IFN regulatory factor family members differentially regulate the expression of type III IFN (IFN-lambda) genes

Virus replication induces the expression of antiviral type I (IFN-alphabeta) and type III (IFN-lambda1-3 or IL-28A/B and IL-29) IFN genes via TLR-dependent and -independent pathways. Although type III IFNs differ genetically from type I IFNs, their similar biological antiviral functions suggest that their expression is regulated in a similar fashion. Structural and functional characterization of the IFN-lambda1 and IFN-lambda3 gene promoters revealed them to be similar to IFN-beta and IFN-alpha genes, respectively. Both of these promoters had functional IFN-stimulated response element and NF-kappaB binding sites. The binding of IFN regulatory factors (IRF) to type III IFN promoter IFN-stimulated response element sites was the most important event regulating the expression of these genes. Ectopic expression of the components of TLR7 (MyD88 plus IRF1/IRF7), TLR3 (Toll/IL-1R domain-containing adapter-inducing factor), or retinoic acid-inducible gene I (RIG-I) signal transduction pathways induced the activation of IFN-lambda1 promoter, whereas the IFN-lambda3 promoter was efficiently activated only by overexpression of MyD88 and IRF7. The ectopic expression of Pin1, a recently identified suppressor for IRF3-dependent antiviral response, decreased the IFN promoter activation induced by any of these three signal transduction pathways, including the MyD88-dependent one. To conclude, the data suggest that the IFN-lambda1 gene is regulated by virus-activated IRF3 and IRF7, thus resembling that of the IFN-beta gene, whereas IFN-lambda2/3 gene expression is mainly controlled by IRF7, thus resembling those of IFN-alpha genes.     

Lambda interferon (IFN-lambda), a type III IFN, is induced by viruses and IFNs and displays potent antiviral activity against select virus infections in vivo

Type III interferons (IFNs) (interleukin-28/29 or lambda interferon [IFN-lambda]) are cytokines with IFN-like activities. Here we show that several classes of viruses induce expression of IFN-lambda1 and -lambda2/3 in similar patterns. The IFN-lambdas were-unlike alpha/beta interferon (IFN-alpha/beta)-induced directly by stimulation with IFN-alpha or -lambda, thus identifying type III IFNs as IFN-stimulated genes. In vitro assays revealed that IFN-lambdas have appreciable antiviral activity against encephalomyocarditis virus (EMCV) but limited activity against herpes simplex virus type 2 (HSV-2), whereas IFN-alpha potently restricted both viruses. Using three murine models for generalized virus infections, we found that while recombinant IFN-alpha reduced the viral load after infection with EMCV, lymphocytic choriomeningitis virus (LCMV), and HSV-2, treatment with recombinant IFN-lambda in vivo did not affect viral load after infection with EMCV or LCMV but did reduce the hepatic viral titer of HSV-2. In a model for a localized HSV-2 infection, we further found that IFN-lambda completely blocked virus replication in the vaginal mucosa and totally prevented development of disease, in contrast to IFN-alpha, which had a more modest antiviral activity. Finally, pretreatment with IFN-lambda enhanced the levels of IFN-gamma in serum after HSV-2 infection. Thus, type III IFNs are expressed in response to most viruses and display potent antiviral activity in vivo against select viruses. The discrepancy between the observed antiviral activity in vitro and in vivo may suggest that IFN-lambda exerts a significant portion of its antiviral activity in vivo via stimulation of the immune system rather than through induction of the antiviral state.     

An important role for type III interferon (IFN-lambda/IL-28) in TLR-induced antiviral activity

Type III IFNs (IFN-lambda/IL-28/29) are cytokines with type I IFN-like antiviral activities, which remain poorly characterized. We herein show that most cell types expressed both types I and III IFNs after TLR stimulation or virus infection, whereas the ability of cells to respond to IFN-lambda was restricted to a narrow subset of cells, including plasmacytoid dendritic cells and epithelial cells. To examine the role of type III IFN in antiviral defense, we generated IL-28Ralpha-deficient mice. These mice were indistinguishable from wild-type mice with respect to clearance of a panel of different viruses, whereas mice lacking the type I IFN receptor (IFNAR(-/-)) were significantly impaired. However, the strong antiviral activity evoked by treatment of mice with TLR3 or TLR9 agonists was significantly reduced in both IL-28RA(-/-) and IFNAR(-/-) mice. The type I IFN receptor system has been shown to mediate positive feedback on IFN-alphabeta expression, and we found that the type I IFN receptor system also mediates positive feedback on IFN-lambda expression, whereas IL-28Ralpha signaling does not provide feedback on either type I or type III IFN expression in vivo. Finally, using bone-marrow chimeric mice we showed that TLR-activated antiviral defense requires expression of IL-28Ralpha only on nonhemopoietic cells. In this compartment, epithelial cells responded to IFN-lambda and directly restricted virus replication. Our data suggest type III IFN to target a specific subset of cells and to contribute to the antiviral response evoked by TLRs.     

The interferon system of teleost fish

Interferons (IFNs) are secreted proteins, which induce vertebrate cells into an antiviral state. In mammals, three families of IFNs (type I IFN, type II IFN and IFN-lambda) can be distinguished on the basis of gene structure, protein structure and functional properties. Type I IFNs, which include IFN-alpha and IFN-beta, are encoded by intron lacking genes and have a major role in the first line of defense against viruses. The human IFN-lambdas have similar biological properties as type I IFNs, but are encoded by intron containing genes. Type II IFN is identical to IFN-gamma, which is produced by T helper 1 cells in response to mitogens and antigens and has a key role in adaptive cell mediated immunity. IFNs, which show structural and functional properties similar to mammalian type I IFNs, have recently been cloned from Atlantic salmon, channel catfish, pufferfish, and zebrafish. Teleost fish appear to have at least two type I IFN genes. Phylogenetic sequence analysis shows that the fish type I IFNs form a group separated from the avian type I IFNs and the mammalian IFN-alpha, -beta and -lambda groups. Interestingly, the fish IFNs possess the same exon/intron structure as the IFN-lambdas, but show most sequence similarity to IFN-alpha. Recently, IFN-gamma genes have also been cloned from several fish species and shown to have the same exon/intron structure as mammalian IFN-gamma genes. The antiviral effect of mammalian type I IFN is exerted through binding to the IFN-alpha/beta-receptor, which triggers signal transduction through the JAK-STAT signal transduction pathway resulting in expression of Mx and other antiviral proteins. Putative IFN receptor genes have been identified in pufferfish. Several interferon regulatory factors and members of the JAK-STAT pathway have also been identified in various fish species. Moreover, Mx and several other interferon stimulated genes have been cloned and studied in fish. Furthermore, antiviral activity of Mx protein from Atlantic salmon and Japanese flounder has recently been demonstrated.     

Ⅲ型干扰素——新型抗病毒细胞因子

干扰素（IFN）是抗病毒感染的第一道防线,Ⅰ型和Ⅱ型干扰素不仅可抑制病毒,而且还能参与天然免疫反应和获得性免疫反应。最近干扰素家族增添一位新成员：Ⅲ型干扰素,即IFN-λ,因其具有类似干扰素的抗病毒活性且能诱导干扰素相关基因的表达而命名。IFN-λ受体与Ⅰ型干扰素的受体不同,但具有与Ⅰ型干扰素类似的诱导表达方式和信号转导通路,并能激活一系列相似的干扰素刺激基因。就IFN-λ家族及其受体、基因表达和信号转导机制、抗病毒作用等进行综述。     

Interferon-lambda contributes to innate immunity of mice against influenza A virus but not against hepatotropic viruses

Virus-infected cells secrete a broad range of interferon (IFN) subtypes which in turn trigger the synthesis of antiviral factors that confer host resistance. IFN-alpha, IFN-beta and other type I IFNs signal through a common universally expressed cell surface receptor, whereas IFN-lambda uses a distinct receptor complex for signaling that is not present on all cell types. Since type I IFN receptor-deficient mice (IFNAR1(0/0)) exhibit greatly increased susceptibility to various viral diseases, it remained unclear to which degree IFN-lambda might contribute to innate immunity. To address this issue we performed influenza A virus infections of mice which carry functional alleles of the influenza virus resistance gene Mx1 and which, therefore, develop a more complete innate immune response to influenza viruses than standard laboratory mice. We demonstrate that intranasal administration of IFN-lambda readily induced the antiviral factor Mx1 in mouse lungs and efficiently protected IFNAR1(0/0) mice from lethal influenza virus infection. By contrast, intraperitoneal application of IFN-lambda failed to induce Mx1 in the liver of IFNAR1(0/0) mice and did not protect against hepatotropic virus infections. Mice lacking functional IFN-lambda receptors were only slightly more susceptible to influenza virus than wild-type mice. However, mice lacking functional receptors for both IFN-alpha/beta and IFN-lambda were hypersensitive and even failed to restrict usually non-pathogenic influenza virus mutants lacking the IFN-antagonistic factor NS1. Interestingly, the double-knockout mice were not more susceptible against hepatotropic viruses than IFNAR1(0/0) mice. From these results we conclude that IFN-lambda contributes to inborn resistance against viral pathogens infecting the lung but not the liver.     

Reversible inhibition of murine cytomegalovirus replication by gamma interferon (IFN-γ) in primary macrophages involves a primed type I IFN-signaling subnetwork for full establishment of an immediate-early antiviral state

Activated macrophages play a central role in controlling inflammatory responses to infection and are tightly regulated to rapidly mount responses to infectious challenge. Type I interferon (alpha/beta interferon [IFN-α/β]) and type II interferon (IFN-γ) play a crucial role in activating macrophages and subsequently restricting viral infections. Both types of IFNs signal through related but distinct signaling pathways, inducing a vast number of interferon-stimulated genes that are overlapping but distinguishable. The exact mechanism by which IFNs, particularly IFN-γ, inhibit DNA viruses such as cytomegalovirus (CMV) is still not fully understood. Here, we investigate the antiviral state developed in macrophages upon reversible inhibition of murine CMV by IFN-γ. On the basis of molecular profiling of the reversible inhibition, we identify a significant contribution of a restricted type I IFN subnetwork linked with IFN-γ activation. Genetic knockout of the type I-signaling pathway, in the context of IFN-γ stimulation, revealed an essential requirement for a primed type I-signaling process in developing a full refractory state in macrophages. A minimal transient induction of IFN-β upon macrophage activation with IFN-γ is also detectable. In dose and kinetic viral replication inhibition experiments with IFN-γ, the establishment of an antiviral effect is demonstrated to occur within the first hours of infection. We show that the inhibitory mechanisms at these very early times involve a blockade of the viral major immediate-early promoter activity. Altogether our results show that a primed type I IFN subnetwork contributes to an immediate-early antiviral state induced by type II IFN activation of macrophages, with a potential further amplification loop contributed by transient induction of IFN-β.     

Biological activity of interleukins-28 and -29: comparison with type I interferons

Despite binding to receptors distinct from those of type I interferons (IFNs), human interleukins-28A, -28B and -29 (IL-28A, IL-28B and IL-29; alternatively named IFN lambda-2 {IFN-lambda2}, IFN-lambda3 and IFN-lambda1, respectively, or collectively, type III IFNs), a small family of three structurally-related cytokines, are, like IFNs, known to induce antiviral activity. To further biologically characterize IL-28A and IL-29, we compared their activities with those of IFNs in a range of human cell lines. We found that they induced antiviral activity in fewer cell lines and more weakly than IFNs; also IL-28A was less active than IL-29. Additionally, we showed IL-28A and IL-29 induced reporter genes--protein MxA promoter linked to luciferase, or interferon stimulated response element (ISRE) linked to secreted alkaline phosphatase (SEAP)--more weakly than IFN. Antiproliferative activity was induced by IFNs in most cell lines, but only in one human glioblastoma cell line, LN319, was dose-dependent IL-29-growth inhibition demonstrable. Polymerase chain reaction (PCR) quantification of messenger (m) RNA of IL-28/29 receptor subunits, IL-28Ralpha and IL-10Rbeta, indicated variable expression levels; although their expression was highest in the responsive LN319 cell line, lower but significant expression of both mRNAs was found in relatively unresponsive cell lines. In conclusion, we found IL-28A and IL-29 act similarly to IFNs, but are less effective generally and have activity in a more limited range of cell lines.     

Lambda interferon (IFN-lambda) in serum is decreased in hantavirus-infected patients, and in vitro-established infection is insensitive to treatment with all IFNs and inhibits IFN-gamma-induced nitric oxide production

Hantaviruses, causing hemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS), are known to be sensitive to nitric oxide (NO) and to pretreatment with type I and II interferons (alpha interferon [IFN-alpha]/IFN-beta and IFN-gamma, respectively). Elevated serum levels of NO and IFN-gamma have been observed in HFRS patients, but little is known regarding the systemic levels of other IFNs and the possible effects of hantaviruses on innate antiviral immune responses. In Puumala virus-infected HFRS patients (n = 18), we report that the levels of IFN-alpha and IFN-beta are similar, whereas the level of IFN-lambda (type III IFN) is significantly decreased, during acute (day of hospitalization) compared to the convalescent phase. The possible antiviral effects of IFN-lambda on the prototypic hantavirus Hantaan virus (HTNV) replication was then investigated. Pretreatment of A549 cells with IFN-lambda alone inhibited HTNV replication, and IFN-lambda combined with IFN-gamma induced additive antiviral effects. We then studied the effect of postinfection treatment with IFNs. Interestingly, an already-established HTNV infection was insensitive to subsequent IFN-alpha, -beta, -gamma, and -lambda stimulation, and HTNV-infected cells produced less NO compared to noninfected cells when stimulated with IFN-gamma and IL-1beta. Furthermore, less phosphorylated STAT1 after IFN treatment was observed in the nuclei of infected cells than in those of noninfected cells. The results suggest that hantavirus can interfere with the activation of antiviral innate immune responses in patients and inhibit the antiviral effects of all IFNs. We believe that future studies addressing the mechanisms by which hantaviruses interfere with the activation and shaping of immune responses may bring more knowledge regarding HFRS and HCPS pathogenesis.     

Crystal structure of Zebrafish interferons I and II reveals conservation of type I interferon structure in vertebrates

Interferons (IFNs) play a major role in orchestrating the innate immune response toward viruses in vertebrates, and their defining characteristic is their ability to induce an antiviral state in responsive cells. Interferons have been reported in a multitude of species, from bony fish to mammals. However, our current knowledge about the molecular function of fish IFNs as well as their evolutionary relationship to tetrapod IFNs is limited. Here we establish the three-dimensional (3D) structure of zebrafish IFN?1 and IFN?2 by crystallography. These high-resolution structures offer the first structural insight into fish cytokines. Tetrapods possess two types of IFNs that play an immediate antiviral role: type I IFNs (e.g., alpha interferon [IFN-α] and beta interferon [IFN-β]) and type III IFNs (lambda interferon [IFN-λ]), and each type is characterized by its specific receptor usage. Similarly, two groups of antiviral IFNs with distinct receptors exist in fish, including zebrafish. IFN?1 and IFN?2 represent group I and group II IFNs, respectively. Nevertheless, both structures reported here reveal a characteristic type I IFN architecture with a straight F helix, as opposed to the remaining class II cytokines, including IFN-λ, where helix F contains a characteristic bend. Phylogenetic trees derived from structure-guided multiple alignments confirmed that both groups of fish IFNs are evolutionarily closer to type I than to type III tetrapod IFNs. Thus, these fish IFNs belong to the type I IFN family. Our results also imply that a dual antiviral IFN system has arisen twice during vertebrate evolution.     

Microbial pathogenesis and type III interferons

The innate immune system possesses a multitude of pathways to sense and respond to microbial pathogens. One such family are the interferons (IFNs), a family of cytokines that are involved in several cellular functions. Type I IFNs are appreciated to be important in several viral and bacterial diseases, while the recently identified type III IFNs (IFNL1, IFNL2, IFNL3, IFNL4) have been studied primarily in the context of viral infection. Viral and bacterial infections however are not mutually exclusive, and often the presence of a viral pathogen increases the pathogenesis of bacterial infection. The role of type III IFN in bacterial and viral-bacterial co-infections has just begun to be explored. In this mini review we discuss type III IFN signaling and its role in microbial pathogenesis with an emphasis on the work that has been conducted with bacterial pathogens.     

Role of type I interferons in the activation of autoreactive B cells

Type I interferons (IFNs) are a family of cytokines involved in the defense against viral infections that play a key role in the activation of both the innate and adaptive immune system. IFNs both directly and indirectly enhance the capacity of B lymphocytes to respond to viral challenge and produce cytotoxic and neutralizing antibodies. However, prolonged type I IFN exposure is not always beneficial to the host. If not regulated properly IFN can drive autoantibody production as well as other parameters of systemic autoimmune disease. Type I IFNs impact B-cell function through a variety of mechanisms, including effects on receptor engagement, Toll-like receptor expression, cell migration, antigen presentation, cytokine responsiveness, cytokine production, survival, differentiation and class-switch recombination. Type I IFNs are also cytotoxic for a variety of cell types and thereby contribute to the accumulation of cell debris that serves as a potential source for autoantigens. Type I IFN engagement of a variety of accessory cells further promotes B-cell survival and activation, as exemplified by the capacity of type I IFNs to increase the level of B-cell survival factors, such as B lymphocyte stimulator, produced by dendritic cells. Therefore, it is not surprising that the loss of expression of the type I IFN receptor can have dramatic effects on the production of autoantibodies and on the clinical features of systemic autoimmune diseases such as systemic lupus erythematosus.     

Role of the interleukin (IL)-28 receptor tyrosine residues for antiviral and antiproliferative activity of IL-29/interferon-lambda 1: similarities with type I interferon signaling

Interferon (IFN)-lambda 1, -lambda 2, and -lambda 3 are the latest members of the class II cytokine family and were shown to have antiviral activity. Their receptor is composed of two chains, interleukin-28R/likely interleukin or cytokine or receptor 2 (IL-28R/LICR2) and IL-10R beta, and mediates the tyrosine phosphorylation of STAT1, STAT2, STAT3, and STAT5. Here, we show that activation of this receptor by IFN-lambda 1 can also inhibit cell proliferation and induce STAT4 phosphorylation, further extending functional similarities with type I IFNs. We used IL-28R/LICR2-mutated receptors to identify the tyrosines required for STAT activation, as well as antiproliferative and antiviral activities. We found that IFN-lambda 1-induced STAT2 tyrosine phosphorylation is mediated through tyrosines 343 and 517 of the receptor, which showed some similarities with tyrosines from type I IFN receptors involved in STAT2 activation. These two tyrosines were also responsible for antiviral and antiproliferative activities of IFN-lambda 1. By contrast, STAT4 phosphorylation (and to some extent STAT3 activation) was independent from IL-28R/LICR2 tyrosine residues. Taken together, these observations extend the functional similarities between IFN-lambdas and type I IFNs and shed some new light on the mechanisms of activation of STAT2 and STAT4 by these cytokines.     

HIV and HCV Activate the Inflammasome in Monocytes and Macrophages via Endosomal Toll-Like Receptors without Induction of Type 1 Interferon

Innate immune sensing of viral infection results in type I interferon (IFN) production and inflammasome activation. Type I IFNs, primarily IFN-α and IFN-β, are produced by all cell types upon virus infection and promote an antiviral state in surrounding cells by inducing the expression of IFN-stimulated genes. Type I IFN production is mediated by Toll-like receptor (TLR) 3 in HCV infected hepatocytes. Type I IFNs are also produced by plasmacytoid dendritic cells (pDC) after sensing of HIV and HCV through TLR7 in the absence of productive pDC infection. Inflammasomes are multi-protein cytosolic complexes that integrate several pathogen-triggered signaling cascades ultimately leading to caspase-1 activation and generation pro-inflammatory cytokines including interleukin (IL)-18 and IL-1β. Here, we demonstrate that HIV and HCV activate the inflammasome, but not Type I IFN production, in monocytes and macrophages in an infection-independent process that requires clathrin-mediated endocytosis and recognition of the virus by distinct endosomal TLRs. Knockdown of each endosomal TLR in primary monocytes by RNA interference reveals that inflammasome activation in these cells results from HIV sensing by TLR8 and HCV recognition by TLR7. Despite its critical role in type I IFN production by pDCs stimulated with HIV, TLR7 is not required for inflammasome activation by HIV. Similarly, HCV activation of the inflammasome in monocytes does not require TLR3 or its downstream signaling adaptor TICAM-1, while this pathway leads to type I IFN in infected hepatocytes. Monocytes and macrophages do not produce type I IFN upon TLR8 or TLR7 sensing of HIV or HCV, respectively. These findings reveal a novel infection-independent mechanism for chronic viral induction of key anti-viral programs and demonstrate distinct TLR utilization by different cell types for activation of the type I IFN vs. inflammasome pathways of inflammation.     

Immunomodulatory functions of type I interferons

Interferon-α (IFNα) and IFNβ, collectively known as type I IFNs, are the major effector cytokines of the host immune response against viral infections. However, the production of type I IFNs is also induced in response to bacterial ligands of innate immune receptors and/or bacterial infections, indicating a broader physiological role for these cytokines in host defence and homeostasis than was originally assumed. The main focus of this Review is the underappreciated immunomodulatory functions of type I IFNs in health and disease. We discuss their function in the regulation of innate and adaptive immune responses, the response to bacterial ligands, inflammasome activation, intestinal homeostasis and inflammatory and autoimmune diseases.