the requirement for type I IFNs in TLR7-stimulated lupus nephritis. Lupus-prone NZM2328, INZM (which lack a functional type I IFN receptor), and NZM2328 IL-1β^-/- mice were treated at 10 wk of age on the right ear with R848 (TLR7 agonist) or control (DMSO). Autoantibody production and proteinuria were assessed throughout treatment. Multiorgan inflammation was assessed at the time of decline in health. Renal infiltrates and mRNA expression were also examined after 14 d of treatment. Both NZM2328 and INZM mice exhibited a decline in survival after 3-4 wk of R848 but not vehicle treatment. Development of splenomegaly and liver inflammation were dependent on type I IFN. Interestingly, autoantibody production, early renal infiltration of dendritic cells, upregulation of IL-1β, and lupus nephritis occurred independent of type I IFN signaling. Development of TLR7-driven lupus nephritis was not abolished by the deletion of IL-1β. Thus, although IFN-α is sufficient to induce nephritis acceleration, our data emphasize a critical role for IFN-independent signaling in TLR7-mediated lupus nephritis. Further, despite upregulation of IL-1β after TLR7 stimulation, deletion of IL-1β is not sufficient to reduce lupus nephritis development in this model.

Kidney disease models: tools to identify mechanisms and potential therapeutic targets

Acute kidney injury (AKI) and chronic kidney disease (CKD) are worldwide public health problems affecting millions of people and have rapidly increased in prevalence in recent years. Due to the multiple causes of renal failure, many animal models have been developed to advance our understanding of human nephropathy. Among these experimental models, rodents have been extensively used to enable mechanistic understanding of kidney disease induction and progression, as well as to identify potential targets for therapy. In this review, we discuss AKI models induced by surgical operation and drugs or toxins, as well as a variety of CKD models (mainly genetically modified mouse models). Results from recent and ongoing clinical trials and conceptual advances derived from animal models are also explored.

Mouse models of lupus: what they tell us and what they don't

Lupus is a complex heterogeneous disease characterised by autoantibody production and immune complex deposition followed by damage to target tissues. Animal models of human diseases are an invaluable tool for defining pathogenic mechanisms and testing of novel therapeutic agents. There are perhaps more applicable murine models of lupus than any other human disease. There are spontaneous models of lupus, inducible models of lupus, transgenic-induced lupus, gene knockout induced lupus and humanised mouse models of lupus. These mouse models of lupus have contributed significantly to our knowledge of the pathogenesis of lupus and served as valuable preclinical models for proof of concept for new therapies. Despite their utility, mouse models of lupus have their distinct limitations. Although similar, mouse and human immune systems are different and thus one cannot assume a mechanism for disease in one is translatable to the other. Efficacy and toxicity of compounds can vary significantly between humans and mice, also limiting direct translation. Finally, the heterogeneous aspects of human lupus, both in clinical presentation, underlying pathogenesis and genetics, are not completely represented in current mouse models. Thus, proving a therapy or mechanism of disease in one mouse model is similar to proving a mechanism/therapy in a limited subset of human lupus. These limitations, however, do not marginalise the importance of animal models nor the significant contributions they have made to our understanding of lupus.

Relevant genetic polymorphisms and kidney expression of Toll-like receptor (TLR)-5 and TLR-9 in lupus nephritis

Toll-like receptor (TLR) genetic polymorphisms may modify their expression causing inflammatory disorders and influencing both susceptibility and severity of lupus erythematosus. We aim to determine whether TLR-5 and TLR-9 gene polymorphisms are implicated in the susceptibility to systemic lupus erythematosus (SLE) and lupus nephritis (LN) and to evaluate their expressions and distributions in renal LN patients' biopsies. The frequencies of two SNP in the TLR-9 gene and one in the TLR-5 gene was examined in 106 SLE patients (among them 37 LN patients) and in 200 matched controls by polymerase chain reaction-restriction fragment-length polymorphisms (PCR-RFLP) analysis. TLR-9 and TLR-5 expressions were assessed by reverse transcription (RT)-PCR and immunohistochemistry carried on LN renal biopsies compared to healthy renal tissue. A significant genotypic and allelic association was revealed between TLR-9-rs352140 and both SLE and LN (P < 0·05). The TLR-9 transcript level was significantly higher in LN biopsies compared to control (P < 0·05). This increase was observed histochemically in the tubulointerstitial compartment. TLR-9 was detectable in LN glomeruli patients but not in normal control glomeruli. No allelic nor genotype association was found with TLR-5-rs5744168 in SLE. but the T allele and the TT genotype were raised significantly in the LN group (P < 0·05). A significant increase in TLR-5 gene expression in LN biopsies, which contrasted with normal kidneys (P < 0·05), was confirmed by an intense and diffuse staining for TLR-5 only in LN tubules (P < 0·05). Our data show that TLR-5 and TLR-9 are susceptible genes to LN and that their expression is dysregulated in LN patients' kidneys, supporting a role of these mediators in the pathogenesis of LN.

Excessive interferon-α signaling in autoimmunity alters glycosphingolipid processing in B cells

Excessive interferon-α (IFN-α) production by innate immune cells is a hallmark of autoimmune diseases. What other cell type secretes IFN-α and how IFN-α affects immune cell metabolism and homeostasis in autoimmunity are largely unclear. Here, we report that autoimmune B cells, arising from two different B cell-specific genetic lesions in mice, secrete IFN-α. In addition, IFN-α, found in abundance in autoimmunity, elicited profound changes in the B cell lipidome, increasing their expression of glycosphingolipids (GSLs) and leading to their CD1d-mediated depletion of iNKT cells in vitro and in vivo. IFN-α receptor blockade could reverse the loss of iNKT cells. Excessive stimulation of B cells with IFN-α altered the expression of enzymes that catalyze critical steps in GSL processing, increasing the expressions of glucosylceramide synthase (GCS) and globotrihexosylceramide synthase (Gb3S) but decreasing that of α-galactosidase A (α-galA). Inhibiting GCS or restoring α-galA expression prevented iNKT depletion by IFN-α-activated B cells. Taken together, our work indicated that excessive IFN-α perturbs GSL metabolism in B cells which in turn adversely affects iNKT homeostasis.

Lupus and proliferative nephritis are PAD4 independent in murine models

Though recent reports suggest that neutrophil extracellular traps (NETs) are a source of antigenic nucleic acids in systemic lupus erythematosus (SLE), we recently showed that inhibition of NETs by targeting the NADPH oxidase complex via cytochrome b-245, β polypeptide (cybb) deletion exacerbated disease in the MRL.Faslpr lupus mouse model. While these data challenge the paradigm that NETs promote lupus, it is conceivable that global regulatory properties of cybb and cybb-independent NETs confound these findings. Furthermore, recent reports indicate that inhibitors of peptidyl arginine deiminase, type IV (Padi4), a distal mediator of NET formation, improve lupus in murine models. Here, to clarify the contribution of NETs to SLE, we employed a genetic approach to delete Padi4 in the MRL.Faslpr model and used a pharmacological approach to inhibit PADs in both the anti-glomerular basement membrane model of proliferative nephritis and a human-serum-transfer model of SLE. In contrast to prior inhibitor studies, we found that deletion of Padi4 did not ameliorate any aspect of nephritis, loss of tolerance, or immune activation. Pharmacological inhibition of PAD activity had no effect on end-organ damage in inducible models of glomerulonephritis. These data provide a direct challenge to the concept that NETs promote autoimmunity and target organ injury in SLE.

Toll-like receptor 9 suppresses lupus disease in Fas-sufficient MRL Mice

Genetic deficiency in TLR9 accelerates pathogenesis in the spontaneous polygenic MRL.Fas^lpr murine model of systemic lupus erythematosus, despite the absence of anti-nucleosome autoantibodies. However, it could be argued that this result was dependent on Fas-deficiency rather than lupus-promoting genes in the MRL genetic background. Here we report the effects of TLR9 deficiency on autoimmune disease independent of the lpr mutation in Fas by characterizing Tlr9^-/- and Tlr9^+/+ mice on the Fas-intact MRL/+ genetic background. By 30 weeks of age, Tlr9-deficient MRL/+ had more severe renal disease, increased T cell activation, and higher titers of anti-Sm and anti-RNA autoantibodies than Tlr9-intact animals, as had been the case in the MRL.Fas^lpr model. In addition, Tlr9-deficient MRL/+ mice had increased numbers of germinal center phenotype B cells and an increase in splenic neutrophils and conventional dendritic cell populations. Thus, the disease accelerating effects of Tlr9 deficiency are separable from those mediated by the Fas mutation in the lupus-prone MRL genetic background. Nonetheless, disease acceleration in Tlr9-deficient MRL/+ mice was phenotypically distinct from that in Fas-deficient counterparts, which has important implications.

Autophagy in Dendritic Cells and B Cells Is Critical for the Inflammatory State of TLR7-Mediated Autoimmunity

Individuals suffering from autoimmune disorders possess a hyperactive cellular phenotype where tolerance to self-antigens is lost. Autophagy has been implicated in both the induction and prevention of autoimmunity, and modulators of this cellular recycling process hold high potential for the treatment of autoimmune diseases. In this study, we determine the effects of a loss of autophagy in dendritic cells (DCs), as well as both B cells and DCs, in a TLR7-mediated model of autoimmunity, similar to systemic lupus erythematosus, where both cell types are critical for disease. Although a loss of DC autophagy slowed disease, the combined loss of autophagy in both cell types resulted in a lethal sepsis-like environment, which included tissue inflammation and hyperproduction of inflammasome-associated cytokines. Ablation of B cell signaling reversed this phenotype, indicating that activation of these cells is an essential step in disease induction. Thus, autophagy plays a dichotomous role in this model of disease.

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.

Beyond pan-B-cell-directed therapy - new avenues and insights into the pathogenesis of SLE

New insights into the mechanisms of autoimmune diseases have been obtained not only from preclinical studies, but also from clinical trials of pan-B-cell-directed therapy. Overall, the results of these clinical trials suggest that more-specific approaches focusing on pathogenic B-cell functions, and perhaps sparing or even enhancing regulatory B-cell activity, might be attractive alternatives. Importantly, pathogenic B-cell subpopulations function within a network of cellular interactions, many of which might require additional interventions to restore immunologic balance and suppress autoimmune disease. Thus, approaches that simultaneously target innate immune cells as well as multiple nodes of T-cell and B-cell interactions might hold the promise of improved therapeutic efficacy. Interfering with B-cell intracellular signalling pathways, altering their intracellular metabolic pathways and perturbing transcription factors are additional options. This Review critically analyses these approaches, examines the role of cytokines and other functions of B-lineage cells separate from antibody secretion, and provides insights into the potential next generation of therapies targeting B-lineage cells.

Apoptotic cell responses in the splenic marginal zone: a paradigm for immunologic reactions to apoptotic antigens with implications for autoimmunity

Apoptotic cells drive innate regulatory responses that result in tolerogenic immunity. This is a critical aspect of cell physiology as apoptotic cells expose potentially dangerous nuclear antigens on the surface in apoptotic blebs, and failure in their recognition, phagocytosis, or destruction can cause dramatic autoimmunity in experimental models and is linked to development and progression of systemic pathology in human. The marginal zone is a specialized splenic environment that serves as a transitional site from circulation to peripheral lymphoid structures. The marginal zone serves a key role in trapping of particulates and initiation of innate responses against systemic microbial pathogens. However in recent years, it has become clear the marginal zone is also important for initiation of immune tolerance to apoptotic cells, driving a coordinated response involving multiple phagocyte and lymphocyte subsets. Recent reports linking defects in splenic macrophage function to systemic lupus erythematosus in a manner analogous to marginal zone macrophages in lupus-prone mice provide an impetus to better understand the mechanistic basis of the apoptotic cell response in the marginal zone and its general applicability to apoptotic cell-driven tolerance at other tissue sites. In this review, we discuss immune responses to apoptotic cells in the spleen in general and the marginal zone in particular, the relationship of these responses to autoimmune disease, and comparisons to apoptotic cell immunity in humans.

Neutrophils, Dendritic Cells, Toll-Like Receptors, and Interferon-α in Lupus Nephritis

Finding better treatments for lupus nephritis requires an understanding of the pathogenesis of the causative systemic disease, how this leads to kidney disease, and how lupus nephritis progresses to end-stage kidney disease. Here, we provide a brief conceptual overview on the related pathomechanisms. As a main focus we discuss in detail the roles of neutrophils, dendritic cells, Toll-like receptors, and interferon-α in the pathogenesis of lupus nephritis by separately reviewing their roles in extrarenal systemic autoimmunity and in intrarenal inflammation and immunopathology.

New insights into B cell biology in systemic lupus erythematosus and Sjögren's syndrome

PURPOSE OF REVIEW

Our understanding of the physiological and pathogenic functions of B cells in systemic lupus erythematosus (SLE) and Primary Sjögren's syndrome (pSS) continues to expand. In this review, we discuss novel insights published in the last 18 months into the roles of B cells in systemic autoimmunity.

RECENT FINDINGS

Data have continued to expand regarding the diverse mechanisms by which innate immune signals including Toll-like receptors (TLRs) regulate the B cell compartment. Localized B cells and long-lived plasma cells have been identified as playing an important role in target tissue including the development of ectopic lymphoid structures in kidney and salivary gland. In addition to pathogenic roles for B cells, there is mounting evidence for regulatory B cell subsets that play a protective role and new insights into the signals that regulate their development.

SUMMARY

The past few years have provided insights into the multiple paths by which innate immune signals can lead to B cell activation in SLE and pSS and the increasingly diverse ways in which B cells contribute to disease expression. Further understanding the imbalance between protective and pathogenic functions for B cells in disease including in understudied target tissue should yield new treatment approaches.

TLR9 Deficiency Leads to Accelerated Renal Disease and Myeloid Lineage Abnormalities in Pristane-Induced Murine Lupus

Systemic lupus erythematosus (SLE) is a chronic, life-threatening autoimmune disorder, leading to multiple organ pathologies and kidney destruction. Analyses of numerous murine models of spontaneous SLE have revealed a critical role for endosomal TLRs in the production of autoantibodies and development of other clinical disease manifestations. Nevertheless, the corresponding TLR9-deficient autoimmune-prone strains consistently develop more severe disease pathology. Injection of BALB/c mice with 2,6,10,14-tetramethylpentadecane (TMPD), commonly known as pristane, also results in the development of SLE-like disease. We now show that Tlr9(-/-) BALB/c mice injected i.p. with TMPD develop more severe autoimmunity than do their TLR-sufficient cohorts. Early indications include an increased accumulation of TLR7-expressing Ly6C(hi) inflammatory monocytes at the site of injection, upregulation of IFN-regulated gene expression in the peritoneal cavity, and an increased production of myeloid lineage precursors (common myeloid progenitors and granulocyte myeloid precursors) in the bone marrow. TMPD-injected Tlr9(-/-) BALB/c mice develop higher autoantibody titers against RNA, neutrophil cytoplasmic Ags, and myeloperoxidase than do TMPD-injected wild-type BALB/c mice. The TMP-injected Tlr9(-/-) mice, and not the wild-type mice, also develop a marked increase in glomerular IgG deposition and infiltrating granulocytes, much more severe glomerulonephritis, and a reduced lifespan. Collectively, the data point to a major role for TLR7 in the response to self-antigens in this model of experimental autoimmunity. Therefore, the BALB/c pristane model recapitulates other TLR7-driven spontaneous models of SLE and is negatively regulated by TLR9.

Alpha 1 Antitrypsin Inhibits Dendritic Cell Activation and Attenuates Nephritis in a Mouse Model of Lupus

Systemic lupus erythematosus (SLE) is an autoimmune disorder with a worldwide distribution and considerable mortality and morbidity. Although the pathogenesis of this disease remains elusive, over-reactive dendritic cells (DCs) play a critical role in the disease development. It has been shown that human alpha-1 antitrypsin (hAAT) has protective effects in type 1 diabetes and rheumatoid arthritis mouse models. In the present study, we tested the effect of AAT on DC differentiation and functions, as well as its protective effect in a lupus-prone mouse model. We showed that hAAT treatment significantly inhibited LPS (TLR4 agonist) and CpG (TLR9 agonist) -induced bone-marrow (BM)-derived conventional and plasmacytoid DC (cDC and pDC) activation and reduced the production of inflammatory cytokines including IFN-I, TNF-α and IL-1β. In MRL/lpr mice, hAAT treatment significantly reduced BM-derived DC differentiation, serum autoantibody levels, and importantly attenuated renal pathology. Our results for the first time demonstrate that hAAT inhibits DC activation and function, and it also attenuates autoimmunity and renal damage in the MRL/lpr lupus model. These results imply that hAAT has a therapeutic potential for the treatment of SLE in humans.

Continuous inhibitory signaling by both SHP-1 and SHIP-1 pathways is required to maintain unresponsiveness of anergic B cells

Cambier et al. show that the tyrosine phosphatase SHP-1 and the inositol phosphatase SHIP-1 are required to maintain B cell anergy.

Many autoreactive B cells persist in the periphery in a state of unresponsiveness called anergy. This unresponsiveness is rapidly reversible, requiring continuous BCR interaction with self-antigen and resultant regulatory signaling for its maintenance. Using adoptive transfer of anergic B cells with subsequent acute induction of gene deletion or expression, we demonstrate that the continuous activities of independent inhibitory signaling pathways involving the tyrosine phosphatase SHP-1 and the inositol phosphatase SHIP-1 are required to maintain anergy. Acute breach of anergy by compromise of either of these pathways leads to rapid cell activation, proliferation, and generation of short-lived plasma cells that reside in extrafollicular foci. Results are consistent with predicted/observed reduction in the Lyn–SHIP-1–PTEN–SHP-1 axis function in B cells from systemic lupus erythematosus patients.

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.

Phenotypic and functional alterations of pDCs in lupus-prone mice

Plasmacytoid dendritic cells (pDCs) were considered to be the major IFNα source in systemic lupus erythematosus (SLE) but their phenotype and function in different disease status have not been well studied. To study the function and phenotype of pDCs in lupus-prone mice we used 7 strains of lupus-prone mice including NZB/W F1, NZB, NZW, NZM2410, B6.NZM^Sle1/2/3, MRL/lpr and BXSB/Mp mice and C57BL/6 as control mice. Increased spleen pDC numbers were found in most lupus mice compared to C57BL/6 mice. The IFNα-producing ability of BM pDCs was similar between lupus and C57BL/6 mice, whereas pDCs from the spleens of NZB/W F1 and NZB mice produced more IFNα than pDCs from the spleens of C57BL/6 mice. Furthermore, spleen pDCs from MRL-lpr and NZM2410 mice showed increased responses to Tlr7 and Tlr9, respectively. As the disease progressed, IFN signature were evaluated in both BM and spleen pDC from lupus prone mice and the number of BM pDCs and their ability to produce IFNα gradually decreased in lupus-prone mice. In conclusion, pDC are activated alone with disease development and its phenotype and function differ among lupus-prone strains, and these differences may contribute to the development of lupus in these mice.

Peptidylarginine deiminase inhibition disrupts NET formation and protects against kidney, skin and vascular disease in lupus-prone MRL/lpr mice

OBJECTIVES

An imbalance between neutrophil extracellular trap (NET) formation and degradation has been described in systemic lupus erythematosus (SLE), potentially contributing to autoantigen externalisation, type I interferon synthesis and endothelial damage. We have demonstrated that peptidylarginine deiminase (PAD) inhibition reduces NET formation and protects against lupus-related vascular damage in the New Zealand Mixed model of lupus. However, another strategy for inhibiting NETs--knockout of NOX2--accelerates lupus in a different murine model, MRL/lpr. Here, we test the effects of PAD inhibition on MRL/lpr mice in order to clarify whether some NET inhibitory pathways may be consistently therapeutic across models of SLE.

METHODS

NET formation and autoantibodies to NETs were characterised in lupus-prone MRL/lpr mice. MRL/lpr mice were also treated with two different PAD inhibitors, Cl-amidine and the newly described BB-Cl-amidine. NET formation, endothelial function, interferon signature, nephritis and skin disease were examined in treated mice.

RESULTS

Neutrophils from MRL/lpr mice demonstrate accelerated NET formation compared with controls. MRL/lpr mice also form autoantibodies to NETs and have evidence of endothelial dysfunction. PAD inhibition markedly improves endothelial function, while downregulating the expression of type I interferon-regulated genes. PAD inhibition also reduces proteinuria and immune complex deposition in the kidneys, while protecting against skin disease.

CONCLUSIONS

PAD inhibition reduces NET formation, while protecting against lupus-related damage to the vasculature, kidneys and skin in various lupus models. The strategy by which NETs are inhibited will have to be carefully considered if human studies are to be undertaken.

Type I IFN Contributes to the Phenotype of Unc93b1D34A/D34A Mice by Regulating TLR7 Expression in B Cells and Dendritic Cells

TLR7 recognizes pathogen-derived and self-derived RNA, and thus a regulatory system for control of the TLR7 response is required to avoid excessive activation. Unc93 homolog B1 (Unc93B1) is a regulator of TLR7 that controls the TLR7 response by transporting TLR7 from the endoplasmic reticulum to endolysosomes. We have previously shown that a D34A mutation in Unc93B1 induces hyperactivation of TLR7, and that Unc93b1(D34A/D34A) mice (D34A mice) have systemic inflammation spontaneously. In this study, we examined the roles of inflammatory cytokines such as IFN-γ, IL-17A, and type I IFNs to understand the mechanism underlying the phenotype in D34A mice. mRNAs for IFN-γ and IL-I7A in CD4(+) T cells increased, but inflammatory phenotype manifesting as thrombocytopenia and splenomegaly was still observed in Ifng(-/-) or Il17a(-/-) D34A mice. In contrast to T cell-derived cytokines, Ifnar1(-/-) D34A mice showed an ameliorated phenotype with lower expression of TLR7 in B cells and conventional dendritic cells (cDCs). The amount of TLR7 decreased in B cells from Ifnar1(-/-) D34A mice, but the percentage of TLR7(+) cells decreased among CD8α(-) cDCs. In conclusion, type I IFNs maintain expression of TLR7 in B cells and cDCs in different ways; total amount of TLR7 is kept in B cells and TLR7(+) population is retained among cDCs. Our results suggested that these TLR7-expressing cells are activated initially and influence TLR7-dependent systemic inflammation.

Cutting Edge: Plasmacytoid Dendritic Cells in Late-Stage Lupus Mice Defective in Producing IFN-α

Plasmacytoid dendritic cells (pDCs) are professional type I IFN producers believed to promote lupus. However, questions exist about whether they function at the same level throughout the course of lupus disease. We analyzed high-purity pDCs sorted from lupus mice. Although pDCs produced a large amount of IFN-α during disease initiation, those sorted from late-stage lupus mice were found to be defective in producing IFN-α. These pDCs expressed an increased level of MHC, suggesting a functional drift to Ag presentation. We examined the potential mechanism behind the defect and identified a novel transcriptional factor, Foxj2, which repressed the expression of several genes in pDCs, but not IFN-α. Dysregulation in pDCs appears to be predisposed, because they exhibited an altered transcriptional profile before the onset of clinical signs. Our results suggest that pDCs do not function the same throughout the disease course and lose the ability to produce IFN-α in late-stage lupus mice.

B Cell-Specific MHC Class II Deletion Reveals Multiple Nonredundant Roles for B Cell Antigen Presentation in Murine Lupus

B cells have both Ab-dependent and Ab-independent functions in systemic autoimmune diseases, including systemic lupus erythematosus (SLE). Ab-independent functions are known to be important, because mice with B cells but no secreted Ig have severe disease. These functions could include roles in lymphoid development, cytokine secretion, and Ag presentation; however, these possibilities have not been directly tested in SLE models. In this study, we show by lineage-specific ablation of MHC class II (MHCII) that B cell Ag presentation plays a nonredundant role in CD4(+) T cell activation and effector differentiation in the MRL.Fas(lpr) mouse model of SLE. MHCII-mediated interactions between B and T cells further promote B cell proliferation and differentiation, and, in fact, inefficient MHCII deletion on B cells led to strong selection of escaped cells in activated and plasmablast compartments, further underscoring the central role of B cell Ag presentation. Despite the leakiness in the system, B cell-specific MHCII deletion resulted in substantially ameliorated clinical disease. Hence, B cell Ag presentation is critical for T and B cell activation and differentiation, as well as target organ damage.