The type I interferon system in the development of lupus

The type I interferon (IFN) system induces inhibition of viral replication, but can also activate the innate and adaptive immune system. An important role of the type I IFN system in autoimmune diseases, including lupus, is suggested by the observation that these disorders display a prominent over-expression of type I IFN regulated genes. The development of autoimmune diseases in some individuals treated with IFN-α directly supports a pivotal role for this cytokine in breaking tolerance and inducing autoimmune reactions. A genetic setup that promotes type I IFN production and/or response and the presence of endogenous inducers of IFN-α production have been described in patients with lupus. Several known environmental risk factors for development of lupus or disease flares may contribute to the ongoing type I IFN production. In the present review we will describe the possible role of the type I IFN system in the lupus disease process. The possible connection between the type I IFN system and some environmental and genetic risk factors for lupus is also discussed.     

Enhanced type I interferon signalling promotes Th1-biased inflammation in cutaneous lupus erythematosus

Recent studies have suggested that type I interferons (IFN) play a role in the pathogenesis of lupus erythematosus (LE), an autoimmune disease of unknown aetiology. Natural interferon-producing plasmacytoid cells have been demonstrated in cutaneous LE (CLE) lesions, along with elevated levels of IFN-alpha mRNA. The hypothesis in the current study was that local production of type I IFNs in CLE induces Th1-biased inflammation via induction of IFN-inducible chemokines such as IP10/CXCL10 leading to the recruitment of chemokine receptor CXCR3 expressing T-cells into skin lesions. Skin biopsies from 21 patients suffering from different types of active cutaneous LE were analysed for the expression of MxA, a protein specifically induced by type I interferons, the IFN-inducible protein IP10/CXCL10, and the chemokine receptor CXCR3, characteristic for Th1 cells, by immunohistochemistry. Additionally, peripheral CD4+ and CD8+ T-cells were investigated for the expression of MxA and CXCR3 by flow cytometry. Cutaneous LE lesions were characterized by strong expression of MxA indicating the induction of localized type I IFN signalling in the skin. Large numbers of infiltrating CXCR3 positive lymphocytes were detected in CLE skin lesions, and correlated closely with lesional MxA expression (epidermis: Spearman's rho = 0.56, p < 0.001; dermis: rho = 0.82, p < 0.001). Intracellular MxA levels of circulating CD4+ and CD8+ T-cells were significantly enhanced in patients with active CLE lesions. The percentage of peripheral T-cells expressing CXCR3 was significantly decreased in specific CLE subtypes. Expression of IP10/CXCL10 in the epidermis links type I IFN signalling and recruitment of CXCR3+ T cells. These results suggest an important role for type I interferon signalling in the pathogenesis of cutaneous lupus erythematosus. It is proposed that type I IFNs induce a Th1-biased inflammatory immune response, with recruitment of CXCR3-expressing T-lymphocytes into the skin.     

Systemic lupus erythematosus: all roads lead to type I interferons

In recent years, the study of systemic lupus erythematosus (SLE) patients has revealed a central role for type I interferon (IFN) in disease pathogenesis. IFN induces the unabated activation of peripheral dendritic cells, which select and activate autoreactive T cells rather than deleting them, thus failing to induce peripheral tolerance. IFN also directly affects T cells and B cells. Furthermore, immune complexes binding to FcgammaR and Toll-like receptors provide an amplification loop for IFN production and B-cell activation in SLE. Polymorphisms in genes that control IFN production or its downstream signaling pathway, such as IRF5, might be responsible for some of these alterations. This novel information is leading to the development of IFN antagonists as a potential therapeutic intervention in SLE, thus bringing hope to SLE patients.     

Fueling autoimmunity: type I interferon in autoimmune diseases

In recent years, active research using genomic, cellular and animal modeling approaches has revealed the fundamental forces driving the development of autoimmune diseases. Type I interferon imprints unique molecular signatures in a list of autoimmune diseases. Interferon is induced by diverse nucleic acid-containing complexes, which trigger innate immune activation of plasmacytoid dendritic cells. Interferon primes, activates or differentiates various leukocyte populations to promote autoimmunity. Accordingly, interferon signaling is essential for the initiation and/or progression of lupus in several experimental models. However, the heterogeneous nature of systemic lupus erythematosus requires better characterization on how interferon pathways are activated and subsequently promote the advancement of autoimmune diseases. Given the central role of type I interferon, various strategies are devised to target these cytokines or related pathways to curtail the progression of autoimmune diseases.     

Cytosolic d-type CpG-oligonucleotides induce a type I interferon response by activating the cGAS-STING signaling pathway

Cytosolic DNA receptor cyclic GMP-AMP (cGAMP) synthase (cGAS) has been shown to be critically involved in the detection of cytosolic, self- and non-self-DNA, initiating a type I IFN response through the adaptor protein Stimulator of Interferon Genes (STING) and interferon regulatory factor 3 (IRF3). Current studies propose that canonical binding of dsDNA by cGAS depends on DNA length, but not on base sequence. In contrast, activation of TLR9 is sequence dependent. It requires unmethylated CpG dinucleotides in microbial DNA, which is mimicked by synthetic oligodeoxynucleotides (ODN). Here, we provide evidence that d -type ODN (D-ODN), but not K-type ODN (K-ODN), bind to human cGAS and activate downstream signaling. Transfection of D-ODN into a TLR9-deficient, human monocytic cell line (THP-1) induced phosphorylation of IRF3 and secretion of IFN. This response was absent in cells with CRISPR/Cas9-mediated cGAS- or STING-deficiency. Utilizing a protein pulldown approach, we further demonstrate direct binding of D-ODN to cGAS. Induction of a type I IFN response by D-ODN was confirmed in human primary monocytes and monocyte-derived macrophages. These results are relevant to our understanding of self–nonself-discrimination by cGAS and to the pharmacologic effects of ODN, which currently are investigated in clinical studies.     

I型干扰素信号通路与系统性红斑狼疮发病机制的研究进展

系统性红斑狼疮（SLE）是一种常见的自身免疫性疾病,多数患者血清中干扰素-α（IFN-α）水平升高,并且在淋巴细胞和组织中出现大量IFN诱导应答基因。含有核酸的免疫复合物作为IFN—α的诱导物,结合外源性因素的作用,可激活体内依赖Toll样受体（TLR）和不依赖TLR等多条信号通路,刺激产生更多的IFN-α,形成恶性循环,启动和维持SLE的自身免疫过程。     

A bioassay for interferon type I based on inhibition of Sendai virus growth

The expression of type I interferons (IFNs) in eukaryotic cells represents a first line of defense against viral infection. Cells pretreated by IFNs do not support viral replication and are protected from virus-induced cell destruction. A challenge of IFN-pretreated cells with vesicular stomatitis virus (VSV) is frequently used to quantitate this cytokine because, on the one hand, the replication of VSV is highly sensitive to IFNs and, on the other hand, in unprotected cells this virus induces a rapid cytopathic effect that can readily be quantified. However, as VSV may infect humans and is known to cause severe disease in a variety of animal species, this virus must be considered a biohazard. In this paper, we describe a bioassay for bovine IFN using Sendai virus, a paramyxovirus that grows readily in MDBK cells yet is released from these cells in a non-infectious form. The sensitivity and dynamic range of this assay are similar to those of the popular VSV-based IFN assay. We demonstrate that the Sendai-virus-based IFN assay permits rapid quantitation of recombinant bovine type I IFN, and also of native type I IFNs which are present in the supernatants of monocyte-derived macrophages infected with various pathogens. In view of the possible artifacts induced by viruses in samples to be assayed for IFN activity, we evaluated several methods of virus inactivation. Treatment with beta-propiolactone led to virus inactivation without affecting the bioactivity of IFNs as detected in the Sendai-virus-based assay.     

Mechanisms of genetic susceptibility to type I diabetes: beyond HLA

An individual's predisposition to Type I diabetes (T1D) is largely determined by complex interactions between several genetic loci and other, nonheritable factors. In T1D, the HLA locus has been known for decades to contribute 50% of the inherited risk. Outside the HLA are many proposed candidate loci with smaller effects, but only two confirmed candidate genes, the INS-VNTR and the CTLA-4 genes, which together do not contribute more than 15% of the risk. Because of the high frequency of the disease-associated DNA variants of these genes, understanding the biological mechanisms of such DNA variation in the context of T1D can have tremendous impact on the development of preventive therapeutics. However, establishing a causal relationship between common DNA variations and disease-predisposing functional effects is not trivial and remains difficult, as the effects are expected to be subtle. The variable-number tandem-repeat (VNTR) region upstream of the insulin gene is known to mediate expression in the thymus and pancreas, whereas various polymorphisms in the 5' and 3' regulatory regions of CTLA-4 are thought to alter gene expression and a coding A49G polymorphism exerts effects on post-translational processing. This review details the latest efforts in elucidating the functional mechanisms that explain the genetic association of the INS-VNTR and CTLA-4 genes with T1D.     

A candidate gene study of the type I interferon pathway implicates IKBKE and IL8 as risk loci for SLE

Systemic Lupus Erythematosus (SLE) is a systemic autoimmune disease in which the type I interferon pathway has a crucial role. We have previously shown that three genes in this pathway, IRF5, TYK2 and STAT4, are strongly associated with risk for SLE. Here, we investigated 78 genes involved in the type I interferon pathway to identify additional SLE susceptibility loci. First, we genotyped 896 single-nucleotide polymorphisms in these 78 genes and 14 other candidate genes in 482 Swedish SLE patients and 536 controls. Genes with P<0.01 in the initial screen were then followed up in 344 additional Swedish patients and 1299 controls. SNPs in the IKBKE, TANK, STAT1, IL8 and TRAF6 genes gave nominal signals of association with SLE in this extended Swedish cohort. To replicate these findings we extracted data from a genomewide association study on SLE performed in a US cohort. Combined analysis of the Swedish and US data, comprising a total of 2136 cases and 9694 controls, implicates IKBKE and IL8 as SLE susceptibility loci (P_meta=0.00010 and P_meta=0.00040, respectively). STAT1 was also associated with SLE in this cohort (P_meta=3.3 × 10⁻⁵), but this association signal appears to be dependent of that previously reported for the neighbouring STAT4 gene. Our study suggests additional genes from the type I interferon system in SLE, and highlights genes in this pathway for further functional analysis.     

PDL-1 upregulation on monocytes and T cells by HIV via type I interferon: restricted expression of type I interferon receptor by CCR5-expressing leukocytes

The programmed death (PD)-1 interacts with its ligand (PDL-1) delivering a negative signal to T cells. During human immunodeficiency virus (HIV)-1 infection PD-1 and PDL-1 expressions are increased. Here we show that monocytes and CCR5(+) T cells of HIV-uninfected donors upregulated PDL-1 upon in vitro exposure to HIV. HIV-induced PDL-1 required interferon (IFN)-alpha, but not IFN-gamma, production. Inhibition of endocytosis, required for HIV-induced IFN-alpha production, prevented PDL-1 upregulation. IFN-alpha-inducing Toll-like receptor (TLR) agonists increased PDL-1 on monocytes and CCR5(+) T cells. CD80 and CD86 were also increased on monocytes and CCR5(+) T cells after HIV exposure, but only CD80 was IFN-alpha-dependent. IFN-alpha-receptor subunit 2 (IFNAR2), was expressed only by CCR5(+) T cells and monocytes, explaining why these leukocytes responded to HIV-induced IFN-alpha. Finally, T cell proliferation was improved by PDL-1 blockade in HIV-treated PBMC. In the setting of HIV infection, IFN-alpha may negatively affect T cell responses by inducing PDL-1.     

系统性红斑狼疮患者中miR-146a表达缺陷与I型干扰素通路过度活化相关

Ι型干扰素(IFN)通路过度活化与固有免疫反应异常在系统性红斑狼疮(SLE)发病中起重要作用。miR-146a作为一个负调控因子,在固有免疫应答中发挥重要作用。为探索miR-146a在SLE发病中的作用,通过实时荧光定量聚合酶链反应技术检测18例SLE患者和11例正常对照miR-146a的表达,发现同正常对照组相比,miR-146a表达水平在SLE患者中明显降低,SLE活动组中下降则更加明显;同时检测miR-146a的靶基因IRAK1和TRAF6 mRNA表达,发现在SLE患者中其水平显著高于正常对照组;进一步分析miR-146a与IFN诱导基因表达之间的关系,结果显示两者之间存在负相关,体外实验也证实miR-146a能够负向调节I型干扰素通路。综上所述,我们的研究结果提示miR-146a可能作为一个新的生物标志物,SLE患者中miR-146a表达水平下降,导致I型干扰素通路负调控作用被削弱,从而参与疾病的发生发展。     

Regulation of the interferon system: evidence that Vero cells have a genetic defect in interferon production.

A clone of Vero cells was isolated and shown to be totally unable to synthesize interferon and insensitive to the toxic effect of poly(rI).poly(rC) treatment. Cells of this clone and mouse L cells were fused by treatment with polyethylene glycol or Sendai virus. Hybrid cell clones were isolated following selection in medium containing hypoxanthine, thymidine and ouabain. The hybrids were sensitive to the antiviral effect of poly(rI).poly(rC) and synthesized mouse, but not primate, interferon. It is proposed that in Vero cells, the gene for interferon synthesis is defective or absent.     

Ingested type I interferon: a potential treatment for autoimmunity.

We have proposed a unifying hypothesis of the etiopathogenesis of autoimmunity that defines autoimmunity as a type I interferon (IFN) immunodeficiency syndrome. We have examined toxicity and potential efficacy in three phase I (type 1 diabetes, rheumatoid arthritis, multiple sclerosis) and one phase II clinical trials in multiple sclerosis (MS). In a phase I open-label trial in type 1 diabetes, ingested IFN-alpha preserved residual beta cell function in recent onset patients. In a second phase I trial, treatment of rheumatoid arthritis (RA) with ingested IFN-alpha reduced the secretion of interleukin-1 (IL-1), a proinflammatory cytokine. In a third phase I trial in MS, there was a significant decrease in peripheral blood mononuclear cell (PBMC) IL-2 and IFN-gamma production after ingesting IFN-alpha. In a phase II randomized, placebo-controlled, double-blind trial in MS, 10,000 IU ingested IFN-alpha significantly decreased gadolinium enhancements compared with the placebo group at month 5. Tumor necrosis factor-alpha (TNF-alpha) and IFN-gamma cytokine secretion in the 10,000 IU group at month 5 showed a significant decrease that corresponded with the effect of ingested IFN-alpha on decreasing gadolinium enhancements. Ingested IFN-alpha was not toxic in any of these clinical trials. These studies suggest that ingested IFN-alpha may have a potential role in the treatment of autoimmunity.     

Trichostatin A blocks type I interferon production by activated plasmacytoid dendritic cells

Plasmacytoid dendritic cells (PDC) represent the main type I interferon (IFN-I) producing cells. Emerging evidence supports a role for IFN-I in autoimmune diseases. Given the central role of PDC in the pathogenesis of systemic lupus erythematosus (SLE), we investigated the effect of Trichostatin A (TSA), a prototypic histone deacetylase inhibitor, on PDC activation. TSA inhibited the production of IFN-I, TRAIL and of the pro-inflammatory cytokines TNFα and IL-6 by CpG-activated PDC. These effects were associated with the inhibition of IFN Regulatory Factor (IRF)-7 nuclear translocation. Furthermore, TSA was also effective in inhibiting the production of IFNα by PDC cultured in vitro in the presence of serum obtained from SLE patients. This study describes a new level of regulation of immune responses by histone deacetylase inhibitors and defines the molecular basis for new strategies to be exploited in the treatment of autoimmune diseases.     

The mitochondrial proteins NLRX1 and TUFM form a complex that regulates type I interferon and autophagy

The mitochondrial protein MAVS (also known as IPS-1, VISA, and CARDIF) interacts with RIG-I-like receptors (RLRs) to induce type I interferon (IFN-I). NLRX1 is a mitochondrial nucleotide-binding, leucine-rich repeats (NLR)-containing protein that attenuates MAVS-RLR signaling. Using Nlrx1(-/-) cells, we confirmed that NLRX1 attenuated IFN-I production, but additionally promoted autophagy during viral infection. This dual function of NLRX1 paralleled the previously described functions of the autophagy-related proteins Atg5-Atg12, but NLRX1 did not associate with Atg5-Atg12. High-throughput quantitative mass spectrometry and endogenous protein-protein interaction revealed an NLRX1-interacting partner, mitochondrial Tu translation elongation factor (TUFM). TUFM interacted with Atg5-Atg12 and Atg16L1 and has similar functions as NLRX1 by inhibiting RLR-induced IFN-I but promoting autophagy. In the absence of NLRX1, increased IFN-I and decreased autophagy provide an advantage for host defense against vesicular stomatitis virus. This study establishes a link between an NLR protein and the viral-induced autophagic machinery via an intermediary partner, TUFM.