Diversity and Relatedness Among the Type I Interferons

Inhibition of CEACAM1 expression in cytokine-activated neutrophils using JAK inhibitors

OBJECTIVES

Carcinoembryonic-antigen-related cell-adhesion molecule 1 (CEACAM1) is an adhesion molecule that acts as a coinhibitory receptor in the immune system. We previously demonstrated that CEACAM1 is predominantly expressed on peripheral blood neutrophils in patients with RA. The aim of the present study was to investigate the effects of Janus kinase inhibitors (JAKi) on cytokine-activated human neutrophils and CEACAM1 expression.

METHODS

Peripheral blood neutrophils were obtained from healthy subjects. Isolated neutrophils were stimulated with tumor necrosis factor-alpha (TNF-α) or granulocyte-macrophage colony-stimulating factor (GM-CSF) in the presence or absence of JAKi. The expression of CEACAM1 in peripheral blood neutrophils was analyzed by flow cytometry. Protein phosphorylation of signal transducer and activator of transcription (STAT)1, STAT3, and STAT5 was assessed by western blot using phospho-specific antibodies.

RESULTS

We found that TNF-α-induced CEACAM1 expression was marginally suppressed after pretreatment with pan-JAK inhibitor, tofacitinib. Moreover, TNF-α induced STAT1 and STAT3 phosphorylation at the late stimulation phase (4 to 16 h). The expressions of CEACAM1 on neutrophils were markedly up-regulated by GM-CSF not by interleukin (IL)-6 stimulation. All JAKi inhibited GM-CSF-induced CEACAM1 expressions on neutrophils, however, the inhibitory effects of baricitinib were larger compared to those of tofacitinib or filgotinib. Moreover, CEACAM1 was marginally upregulated in interferon (IFN)-γ stimulated neutrophils. Similarly, JAKi inhibited IFN-γ-induced CEACAM1 expressions on neutrophils.

CONCLUSIONS

We demonstrated that JAKi prevent GM-CSF-induced CEACAM1 expression in neutrophils, and JAKi-induced inhibition depends on their selectivity against JAK isoforms. These findings suggest that JAKi can modulate the expression of CEACAM1 in cytokine-activated neutrophils, thereby limiting their activation.

Interferon-β decreases LPS-induced neutrophil recruitment to cardiac fibroblasts

Introduction: Cardiac fibroblasts (CF) are crucial cells in damaged heart tissues, expressing TLR4, IFN-receptor and responding to lipopolysaccharide (LPS) and interferon-β (IFN-β) respectively. While CF interact with immune cells; however, their relationship with neutrophils remains understudied. Additionally, theimpact of LPS and IFN-β on CF-neutrophil interaction is poorly understood. Methods: Isolated CF from adult rats were treated with LPS, with or without IFN-β. This study examined IL-8 secretion, ICAM-1 and VCAM-1 expression, and neutrophil recruitment, as well as their effects on MMPs activity. Results: LPS triggered increased IL-8 expression and secretion, along with elevated ICAM-1 and VCAM-1 expression, all of which were blocked by TAK-242. Pre-treatment with IFN-β countered these LPS effects. LPS treated CF showed higher neutrophil recruitment (migration and adhesion) compared to unstimulated CF, an effect prevented by IFN-β. Ruxolitinib blocked these IFN-β anti-inflammatory effects, implicating JAK signaling. Analysis of culture medium zymograms from CF alone, and CF-neutrophils interaction, revealed that MMP2 was mainly originated from CF, while MMP9 could come from neutrophils. LPS and IFN-β boosted MMP2 secretion by CF. MMP9 activity in CF was low, and LPS or IFN-β had no significant impact. Pre-treating CF with LPS, IFN-β, or both before co-culture with neutrophils increased MMP2. Neutrophil co-culture increased MMP9 activity, with IFN-β pre-treatment reducing MMP9 compared to unstimulated CF. Conclusion: In CF, LPS induces the secretion of IL-8 favoring neutrophils recruitment and these effects were blocked by IFN-. The results highlight that CF-neutrophil interaction appears to influence the extracellular matrix through MMPs activity modulation.

Heterogeneity and functions of the 13 IFN-α subtypes - lucky for some?

Type I IFNs are critical for host responses to viral infection and are also implicated in the pathogenesis of multiple autoimmune diseases. Multiple subtypes exist within the type I IFN family, in particular 13 distinct IFN-α genes, which signal through the same heterodimer receptor that is ubiquitously expressed by mammalian cells. Both evolutionary genetic studies and functional antiviral assays strongly suggest differential functions and activity between the 13 IFN-α subtypes, yet we still lack a clear understanding of these different roles. This review summarizes the evidence from studies describing differential functions of IFN-α subtypes and highlights potential reasons for discrepancies between the reports. We examine both acute and chronic viral infection, as well as autoimmunity, and integrate a more recent awareness of the importance of anti-IFN-α autoantibodies in shaping the type I IFN responses in these different conditions.

Emerging Roles of Type-I Interferons in Neuroinflammation, Neurological Diseases, and Long-Haul COVID

Interferons (IFNs) are pleiotropic cytokines originally identified for their antiviral activity. IFN-α and IFN-β are both type I IFNs that have been used to treat neurological diseases such as multiple sclerosis. Microglia, astrocytes, as well as neurons in the central and peripheral nervous systems, including spinal cord neurons and dorsal root ganglion neurons, express type I IFN receptors (IFNARs). Type I IFNs play an active role in regulating cognition, aging, depression, and neurodegenerative diseases. Notably, by suppressing neuronal activity and synaptic transmission, IFN-α and IFN-β produced potent analgesia. In this article, we discuss the role of type I IFNs in cognition, neurodegenerative diseases, and pain with a focus on neuroinflammation and neuro-glial interactions and their effects on cognition, neurodegenerative diseases, and pain. The role of type I IFNs in long-haul COVID-associated neurological disorders is also discussed. Insights into type I IFN signaling in neurons and non-neuronal cells will improve our treatments of neurological disorders in various disease conditions.

Superior antiviral activity of IFNβ in genital HSV-1 infection

Type I interferons (IFNs) present the first line of defense against viral infections, providing antiviral, immunomodulatory and antiproliferative effects. The type I IFN family contains 12 IFNα subtypes and IFNβ, and although they share the same receptor, they are classified as non-redundant, capable to induce a variety of different IFN-stimulated genes. However, the biological impact of individual subtypes remains controversial. Recent data propose a subtype-specificity of type I IFNs revealing unique effector functions for different viruses and thus expanding the implications for IFNα-based antiviral immunotherapies. Despite extensive research, drug-resistant infections with herpes simplex virus type 1 (HSV-1), which is the common agent of recurrent orogenital lesions, are still lacking a protective or curing therapeutic. However, due to the risk of generalized infections in immunocompromised hosts as well as the increasing incidence of resistance to conventional antiherpetic agents, HSV infections raise major health concerns. Based on their pleiotropic effector functions, the application of type I IFNs represents a promising approach to inhibit HSV-1 replication, to improve host immunity and to further elucidate their qualitative differences. Here, selective IFNα subtypes and IFNβ were evaluated for their therapeutic potential in genital HSV-1 infections. Respective in vivo studies in mice revealed subtype-specific differences in the reduction of local viral loads. IFNβ had the strongest antiviral efficacy against genital HSV-1 infection in mice, whereas IFNα1, IFNα4, and IFNα11 had no impact on viral loads. Based on flow cytometric analyses of underlying immune responses at local and peripheral sites, these differences could be further assigned to specific modulations of the antiviral immunity early during HSV-1 infection. IFNβ led to enhanced systemic cytokine secretion and elevated cytotoxic responses, which negatively correlated with viral loads in the vaginal tract. These data provide further insights into the diversity of type I IFN effector functions and their impact on the immunological control of HSV-1 infections.

Regulation of T-independent B-cell responses by microRNA-146a

The microRNA, miR-146a, is a negative feedback regulator of the central immune transcription factor, nuclear factor kappa B (NFkB). MiR-146a plays important roles in the immune system, and miR-146a deficient mice show a complex phenotype with features of chronic inflammation and autoimmune disease. In this study, we examined the role of miR-146a in extrafollicular B-cell responses, finding that miR-146a suppresses cellular responses in vivo and in vitro. Gene expression profiling revealed that miR-146a-deficient B-cells showed upregulation of interferon pathway genes, including Traf6, a known miR-146a target. We next interrogated the role of TRAF6 in these B-cell responses, finding that TRAF6 is required for proliferation by genetic and pharmacologic inhibition. Together, our findings demonstrate a novel role for miR-146a and TRAF6 in the extrafollicular B-cell responses, which have recently been tied to autoimmune disease pathogenesis. Our work highlights the pathogenetic role of miR-146a and the potential of pharmacologic inhibition of TRAF6 in autoimmune diseases in which miR-146a is deregulated.

Herbal extracts that induce type I interferons through Toll-like receptor 4 signaling

Background

A mixture of five herbal extracts called internatural (INT), which is prepared from pumpkin seeds, purple turmeric, pearl barley, corn pistil, and cinnamon, is widely used by people in Japan and elsewhere for its immunity-enhancing effects and general health. Although anecdotal evidence indicates its efficacy, the mechanisms by which INT boosts immunity have remained unknown.

Objective

The aim of this study was to investigate whether INT induces type I interferons (IFNs) in murine bone marrow-derived macrophages (BMDMs) and by what mechanism.

Design

We measured induction of type I IFNs (IFNβ and IFNα) in BMDMs treated with INT or other Toll-like receptor ligands: bacterial lipopolysaccharides (LPS), dsRNA, poly(I:C), and CpG oligonucleotides. To investigate whether INT signals through Toll-like receptor 4 (TLR4), we tested TLR4-specific inhibitor. We also tested if INT utilizes TLR4 adaptors, toll/IL-1 receptor (TIR) domain-containing adaptor (TRIF), or myeloid differentiation factor 88 (MyD88), we examined INT induction of IFNβ in TRIF-KO and MyD88-KO BMDMs. We then investigated whether INT provides an antiviral effect upon fibroblasts either directly or indirectly using the encephalomyocarditis virus (EMCV) model.

Results

We first observed that INT, when added to BMDMs, potently induces type I IFNs (IFNβ and IFNα) within 2 h. INT induction of IFN expression was mediated by TLR4, which signaled through the TRIF/MyD88 adaptors, similar to LPS. A high-molecular-weight fraction (MW > 10,000) of INT extracts contained IFN-inducing activity. Supernatants from INT-treated BMDMs protected untreated fibroblast from EMCV infection as reduced viral titers.

Conclusions

INT induced type I IFN mRNA and proteins in BMDMs and other cell types. This induction was mediated by TLR4, which transduces signals using the TRIF/MyD88 pathway. The high-MW component of INT contained type I IFN inducing activity. The supernatants from INT-treated cells displayed antiviral activity and protected cells from EMCV infection. These findings indicate that INT is a novel natural IFN inducer that strengthens host’s innate immunity.

The Role of the Z-DNA Binding Domain in Innate Immunity and Stress Granules

Both DNA and RNA can maintain left-handed double helical Z-conformation under physiological condition, but only when stabilized by Z-DNA binding domain (ZDBD). After initial discovery in RNA editing enzyme ADAR1, ZDBD has also been described in pathogen-sensing proteins ZBP1 and PKZ in host, as well as virulence proteins E3L and ORF112 in viruses. The host-virus antagonism immediately highlights the importance of ZDBD in antiviral innate immunity. Furthermore, Z-RNA binding has been shown to be responsible for the localization of these ZDBD-containing proteins to cytoplasmic stress granules that play central role in coordinating cellular response to stresses. This review sought to consolidate current understanding of Z-RNA sensing in innate immunity and implore possible roles of Z-RNA binding within cytoplasmic stress granules.

Context Is Key: Delineating the Unique Functions of IFNα and IFNβ in Disease

Type I interferons (IFNs) are critical effector cytokines of the immune system and were originally known for their important role in protecting against viral infections; however, they have more recently been shown to play protective or detrimental roles in many disease states. Type I IFNs consist of IFNα, IFNβ, IFNϵ, IFNκ, IFNω, and a few others, and they all signal through a shared receptor to exert a wide range of biological activities, including antiviral, antiproliferative, proapoptotic, and immunomodulatory effects. Though the individual type I IFN subtypes possess overlapping functions, there is growing appreciation that they also have unique properties. In this review, we summarize some of the mechanisms underlying differential expression of and signaling by type I IFNs, and we discuss examples of differential functions of IFNα and IFNβ in models of infectious disease, cancer, and autoimmunity.

In cardiac fibroblasts, interferon-beta attenuates differentiation, collagen synthesis, and TGF-β1-induced collagen gel contraction

Cardiac fibroblasts (CF) play a key role in the homeostasis of the extracellular matrix in cardiac tissue and are newly recognized as inflammatory supporter cells. Besides, CF-to-Cardiac myofibroblast differentiation is commanded by TGF-b, through SMAD signaling pathways, and these last cells are strongly implicated in cardiac fibrosis. In the heart IFN-β is produced by CF; however, the role of IFN-β, STAT proteins, and STAT-homo or heterodimers in the regulation of CF function with or without a fibrotic environment is unknown. CF were isolated from hearts of adult rats, and by western blot analysis we studied STAT1, STAT2, and STAT3 phosphorylation and through specific siRNA against these proteins we analyzed their role in CF functions such as differentiation (α-SMA expression); and pro-collagen type-I synthesis and secretion expression levels; collagen gels contraction and CF migration. In cultured adult rats CF, IFN-β increases phosphorylation of STAT1, STAT2, and STAT3. Both STAT1 and STAT2 were involved in decreasing α-SMA and CF migration induced by TGF-β1. Also, IFN-β through STAT1 regulated pro-collagen type-I protein expression levels, and collagen gels contraction induced by TGF-β1. STAT3 was not involved in any effects of IFN-β studied. In conclusion, IFN-β through STAT1 and STAT2 shows antifibrotic effects on CF TGF-β1-treated, whereas STAT3 did not participate in such effect.

The transcription factor NFAT5 limits infection-induced type I interferon responses

Huerga Encabo et al. show that NFAT5, previously characterized as a pro-inflammatory transcription factor, limits the IFN-I response to control antiviral defenses and preserve HSC quiescence. NFAT5 represses IFN-I and ISG expression through an evolutionarily conserved DNA element that prevents IRF3 recruitment to the IFNB1 enhanceosome.

Type I interferon (IFN-I) provides effective antiviral immunity but can exacerbate harmful inflammatory reactions and cause hematopoietic stem cell (HSC) exhaustion; therefore, IFN-I expression must be tightly controlled. While signaling mechanisms that limit IFN-I induction and function have been extensively studied, less is known about transcriptional repressors acting directly on IFN-I regulatory regions. We show that NFAT5, an activator of macrophage pro-inflammatory responses, represses Toll-like receptor 3 and virus-induced expression of IFN-I in macrophages and dendritic cells. Mice lacking NFAT5 exhibit increased IFN-I production and better control of viral burden upon LCMV infection but show exacerbated HSC activation under systemic poly(I:C)-induced inflammation. We identify IFNβ as a primary target repressed by NFAT5, which opposes the master IFN-I inducer IRF3 by binding to an evolutionarily conserved sequence in the IFNB1 enhanceosome that overlaps a key IRF site. These findings illustrate how IFN-I responses are balanced by simultaneously opposing transcription factors.

Evolutionary Pattern of Interferon Alpha Genes in Bovidae and Genetic Diversity of IFNAA in the Bovine Genome

Interferons are secretory proteins induced in response to specific extracellular stimuli which stimulate intra- and intercellular networks for regulating innate and acquired immunity, resistance to viral infections, and normal and tumor cell survival and death. Type 1 interferons plays a major role in the CD8 T-cell response to viral infection. The genomic analysis carried out here for type I interferons within Bovidae family shows that cattle, bison, water buffalo, goat, and sheep (all Bovidae), have different number of genes of the different subtypes, with a large increase in the numbers, compared to human and mouse genomes. A phylogenetic analysis of the interferon alpha (IFNA) proteins in this group shows that the genes do not follow the evolutionary pattern of the species, but rather a cycle of duplications and deletions in the different species. In this study we also studied the genetic diversity of the bovine interferon alpha A (IFNAA), as an example of the IFNA genes in cattle, sequencing a fragment of the coding sequence in 18 breeds of cattle from Pakistan, Nigeria and USA. Similarity analysis allowed the allocation of sequences into 22 haplotypes. Bhagnari, Brangus, Sokoto Gudali, and White Fulani, had the highest number of haplotypes, while Angus, Hereford and Nari Master had the least. However, when analyzed by the average haplotype count, Angus, Bhagnari, Hereford, Holstein, Muturu showed the highest values, while Cholistani, Lohani, and Nari Master showed the lowest values. Haplotype 4 was found in the highest number of individuals (74), and in 15 breeds. Sequences for yak, bison, and water buffalo, were included within the bovine haplotypes. Medium Joining network showed that the sequences could be divided into 4 groups: one with highly similar haplotypes containing mostly Asian and African breeds, one with almost all of the Bos taurus American breeds, one mid-diverse group with mostly Asian and African sequences, and one group with highly divergent haplotypes with five N'Dama sequences and one from each of White Fulani, Dhanni, Tharparkar, and Bhagnari. The large genetic diversity found in IFNAA could be a very good indication of the genetic variation among the different genes of IFNA and could be an adaptation for these species in response to viral challenges they face.

IFN-β Plays Both Pro- and Anti-inflammatory Roles in the Rat Cardiac Fibroblast Through Differential STAT Protein Activation

Cardiac fibroblasts (CFs) contribute to theinflammatory response to tissue damage, secreting both pro- and anti-inflammatory cytokines and chemokines. Interferon beta (IFN-β) induces the phosphorylation of signal transducer and activator of transcription (STAT) proteins through the activation of its own receptor, modulating the secretion of cytokines and chemokines which regulate inflammation. However, the role of IFN-β and STAT proteins in modulating the inflammatory response of CF remains unknown. CF were isolated from adult male rats and subsequently stimulated with IFN-β to evaluate the participation of STAT proteins in secreting chemokines, cytokines, cell adhesion proteins expression and in their capacity to recruit neutrophils. In addition, in CF in which the TRL4 receptor was pre-activated, the effect of INF-β on the aforementioned responses was also evaluated. Cardiac fibroblasts stimulation with IFN-β showed an increase in STAT1, STAT2, and STAT3 phosphorylation. IFN-β stimulation through STAT1 activation increased proinflammatory chemokines MCP-1 and IP-10 secretion, whereas IFN-β induced activation of STAT3 increased cytokine secretion of anti-inflammatory IL-10. Moreover, in TLR4-activated CF, IFN-β through STAT2 and/or STAT3, produced an anti-inflammatory effect, reducing pro-IL-1β, TNF-α, IL-6, MCP-1, and IP-10 secretion; and decreasing neutrophil recruitment by decreasing ICAM-1 and VCAM-1 expression. Altogether, our results indicate that IFN-β exerts both pro-inflammatory and anti-inflammatory effects in non-stimulated CF, through differential activation of STAT proteins. When CF were previously treated with an inflammatory agent such as TLR-4 activation, IFN-β effects were predominantly anti-inflammatory.

Gene therapy with plasmids encoding IFN-β or IFN-α14 confers long-term resistance to HIV-1 in humanized mice

Because endogenous interferon type I (IFN-I) produced by HIV-1 infection might complicate the analysis of therapeutically administered IFN-I, we tested different humanized mouse models for induction of IFN-I during HIV-1 infection. While HIV-1 induced high levels of IFN-α in BLT mice, IFN-I was undetectable following infection in the Hu-PBL mouse model, in which only T cells expand. We therefore tested the effect of treatment with Pegylated IFN-2 (pegasys), in Hu-PBL mice. Pegasys prevented CD4 T cell depletion and reduced the viral load for 10 days, but the effect waned thereafter. We next expressed IFN-I subsets (IFN-α2, −α6, −α8, −α14, and −β) in Hu-PBL mice by hydrodynamic injection of plasmids encoding them and 2 days later infected the mice with HIV-1. CD4 T cell depletion was prevented in all subtypes of IFN-I-expressing mice by day 10. However, at day 40 post-infection, protection was seen in IFN-β- and IFN-α14-expressing mice, but not the others. The viral load followed an inverse pattern and was highest in control mice and lowest in IFN-β- and IFN-α14-expressing mice until day 40 after infection. These results show that gene therapy with plasmids encoding IFN-β and −α14, but not the commonly used −α2, confers long-term suppression of HIV-1 replication.

Identification of new type I interferon-stimulated genes and investigation of their involvement in IFN-β activation

Virus infection induces the production of type I interferons (IFNs). IFNs bind to their heterodimeric receptors to initiate downstream cascade of signaling, leading to the up-regulation of interferon-stimulated genes (ISGs). ISGs play very important roles in innate immunity through a variety of mechanisms. Although hundreds of ISGs have been identified, it is commonly recognized that more ISGs await to be discovered. The aim of this study was to identify new ISGs and to probe their roles in regulating virus-induced type I IFN production. We used consensus interferon (Con-IFN), an artificial alpha IFN that was shown to be more potent than naturally existing type I IFN, to treat three human immune cell lines, CEM, U937 and Daudi cells. Microarray analysis was employed to identify those genes whose expressions were up-regulated. Six hundred and seventeen genes were up-regulated more than 3-fold. Out of these 617 genes, 138 were not previously reported as ISGs and thus were further pursued. Validation of these 138 genes using quantitative reverse transcription PCR (qRT-PCR) confirmed 91 genes. We screened 89 genes for those involved in Sendai virus (SeV)-induced IFN-β promoter activation, and PIM1 was identified as one whose expression inhibited SeV-mediated IFN-β activation. We provide evidence indicating that PIM1 specifically inhibits RIG-I- and MDA5-mediated IFN-β signaling. Our results expand the ISG library and identify PIM1 as an ISG that participates in the regulation of virus-induced type I interferon production.

IFN-β: A Contentious Player in Host-Pathogen Interaction in Tuberculosis

Tuberculosis (TB) is a major health threat to the human population worldwide. The etiology of the disease is Mycobacterium tuberculosis (Mtb), a highly successful intracellular pathogen. It has the ability to manipulate the host immune response and to make the intracellular environment suitable for its survival. Many studies have addressed the interactions between the bacteria and the host immune cells as involving many immune mediators and other cellular players. Interferon-β (IFN-β) signaling is crucial for inducing the host innate immune response and it is an important determinant in the fate of mycobacterial infection. The role of IFN-β in protection against viral infections is well established and has been studied for decades, but its role in mycobacterial infections remains much more complicated and debatable. The involvement of IFN-β in immune evasion mechanisms adopted by Mtb has been an important area of investigation in recent years. These advances have widened our understanding of the pro-bacterial role of IFN-β in host–pathogen interactions. This pro-bacterial activity of IFN-β appears to be correlated with its anti-inflammatory characteristics, primarily by antagonizing the production and function of interleukin 1β (IL-1β) and interleukin 18 (IL-18) through increased interleukin 10 (IL-10) production and by inhibiting the nucleotide-binding domain and leucine-rich repeat protein-3 (NLRP3) inflammasome. Furthermore, it also fails to provoke a proper T helper 1 (Th1) response and reduces the expression of major histocompatibility complex II (MHC-II) and interferon-γ receptors (IFNGRs). Here we will review some studies to provide a paradigm for the induction, regulation, and role of IFN-β in mycobacterial infection. Indeed, recent studies suggest that IFN-β plays a role in Mtb survival in host cells and its downregulation may be a useful therapeutic strategy to control Mtb infection.

Virus-Triggered ATP Release Limits Viral Replication through Facilitating IFN-β Production in a P2X7-Dependent Manner

Accumulating evidence shows that innate immune responses are associated with extracellular nucleotides, particularly ATP. In this article, we demonstrate extensive protection of ATP/P2X7 signaling in a host against viral infection. Interestingly, we observed a significant increase in ATP as a danger signal in vesicular stomatitis virus (VSV)-infected cell supernatant and VSV-infected mice in an exocytosis- and pannexin channel-dependent manner. Furthermore, extracellular ATP reduces the replication of VSV, Newcastle disease virus, murine leukemia virus, and HSV in vivo and in vitro through the P2X7 receptor. Meanwhile, ATP significantly increases IFN-β expression in a concentration- and time-dependent manner. Mechanistically, ATP facilitates IFN-β secretion through P38/JNK/ATF-2 signaling pathways, which are crucial in promoting antiviral immunity. Taken together, these results demonstrate the protective role of extracellular ATP and P2X7 in viral infection and suggest a potential therapeutic role for ATP/P2X7 in viral diseases.

Role of interferon in melanoma: old hopes and new perspectives

INTRODUCTION

Interferons (IFNs) play a key role in modulating anti-microbial and antitumor immune responses. In oncology, past attempts to exploit IFNs therapeutically did not fulfill expectations, and had only modest clinical results, mostly limited to adjuvant melanoma treatment. The recent successes of immunotherapy in oncology have brought new attention to the potential of immune-modulatory agents like the IFNs. Areas covered: The authors review the biological effects of IFN on melanoma and immune cells. Then, the authors summarize the clinical results of adjuvant and therapeutic IFN in melanoma, giving focus to possible prognostic factors and new on-going clinical trials. Expert opinion: IFNs offer intriguing opportunities for synergism between conventional treatments and recently introduced molecular-targeted and immunotherapy approaches. However, the full comprehension of all IFN effects and their multiple biologic links is challenging. A strong commitment toward parallel translational research is needed to facilitate the interpretation of IFN's expected and unexpected effects, guiding the rational design of informative clinical studies.

The Essential Role of Type I Interferons in Differentiation and Activation of Tumor-Associated Neutrophils

Type I interferons (IFNs) were first characterized in the process of viral interference. However, since then, IFNs are found to be involved in a wide range of biological processes. In the mouse, type I IFNs comprise a large family of cytokines. At least 12 IFN-α and one IFN-β can be found and they all signal through the same receptor (IFNAR). A hierarchy of expression has been established for type I IFNs, where IFN-β is induced first and it activates in a paracrine and autocrine fashion a cascade of other type I IFNs. Besides its importance in the induction of the IFN cascade, IFN-β is also constitutively expressed in low amounts under normal non-inflammatory conditions, thus facilitating "primed" state of the immune system. In the context of cancer, type I IFNs show strong antitumor function as they play a key role in mounting antitumor immune responses through the modulation of neutrophil differentiation, activation, and migration. Owing to their plasticity, neutrophils play diverse roles during cancer development and metastasis since they possess both tumor-promoting (N2) and tumor-limiting (N1) properties. Notably, the differentiation into antitumor phenotype is strongly supported by type I IFNs. It could also be shown that these cytokines are critical for the suppression of neutrophil migration into tumor and metastasis site by regulating chemokine receptors, e.g., CXCR2 on these cells and by influencing their longevity. Type I IFNs limit the life span of neutrophils by influencing both, the extrinsic as well as the intrinsic apoptosis pathways. Such antitumor neutrophils efficiently suppress the pro-angiogenic factors expression, e.g., vascular endothelial growth factor and matrix metallopeptidase 9. This in turn restricts tumor vascularization and growth. Thus, type I IFNs appear to be the part of the natural tumor surveillance mechanism. Here we provide an up to date review of how type I IFNs influence the pro- and antitumor properties of neutrophils. Understanding these mechanisms is particularly important from a therapeutic point of view.

Early treatment with reverse transcriptase inhibitors significantly suppresses peak plasma IFNα in vivo during acute simian immunodeficiency virus infection

Innate interferons (IFN) are comprised of multiple Type I and III subtypes. The in vivo kinetics of subtype responses during human immunodeficiency virus (HIV) infection is not well defined. Using the acute simian immunodeficiency virus (SIV) infection model, we show that plasma IFNα levels peak at day 10 post-infection (pi) after which they rapidly declined. The mRNA expression of Type I and III IFN subtypes were significantly elevated in the lymph nodes (LN) at day 10 pi. Though the expression levels of all subtypes declined by day 14-31 pi, numerous subtypes remained elevated suggesting that ongoing viral replication in LN continues to drive induction of these subtypes. Interestingly, treatment with reverse transcriptase (RT) inhibitors at day 7 pi significantly suppressed plasma IFNα responses by day 10 pi that significantly correlated with cell-associated SIV DNA loads suggesting that RT byproducts such as viral DNA likely plays a role in driving IFN responses during acute SIV infection. Quantification of Type I and III subtype transcripts in sorted subsets of LN CD4+ and CD8+ T cells, CD14+/CD14- monocytes/macrophages, and total CD11c/CD123+ dendritic cells (DC) at day 10 pi showed that DC expressed ∼3-4 log more subtype transcripts as compared to the other subsets. Taken together, our results provide new insights into the kinetics of innate interferon responses during early stages of infection, and provide evidence that DC's are a major in vivo source of innate IFN during acute SIV infection.

Protein phosphatase 1 abrogates IRF7-mediated type I IFN response in antiviral immunity

Interferon (IFN) regulatory factor 7 (IRF7) plays a key role in the production of IFN-α in response to viral infection, and phosphorylation at IRF7 C-terminal serine sites is prelude to its function. However, phosphatases that negatively regulate IRF7 phosphorylation and activity have not been reported. In this study, we have identified a conserved protein phosphatase 1 (PP1)-binding motif in human and mouse IRF7 proteins, and shown that PP1 physically interacts with IRF7. Exogenous expression of PP1 subunits (PP1α, β, or γ) ablates IKKε-stimulated IRF7 phosphorylation and dramatically attenuates IRF7 transcriptional activity. Inhibition of PP1 activity significantly increases IRF7 phosphorylation and IRF7-mediated IFN-α production in response to Newcastle disease virus (NDV) infection or Toll-like receptor 7 (TLR7) challenge, leading to impaired viral replication. In addition, IFN treatment, TLR challenges and viral infection induce PP1 expression. Our findings disclose for the first time a pivotal role for PP1 in impeding IRF7-mediated IFN-α production in host immune responses.

Interferons, signal transduction pathways, and the central nervous system

The interferon (IFN) family of cytokines participates in the development of innate and acquired immune defenses against various pathogens and pathogenic stimuli. Discovered originally as a proteinaceous substance secreted from virus-infected cells that afforded immunity to neighboring cells from virus infection, these cytokines are now implicated in various human pathologies, including control of tumor development, cell differentiation, and autoimmunity. It is now believed that the IFN system (IFN genes and the genes induced by them, and the factors that regulate these processes) is a generalized alarm of cellular stress, including DNA damage. IFNs exert both beneficial and deleterious effects on the central nervous system (CNS). Our knowledge of the IFN-regulated processes in the CNS is far from being clear. In this article, we reviewed the current understanding of IFN signal transduction pathways and gene products that might have potential relevance to diseases of the CNS.

High-throughput quantitative real-time RT-PCR assay for determining expression profiles of types I and III interferon subtypes

Described in this report is a qRT-PCR assay for the analysis of seventeen human IFN subtypes in a 384-well plate format that incorporates highly specific locked nucleic acid (LNA) and molecular beacon (MB) probes, transcript standards, automated multichannel pipetting, and plate drying. Determining expression among the type I interferons (IFN), especially the twelve IFN-α subtypes, is limited by their shared sequence identity; likewise, the sequences of the type III IFN, especially IFN-λ2 and -λ3, are highly similar. This assay provides a reliable, reproducible, and relatively inexpensive means to analyze the expression of the seventeen interferon subtype transcripts.

Identification of type I IFN in Chinese giant salamander (Andrias davidianus) and the response to an iridovirus infection

The type I IFNs play a major role in the first line of defense against virus infections. In this study, the type I IFN gene designated gsIFN was identified and characterized in the Chinese giant salamander (Andrias davidianus). The genomic DNA of gsIFN contains 5 exons and 4 introns and has a total length of 5622 bp. The full-length cDNA sequence of gsIFN is 1113 bp and encodes a putative protein of 186 amino acids that has a 43% identity to type I IFN of Xenopus tropicalis. The deduced amino acid sequence has the C-terminal CAWE motif, that is mostly conserved in the higher vertebrate type I IFNs. Real-time fluorescence quantitative RT-PCR analysis revealed broad expression of gsIFN in vivo and the highest level expression in blood, kidney and spleen. Additionally, the expression of gsIFN at the mRNA level was significantly induced in peripheral blood leucocytes after stimulation with poly I:C and after infection with the Chinese giant salamander iridovirus (GSIV). A plasmid expressing gsIFN was constructed and transfected into the Chinese giant salamander muscle cell line. Expression of the IFN-inducible gene Mx was up-regulated in the gsIFN-overexpressing cells after GSIV infection. The virus load and titer were significantly reduced compared with that in control cells. Additionally, a lower level of virus major capsid protein synthesis was confirmed by immunofluorescence assay compared to the control cells. These results suggest that the gsIFN gene plays an important role in the antiviral innate immune response.

Mature human odontoblasts express virus-recognizing toll-like receptors

AIM

To study the expression of toll-like receptors (TLR) -3, -7, -8 and -9 as well as interferon receptors alpha and gamma (IFNAR1/IFNAR2 and IFNGR1/IFNGR2), which play important roles in the defence against viruses.

METHODOLOGY

DNA microarray and quantitative PCR analyses of TLR3, -7, -8 and -9 as well as IFNAR1/IFNAR2 and IFNGR1/IFNGR2 genes in mature native human odontoblasts and pulp were performed. Immunohistochemistry was used to confirm TLR8 protein in odontoblasts of healthy and carious human teeth.

RESULTS

TLR3, -7, -8 and -9 mRNAs were detected both in odontoblasts and in pulp, but TLR8 expression level was higher in the odontoblasts. IFNAR and IFNGR expression was observed in both tissues. Immunohistochemical analysis of healthy teeth revealed positive TLR8 staining in the pre-dentine and the dentine but varying staining patterns in the different portions of tooth. Lighter TLR8 staining was observed in dentine of mildly carious teeth. In teeth with carious lesions extending into the mid-dentine, only very weak staining was detected.

CONCLUSIONS

The finding of these virus-recognition-related genes in odontoblasts strengthens the view that odontoblasts participate in the immune response of the dentine-pulp complex.

Bridging the species divide: transgenic mice humanized for type-I interferon response

We have generated transgenic mice that harbor humanized type I interferon receptors (IFNARs) enabling the study of type I human interferons (Hu-IFN-Is) in mice. These “HyBNAR” (Hybrid IFNAR) mice encode transgenic variants of IFNAR1 and IFNAR2 with the human extracellular domains being fused to transmembrane and cytoplasmic segments of mouse sequence. B16F1 mouse melanoma cells harboring the HyBNAR construct specifically bound Hu-IFN-Is and were rendered sensitive to Hu-IFN-I stimulated anti-proliferation, STAT1 activation and activation of a prototypical IFN-I response gene (MX2). HyBNAR mice were crossed with a transgenic strain expressing the luciferase reporter gene under the control of the IFN-responsive MX2 promoter (MX2-Luciferase). Both the HyBNAR and HyBNAR/MX2-Luciferase mice were responsive to all Hu-IFN-Is tested, inclusive of IFNα2A, IFNβ, and a human superagonist termed YNSα8. The mice displayed dose-dependent pharmacodynamic responses to Hu-IFN-I injection, as assessed by measuring the expression of IFN-responsive genes. Our studies also demonstrated a weak activation of endogenous mouse interferon response, especially after high dose administration of Hu-IFNs. In sharp contrast to data published for humans, our pharmacodynamic readouts demonstrate a very short-lived IFN-I response in mice, which is not enhanced by sub-cutaneous (SC) injections in comparison to other administration routes. With algometric differences between humans and mice taken into account, the HyBNAR mice provides a convenient non-primate pre-clinical model to advance the study of human IFN-Is.

Subtypes of type I IFN differentially enhance cytokine expression by suboptimally stimulated CD4(+) T cells

Human type I interferons (IFNs) include IFN-β and 12 subtypes of IFN-α. During viral infection, infiltrating memory CD4(+) T cells are exposed to IFNs, but their impact on memory T-cell function is poorly understood. To address this, we pretreated PBMCs with different IFNs for 16 h before stimulation with Staphylococcus aureus enterotoxin B and measured cytokine expression by flow cytometry. IFN-α8 and -α10 most potently enhanced expression of IFN-γ, IL-2, and IL-4. Potency among the subtypes differed most at doses between 10 and 100 U/mL. While enhancement of IL-2 and IL-4 correlated with the time of preincubation with type I IFN, IFN-γ production was enhanced best when IFN-α was added immediately preceding or simultaneously with T-cell stimulation. Comparison of T-cell responses to multiple doses of Staphylococcus aureus enterotoxin B and to peptide libraries from RSV or CMV demonstrated that IFN-α best enhanced cytokine expression when CD4(+) T cells were suboptimally stimulated. We conclude that type I IFNs enhance Th1 and Th2 function with dose dependency and subtype specificity, and best when T-cell stimulation is suboptimal. While type I IFNs may beneficially enhance CD4(+) T-cell memory responses to vaccines or viral pathogens, they may also enhance the function of resident Th2 cells and exacerbate allergic inflammation.

Genomic analysis and mRNA expression of equine type I interferon genes

This study aimed at identifying all of the type I interferon (IFN) genes of the horse and at monitoring their expression in equine cells on in vitro induction. We identified 32 putative type I IFN loci on horse chromosome 23 and an unplaced genomic scaffold. A phylogentic analysis characterized these into 8 different type I IFN classes, that is, putative functional genes for 6 IFN-α, 4 IFN-β, 8 IFN-ω (plus 4 pseudogenes), 3 IFN-δ (plus 1 pseudogene), 1 IFN-κ and 1 IFN-ε, plus 1 IFN-ν pseudogene, and 3 loci belonging to what has previously been called IFN-αω. Our analyses indicate that the IFN-αω genes are quite distinct from both IFN-α and IFN-ω, and we refer to this type I IFN as IFN-μ. Results from cell cultures showed that leukocytes readily expressed IFN-α, IFN-β, IFN-δ, IFN-μ, and IFN-ω mRNA on induction with, for example, live virus; while fibroblasts only expressed IFN-β mRNA on stimulation. IFN-κ or IFN-ε expression was not consistently induced in these cell cultures. Thus, the equine type I IFN family comprised 8 classes, 7 of which had putative functional genes, and mRNA expression of 5 was induced in vitro. Moreover, a relatively low number of IFN-α subtypes was found in the horse compared with other eutherian mammals.

Differential effects of type I and II interferons on myeloid cells and resistance to intracellular bacterial infections

The type I and II interferons (IFNs) play important roles in regulating immune responses during viral and bacterial infections and in the context of autoimmune and neoplastic diseases. These two IFN types bind to distinct cell surface receptors that are expressed by nearly all cells to trigger signal transduction events and elicit diverse cellular responses. In some cases, type I and II IFNs trigger similar cellular responses, while in other cases, the IFNs have unique or antagonistic effects on host cells. Negative regulators of IFN signaling also modulate cellular responses to the IFNs and play important roles in maintaining immunological homeostasis. In this review, we provide an overview of how IFNs stimulate cellular responses. We discuss the disparate effects of type I and II IFNs on host resistance to certain intracellular bacterial infections and provide an overview of models that have been proposed to account for these disparate effects. Mechanisms of antagonistic cross talk between type I and II IFNs are also introduced.

Stabilization of human interferon-α1 mRNA by its antisense RNA

Antisense transcription is a widespread phenomenon in the mammalian genome and is believed to play a role in regulating gene expression. However, the exact functional significance of antisense transcription is largely unknown. Here, we show that natural antisense (AS) RNA is an important modulator of interferon-α1 (IFN-α1) mRNA levels. A ~4-kb, spliced IFN-α1 AS RNA targets a single-stranded region within a conserved secondary structure element of the IFN-α1 mRNA, an element which was previously reported to function as the nuclear export element. Following infection of human Namalwa lymphocytes with Sendai virus or infection of guinea pig 104C1 fetal fibroblasts with influenza virus A/PR/8/34, expression of IFN-α1 AS RNA becomes elevated. This elevated expression results in increased IFN-α1 mRNA stability because of the cytoplasmic (but not nuclear) interaction of the AS RNA with the mRNA at the single-stranded region. This results in increased IFN-α protein production. The silencing of IFN-α1 AS RNA by sense oligonucleotides or over-expression of antisense oligoribonucleotides, which were both designed from the target region, confirmed the critical role of the AS RNA in the post-transcriptional regulation of IFN-α1 mRNA levels. This AS RNA stabilization effect is caused by the prevention of the microRNA (miRNA)-induced destabilization of IFN-α1 mRNA due to masking of the miR-1270 binding site. This discovery not only reveals a regulatory pathway for controlling IFN-α1 gene expression during the host innate immune response against virus infection but also suggests a reason for the large number of overlapping complementary transcripts with previously unknown function.

Modelling the interactions between TLR4 and IFNβ pathways

Bacterial lipopolysaccharide (LPS) association with their connate receptor TLR4 triggers Type I interferon signaling cascade through its MyD88 independent downstream. Compared to plethora of reported empirical data on both TLR4 and Type I interferon pathways, there is no known model to decipher crosstalk mechanisms between these two crucial innate immune pathogen activated pathways regulating vital transcriptional factors such as nuclear factor-κB (NFκB), IFNβ, the interferon-stimulated gene factor-3 (ISGF3) and an important cancer drug target protein kinase-R (PKR). Innate immune system is based on a sensitive balance of intricate interactions. In elucidating these interactions, in silico integration of pathways has great potential. Attempts confined to single pathway may not be effective in truly addressing source of real systems behavior. This is the first report combining toll-like receptor-4 (TLR4) and interferon beta (IFNβ) pathways in a single in silico model, analyzing their interactions, pinpointing the source of delay in PKR late phase activity and limiting the transcription of IFN and PKR by using a method including an statistical physics technique in reaction equations. The model quite successfully recapitulates published interferon regulatory factor-3 (IRF3) and IFNβ data from mouse macrophages and PKR data from mouse embryonic fibroblast cell lines. The simulations end up with an estimate of IRF3, IFNβ, ISGF3 dose dependent profiles mimicking nonlinear dose response characteristic of the system. Involvement of concomitant PKR downstream can unravel elusive mechanisms in specific profiles like NFκB regulation.

Visualizing production of beta interferon by astrocytes and microglia in brain of La Crosse virus-infected mice

Beta interferon (IFN-β) is a major component of innate immunity in mammals, but information on the in vivo source of this cytokine after pathogen infection is still scarce. To identify the cell types responsible for IFN-β production during viral encephalitis, we used reporter mice that express firefly luciferase under the control of the IFN-β promoter and stained organ sections with luciferase-specific antibodies. Numerous luciferase-positive cells were detected in regions of La Crosse virus (LACV)-infected mouse brains that contained many infected cells. Double-staining experiments with cell-type-specific markers revealed that similar numbers of astrocytes and microglia of infected brains were luciferase positive, whereas virus-infected neurons rarely contained detectable levels of luciferase. Interestingly, if a mutant LACV unable of synthesizing the IFN-antagonistic factor NSs was used for challenge, the vast majority of the IFN-β-producing cells in infected brains were astrocytes rather than microglia. Similar conclusions were reached in a second series of experiments in which conditional reporter mice expressing the luciferase reporter gene solely in defined cell types were infected with wild-type or mutant LACV. Collectively, our data suggest that glial cells rather than infected neurons represent the major source of IFN-β in LACV-infected mouse brains. They further indicate that IFN-β synthesis in astrocytes and microglia is differentially affected by the viral IFN antagonist, presumably due to differences in LACV susceptibility of these two cell types.

Recruitment of histone deacetylase 3 to the interferon-A gene promoters attenuates interferon expression

BACKGROUND

Induction of Type I Interferon (IFN) genes constitutes an essential step leading to innate immune responses during virus infection. Sendai virus (SeV) infection of B lymphoid Namalwa cells transiently induces the transcriptional expression of multiple IFN-A genes. Although transcriptional activation of IFN-A genes has been extensively studied, the mechanism responsible for the attenuation of their expression remains to be determined.

PRINCIPAL FINDINGS

In this study, we demonstrate that virus infection of Namalwa cells induces transient recruitment of HDAC3 (histone deacetylase 3) to IFN-A promoters. Analysis of chromatin-protein association by Chip-QPCR demonstrated that recruitment of interferon regulatory factor (IRF)3 and IRF7, as well as TBP correlated with enhanced histone H3K9 and H3K14 acetylation, whereas recruitment of HDAC3 correlated with inhibition of histone H3K9/K14 acetylation, removal of IRF7 and TATA-binding protein (TBP) from IFN-A promoters and inhibition of virus-induced IFN-A gene transcription. Additionally, HDAC3 overexpression reduced, and HDAC3 depletion by siRNA enhanced IFN-A gene expression. Furthermore, activation of IRF7 enhanced histone H3K9/K14 acetylation and IFN-A gene expression, whereas activation of both IRF7 and IRF3 led to recruitment of HDAC3 to the IFN-A gene promoters, resulting in impaired histone H3K9 acetylation and attenuation of IFN-A gene transcription.

CONCLUSION

Altogether these data indicate that reversal of histone H3K9/K14 acetylation by HDAC3 is required for attenuation of IFN-A gene transcription during viral infection.

Effects of IFN-α as a signal-3 cytokine on human naïve and antigen-experienced CD8(+) T cells

IFN-α/β link innate and adaptive immune responses by directly acting on naïve CD8(+) T cells. This concept unveiled in mice remains unexplored in humans. To investigate that, human CD8(+) CD45RO(-) cells were stimulated with beads coated with anti-CD3 and anti-CD28 mAb, mimicking Ag (type-1) and co-stimulatory (type-2) signals, in the presence or absence of IFN-α and their transcriptional profiles were defined by cDNA-microarrays. We show that IFN-α provides a strong third signal directly to human CD8(+) T cells resulting in regulation of critical genes for their overall activation. This transcriptional effect was substantiated at the protein level and verified by functional assays. Interestingly, the biological effects derived from this stimulation vary depending on the CD8(+) T-cell population. Thus, whereas IFN-α increases the proliferative capacity of naïve CD8(+) T cells, it inhibits or does not affect the proliferation of Ag-experienced cells, such as memory and effector CTL, including CMV-specific lymphocytes. Cytolysis and IFN-γ-secretion of all these populations are enhanced by IFN-α-derived signals, which are critical in naïve CD8(+) T cells for acquisition of effector functions. Our findings in human CD8(+) T cells are informative to understand and improve IFN-α-based therapies for viral and malignant diseases.

Interferons as potential adjuvants in prophylactic vaccines

IMPORTANCE OF THE FIELD

Vaccines are still one of the best approaches to manage infectious diseases. Despite the advances in drug therapies, prophylactic medicine is still more cost efficient and minimizes the burden in the heath system. Despite all the research in vaccine development, many infectious diseases are still without an effective vaccine. The use of adjuvants in vaccines has been one successful strategy to increase efficacy. IFNs are widely expressed cytokines that have potent antiviral effects. These cytokines are the first line of defense against viral infections and have important roles in immuno surveillance for malignant cells. One of the most promising uses of IFNs is as adjuvants that are co-applied with antigen in vaccines.

AREAS COVERED IN THIS REVIEW

In this review, a cumulative analysis of many of the studies that have used IFN-α, -β, -γ and -λ as adjuvants between 1987 and the present suggests that many do possess the capacity to serve as potent immunoadjuvants for vaccination.

WHAT THE READER WILL GAIN

This review provides a very large collection of studies involving all types of IFNs used as adjuvants in vaccines using different vaccination strategies and various animal models.

TAKE HOME MESSAGE

It is clear that the use of IFNs not only improved the efficacy and safety of most vaccines, but also had important immunomodulatory effect directing T(H)1 immune responses.

The differential activity of interferon-α subtypes is consistent among distinct target genes and cell types

IFN-α proteins have been described to originate from 14 individual genes and allelic variants. However, the exceptional diversity of IFN-α and its functional impact are still poorly understood. To characterize the biological activity of IFN-α subtypes in relation to the cellular background, we investigated the effect of IFN-α treatment in primary fibroblasts and endothelial cells of vascular or lymphatic origin. The cellular response was evaluated for 13 distinct IFN-α proteins with respect to transcript regulation of the IFN-stimulated genes (ISGs) IFIT1, ISG15, CXCL10, CXCL11 and CCL8. The IFN-α proteins displayed a remarkably consistent potency in gene induction irrespective of target gene and cellular background which led to the classification of IFN-α subtypes with low (IFN-α1), intermediate (IFN-α2a, -4a, -4b, -5, -16, -21) and high (IFN-α2b, -6, -7, -8, -10, -14) activity. The differential potency of IFN-α classes was confirmed at the ISG protein level and the functional protection of cells against influenza virus infection. Differences in IFN activity were only observed at subsaturating levels of IFN-α proteins and did not affect the time course of ISG regulation. Cell-type specific responses were apparent for distinct target genes independent of IFN-α subtype and were based on different levels of basal versus inducible gene expression. While fibroblasts presented with a high constitutive level of IFIT1, the expression in endothelial cells was strongly induced by IFN-α. In contrast, CXCL10 and CXCL11 transcript levels were generally higher in endothelial cells despite a pronounced induction by IFN-α in fibroblasts. In summary, the divergent potency of IFN-α proteins and the cell-type specific regulation of individual IFN target genes may allow for the fine tuning of cellular responses to pathogen defense.

Counter-regulation mechanism of IL-4 and IFN-α signal transduction through cytosolic retention of the pY-STAT6:pY-STAT2:p48 complex

IFN-α and IL-4 induce Th1 and Th2 responses, respectively, and often display antagonistic actions against each other. To elucidate the molecular mechanism of counter-regulation, we have investigated the signal interception by IFN-α and IL-4, employing a human B-cell line Ramos, sensitive to both cytokines. In these cells, IFN-α effectively inhibited IL-4-induced Fc epsilon receptor II (CD23) expression, whereas IL-4 suppressed IFN-α-mediated IRF7 expression. The counter-regulatory action by IL-4 and IFN-α proceeded with a delayed kinetics requiring 4 h. Notably, IFN-α did not affect the IL-4-induced tyrosine phosphorylation of STAT6, but induced a time-dependent cytoplasmic accumulation of phosphotyrosine(pY)-STAT6 and a corresponding decrease in nuclear pY-STAT6. By confocal analysis and co-immunoprecipitation assays, we demonstrated the colocalization and molecular interaction of IL-4-induced pY-STAT6 with IFN-α-induced pY-STAT2:p48 in the cytosol. In addition, the over-expression of STAT2 or STAT6 induced the concomitant cytosolic accumulation of pY-STAT6 or pY-STAT2, leading to the suppression of IL-4-induced CD23 or IFN-α-induced IRF7 gene expression, respectively. Our data suggest that the signals ensued by IFN-α and IL-4 induce cytoplasmic sequestration of IL-4-activated STAT6 and IFN-α-activated STAT2:p48 in B cells through the formation of pY-STAT6:pY-STAT2:p48 complex, which provides a novel mechanism by which IFN-α and IL-4 cross-regulate their signaling into the nucleus.

The small interferon-induced transmembrane genes and proteins

Interferon-induced transmembrane (IFITM) genes are transcribed in most tissues and are with the exception of IFITM5 interferon inducible. They are involved in early development, cell adhesion, and control of cell growth. Most IFITM genes are activated in response to bacterial and viral infections, and the exact host immune defense mechanisms are still unknown. Elevated gene expression triggered by past or chronic inflammation could prevent spreading of pathogens by limiting host cell proliferation. Accordingly, induction in cells with low basal protein levels is sufficient to drive growth arrest and a senescence-like morphology. On the other hand, loss of IFITM levels in cancer is correlated with pronounced malignancy; thus, these genes are considered as tumor suppressors. However, several cancer cells have deregulated high levels of IFITM transcripts, indicating a tumor progression stage where at least one of the interferon-controlled antiproliferative pathways has been silenced. Phylogenetic analyses of the protein coding genomic sequences suggest a single interferon-inducible gene in the common ancestor of rodents and primates. Biological functions studied so far may have evolved in parallel, and functional characterization of IFITM proteins will provide insight into innate immune defense, cancer development, and other pathways.

Epigenetic silencing of interferon-kappa in human papillomavirus type 16-positive cells

We have investigated interferon-kappa (IFN-kappa) regulation in the context of human papillomavirus (HPV)-induced carcinogenesis using primary human foreskin keratinocytes (HFK), immortalized HFKs encoding individual oncoproteins of HPV16 (E6, E7, and E6/E7), and cervical carcinoma cells. Here, IFN-kappa was suppressed in the presence of E6, whereas its expression was not affected in HFKs or E7-immortalized HFKs. Transcription could be reactivated after DNA demethylation but was decreased again upon drug removal. Partial reactivation could also be accomplished when E6 was knocked down, suggesting a contribution of E6 in IFN-kappa de novo methylation. We identified a single CpG island near the transcriptional start site as being involved in selective IFN-kappa expression. To prove the functional relevance of IFN-kappa in building up an antiviral response, IFN-kappa was ectopically expressed in cervical carcinoma cells where protection against vesicular stomatitis virus-mediated cytolysis could be achieved. Reconstitution of IFN-kappa was accompanied by an increase of p53, MxA, and IFN-regulatory factors, which was reversed by knocking down either IFN-kappa or p53 by small interfering RNA. This suggests the existence of a positive feedback loop between IFN-kappa, p53, and components of IFN signaling pathway to maintain an antiviral state. Our in vitro findings were further corroborated in biopsy samples of cervical cancer patients, in which IFN-kappa was also downregulated when compared with normal donor tissue. This is the first report showing an epigenetic silencing of type I IFN after HPV16 oncogene expression and revealing a novel strategy on how high-risk HPVs can abolish the innate immune response in their genuine host cells.

Long-term pegylated interferon-alpha and its potential in the treatment of melanoma

Conventional interferons including interferon-alpha (IFN-alpha) are cytokines used for years in the treatment of solid tumors and hematological malignancies. Their half-life is short. Pegylated forms of IFN-alpha present an improved pharmacokinetic profile that rendered them the preferred IFNs in hepatitis therapy. In the last decade, pegylated interferons (PegIFNs) have been investigated in melanoma patients. We review the scientific published literature on biology, pharmacokinetics, side effects and clinical applications of PegIFN-alpha in the treatment of stage III and IV melanoma. In the adjuvant setting, PegIFNalpha-2b has significant prolonged distant metastases free survival in patients with microscopic nodal involvement (stage TxN1aM0) and therefore is a promising treatment option in this patient population. In the palliative setting, monotherapy with PegIFNalpha-2alpha can induce complete remissions in a minority of stage IV melanoma patients. The combination of monochemotherapy is feasible and may result in lasting complete remissions. Ongoing research must focus on the identification of patients who mostly benefit, so that unnecessary toxicity would be avoided. Combining PegIFNs and chemotherapy or targeted agents deserves further exploration.

Differential regulation of human interferon A gene expression by interferon regulatory factors 3 and 7

Differential expression of the human interferon A (IFN-A) gene cluster is modulated following paramyxovirus infection by the relative amounts of active interferon regulatory factor 3 (IRF-3) and IRF-7. IRF-3 expression activates predominantly IFN-A1 and IFN-B, while IRF-7 expression induces multiple IFN-A genes. IFN-A1 gene expression is dependent on three promoter proximal IRF elements (B, C, and D modules, located at positions -98 to -45 relative to the mRNA start site). IRF-3 binds the C module of IFN-A1, while other IFN-A gene promoters are responsive to the binding of IRF-7 to the B and D modules. Maximal expression of IFN-A1 is observed with complete occupancy of the three modules in the presence of IRF-7. Nucleotide substitutions in the C modules of other IFN-A genes disrupt IRF-3-mediated transcription, whereas a G/A substitution in the D modules enhances IRF7-mediated expression. IRF-3 exerts dual effects on IFN-A gene expression, as follows: a synergistic effect with IRF-7 on IFN-A1 expression and an inhibitory effect on other IFN-A gene promoters. Chromatin immunoprecipitation experiments reveal that transient binding of both IRF-3 and IRF-7, accompanied by CBP/p300 recruitment to the endogenous IFN-A gene promoters, is associated with transcriptional activation, whereas a biphasic recruitment of IRF-3 and CBP/p300 represses IFN-A gene expression. This regulatory mechanism contributes to differential expression of IFN-A genes and may be critical for alpha interferon production in different cell types by RIG-I-dependent signals, leading to innate antiviral immune responses.

Identification of an Atlantic salmon IFN multigene cluster encoding three IFN subtypes with very different expression properties

A cluster of 11 interferon (IFN) genes were identified in the Atlantic salmon genome linked to the growth hormone 1 gene. The genes encode three different IFN subtypes; IFNa (two genes), IFNb (four genes) and IFNc (five genes), which show 22-32% amino acid sequence identity. Expression of the fish IFNs were studied in head kidney, leukocytes or TO cells after stimulation with the dsRNA poly I:C or the imidazoquinoline S-27609. In mammals, poly I:C induces IFN-beta through the RIG-I/MDA5 or the TLR3 pathway, both of which are dependent on NF-kB. In contrast, S-27609 induces mammalian IFN-alpha in plasmacytoid dendritic cells through the TLR7 pathway independent of NF-kappaB. The presence of an NF-kappaB site in their promoters and their strong up-regulation by poly I:C, suggest that salmon IFNa1/IFNa2 are induced through similar pathways as IFN-beta. In contrast, the apparent lack of NF-kappaB motif in the promoter and the strong upregulation by S-27609 in head kidney and leukocytes, suggest that IFNb genes are induced through a pathway similar to mammalian IFN-alpha. IFNc genes showed expression patterns different from both IFNa and IFNb. Taken together, salmon IFNa and IFNb are not orthologs of mammalian IFN-beta and IFN-alpha, respectively, but appear to utilize similar induction pathways.

Local type I IFN receptor signaling protects against virus spread within the central nervous system

Several neurotropic viruses such as vesicular stomatitis virus (VSV) induce peripheral neutralizing Ab responses and still can infect cells within the CNS. To address whether local type I IFN receptor (IFNAR) triggering plays a role in controlling virus replication within the brain, we generated mice with a cell type-specific IFNAR deletion in neuroectodermal cells of the CNS (NesCre(+/-)IFNAR(flox/flox)). Intranasal VSV infection with 10(3) PFU was well tolerated by wild-type mice, whereas conventional IFNAR(-/-) mice died within 2-3 days. In contrast, brain-specific NesCre(+/-)IFNAR(flox/flox) mice survived until day 5-6 and then became hemiplegic and died. Terminally ill NesCre(+/-)IFNAR(flox/flox) mice showed 10- to 100-fold higher virus loads in the brain than IFNAR(-/-) mice, whereas little or no virus was found in other organs. In wild-type animals, virus could be reisolated only from the olfactory bulb until day 6 where also STAT1 activation as a measure of IFNAR triggering was detected. Virus infection was found exclusively in glomerular structures of the olfactory bulb, whereas surrounding cells that showed STAT1 phosphorylation as a measure of IFNAR trigging were free of virus. Our data indicate that upon intranasal VSV instillation, early and localized IFNAR triggering in the glomerular layer of the olfactory bulb is critically required to prevent viral spread over the entire CNS and thus confers survival.

Interferons and their use in persistent viral infections

In 2007, the world celebrated the 50th anniversary of the discovery of interferon (IFN) by Isaacs and Lindenmann. Subsequently, the IFN-alpha gene was cloned, fully sequenced and IFN-alpha was produced in recombinant form. Recombinant IFN-alpha is now used as the basis for treatment of chronic hepatitis C virus infection and can also be used to treat certain forms of chronic hepatitis B virus infections. IFNs have also been used in other viral infections, although with less success. The antiviral mechanisms of IFNs are reviewed in this chapter as well as the utility of IFNs in the treatment of persistent viral infections.