CD8(+) T cell-mediated skin disease in mice lacking IRF-2, the transcriptional attenuator of interferon-alpha/beta signaling

Transcriptional Control of Interferon-Stimulated Genes

Interferon-induced genes (ISG) are among the best -studied groups of coregulated genes. Nevertheless, intense research into their regulation, supported by new technologies, is continuing to provide insights into their many layers of transcriptional regulation and to reveal how cellular transcriptomes change with pathogen-induced innate and adaptive immunity. This article gives an overview of recent findings on ISG regulation, paying attention to contributions beyond the canonical JAK-STAT pathways.

Interferons and interferon-related pathways in heart disease

Interferons (IFNs) and IFN-related pathways play key roles in the defence against microbial infection. However, these processes may also be activated during the pathogenesis of non-infectious diseases, where they may contribute to organ injury, or function in a compensatory manner. In this review, we explore the roles of IFNs and IFN-related pathways in heart disease. We consider the cardiac effects of type I IFNs and IFN-stimulated genes (ISGs); the emerging role of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway; the seemingly paradoxical effects of the type II IFN, IFN-γ; and the varied actions of the interferon regulatory factor (IRF) family of transcription factors. Recombinant IFNs and small molecule inhibitors of mediators of IFN receptor signaling are already employed in the clinic for the treatment of some autoimmune diseases, infections, and cancers. There has also been renewed interest in IFNs and IFN-related pathways because of their involvement in SARS-CoV-2 infection, and because of the relatively recent emergence of cGAS-STING as a pattern recognition receptor-activated pathway. Whether these advances will ultimately result in improvements in the care of those experiencing heart disease remains to be determined.

The gene regulatory basis of bystander activation in CD8+ T cells

CD8+ T cells are classically recognized as adaptive lymphocytes based on their ability to recognize specific foreign antigens and mount memory responses. However, recent studies indicate that some antigen-inexperienced CD8+ T cells can respond to innate cytokines alone in the absence of cognate T cell receptor stimulation, a phenomenon referred to as bystander activation. Here, we demonstrate that neonatal CD8+ T cells undergo a robust and diverse program of bystander activation, which corresponds to enhanced innate-like protection against unrelated pathogens. Using a multi-omics approach, we found that the ability of neonatal CD8+ T cells to respond to innate cytokines derives from their capacity to undergo rapid chromatin remodeling, resulting in the usage of a distinct set of enhancers and transcription factors typically found in innate-like T cells. We observed that the switch between innate and adaptive functions in the CD8+ T cell compartment is mediated by changes in the abundance of distinct subsets of cells. The innate CD8+ T cell subset that predominates in early life was also present in adult mice and humans. Our findings provide support for the layered immune hypothesis and indicate that the CD8+ T cell compartment is more functionally diverse than previously thought.

The MEF2A transcription factor interactome in cardiomyocytes

Transcriptional regulators encoded by the Myocyte Enhancer Factor 2 (MEF2) gene family play a fundamental role in cardiac development, homeostasis and pathology. Previous studies indicate that MEF2A protein-protein interactions serve as a network hub in several cardiomyocyte cellular processes. Based on the idea that interactions with regulatory protein partners underly the diverse roles of MEF2A in cardiomyocyte gene expression, we undertook a systematic unbiased screen of the MEF2A protein interactome in primary cardiomyocytes using an affinity purification-based quantitative mass spectrometry approach. Bioinformatic processing of the MEF2A interactome revealed protein networks involved in the regulation of programmed cell death, inflammatory responses, actin dynamics and stress signaling in primary cardiomyocytes. Further biochemical and functional confirmation of specific protein-protein interactions documented a dynamic interaction between MEF2A and STAT3 proteins. Integration of transcriptome level data from MEF2A and STAT3-depleted cardiomyocytes reveals that the balance between MEF2A and STAT3 activity exerts a level of executive control over the inflammatory response and cardiomyocyte cell survival and experimentally ameliorates Phenylephrine induced cardiomyocyte hypertrophy. Lastly, we identified several MEF2A/STAT3 co-regulated genes, including the MMP9 gene. Herein, we document the cardiomyocyte MEF2A interactome, which furthers our understanding of protein networks involved in the hierarchical control of normal and pathophysiological cardiomyocyte gene expression in the mammalian heart.

The Experimental Animal Models in Psoriasis Research: A Comprehensive Review

Psoriasis is an autoimmune, chronic, inflammatory skin condition mediated by T cells. It differs from other inflammatory conditions by causing significant alterations in epidermal cell proliferation and differentiation that are both complicated and prominent. The lack of an appropriate animal model has significantly hindered studies into the pathogenic mechanisms of psoriasis since animals other than humans typically do not exhibit the complex phenotypic features of human psoriasis. A variety of methods, including spontaneous mutations, drug-induced mutations, genetically engineered animals, xenotransplantation models, and immunological reconstitution approaches, have all been employed to study specific characteristics in the pathogenesis of psoriasis. Although some of these approaches have been used for more than 50 years and far more models have been introduced recently, they have surprisingly not yet undergone detailed validation. Despite their limitations, these models have shown a connection between keratinocyte hyperplasia, vascular hyperplasia, and a cell-mediated immune response in the skin. The xenotransplantation of diseased or unaffected human skin onto immune-compromised recipients has also significantly aided psoriasis research. This technique has been used in a variety of ways to investigate the function of T lymphocytes and other cells, including preclinical therapeutic studies. The design of pertinent in vivo and in vitro psoriasis models is currently of utmost concern and a crucial step toward its cure. This article outlines the general approach in the development of psoriasis-related animal models, aspects of some specific models, along with their strengths and limitations.

The transcription factor IRF2 drives interferon-mediated CD8+ T cell exhaustion to restrict anti-tumor immunity

Type I and II interferons (IFNs) stimulate pro-inflammatory programs that are critical for immune activation, but also induce immune-suppressive feedback circuits that impede control of cancer growth. Here, we sought to determine how these opposing programs are differentially induced. We demonstrated that the transcription factor interferon regulatory factor 2 (IRF2) was expressed by many immune cells in the tumor in response to sustained IFN signaling. CD8+ T cell-specific deletion of IRF2 prevented acquisition of the T cell exhaustion program within the tumor and instead enabled sustained effector functions that promoted long-term tumor control and increased responsiveness to immune checkpoint and adoptive cell therapies. The long-term tumor control by IRF2-deficient CD8+ T cells required continuous integration of both IFN-I and IFN-II signals. Thus, IRF2 is a foundational feedback molecule that redirects IFN signals to suppress T cell responses and represents a potential target to enhance cancer control.

IRF2 integrates inflammatory signals to balance T cell exhaustion

The transcription factor interferon regulatory factor 2 (IRF2) translates interferon signaling to regulate T cells. In this issue of Immunity, Lukhele et al. identify IRF2 in tumor-infiltrating T cells as a sensor for extrinsic signals that drives an exhaustion program.

Postnatal expansion of mesenteric lymph node stromal cells towards reticular and CD34+ stromal cell subsets

Gut-draining mesenteric lymph nodes (LN) provide the framework to shape intestinal adaptive immune responses. Based on the transcriptional signatures established by our previous work, the composition and immunomodulatory function of LN stromal cells (SC) vary according to location. Here, we describe the single-cell composition and development of the SC compartment within mesenteric LNs derived from postnatal to aged mice. We identify CD34⁺ SC and fibroblastic reticular stromal cell (FRC) progenitors as putative progenitors, both supplying the typical rapid postnatal mesenteric LN expansion. We further establish the location-specific chromatin accessibility and DNA methylation landscape of non-endothelial SCs and identify a microbiota-independent core epigenomic signature, showing characteristic differences between SCs from mesenteric and skin-draining peripheral LNs. The epigenomic landscape of SCs points to dynamic expression of Irf3 along the differentiation trajectories of FRCs. Accordingly, a mesenchymal stem cell line acquires a Cxcl9⁺ FRC molecular phenotype upon lentiviral overexpression of Irf3, and the relevance of Irf3 for SC biology is further underscored by the diminished proportion of Ccl19⁺ and Cxcl9⁺ FRCs in LNs of Irf3^-/- mice. Together, our data constitute a comprehensive transcriptional and epigenomic map of mesenteric LNSC development in early life and dissect location-specific, microbiota-independent properties of non-endothelial SCs.

When does hepatitis B virus meet long-stranded noncoding RNAs?

Hepatitis B virus (HBV) infection in humans and its associated diseases are long-standing problems. HBV can produce a large number of non-self-molecules during its life cycle, which acts as targets for innate immune recognition and initiation. Among these, interferon and its large number of downstream interferon-stimulated gene molecules are important early antiviral factors. However, the development of an effective antiviral immune response is not simple and depends not only on the delicate regulation of the immune response but also on the various mechanisms of virus-related immune escape and immune tolerance. Therefore, despite there being a relatively well-established consensus on the major pathways of the antiviral response and their component molecules, the complete clearance of HBV remains a challenge in both basic and clinical research. Long-noncoding RNAs (lncRNAs) are generally >200 bp in length and perform different functions in the RNA strand encoding the protein. As an important part of the IFN-inducible genes, interferon-stimulated lncRNAs are involved in the regulation of several HBV infection-related pathways. This review traces the basic elements of such pathways and characterizes the various recent targets of lncRNAs, which not only complement the regulatory mechanisms of pathways related to chronic HBV infection, fibrosis, and cancer promotion but also present with new potential therapeutic targets for controlling HBV infection and the malignant transformation of hepatocytes.

Association Between Psoriasis and Nonalcoholic Fatty Liver Disease Among Outpatient US Adults

IMPORTANCE

Recent studies have shown an association between psoriasis and nonalcoholic fatty liver disease (NAFLD) in US inpatients, but the association is still unclear in the outpatient US population.

OBJECTIVE

To assess whether psoriasis is associated with NAFLD in outpatient US adults.

DESIGN, SETTING, AND PARTICIPANTS

This population-based cross-sectional study used data on US adults aged 20 to 59 years from the National Health and Nutrition Examination Survey (NHANES) 2003-2006 and 2009-2014 cycles. Data were analyzed from June to September 2021.

EXPOSURES

Self-reported psoriasis.

MAIN OUTCOMES AND MEASURES

The main outcome was NAFLD, defined as a US fatty liver index score greater than 30. Sampling weights were calculated according to NHANES guidelines.

RESULTS

Among 5672 adults included in this study (mean age, 38.9 years [95% CI, 38.4-39.3 years]; 2999 [51.1%] female), 148 (3.0%) had psoriasis and 5524 (97.0%) did not have psoriasis. A total of 1558 participants (26.8%) were classified as having NAFLD. Compared with participants without psoriasis, those with psoriasis had a higher prevalence of NAFLD (32.7% [52] vs 26.6% [1506]). In a multivariable logistic regression model adjusted for age, sex, race and ethnicity, educational level, family income, marital status, NHANES cycles, diabetes, metabolic syndrome, and smoking and alcohol drinking status, psoriasis was associated with NAFLD (odds ratio [OR], 1.67; 95% CI, 1.03-2.70). In subgroup analyses, psoriasis was associated with NAFLD among men (OR, 2.16; 95% CI, 1.10-4.24), among those aged 20 to 39 years (OR, 2.48; 95% CI, 1.09-5.67), and among those without diabetes (1.70; 95% CI, 1.05-2.76). An association between psoriasis and NAFLD was found in sensitivity analyses that excluded potential hepatotoxic medication use (OR, 1.72; 95% CI, 1.01-2.95) or non-Hispanic Black participants (OR, 1.76; 95% CI, 1.07-2.87), redefined NAFLD based on the hepatic steatosis index score (OR, 1.59; 95% CI, 1.01-2.50), and used inverse probability of treatment weighting (OR, 1.43; 95% CI, 1.09-1.86).

CONCLUSIONS AND RELEVANCE

In this cross-sectional study, psoriasis was associated with NAFLD in the outpatient US adult population in adjusted models. This association may be important to consider in the context of clinicians prescribing potentially hepatotoxic medication for psoriasis management.

The P5-type ATPase ATP13A1 modulates major histocompatibility complex I-related protein 1 (MR1)-mediated antigen presentation

The monomorphic antigen-presenting molecule major histocompatibility complex-I-related protein 1 (MR1) presents small-molecule metabolites to mucosal-associated invariant T (MAIT) cells. The MR1-MAIT cell axis has been implicated in a variety of infectious and noncommunicable diseases, and recent studies have begun to develop an understanding of the molecular mechanisms underlying this specialized antigen presentation pathway. However, proteins regulating MR1 folding, loading, stability, and surface expression remain to be identified. Here, we performed a gene trap screen to discover novel modulators of MR1 surface expression through insertional mutagenesis of an MR1-overexpressing clone derived from the near-haploid human cell line HAP1 (HAP1.MR1). The most significant positive regulators identified included β2-microglobulin, a known regulator of MR1 surface expression, and ATP13A1, a P5-type ATPase in the endoplasmic reticulum (ER) not previously known to be associated with MR1-mediated antigen presentation. CRISPR/Cas9-mediated knockout of ATP13A1 in both HAP1.MR1 and THP-1 cell lines revealed a profound reduction in MR1 protein levels and a concomitant functional defect specific to MR1-mediated antigen presentation. Collectively, these data are consistent with the ER-resident ATP13A1 being a key posttranscriptional determinant of MR1 surface expression.

Comparative Analysis of Six IRF Family Members in Alveolar Epithelial Cell-Intrinsic Antiviral Responses

Host cell-intrinsic antiviral responses are largely mediated by pattern-recognition receptor (PRR) signaling and the interferon (IFN) system. The IFN regulatory factor (IRF) family of transcription factors takes up a central role in transcriptional regulation of antiviral innate immunity. IRF3 and IRF7 are known to be key players downstream of PRRs mediating the induction of type I and III IFNs. IFN signaling then requires IRF9 for the expression of the full array of interferon stimulated genes (ISGs) ultimately defining the antiviral state of the cell. Other members of the IRF family clearly play a role in mediating or modulating IFN responses, such as IRF1, IRF2 or IRF5, however their relative contribution to mounting a functional antiviral response is much less understood. In this study, we systematically and comparatively assessed the impact of six members of the IRF family on antiviral signaling in alveolar epithelial cells. We generated functional knockouts of IRF1, -2, -3, -5, -7, and -9 in A549 cells, and measured their impact on the expression of IFNs and further cytokines, ISGs and other IRFs, as well as on viral replication. Our results confirmed the vital importance of IRF3 and IRF9 in establishing an antiviral state, whereas IRF1, 5 and 7 were largely dispensable. The previously described inhibitory activity of IRF2 could not be observed in our experimental system.

TLR3 controls constitutive IFN-β antiviral immunity in human fibroblasts and cortical neurons

Human herpes simplex virus 1 (HSV-1) encephalitis can be caused by inborn errors of the TLR3 pathway, resulting in impairment of CNS cell-intrinsic antiviral immunity. Deficiencies of the TLR3 pathway impair cell-intrinsic immunity to vesicular stomatitis virus (VSV) and HSV-1 in fibroblasts, and to HSV-1 in cortical but not trigeminal neurons. The underlying molecular mechanism is thought to involve impaired IFN-α/β induction by the TLR3 recognition of dsRNA viral intermediates or by-products. However, we show here that human TLR3 controls constitutive levels of IFNB mRNA and secreted bioactive IFN-β protein, and thereby also controls constitutive mRNA levels for IFN-stimulated genes (ISGs) in fibroblasts. Tlr3-/- mouse embryonic fibroblasts also have lower basal ISG levels. Moreover, human TLR3 controls basal levels of IFN-β secretion and ISG mRNA in induced pluripotent stem cell-derived cortical neurons. Consistently, TLR3-deficient human fibroblasts and cortical neurons are vulnerable not only to both VSV and HSV-1, but also to several other families of viruses. The mechanism by which TLR3 restricts viral growth in human fibroblasts and cortical neurons in vitro and, by inference, by which the human CNS prevents infection by HSV-1 in vivo, is therefore based on the control of early viral infection by basal IFN-β immunity.

IRF2BP2 Mutation Is Associated with Increased STAT1 and STAT5 Activation in Two Family Members with Inflammatory Conditions and Lymphopenia

Interferon regulatory factor 2 binding protein 2 (IRF2BP2) is a transcriptional coregulator that has an important role in the regulation of the immune response. IRF2BP2 has been associated with the Janus kinase (JAK)-signal transducers and activators of transcription (STAT) pathway, but its exact role remains elusive. Here, we identified a novel clinical variant, IRF2BP2 c.625_665del, from two members of a family with inflammatory conditions and investigated the function of IRF2BP2 and c.625_665del mutation in JAK-STAT pathway activation and inflammatory signaling. The levels of constitutive and cytokine-induced phosphorylation of STATs and total STAT1 in peripheral blood monocytes, T cells, and B cells from the patients and four healthy controls were measured by flow cytometry. Inflammation-related gene expression was studied in peripheral blood mononuclear cells using direct digital detection of mRNA (NanoString). Finally, we studied the relationship between IRF2BP2 and STAT1 activation using a luciferase reporter system in a cell model. Our results show that patients having the IRF2BP2 c.625_665del mutation presented overexpression of STAT1 protein and increased constitutive activation of STAT1. In addition, interferon-induced JAK-STAT signaling was upregulated, and several interferon-inducible genes were overexpressed. Constitutive phosphorylation of STAT5 was also found to be upregulated in CD4⁺ T cells from the patients. Using a cell model, we show that IRF2BP2 was needed to attenuate STAT1 transcriptional activity and that IRF2BP2 c.625_665del mutation failed in this. We conclude that IRF2BP2 has an important role in suppressing immune responses elicited by STAT1 and STAT5 and suggest that aberrations in IRF2BP2 can lead to abnormal function of intrinsic immunity.

The Effects of Interferons on Allogeneic T Cell Response in GVHD: The Multifaced Biology and Epigenetic Regulations

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative therapy for hematological malignancies. This beneficial effect is derived mainly from graft-versus-leukemia (GVL) effects mediated by alloreactive T cells. However, these alloreactive T cells can also induce graft-versus-host disease (GVHD), a life-threatening complication after allo-HSCT. Significant progress has been made in the dissociation of GVL effects from GVHD by modulating alloreactive T cell immunity. However, many factors may influence alloreactive T cell responses in the host undergoing allo-HSCT, including the interaction of alloreactive T cells with both donor and recipient hematopoietic cells and host non-hematopoietic tissues, cytokines, chemokines and inflammatory mediators. Interferons (IFNs), including type I IFNs and IFN-γ, primarily produced by monocytes, dendritic cells and T cells, play essential roles in regulating alloreactive T cell differentiation and function. Many studies have shown pleiotropic effects of IFNs on allogeneic T cell responses during GVH reaction. Epigenetic mechanisms, such as DNA methylation and histone modifications, are important to regulate IFNs’ production and function during GVHD. In this review, we discuss recent findings from preclinical models and clinical studies that characterize T cell responses regulated by IFNs and epigenetic mechanisms, and further discuss pharmacological approaches that modulate epigenetic effects in the setting of allo-HSCT.

Evolution of the IRF Family in Salmonids

Interferon regulatory factors (IRFs) as a family, are major regulators of the innate antiviral response in vertebrates principally involved in regulating the expression of interferons (IFNs) and interferon-stimulated genes (ISGs). To date, nine IRFs have been identified in mammals with a 10th member also found in several avian and fish species. Through genome mining and phylogenetic analysis, we identified and characterised 23 irf genes in 6 salmonid species. This larger repertoire of IRF in salmonids results from two additional whole-genome duplications which occurred in early teleosts and salmonids, respectively. Synteny analysis was then used to identify and confirm which paralogues belonged to each subgroup and a new nomenclature was assigned to the salmonid IRFs. Furthermore, we present a full set of Real-Time PCR primers for all rainbow trout IRFs, confirmed by sequencing to ensure paralogue specificity. RT PCR was then used to examine the response of all trout irf genes in vivo, following Vibrio anguillarum and poly I:C stimulation, indicating potential functional divergence between paralogues. Overall, this study presents a comprehensive overview of the IRF family in salmonids and highlights some novel roles for the salmonid-specific IRFs in immunity.

Role of interferon regulatory factor-mediated signaling in psoriasis

Psoriasis is a chronic inflammatory disease that involves both the innate and adaptive immune systems. Type I interferons (IFNs), the production of which is partially regulated by toll-like receptors (TLRs), play an important role in the pathogenesis of psoriasis, especially psoriasis caused by skin trauma, known as the Koebner phenomenon. IFN regulatory factors (IRFs) function in both innate and adaptive immune responses, and their effect is associated with the regulation of type I IFNs. In this review, we focus on recent advances in understanding the expression of TLRs, IRFs, and type I IFNs in psoriasis. We also highlight the interplay among TLRs, IRFs, and type I IFNs.

Identification of Interleukin1β as an Amplifier of Interferon alpha-induced Antiviral Responses

The induction of an interferon-mediated response is the first line of defense against pathogens such as viruses. Yet, the dynamics and extent of interferon alpha (IFNα)-induced antiviral genes vary remarkably and comprise three expression clusters: early, intermediate and late. By mathematical modeling based on time-resolved quantitative data, we identified mRNA stability as well as a negative regulatory loop as key mechanisms endogenously controlling the expression dynamics of IFNα-induced antiviral genes in hepatocytes. Guided by the mathematical model, we uncovered that this regulatory loop is mediated by the transcription factor IRF2 and showed that knock-down of IRF2 results in enhanced expression of early, intermediate and late IFNα-induced antiviral genes. Co-stimulation experiments with different pro-inflammatory cytokines revealed that this amplified expression dynamics of the early, intermediate and late IFNα-induced antiviral genes can also be achieved by co-application of IFNα and interleukin1 beta (IL1β). Consistently, we found that IL1β enhances IFNα-mediated repression of viral replication. Conversely, we observed that in IL1β receptor knock-out mice replication of viruses sensitive to IFNα is increased. Thus, IL1β is capable to potentiate IFNα-induced antiviral responses and could be exploited to improve antiviral therapies.

Innate immune responses contribute to the control of viral infections and the induction of interferon alpha (IFNα)-mediated antiviral responses is an important component. However, IFNα induces a multitude of antiviral response genes and the expression dynamics of these genes can be classified as early, intermediate and late. Here we show, based on a mathematical modeling approach, that mRNA stability as well as the negative regulator IRF2 control the expression dynamics of IFNα-induced antiviral genes. Knock-down of IRF2 resulted in the amplified IFNα-mediated induction of the antiviral genes and this amplified expression of antiviral genes could be functionally mimicked by co-stimulation with IFNα and IL1β. We observed that co-stimulation with IFNα and IL1β enhanced the repression of virus replication and that knock-out of the IL1 receptor in mice resulted in increased replication of a virus sensitive to IFNα. In sum, our studies identified IL1β as an important amplifier of IFNα-induced antiviral responses.

IRF2 maintains the stemness of colonic stem cells by limiting physiological stress from interferon

The physiological stresses that diminish tissue stem-cell characteristics remain largely unknown. We previously reported that type I interferon (IFN), which is essential for host antiviral responses, is a physiological stressor for hematopoietic stem cells (HSCs) and small intestinal stem cells (ISCs) and that interferon regulatory factor-2 (IRF2), which attenuates IFN signaling, maintains their stemness. Here, using a dextran sodium sulfate (DSS)-induced colitis model, we explore the role of IRF2 in maintaining colonic epithelial stem cells (CoSCs). In mice with a conditional Irf2 deletion in the intestinal epithelium (hereafter Irf2ΔIEC mice), both the number and the organoid-forming potential of CoSCs were markedly reduced. Consistent with this finding, the ability of Irf2ΔIEC mice to regenerate colon epithelium after inducing colitis was severely impaired, independently of microbial dysbiosis. Mechanistically, CoSCs differentiated prematurely into transit-amplifying (TA) cells in Irf2ΔIEC mice, which might explain their low CoSC counts. A similar phenotype was induced in wild-type mice by repeated injections of low doses of poly(I:C), which induces type I IFN. Collectively, we demonstrated that chronic IFN signaling physiologically stresses CoSCs. This study provides new insight into the development of colitis and molecular mechanisms that maintain functional CoSCs throughout life.

The influence of interferon on healthy and diseased skin

Type I interferons (IFNs) are an immunomodulatory class of cytokines that serve to protect against viral and bacterial infection. In addition, mounting evidence suggests IFNs, particularly type I but also IFNγ, are important to the pathogenesis of autoimmune and inflammatory skin diseases, such as cutaneous lupus erythematosus (CLE). Understanding the role of IFNs is relevant to anti-viral responses in the skin, skin biology, and therapeutics for these IFN-related conditions. Type I IFNs (α and β) are produced by recruited inflammatory cells and by the epidermis itself (IFNκ) and have important roles in autoimmune and inflammatory skin disease. Here, we review the current literature utilizing a PubMed database search using terms [interferon/IFN/type I IFN AND lupus/ cutaneous lupus/CLE/dermatomyositis/Sjogrens/psoriasis/lichen planus/morphea/alopecia areata/vitiligo] with a focus on the role of IFNs in basic keratinocyte biology and their implications in the cutaneous autoimmune and inflammatory diseases: cutaneous lupus erythematosus, dermatomyositis, Sjogren's syndrome, psoriasis, lichen planus, alopecia areata and vitiligo. We provide information about genes and proteins induced by IFNs and how downstream mechanisms relate to clinical disease.

Regulated IFN signalling preserves the stemness of intestinal stem cells by restricting differentiation into secretory-cell lineages

Intestinal stem cells (ISCs) are located at the crypt base and fine-tune the balance of their self-renewal and differentiation^1,2, but the physiological mechanism involved in regulating that balance remains unknown. Here we describe a transcriptional regulator that preserves the stemness of ISCs by restricting their differentiation into secretory-cell lineages. Interferon regulatory factor 2 (IRF2) negatively regulates interferon signalling³, and mice completely lacking Irf2⁴ or with a selective Irf2 deletion in their intestinal epithelial cells have significantly fewer crypt Lgr5^hi ISCs than control mice. Although the integrity of intestinal epithelial cells was unimpaired at steady state in Irf2-deficient mice, regeneration of their intestinal epithelia after 5-fluorouracil-induced damage was severely impaired. Similarly, extended treatment with low-dose poly(I:C) or chronic infection of lymphocytic choriomeningitis virus clone 13 (LCMV C13)⁵ caused a functional decline of ISCs in wild-type mice. In contrast, massive accumulations of immature Paneth cells were found at the crypt base of Irf2^-/- as well as LCMV C13-infected wild-type mice, indicating that excess interferon signalling directs ISCs towards a secretory-cell fate. Collectively, our findings indicate that regulated interferon signalling preserves ISC stemness by restricting secretory-cell differentiation.

Animal models of psoriasis-highlights and drawbacks

Research into the pathophysiology of psoriasis remains challenging, because this disease does not occur naturally in laboratory animals. However, specific aspects of its complex immune-pathology can be illuminated through transgenic, knockout, xenotransplantation, immunological reconstitution, drug-induced, or spontaneous mutation models in rodents. Although some of these approaches have already been pursued for more than 5 decades and even more models have been described in recent times, they have surprisingly not yet been systematically validated. As a consequence, researchers regularly examine specific aspects that only partially reflect the complex overall picture of the human disease. Nonetheless, animal models are of great utility to investigate inflammatory mediators, the communication between cells of the innate and the adaptive immune systems, the role of resident cells as well as new therapies. Of note, various manipulations in experimental animals resulted in rather similar phenotypes. These were called "psoriasiform", "psoriasis-like" or even "psoriasis" usually on the basis of some similarities with the human disorder. Xenotransplantation of human skin onto immunocompromised animals can overcome this limitation only in part. In this review, we elucidate approaches for the generation of animal models of psoriasis and assess their strengths and limitations with a certain focus on more recently developed models.

Expression pattern of the interferon regulatory factor family members in influenza virus induced local and systemic inflammatory responses

Type I interferon is considered to be a key cytokine in influenza virus-induced acute lung injury (ALI), in which IRF3 and IRF7 play particularly important roles. However, whether all nine members of IRF family are involved in influenza virus-induced immune response is currently unknown. In this study, we found that all members of IRF family responded to influenza virus. The IRF family expression profile seems to be related to the pathogenicity of the particular influenza virus strain. The influenza virus mainly relies on endosomal TLR signals and the positive feedback loop of IFN-I to cause either direct or indirect different expression of all IRF family members locally or systemically. Interestingly, IRF6 was somewhat different from other IRF family members during influenza virus infection. Overall, the expression profile of the IRF family may be a valuable reference for the prevention and treatment of influenza complications, which encourage further, more in-depth research.

A peptide derived from phage-display limits psoriasis-like lesions in mice

BACKGROUND

Psoriasis is a pro-inflammatory disease with unknown etiology, that is characterized by skin inflammation and keratinocytes hyperproliferation. Specific inhibition of inflammation has shown positive effects avoiding the progression of the psoriatic lesions in different animal models of the disease, turning this strategy as a remarkable therapeutic alternative.

OBJECTIVE

To screen the effectiveness of a novel IFN-α/β signalling inhibitor in the development reduction of skin lesions in IMQ and TPA mice models of psoriasis.

METHODS

We used a Phage-peptide library for the screening of a peptide with inhibitory effects on the development of psoriasis-like lesions in mice. To evaluate the in vivo effect of the phage-peptides (Phpep3D) and the derived peptide (Pep3D), we administered Phpep3D or Pep3D intradermally in mice with imiquimod (IMQ)-induced psoriasis and 12-O-tetradecanoyl phorbol-13-acetate (TPA)-induced psoriasis. We scored the lesions, and we determined the number of neutrophils and the production of some pro-inflammatory cytokines in the lesions.

RESULTS

In this work, we describe how the Ph3pepD and Pep3D reduced skin thickness, redness, and acanthosis despite the presence of the psoriasis inducers, IMQ or TPA. We also found that Pep3D reduced the number of GR1+ infiltrated cells and decreased the production of IL-17A and TNFα in the psoriatic skin of mice. In-silico, docking analysis showed that Pep3D may interact with the interferon-alpha receptor, but further analyses should be performed to uncover the mechanism of action of this peptide.

CONCLUSION

Our results suggest that Pep3D could be used as a new treatment for psoriasis.

Exacerbated Imiquimod-Induced Psoriasis-Like Skin Inflammation in IRF5-Deficient Mice

Interferon regulatory factors (IRFs) play diverse roles in the regulation of the innate and adaptive immune responses in various diseases. In psoriasis, IRF2 is known to be involved in pathogenesis, while studies on other IRFs are limited. In this study, we investigated the role of IRF5 in psoriasis using imiquimod-induced psoriasis-like dermatitis. Although IRF5 is known to play a critical role in the induction of proinflammatory cytokines by immune cells, such as dendritic cells (DCs), macrophages, and monocytes, IRF5 deficiency unexpectedly exacerbated psoriasiform skin inflammation. The interferon-α and tumor necrosis factor-α mRNA expression levels were decreased, while levels of Th17 cytokines including IL-17, IL-22, and IL-23 were increased in IRF5-deficient mice. Furthermore, IL-23 expression in DCs from IRF5-deficient mice was upregulated both in steady state and after toll-like receptor 7/8 agonist stimulation. Importantly, the expression of IRF4, which is also important for the IL-23 production in DCs, was augmented in DCs from IRF5-deficient mice. Taken together, our results suggest that IRF5 deficiency induces the upregulation of IRF4 in DCs followed by augmented IL-23 production, resulting in the amplification of Th17 responses and the exacerbation of imiquimod-induced psoriasis-like skin inflammation. The regulation of IRF4 or IRF5 expression may be a novel therapeutic approach to psoriasis.

ZBED2 is an antagonist of interferon regulatory factor 1 and modifies cell identity in pancreatic cancer

Lineage plasticity is a prominent feature of pancreatic ductal adenocarcinoma (PDA) cells, which can occur via deregulation of lineage-specifying transcription factors. Here, we show that the zinc finger protein ZBED2 is aberrantly expressed in PDA and alters tumor cell identity in this disease. Unexpectedly, our epigenomic experiments reveal that ZBED2 is a sequence-specific transcriptional repressor of IFN-stimulated genes, which occurs through antagonism of IFN regulatory factor 1 (IRF1)-mediated transcriptional activation at cooccupied promoter elements. Consequently, ZBED2 attenuates the transcriptional output and growth arrest phenotypes downstream of IFN signaling in multiple PDA cell line models. We also found that ZBED2 is preferentially expressed in the squamous molecular subtype of human PDA, in association with inferior patient survival outcomes. Consistent with this observation, we show that ZBED2 can repress the pancreatic progenitor transcriptional program, enhance motility, and promote invasion in PDA cells. Collectively, our findings suggest that high ZBED2 expression is acquired during PDA progression to suppress the IFN response pathway and to promote lineage plasticity in this disease.

Dendritic cells: The driver of psoriasis

Psoriasis is a chronic skin inflammatory disorder, the immune mechanism of which has been profoundly elucidated in the past few years. The dominance of the interleukin (IL)-23/IL-17 axis is a significant breakthrough in the understanding of the pathogenesis of psoriasis, and treatment targeting IL-23 and IL-17 has successfully benefited patients with the disease. The skin contains a complex network of dendritic cells (DC) mainly composed of epidermal Langerhans cells, bone marrow-derived dermal conventional DC, plasmacytoid DC and inflammatory DC. As the prominent cellular source of α-interferon, tumor necrosis factor-α, IL-12 and IL-23, DC play a pivotal role in psoriasis. Thus, targeting pathogenic DC subsets is a valid strategy for alleviating and preventing psoriasis and other DC-derived diseases. In this review, we survey the known role of DC in this disease.

Molecular characterization and expression profile of interferon-stimulated gene 15 (ISG15) in the endometrium of goat (Capra hircus)

Interferon-stimulated gene 15 (ISG15), a ubiquitin-like protein, is responsible for uterine receptivity, implantation and conceptus development in different ruminant species, but in goat (Capra hircus) its role is yet to be explicated. In the present study, the ISG15 gene was cloned, characterized and its temporal expression profile was examined in the endometrium of caprine (cp). A fragment of cpISG15 gene, 1033 bp in length, was amplified, cloned and sequenced from genomic DNA covering the coding region. Sequence analysis of cpISG15 gene revealed that it was comprised of two exons of 59 bp and 496 bp encoding a peptide of 157 amino acids. Complementary DNA (cDNA) and deduced amino acid sequences of cpISG15 exhibited 99 and 98, 93 and 88, 94 and 89, 76 and 66, and 73 and 62% identity with that of sheep, cattle, buffalo, human and mice, respectively. Further, relative expression of cpISG15 mRNA and protein was determined by quantitative real-time PCR (qPCR) and Western blot, respectively, in the endometrium of pregnant and cyclic does. Both cpISG15 mRNA and protein were expressed maximally (P < 0.05) in the endometrium during early stage of pregnancy (16-24 d) as compared to cyclic does, but no significant difference was observed in cpISG15 mRNA and protein expression in the endometrium between the later stage of pregnancy (25-40 d) and cyclic does. It is concluded that cpISG15 is almost similar in structure and probably in function also to other species as it has been found significantly upregulated during early pregnancy.

Junin Virus Triggers Macrophage Activation and Modulates Polarization According to Viral Strain Pathogenicity

The New World arenavirus Junin (JUNV) is the etiological agent of Argentine hemorrhagic fever (AHF). Previous studies of human macrophage infection by the Old-World arenaviruses Mopeia and Lassa showed that while the non-pathogenic Mopeia virus replicates and activates human macrophages, the pathogenic Lassa virus replicates but fails to activate human macrophages. Less is known in regard to the impact of New World arenavirus infection on the human macrophage immune response. Macrophage activation is critical for controlling infections but could also be usurped favoring immune evasion. Therefore, it is crucial to understand how the JUNV infection modulates macrophage plasticity to clarify its role in AHF pathogenesis. With this aim in mind, we compared infection with the attenuated Candid 1 (C#1) or the pathogenic P strains of the JUNV virus in human macrophage cultures. The results showed that both JUNV strains similarly replicated and induced morphological changes as early as 1 day post-infection. However, both strains differentially induced the expression of CD71, the receptor for cell entry, the activation and maturation molecules CD80, CD86, and HLA-DR and selectively modulated cytokine production. Higher levels of TNF-α, IL-10, and IL-12 were detected with C#1 strain, while the P strain induced only higher levels of IL-6. We also found that C#1 strain infection skewed macrophage polarization to M1, whereas the P strain shifted the response to an M2 phenotype. Interestingly, the MERTK receptor, that negatively regulates the immune response, was down-regulated by C#1 strain and up-regulated by P strain infection. Similarly, the target genes of MERTK activation, the cytokine suppressors SOCS1 and SOCS3, were also increased after P strain infection, in addition to IRF-1, that regulates type I IFN levels, which were higher with C#1 compared with P strain infection. Together, this differential activation/polarization pattern of macrophages elicited by P strain suggests a more evasive immune response and may have important implications in the pathogenesis of AHF and underpinning the development of new potential therapeutic strategies.

IRF2 is a master regulator of human keratinocyte stem cell fate

Resident adult epithelial stem cells maintain tissue homeostasis by balancing self-renewal and differentiation. The stem cell potential of human epidermal keratinocytes is retained in vitro but lost over time suggesting extrinsic and intrinsic regulation. Transcription factor-controlled regulatory circuitries govern cell identity, are sufficient to induce pluripotency and transdifferentiate cells. We investigate whether transcriptional circuitry also governs phenotypic changes within a given cell type by comparing human primary keratinocytes with intrinsically high versus low stem cell potential. Using integrated chromatin and transcriptional profiling, we implicate IRF2 as antagonistic to stemness and show that it binds and regulates active cis-regulatory elements at interferon response and antigen presentation genes. CRISPR-KD of IRF2 in keratinocytes with low stem cell potential increases self-renewal, migration and epidermis formation. These data demonstrate that transcription factor regulatory circuitries, in addition to maintaining cell identity, control plasticity within cell types and offer potential for therapeutic modulation of cell function.

Epidermal homeostasis requires long term stem cell function. Here, the authors apply transcriptional circuitry analysis based on integrated epigenomic profiling of primary human keratinocytes with high and low stem cell function to identify IRF2 as a negative regulator of stemness.

Adenoviral gene transfer of a single-chain IL-23 induces psoriatic arthritis-like symptoms in NOD mice

Previously, we demonstrated that intratumoral delivery of adenoviral vector encoding single-chain (sc)IL-23 (Ad.scIL-23) was able to induce systemic antitumor immunity. Here, we examined the role of IL-23 in diabetes in nonobese diabetic mice. Intravenous delivery of Ad.scIL-23 did not accelerate the onset of hyperglycemia but instead resulted in the development of psoriatic arthritis. Ad.scIL-23-treated mice developed erythema, scales, and thickening of the skin, as well as intervertebral disc degeneration and extensive synovial hypertrophy and loss of articular cartilage in the knees. Immunological analysis revealed activation of conventional T helper type 17 cells and IL-17-producing γδ T cells along with a significant depletion and suppression of T cells in the pancreatic lymph nodes. Furthermore, treatment with anti-IL-17 antibody reduced joint and skin psoriatic arthritis pathologies. Thus, these Ad.scIL-23-treated mice represent a physiologically relevant model of psoriatic arthritis for understanding disease progression and for testing therapeutic approaches.-Flores, R. R., Carbo, L., Kim, E., Van Meter, M., De Padilla, C. M. L., Zhao, J., Colangelo, D., Yousefzadeh, M. J., Angelini, L. A., Zhang, L., Pola, E., Vo, N., Evans, C. H., Gambotto, A., Niedernhofer, L. J., Robbins, P. D. Adenoviral gene transfer of a single-chain IL-23 induces psoriatic arthritis-like symptoms in NOD mice.

Type1 Interferons Potential Initiating Factors Linking Skin Wounds With Psoriasis Pathogenesis

Psoriasis is a chronic autoimmune skin disease that can often be triggered upon skin injury, known as Koebner phenomenon. Type 1 interferons (IFNα and IFNβ), key cytokines that activate autoimmunity during viral infection, have been suggested to play an indispensable role in initiating psoriasis during skin injury. Type 1 IFN-inducible gene signature has been identified as one of the major upregulated gene signatures in psoriatic skin. Type 1 IFNs treatments often directly induce or exacerbate psoriasis, whereas blocking type 1 IFNs signaling pathway in animal models effectively inhibits the development of T cell-mediated skin inflammation and psoriasis-like inflammatory diseases. Epidermal keratinocytes (KCs) occupy the outermost position in the skin and are the first responder to skin injury. Skin injury rapidly induces IFNβ from KCs and IFNα from dermal plasmacytoid dendritic cells (pDCs) through distinct mechanisms. Host antimicrobial peptide LL37 potentiates double-stranded RNA (dsRNA) immune pathways in keratinocytes and single-stranded RNA or DNA pathways in pDCs, leading to production of distinct type 1 IFN genes. IFNβ from KC promotes dendritic cell maturation and the subsequent T cell proliferation, contributing to autoimmune activation during skin injury and psoriasis pathogenesis. Accumulating evidences have indicated an important role of this dsRNA immune pathway in psoriasis pathogenesis. Together, this review describes how skin injury induces type 1 IFNs from skin cells and how this may initiate autoimmune cascades that trigger psoriasis. Targeting keratinocytes or type 1 IFNs in combination with T cell therapy may result in more sustainable effect to treat auto-inflammatory skin diseases such as psoriasis.

Type I interferon signaling, regulation and gene stimulation in chronic virus infection

Type I Interferons (IFN-I) mediate numerous immune interactions during viral infections, from the establishment of an antiviral state to invoking and regulating innate and adaptive immune cells that eliminate infection. While continuous IFN-I signaling plays critical roles in limiting virus replication during both acute and chronic infections, sustained IFN-I signaling also leads to chronic immune activation, inflammation and, consequently, immune exhaustion and dysfunction. Thus, an understanding of the balance between the desirable and deleterious effects of chronic IFN-I signaling will inform our quest for IFN-based therapies for chronic viral infections as well as other chronic diseases, including cancer. As such the factors involved in induction, propagation and regulation of IFN-I signaling, from the initial sensing of viral nucleotides within the cell to regulatory downstream signaling factors and resulting IFN-stimulated genes (ISGs) have received significant research attention. This review summarizes recent work on IFN-I signaling in chronic infections, and provides an update on therapeutic approaches being considered to counter such infections.

Differential Regulation of Type I and Type III Interferon Signaling

Interferons (IFNs) are very powerful cytokines, which play a key role in combatting pathogen infections by controlling inflammation and immune response by directly inducing anti-pathogen molecular countermeasures. There are three classes of IFNs: type I, type II and type III. While type II IFN is specific for immune cells, type I and III IFNs are expressed by both immune and tissue specific cells. Unlike type I IFNs, type III IFNs have a unique tropism where their signaling and functions are mostly restricted to epithelial cells. As such, this class of IFN has recently emerged as a key player in mucosal immunity. Since the discovery of type III IFNs, the last 15 years of research in the IFN field has focused on understanding whether the induction, the signaling and the function of these powerful cytokines are regulated differently compared to type I IFN-mediated immune response. This review will cover the current state of the knowledge of the similarities and differences in the signaling pathways emanating from type I and type III IFN stimulation.

The Molecular Basis of Viral Inhibition of IRF- and STAT-Dependent Immune Responses

The antiviral innate immunity is the first line of host defense against virus infections. In mammalian cells, viral infections initiate the expression of interferons (IFNs) in the host that in turn activate an antiviral defense program to restrict viral replications by induction of IFN stimulated genes (ISGs), which are largely regulated by the IFN-regulatory factor (IRF) family and signal transducer and activator of transcription (STAT) family transcription factors. The mechanisms of action of IRFs and STATs involve several post-translational modifications, complex formation, and nuclear translocation of these transcription factors. However, many viruses, including human immunodeficiency virus (HIV), Zika virus (ZIKV), and herpes simplex virus (HSV), have evolved strategies to evade host defense, including alteration in IRF and STAT post-translational modifications, disturbing the formation and nuclear translocation of the transcription complexes as well as proteolysis/degradation of IRFs and STATs. In this review, we discuss and summarize the molecular mechanisms by which how viral components may target IRFs and STATs to antagonize the establishment of antiviral host defense. The underlying host-viral interactions determine the outcome of viral infection. Gaining mechanistic insight into these processes will be crucial in understanding how viral replication can be more effectively controlled and in developing approaches to improve virus infection outcomes.

The Interferon (IFN) Class of Cytokines and the IFN Regulatory Factor (IRF) Transcription Factor Family

Interferons (IFNs) are a broad class of cytokines elicited on challenge to the host defense and are essential for mobilizing immune responses to pathogens. Divided into three classes, type I, type II, and type III, all IFNs share in common the ability to evoke antiviral activities initiated by the interaction with their cognate receptors. The nine-member IFN regulatory factor (IRF) family, first discovered in the context of transcriptional regulation of type I IFN genes following viral infection, are pivotal for the regulation of the IFN responses. In this review, we briefly describe cardinal features of the three types of IFNs and then focus on the role of the IRF family members in the regulation of each IFN system.

Host-Intrinsic Interferon Status in Infection and Immunity

Most genetic ablations of interferon (IFN) signaling abolish both the experimentally induced IFN response and constitutive IFN, whose effects are well established in autoimmunity but understudied during infection. In host-pathogen interactions, most IFN-mediated responses are attributed to infection-driven IFN. However, IFNs confer their activity by regulating networks of interferon-stimulated genes (ISGs), a process that requires de novo transcription and translation of both IFN and downstream ISGs through feedback of IFN receptor signaling. Due to the temporal requirement for IFN activity, many rapid antimicrobial responses may instead result from pre-established IFN signature stemming from host-intrinsic processes. Addressing the permeating effects of constitutive IFN is therefore needed to accurately describe immunity as host intrinsic or pathogen induced.

Decreased A-to-I RNA editing as a source of keratinocytes' dsRNA in psoriasis

Recognition of dsRNA molecules activates the MDA5-MAVS pathway and plays a critical role in stimulating type-I interferon responses in psoriasis. However, the source of the dsRNA accumulation in psoriatic keratinocytes remains largely unknown. A-to-I RNA editing is a common co- or post-transcriptional modification that diversifies adenosine in dsRNA, and leads to unwinding of dsRNA structures. Thus, impaired RNA editing activity can result in an increased load of endogenous dsRNAs. Here we provide a transcriptome-wide analysis of RNA editing across dozens of psoriasis patients, and we demonstrate a global editing reduction in psoriatic lesions. In addition to the global alteration, we also detect editing changes in functional recoding sites located in the IGFBP7, COPA, and FLNA genes. Accretion of dsRNA activates autoimmune responses, and therefore the results presented here, linking for the first time an autoimmune disease to reduction in global editing level, are relevant to a wide range of autoimmune diseases.

IFN Regulatory Factor 2 Inhibits Expression of Glycolytic Genes and Lipopolysaccharide-Induced Proinflammatory Responses in Macrophages

Rapid initiation and timely resolution of inflammatory response in macrophages are synergistic events that are known to be equally critical to optimal host defense against pathogen infections. However, the regulation of these processes, in particular by a specific cellular metabolic program, has not been well understood. In this study, we found that IFN regulatory factor 2 (IRF2) underwent an early degradation in a proteasome-mediated pathway in LPS-treated mouse macrophages, followed by a later recovery of the expression via transactivation. We showed that IRF2 was anti-inflammatory in that knockdown of this protein promoted the production of LPS-induced proinflammatory mediators. Mechanistically, although IRF2 apparently did not target the proximal cytoplasmic signaling events upon LPS engagements, it inhibited HIF-1α-dependent expression of glycolytic genes and thereby cellular glycolysis, sequential events necessary for the IRF2 anti-inflammatory activity. We found that macrophages in endotoxin tolerant state demonstrated deficiency in LPS-augmented glycolysis, which was likely caused by failed downregulation of IRF2 and the ensuing upregulation of the glycolytic genes in these cells. In contrast to observations with LPS, knockdown of IRF2 decreased IL-4-induced macrophage alternative activation. The pro-IL-4 activity of IRF2 was dependent on KLF4, a key mediator of the alternative activation, which was transcriptionally induced by IRF2. In conclusion, our data suggest that IRF2 is an important regulator of the proinflammatory response in macrophages by controlling HIF-1α-dependent glycolytic gene expression and glycolysis. This study also indicates IRF2 as a novel therapeutic target to treat inflammatory disorders associated with dysregulations of macrophage activations.

Negative regulation of type I IFN signaling

Type I IFNs (α, β, and others) are a family of cytokines that are produced in physiological conditions as well as in response to the activation of pattern recognition receptors. They are critically important in controlling the host innate and adaptive immune response to viral and some bacterial infections, cancer, and other inflammatory stimuli. However, dysregulation of type I IFN production or response can contribute to immune pathologies termed "interferonopathies", pointing to the importance of balanced activating signals with tightly regulated mechanisms of tuning this signaling. Here, we summarize the recent advances of how type I IFN production and response are controlled at multiple levels of the type I IFN signaling cascade.

Scanning the Immunopathogenesis of Psoriasis

Psoriasis is a chronic inflammatory skin disease, the immunologic model of which has been profoundly revised following recent advances in the understanding of its pathophysiology. In the current model, a crosstalk between keratinocytes, neutrophils, mast cells, T cells, and dendritic cells is thought to create inflammatory and pro-proliferative circuits mediated by chemokines and cytokines. Various triggers, including recently identified autoantigens, Toll-like receptor agonists, chemerin, and thymic stromal lymphopoietin may activate the pathogenic cascade resulting in enhanced production of pro-inflammatory and proliferation-inducing mediators such as interleukin (IL)-17, tumor necrosis factor (TNF)-α, IL-23, IL-22, interferon (IFN)-α, and IFN-γ by immune cells. Among these key cytokines lie therapeutic targets for currently approved antipsoriatic therapies. This review aims to provide a comprehensive overview on the immune-mediated mechanisms characterizing the current pathogenic model of psoriasis.

IRF-2 haploinsufficiency causes enhanced imiquimod-induced psoriasis-like skin inflammation

BACKGROUNDS

IFN regulatory factor (IRF)-2 is one of the potential susceptibility genes for psoriasis, but how this gene influences psoriasis pathogenesis is unclear. Topical application of imiquimod (IMQ), a TLR7 ligand, induces psoriasis-like skin lesions in mice.

OBJECTIVE

The aim of this study was to investigate whether IRF-2 gene status would influence severity of skin disease in IMQ-treated mice.

METHODS

Imiquimod-induced psoriasis-like skin inflammation was assessed by clinical findings, histology, and cytokine expression. The effects of imiquimod or IFN on peritoneal macrophages were analyzed in vitro.

RESULTS

IMQ-induced skin inflammation assessed by clinical findings and histology was more severe in IRF-2^+/- mice than in wild-type mice. In inflamed skin, mRNA expression levels of tumor necrosis factor (TNF)-α, IL-12/23p40, IL-17A, and IL-22 were significantly elevated in IRF-2^+/- mice compared to wild-type mice. Stimulation of peritoneal macrophages by IMQ significantly increased mRNA levels of TNF-α, IL-12/23p40, IL-23p19, IL-12p35, and IL-36. Interestingly, macrophages from IRF-2^+/- mice expressed higher levels of TNF-α, IL-12/23p40, and IL-36 compared to those from wild-type mice 24 h after stimulation, while they expressed similar levels of IL-12p35 and IL-23p19. Moreover, elevated mRNA expression of inducible nitric oxide synthase was observed only in IMQ-stimulated macrophages derived from IRF-2^+/- mice, which correlated with angiogenesis in IMQ-treated ears of IRF-2^+/- mice.

CONCLUSIONS

These results suggest that IRF-2 haploinsufficiency creates heightened biologic responses to IFN-α that phenotypically lead to enhanced angiogenesis and psoriasis-like inflammation within skin.

Antimicrobial Peptide LL37 and MAVS Signaling Drive Interferon-β Production by Epidermal Keratinocytes during Skin Injury

Type 1 interferons (IFNs) promote inflammation in the skin but the mechanisms responsible for inducing these cytokines are not well understood. We found that IFN-β was abundantly produced by epidermal keratinocytes (KCs) in psoriasis and during wound repair. KC IFN-β production depended on stimulation of mitochondrial antiviral-signaling protein (MAVS) by the antimicrobial peptide LL37 and double stranded-RNA released from necrotic cells. MAVS activated downstream TBK1 (TANK-Binding Kinase 1)-AKT (AKT serine/threonine kinase 1)-IRF3 (interferon regulatory factor 3) signaling cascade leading to IFN-β production and then promoted maturation of dendritic cells. In mice, the production of epidermal IFN-β by LL37 required MAVS, and human wounded and/or psoriatic skin showed activation of MAVS-associated IRF3 and induction of MAVS and IFN-β gene signatures. These findings show that KCs are an important source of IFN-β and MAVS is critical to this function, and demonstrates how the epidermis triggers unwanted skin inflammation under disease conditions.

Ctenopharyngodon idella IRF2 and ATF4 down-regulate the transcriptional level of PRKRA

PRKRA (interferon-inducible double-stranded RNA-dependent protein kinase activator A) is a protective protein which regulates the adaptation of cells to ER stress and virus-stimulated signaling pathways by activating PKR. In the present study, a grass carp (Ctenopharyngodon idella) PRKRA full-length cDNA (named CiPRKRA, KT891991) was cloned and identified. The full-length cDNA is comprised of a 5' UTR (36 bp), a 3' UTR (350 bp) and the longest ORF (882 bp) encoding a polypeptide of 293 amino acids. The deduced amino acid sequence of CiPRKRA contains three typical dsRNA binding motifs (dsRBM). Phylogenetic tree analysis revealed a closer evolutionary relationship of CiPRKRA with other fish PRKRA, especially with Danio rerio PRKRA. qRT-PCR showed that CiPRKRA was significantly up-regulated after stimulation with tunicamycin (Tm) and Poly I:C in C. idella kidney (CIK) cells. To further study its transcriptional regulation, the partial promoter sequence of CiPRKRA (1463 bp) containing one ISRE and one CARE was cloned by Tail-PCR. Subsequently, grass carp IRF2 (CiIRF2) and ATF4 (CiATF4) were expressed in Escherichia coli BL21 and purified by affinity chromatography with the Ni-NTA His-Bind Resin. In vitro, both CiIRF2 and CiATF4 bound to CiPRKRA promoter with high affinity by gel mobility shift assays, revealing that IRF2 and ATF4 might be potential transcriptional regulatory factors for CiPRKRA. Dual-luciferase reporter assays were applied to further investigate the transcriptional regulation of CiPRKRA in vivo. Recombinant plasmid of pGL3-PRKRAPro was constructed and transiently co-transfected into CIK cells with pcDNA3.1-CiIRF2 and pcDNA3.1-CiATF4, respectively. The results showed that both CiIRF2 and CiATF4 significantly decreased the luciferase activity of pGL3-PRKRAPro, suggesting that they play a negative role in CiPRKRA transcription.

PRDM16 represses the type I interferon response in adipocytes to promote mitochondrial and thermogenic programing

Brown adipose has the potential to counteract obesity, and thus, identifying signaling pathways that regulate the activity of this tissue is of great clinical interest. PRDM16 is a transcription factor that activates brown fat-specific genes while repressing white fat and muscle-specific genes in adipocytes. Whether PRDM16 also controls other gene programs to regulate adipocyte function was unclear. Here, we identify a novel role for PRDM16 in suppressing type I interferon (IFN)-stimulated genes (ISGs), including Stat1, in adipocytes in vitro and in vivo Ectopic activation of type I IFN signaling in brown adipocytes induces mitochondrial dysfunction and reduces uncoupling protein 1 (UCP1) expression. Prdm16-deficient adipose displays an exaggerated response to type I IFN, including higher STAT1 levels and reduced mitochondrial gene expression. Mechanistically, PRDM16 represses ISGs through binding to promoter regions of these genes and blocking the activating function of IFN regulatory factor 1 (IRF1). Together, these data indicate that PRDM16 diminishes responsiveness to type I IFN in adipose cells to promote thermogenic and mitochondrial function.

Triad of human cellular proteins, IRF2, FAM111A, and RFC3, restrict replication of orthopoxvirus SPI-1 host-range mutants

Viruses and their hosts can reach balanced states of evolution ensuring mutual survival, which makes it difficult to appreciate the underlying dynamics. To uncover hidden interactions, virus mutants that have lost defense genes may be used. Deletion of the gene that encodes serine protease inhibitor 1 (SPI-1) of rabbitpox virus and vaccinia virus, two closely related orthopoxviruses, prevents their efficient replication in human cells, whereas certain other mammalian cells remain fully permissive. Our high-throughput genome-wide siRNA screen identified host factors that prevent reproduction and spread of the mutant viruses in human cells. More than 20,000 genes were interrogated with individual siRNAs and those that prominently increased replication of the SPI-1 deletion mutant were subjected to a secondary screen. The top hits based on the combined data-replication factor C3 (RFC3), FAM111A, and interferon regulatory factor 2 (IRF2)-were confirmed by custom assays. The siRNAs to RFC1, RFC2, RFC4, and RFC5 mRNAs also enhanced spread of the mutant virus, strengthening the biological significance of the RFC complex as a host restriction factor for poxviruses. Whereas association with proliferating cell nuclear antigen and participation in processive genome replication are common features of FAM111A and RFC, IRF2 is a transcriptional regulator. Microarray analysis, quantitative RT-PCR, and immunoblotting revealed that IRF2 regulated the basal level expression of FAM111A, suggesting that the enhancing effect of depleting IRF2 on replication of the SPI-1 mutant was indirect. Thus, the viral SPI-1 protein and the host IRF2, FAM111A, and RFC complex likely form an interaction network that influences the ability of poxviruses to replicate in human cells.