Ligand-induced Assembling of the Type I Interferon Receptor on Supported Lipid Bilayers

Structural and Functional Characterization of a Fish Type I Subgroup d IFN Reveals Its Binding to Receptors

Teleost fish type I IFNs and the associated receptors from the cytokine receptor family B (CRFB) are characterized by remarkable diversity and complexity. How the fish type I IFNs bind to their receptors is still not fully understood. In this study, we demonstrate that CRFB1 and CRFB5 constitute the receptor pair through which type I subgroup d IFN (IFNd) from large yellow croaker, Larimichthys crocea, activates the conserved JAK-STAT signaling pathway as a part of the antiviral response. Our data suggest that L. crocea IFNd (LcIFNd) has a higher binding affinity with L. crocea CRFB5 (LcCRFB5) than with LcCRFB1. Furthermore, we report the crystal structure of LcIFNd at a 1.49-Å resolution and construct structural models of LcIFNd in binary complexes with predicted structures of extracellular regions of LcCRFB1 and LcCRFB5, respectively. Despite striking similarities in overall architectures of LcIFNd and its ortholog human IFN-ω, the receptor binding patterns between LcIFNd and its receptors show that teleost and mammalian type I IFNs may have differentially selected helices that bind to their homologous receptors. Correspondingly, key residues mediating binding of LcIFNd to LcCRFB1 and LcCRFB5 are largely distinct from the receptor-interacting residues in other fish and mammalian type I IFNs. Our findings reveal a ligand/receptor complex binding mechanism of IFNd in teleost fish, thus providing new insights into the function and evolution of type I IFNs.

Tissue factor binds to and inhibits interferon-α receptor 1 signaling

Tissue factor (TF), which is a member of the cytokine receptor family, promotes coagulation and coagulation-dependent inflammation. TF also exerts protective effects through unknown mechanisms. Here, we showed that TF bound to interferon-α receptor 1 (IFNAR1) and antagonized its signaling, preventing spontaneous sterile inflammation and maintaining immune homeostasis. Structural modeling and direct binding studies revealed binding of the TF C-terminal fibronectin III domain to IFNAR1, which restricted the expression of interferon-stimulated genes (ISGs). Podocyte-specific loss of TF in mice (PodΔF3) resulted in sterile renal inflammation, characterized by JAK/STAT signaling, proinflammatory cytokine expression, disrupted immune homeostasis, and glomerulopathy. Inhibiting IFNAR1 signaling or loss of Ifnar1 expression in podocytes attenuated these effects in PodΔF3 mice. As a heteromer, TF and IFNAR1 were both inactive, while dissociation of the TF-IFNAR1 heteromer promoted TF activity and IFNAR1 signaling. These data suggest that the TF-IFNAR1 heteromer is a molecular switch that controls thrombo-inflammation.

HIV-1 Infection Results in Sphingosine-1-Phosphate Receptor 1 Dysregulation in the Human Thymus

Regeneration of functional naïve T lymphocytes following the onset of human immunodeficiency virus (HIV) infection remains a crucial issue for people living with HIV (PLWH), even when adhering to antiretroviral therapy (ART). Thus far, reports on the impact of HIV-1 infection on the entry of thymic precursors and the egress of functional naïve T lymphocytes to and from the thymus are limited. We examined the impact of HIV-1 on Sphingosine-1-phosphate (S1P) signaling, which governs the egress of functional naïve thymocytes from the thymus to the periphery. Using in vitro experiments with primary human thymocytes and in vivo and ex vivo studies with humanized mice, we show that HIV-1 infection results in upregulation of the expression of S1P receptor 1 (S1PR1) in the human thymus. Intriguingly, this upregulation occurs during intrathymic infection (direct infection of the human thymic implant) as well as systemic infection in humanized mice. Moreover, considering the dysregulation of pro- and anti-inflammatory cytokines in infected thymi, the increased expression of S1PR1 in response to in vitro exposure to Interferon-Beta (IFN-β) and Tumor Necrosis Factor-Alpha (TNF-α) indicates that cytokine dysregulation following HIV infection may contribute to upregulation of S1PR1. Finally, an increased presence of CD3hiCD69- (fully mature) as well as CD3hiCD69+ (less mature) T cells in the spleen during HIV infection in humanized mice, combined with earlier expression of S1PR1 during thymocyte development, suggests that upregulation of S1PR1 may translate to increased or accelerated egress from the thymus. The egress of thymocytes that are not functionally mature from the thymus to peripheral blood and lymphoid organs may have implications for the immune function of PLWH.

Antiviral effects of interferon-stimulated genes in bats

The interferon pathway is the first line of defense in viral infection in all mammals, and its induction stimulates broad expression of interferon-stimulated genes (ISGs). In mice and also humans, the antiviral function of ISGs has been extensively studied. As an important viral reservoir in nature, bats can coexist with a variety of pathogenic viruses without overt signs of disease, yet only limited data are available for the role of ISGs in bats. There are multiple species of bats and work has begun deciphering the differences and similarities between ISG function of human/mouse and different bat species. This review summarizes the current knowledge of conserved and bat-specific-ISGs and their known antiviral effector functions.

Molecular and cellular factors determining the functional pleiotropy of cytokines

Cytokines are soluble factors vital for mammalian physiology. Cytokines elicit highly pleiotropic activities, characterized by their ability to induce a wide spectrum of functional responses in a diverse range of cell subsets, which makes their study very challenging. Cytokines activate signalling via receptor dimerization/oligomerization, triggering activation of the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) signalling pathway. Given the strong crosstalk and shared usage of key components of cytokine signalling pathways, a long-standing question in the field pertains to how functional diversity is achieved by cytokines. Here, we discuss how biophysical - for example, ligand-receptor binding affinity and topology - and cellular - for example, receptor, JAK and STAT protein levels, endosomal compartment - parameters contribute to the modulation and diversification of cytokine responses. We review how these parameters ultimately converge into a common mechanism to fine-tune cytokine signalling that involves the control of the number of Tyr residues phosphorylated in the receptor intracellular domain upon cytokine stimulation. This results in different kinetics of STAT activation, and induction of specific gene expression programs, ensuring the generation of functional diversity by cytokines using a limited set of signalling intermediaries. We describe how these first principles of cytokine signalling have been exploited using protein engineering to design cytokine variants with more specific and less toxic responses for immunotherapy.

Antiviral Effect of pIFNLs against PEDV and VSV Infection in Different Cells

Type III and type I interferon have similar mechanisms of action, and their different receptors lead to different distributions in tissue. On mucosal surfaces, type III interferon exhibits strong antiviral activity. Porcine epidemic diarrhea virus (PEDV) is an economically important enteropathogenic coronavirus, which can cause a high incidence rate and mortality in piglets. Here, we demonstrate that porcine interferon lambda 1 (pIFNL1) and porcine interferon lambda 3 (pIFNL3) can inhibit the proliferation of vesicular stomatitis virus with an enhanced green fluorescent protein (VSV-EGFP) in different cells, and also show strong antiviral activity when PEDV infects Vero cells. Both forms of pIFNLs were shown to be better than porcine interferon alpha (pIFNα), the antiviral activity of pIFNL1 is lower than that of pIFNL3. Therefore, our results provide experimental evidence for the inhibition of PEDV infection by pIFNLs, which may provide a promising treatment for the prevention and treatment of Porcine epidemic diarrhea (PED) in piglets.

Molecular and Structural Basis of Receptor Binding and Signaling of a Fish Type I IFN with Three Disulfide Bonds

In mammals, type I IFNs, which commonly contain one or two disulfide bonds, activate the JAK-STAT signaling pathway through binding to the common cell surface receptor formed by IFN-α/β receptor (IFNAR)1 and IFNAR2 subunits. Although type I IFNs are also known to be essential for antiviral defense in teleost fish, very little is known about mechanisms underlying the recognition of fish type I IFNs by associated receptors. In this study, we demonstrate that a type I IFN of large yellow croaker Larimichthys crocea (LcIFNi), belonging to a new subgroup of fish type I IFNs, triggers antiviral response via the conserved JAK-STAT pathway through stable binding with a heterodimeric receptor comprising subunits LcCRFB5 and LcCRFB2. LcIFNi binds to LcCRFB5 with a much higher affinity than to LcCRFB2. Furthermore, we determined the crystal structure of LcIFNi at a 1.39 Å resolution. The high-resolution structure is, to our knowledge, the first reported structure of a type I IFN with three disulfide bonds, all of which were found to be indispensable for folding and stability of LcIFNi. Using structural analysis, mutagenesis, and biochemical assays, we identified key LcIFNi residues involved in receptor interaction and proposed a structural model of LcIFNi bound to the LcCRFB2–LcCRFB5 receptor. The results show that LcIFNi–LcCRFB2 exhibits a similar binding pattern to human IFN-ω–IFNAR2, whereas the binding pattern of LcIFNi–LcCRFB5 is quite different from that of IFN-ω–IFNAR1. Altogether, our findings reveal the structural basis for receptor interaction and signaling of a type I IFN with three disulfide bonds and provide new insights into the mechanisms underlying type I IFN recognition in teleosts.

Life-threatening viral disease in a novel form of autosomal recessive IFNAR2 deficiency in the Arctic

Type I interferons (IFN-I) play a critical role in human antiviral immunity, as demonstrated by the exceptionally rare deleterious variants of IFNAR1 or IFNAR2. We investigated five children from Greenland, Canada, and Alaska presenting with viral diseases, including life-threatening COVID-19 or influenza, in addition to meningoencephalitis and/or hemophagocytic lymphohistiocytosis following live-attenuated viral vaccination. The affected individuals bore the same homozygous IFNAR2 c.157T>C, p.Ser53Pro missense variant. Although absent from reference databases, p.Ser53Pro occurred with a minor allele frequency of 0.034 in their Inuit ancestry. The serine to proline substitution prevented cell surface expression of IFNAR2 protein, small amounts of which persisted intracellularly in an aberrantly glycosylated state. Cells exclusively expressing the p.Ser53Pro variant lacked responses to recombinant IFN-I and displayed heightened vulnerability to multiple viruses in vitro-a phenotype rescued by wild-type IFNAR2 complementation. This novel form of autosomal recessive IFNAR2 deficiency reinforces the essential role of IFN-I in viral immunity. Further studies are warranted to assess the need for population screening.

Interferon-β Activity Is Affected by S100B Protein

Interferon-β (IFN-β) is a pleiotropic cytokine secreted in response to various pathological conditions and is clinically used for therapy of multiple sclerosis. Its application for treatment of cancer, infections and pulmonary diseases is limited by incomplete understanding of regulatory mechanisms of its functioning. Recently, we reported that IFN-β activity is affected by interactions with S100A1, S100A4, S100A6, and S100P proteins, which are members of the S100 protein family of multifunctional Ca²⁺-binding proteins possessing cytokine-like activities (Int J Mol Sci. 2020;21(24):9473). Here we show that IFN-β interacts with one more representative of the S100 protein family, the S100B protein, involved in numerous oncological and neurological diseases. The use of chemical crosslinking, intrinsic fluorescence, and surface plasmon resonance spectroscopy revealed IFN-β binding to Ca²⁺-loaded dimeric and monomeric forms of the S100B protein. Calcium depletion blocks the S100B–IFN-β interaction. S100B monomerization increases its affinity to IFN-β by 2.7 orders of magnitude (equilibrium dissociation constant of the complex reaches 47 pM). Crystal violet assay demonstrated that combined application of IFN-β and S100B (5–25 nM) eliminates their inhibitory effects on MCF-7 cell viability. Bioinformatics analysis showed that the direct modulation of IFN-β activity by the S100B protein described here could be relevant to progression of multiple oncological and neurological diseases.

Development of highly stable and de-immunized versions of recombinant alpha interferon: Promising candidates for the treatment of chronic and emerging viral diseases

Human interferon alpha (hIFN-α) administration constitutes the current FDA approved therapy for chronic Hepatitis B and C virus infections. Additionally, hIFN-α treatment efficacy was recently demonstrated in patients with COVID-19. Thus, hIFN-α constitutes a therapeutic alternative for those countries where vaccination is inaccessible and for people who did not respond effectively to vaccination. However, hIFN-α2b exhibits a short plasma half-life resulting in the occurrence of severe side effects. To optimize the cytokine's pharmacokinetic profile, we developed a hyperglycosylated IFN, referred to as GMOP-IFN.

Given the significant number of reports showing neutralizing antibodies (NAb) formation after hIFN-α administration, here we applied the DeFT (De-immunization of Functional Therapeutics) approach to develop functional, de-immunized versions of GMOP-IFN. Two GMOP-IFN variants exhibited significantly reduced ex vivo immunogenicity and null antiproliferative activity, while preserving antiviral function. The results obtained in this work indicate that the new de-immunized GMOP-IFN variants constitute promising candidates for antiviral therapy.

Interferon Receptor Trafficking and Signaling: Journey to the Cross Roads

Like most plasma membrane proteins, type I interferon (IFN) receptor (IFNAR) traffics from the outer surface to the inner compartments of the cell. Long considered as a passive means to simply control subunits availability at the plasma membrane, an array of new evidence establishes IFNAR endocytosis as an active contributor to the regulation of signal transduction triggered by IFN binding to IFNAR. During its complex journey initiated at the plasma membrane, the internalized IFNAR complex, i.e. IFNAR1 and IFNAR2 subunits, will experience post-translational modifications and recruit specific effectors. These finely tuned interactions will determine not only IFNAR subunits destiny (lysosomal degradation vs. plasma membrane recycling) but also the control of IFN-induced signal transduction. Finally, the IFNAR system perfectly illustrates the paradigm of the crosstalk between membrane trafficking and intracellular signaling. Investigating the complexity of IFN receptor intracellular routes is therefore necessary to reveal new insight into the role of IFNAR membrane dynamics in type I IFNs signaling selectivity and biological activity.

Interferon Beta Activity Is Modulated via Binding of Specific S100 Proteins

Interferon-β (IFN-β) is a pleiotropic cytokine used for therapy of multiple sclerosis, which is also effective in suppression of viral and bacterial infections and cancer. Recently, we reported a highly specific interaction between IFN-β and S100P lowering IFN-β cytotoxicity to cancer cells (Int J Biol Macromol. 2020; 143: 633–639). S100P is a member of large family of multifunctional Ca²⁺-binding proteins with cytokine-like activities. To probe selectivity of IFN-β—S100 interaction with respect to S100 proteins, we used surface plasmon resonance spectroscopy, chemical crosslinking, and crystal violet assay. Among the thirteen S100 proteins studied S100A1, S100A4, and S100A6 proteins exhibit strictly Ca²⁺-dependent binding to IFN-β with equilibrium dissociation constants, K_d, of 0.04–1.5 µM for their Ca²⁺-bound homodimeric forms. Calcium depletion abolishes the S100—IFN-β interactions. Monomerization of S100A1/A4/A6 decreases K_d values down to 0.11–1.0 nM. Interferon-α is unable of binding to the S100 proteins studied. S100A1/A4 proteins inhibit IFN-β-induced suppression of MCF-7 cells viability. The revealed direct influence of specific S100 proteins on IFN-β activity uncovers a novel regulatory role of particular S100 proteins, and opens up novel approaches to enhancement of therapeutic efficacy of IFN-β.

The Molecular Interactions of ZIKV and DENV with the Type-I IFN Response

Zika Virus (ZIKV) and Dengue Virus (DENV) are related viruses of the Flavivirus genus that cause significant disease in humans. Existing control measures have been ineffective at curbing the increasing global incidence of infection for both viruses and they are therefore prime targets for new vaccination strategies. Type-I interferon (IFN) responses are important in clearing viral infection and for generating efficient adaptive immune responses towards infection and vaccination. However, ZIKV and DENV have evolved multiple molecular mechanisms to evade type-I IFN production. This review covers the molecular interactions, from detection to evasion, of these viruses with the type-I IFN response. Additionally, we discuss how this knowledge can be exploited to improve the design of new vaccine strategies.

Herpes Simplex Virus Type 1 Interactions with the Interferon System

The interferon (IFN) system is one of the first lines of defense activated against invading viral pathogens. Upon secretion, IFNs activate a signaling cascade resulting in the production of several interferon stimulated genes (ISGs), which work to limit viral replication and establish an overall anti-viral state. Herpes simplex virus type 1 is a ubiquitous human pathogen that has evolved to downregulate the IFN response and establish lifelong latent infection in sensory neurons of the host. This review will focus on the mechanisms by which the host innate immune system detects invading HSV-1 virions, the subsequent IFN response generated to limit viral infection, and the evasion strategies developed by HSV-1 to evade the immune system and establish latency in the host.

Autoreactive B cells in SLE, villains or innocent bystanders?

The current concepts for development of autoreactive B cells in SLE (systemic lupus erythematosus) focus on extrinsic stimuli and factors that provoke B cells into tolerance loss. Traditionally, major tolerance loss pathways are thought to be regulated by factors outside the B cell including autoantigen engagement of the B-cell receptor (BCR) with simultaneous type I interferon (IFN) produced by dendritic cells, especially plasmacytoid dendritic cells (pDCs). Later, in autoreactive follicles, B-cells encounter T-follicular helper cells (Tfh) that produce interleukin (IL)-21, IL-4 and pathogenic cytokines, IL-17 and IFN gamma (IFNɣ). This review discusses these mechanisms and also highlights recent advances pointing to the peripheral transitional B-cell stage as a major juncture where transient autocrine IFNβ expression by developing B-cells imprints a heightened susceptibility to external factors favoring differentiation into autoantibody-producing plasmablasts. Recent studies highlight transitional B-cell heterogeneity as a determinant of intrinsic resistance or susceptibility to tolerance loss through the shaping of B-cell responsiveness to cytokines and other environment factors.

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.

Quantitative systems pharmacology of interferon alpha administration: A multi-scale approach

The therapeutic effect of a drug is governed by its pharmacokinetics which determine the downstream pharmacodynamic response within the cellular network. A complete understanding of the drug-effect relationship therefore requires multi-scale models which integrate the properties of the different physiological scales. Computational modelling of these individual scales has been successfully established in the past. However, coupling of the scales remains challenging, although it will provide a unique possibility of mechanistic and holistic analyses of therapeutic outcomes for varied treatment scenarios. We present a methodology to combine whole-body physiologically-based pharmacokinetic (PBPK) models with mechanistic intracellular models of signal transduction in the liver for therapeutic proteins. To this end, we developed a whole-body distribution model of IFN-α in human and a detailed intracellular model of the JAK/STAT signalling cascade in hepatocytes and coupled them at the liver of the whole-body human model. This integrated model infers the time-resolved concentration of IFN-α arriving at the liver after intravenous injection while simultaneously estimates the effect of this dose on the intracellular signalling behaviour in the liver. In our multi-scale physiologically-based pharmacokinetic/pharmacodynamic (PBPK/PD) model, receptor saturation is seen at low doses, thus giving mechanistic insights into the pharmacodynamic (PD) response. This model suggests a fourfold lower intracellular response after administration of a typical IFN-α dose to an individual as compared to the experimentally observed responses in in vitro setups. In conclusion, this work highlights clear differences between the observed in vitro and in vivo drug effects and provides important suggestions for future model-based study design.

Decreased Methylation of IFNAR Gene Promoter from Peripheral Blood Mononuclear Cells Is Associated with Oxidative Stress in Chronic Hepatitis B

Type I interferons (IFNs) play an antiviral effect by binding to type I interferon receptor (IFNAR). Oxidative stress might induce the gene promoter methylation. The purpose of our study was to evaluate the potential relationship between the methylation of IFNAR promoter and the status of oxidative stress in chronic hepatitis B (CHB). The methylation level of the IFNAR promoter in patients with CHB and healthy controls (HCs) was determined by methylation-specific polymerase chain reaction (MS-PCR). The quantitative real-time PCR (RT-qPCR) was used to evaluate the IFNAR mRNA status in peripheral blood mononuclear cells from CHB and HCs. Level of plasma-soluble IFNAR and oxidative stress parameters, including malondialdehyde (MDA) and glutathione (GSH) were determined by enzyme-linked immunosorbent assay (ELISA). The frequency of IFNAR promoter methylation in CHB patients was significantly lower than that of HCs. The IFNAR mRNA level of patients with CHB was higher than HCs. MDA level was higher in CHB patients, whereas GSH level was lower in CHB patients than that of HCs. In CHB patients, plasma MDA level was significantly higher with IFNAR promoter methylation than unmethylation, and soluble IFNAR in the circulation of methylated patients with CHB was decreased than unmethylated patients with CHB. Our results indicated that the IFNAR promoter methylation might have a potential relationship with the status of oxidative stress.

[Endosomal control of intracellular signaling]

Membrane receptors control essential processes such as cell growth, adhesion, differentiation and metabolism through the activation of specific signaling pathways. Nowadays, these receptors are not only known to signal from the plasma membrane but also from intracellular compartments. Indeed, after being internalized with their ligands via different endocytic pathways, some membrane receptors can initiate signal only after reaching the sorting endosome where they associate with specific protein partners. This review illustrates how this spatio-temporal regulation of signal transduction can occur, with several examples, including interferon receptors which activate JAK/STAT signaling pathways. The literature presented here explains why this control of signaling pathways occuring at the endosomal level creates a higher degree of tuning for the affected cellular processes.

Interferon-α Subtypes As an Adjunct Therapeutic Approach for Human Immunodeficiency Virus Functional Cure

Human immunodeficiency virus (HIV) establishes life-long latency in infected individuals. Although highly active antiretroviral therapy (HAART) has had a significant impact on the course of HIV infection leading to a better long-term outcome, the pool of latent reservoir remains substantial even under HAART. Numerous approaches have been under development with the goal of eradicating the latent HIV reservoir though with limited success. Approaches that combine immune-mediated control of HIV to activate both the innate and the adaptive immune system under suppressive therapy along with "shock and kill" drugs may lead to a better control of the reactivated virus. Interferon-α (IFN-α) is an innate cytokine that has been shown to activate intracellular defenses capable of restricting and controlling HIV. IFN-α, however, harbors numerous functional subtypes that have been reported to display different binding affinities and potency. Recent studies have suggested that certain subtypes such as IFN-α8 and IFN-α14 have potent anti-HIV activity with little or no immune activation, whereas other subtypes such as IFN-α4, IFN-α5, and IFN-α14 activate NK cells. Could these subtypes be used in combination with other strategies to reduce the latent viral reservoir? Here, we review the role of IFN-α subtypes in HIV infection and discuss the possibility that certain subtypes could be potential adjuncts to a "shock and kill" or therapeutic vaccination strategy leading to better control of the latent reservoir and subsequent functional cure.

Endothelial cell functions impaired by interferon in vitro: Insights into the molecular mechanism of thrombotic microangiopathy associated with interferon therapy

INTRODUCTION

Interferon (IFN)-α and IFN-β approved for treatment of chronic hepatitis C viral infection and multiple sclerosis respectively have been linked to thrombotic microangiopathy (TMA) affecting renal function. Since the molecular mechanisms underlying this severe complication remain largely unclear, we aimed to investigate whether IFN affects directly in vitro endothelial cell functions associated with angiogenesis and blood haemostasis, as well as endothelial cell-derived vasodilators of nitric oxide (NO) and prostacyclin.

METHODS

Proliferation and survival of human umbilical vein endothelial cells (HUVECs) were measured by BrdU incorporation and alamarBlue assays. Angiogenesis was evaluated in co-cultures of HUVECs and human dermal fibroblasts. Fibrinolysis molecules were measured with ELISA. NO and prostacyclin were measured using a fluorescent NO-specific probe and a competitive enzyme immunoassay, respectively.

RESULTS

HUVEC proliferation was dose-dependently inhibited by IFN-β1a and IFN-β1b, but not by IFN-α2a and IFN-α2b. Consistently, IFN-β1a and IFN-β1b also reduced survival of HUVECs, but this again was not observed with IFN-α. However, both IFN subtypes inhibited VEGF-induced development of capillary-like structures, but the effect of IFN-α was less potent than IFN-β. In addition, both IFN subtypes upregulated interferon inducible protein 10 production from treated co-cultures while suppressing angiogenesis. Furthermore, intracellular NO generation was reduced by IFN-α2a and IFN-β1a, whereas prostacyclin release from HUVECs was not affected by IFN. Importantly, both IFN-β1a- and IFN-β1b-treated HUVECs showed a marked reduction in urokinase-type plasminogen activator release and a much greater secretion of plasminogen activator inhibitor-1 than tissue-type plasminogen activator compared with untreated cells, suggesting decreased fibrinolytic activity. IFN-α, however was less effective in modulating the fibrinolysis system.

CONCLUSIONS

We demonstrate the detrimental effects of IFN on endothelial cell functions mediated with angiogenesis and fibrinolysis, which could potentially cause the loss of physiological endothelium thromboresistance and facilitate the development of vascular complications in a clinical setting. Mechanistically, our findings have implications for understanding how IFN therapy can foster the development of TMA.

Cutting Edge: Endogenous IFN-β Regulates Survival and Development of Transitional B Cells

The transitional stage of B cell development is a formative stage in the spleen where autoreactive specificities are censored as B cells gain immune competence, but the intrinsic and extrinsic factors regulating survival of transitional stage 1 (T1) B cells are unknown. We report that B cell expression of IFN-β is required for optimal survival and TLR7 responses of transitional B cells in the spleen and was overexpressed in T1 B cells from BXD2 lupus-prone mice. Single-cell gene expression analysis of B6 Ifnb^+/+ versus B6 Ifnb^-⁄- T1 B cells revealed heterogeneous expression of Ifnb in wild-type B cells and distinct gene expression patterns associated with endogenous IFN-β. Single-cell analysis of BXD2 T1 B cells revealed that Ifnb is expressed in early T1 B cell development with subsequent upregulation of Tlr7 and Ifna1 Together, these data suggest that T1 B cell expression of IFN-β plays a key role in regulating responsiveness to external factors.

IFNAR2-dependent gene expression profile induced by IFN-α in Pteropus alecto bat cells and impact of IFNAR2 knockout on virus infection

Bats are important reservoirs of many viruses, which are capable of infecting the host without inducing obvious clinical diseases. Interferon and the downstream interferon regulated genes (IRGs) are known to act as the first line of defense against viral infections. Little is known about the transcriptional profile of genes being induced by interferon in bats and their role in controlling virus infection. In this study, we constructed IFNAR2 knockout bat cell lines using CRISPR technology and further characterized gene expression profiles induced by the most abundant IFN-α (IFN-α3). Firstly, we demonstrated that the CRISPR/Cas9 system is applicable for bat cells as this represents the first CRIPSR knockout cell line for bats. Our results showed the pleiotropic effect of IFN-α3 on the bat kidney cell line, PaKiT03. As expected, we confirmed that IFNAR2 is indispensable for IFN-a signaling pathway and plays an important role in antiviral immunity. Unexpectedly, we also identified novel IFNAR2-dependent IRGs which are enriched in pathways related to cancer. To our knowledge, this seems to be bat-specific as no such observation has been reported for other mammalian species. This study expands our knowledge about bat immunology and the cell line established can provide a powerful tool for future study into virus-bat interaction and cancer biology.

Targeting interferon-alpha to dendritic cells enhances a CD8+ T cell response to a human CD40-targeted cancer vaccine

Targeting antigens to antigen presenting cells (APC) enhances the potency of recombinant protein CD8⁺ T cell vaccines. Recent comparisons of recombinant protein-based dendritic cell (DC) targeting vaccines revealed differences in cross-presentation and identified CD40 as a potent human DC receptor target for antigen cross-presentation. Contrary to in vitro-derived monocyte (mo)DC, we found that interferon-alpha (IFNα) stimulation of human blood-derived DC was necessary for an antigen-specific IFNγ CD8⁺ T cell response to a CD40 targeted cancer vaccine. Importantly, targeting an adjuvant in the form of IFNα to DC increased their potency to elicit antigen-specific production of IFNγ by CD8⁺ T cells. Thus, we introduce the concept of DC adjuvant targeting to enhance the potency of vaccination.

The molecular basis for differential type I interferon signaling

Type I interferons (IFN-1) are cytokines that affect the expression of thousands of genes, resulting in profound cellular changes. IFN-1 activates the cell by dimerizing its two-receptor chains, IFNAR1 and IFNAR2, which are expressed on all nucleated cells. Despite a similar mode of binding, the different IFN-1s activate a spectrum of activities. The causes for differential activation may stem from differences in IFN-1-binding affinity, duration of binding, number of surface receptors, induction of feedbacks, and cell type-specific variations. All together these will alter the signal that is transmitted from the extracellular domain inward. The intracellular domain binds, directly or indirectly, different effector proteins that transmit signals. The composition of effector molecules deviates between different cell types and tissues, inserting an additional level of complexity to the system. Moreover, IFN-1s do not act on their own, and clearly there is much cross-talk between the activated effector molecules by IFN-1 and other cytokines. The outcome generated by all of these factors (processing step) is an observed phenotype, which can be the transformation of the cell to an antiviral state, differentiation of the cell to a specific immune cell, senescence, apoptosis, and many more. IFN-1 activities can be divided into robust and tunable. Antiviral activity, which is stimulated by minute amounts of IFN-1 and is common to all cells, is termed robust. The other activities, which we term tunable, are cell type-specific and often require more stringent modes of activation. In this review, I summarize the current knowledge on the mode of activation and processing that is initiated by IFN-1, in perspective of the resulting phenotypes.

IFNAR1 expression level in Iranian multiple sclerosis patients treated with IFN-B

BACKGROUND

Multiple sclerosis (MS) as an auto-immune disease is an inflammatory, demyelinating disease of the central nervous system. Certain genes have shown to be involved in the initiation of MS but the specific role of some of them, e.g. IFNAR1 has not been identified in certain populations yet.

OBJECTIVE

The IFNAR1 as a type I membrane protein shapes one of the two chains of a receptor for interferons alpha and beta.

METHODS

To find out how IFNAR1 functions in the Iranian population, the researchers compared the expression level of this gene in relapsing-remitting MS (RR-MS) samples with normal individuals. RNA from the whole blood of 50 RR-MS patients and 50 normal controls were extracted. All patients were HLA-DRB1*15 negative and were responders to interferon-beta with a normal vitamin D level. The level of IFNAR1 gene expression was measured using quantitative RT-PCR.

RESULTS

According to the results the RR-MS patients manifested a statistically higher expression level of IFNAR1 than their normal counterparts (p= 0.012). Age-wise, females between the ages, 30 to 40 had a significant increase (p= 0.046) but males under 30 showed a statistically meaningful decrease in the expression level (p= 0.04). In terms of sex, only the female patients manifested a statistically significant increase in IFNAR1 (p= 0.004).

CONCLUSIONS

The overall results show an increase in IFNAR1 level in MS patients treated with IFN-B.

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.

Receptor dimer stabilization by hierarchical plasma membrane microcompartments regulates cytokine signaling

The interaction dynamics of signaling complexes is emerging as a key determinant that regulates the specificity of cellular responses. We present a combined experimental and computational study that quantifies the consequences of plasma membrane microcompartmentalization for the dynamics of type I interferon receptor complexes. By using long-term dual-color quantum dot (QD) tracking, we found that the lifetime of individual ligand-induced receptor heterodimers depends on the integrity of the membrane skeleton (MSK), which also proved important for efficient downstream signaling. By pair correlation tracking and localization microscopy as well as by fast QD tracking, we identified a secondary confinement within ~300-nm-sized zones. A quantitative spatial stochastic diffusion-reaction model, entirely parameterized on the basis of experimental data, predicts that transient receptor confinement by the MSK meshwork allows for rapid reassociation of dissociated receptor dimers. Moreover, the experimentally observed apparent stabilization of receptor dimers in the plasma membrane was reproduced by simulations of a refined, hierarchical compartment model. Our simulations further revealed that the two-dimensional association rate constant is a key parameter for controlling the extent of MSK-mediated stabilization of protein complexes, thus ensuring the specificity of this effect. Together, experimental evidence and simulations support the hypothesis that passive receptor confinement by MSK-based microcompartmentalization promotes maintenance of signaling complexes in the plasma membrane.

Spatiotemporally Controlled Reorganization of Signaling Complexes in the Plasma Membrane of Living Cells

Triggered immobilization of proteins in the plasma membrane of living cells into functional micropatterns is established by using an adaptor protein, which is comprised of an antiGFP nanobody fused to the HaloTag protein. Efficient in situ reorganization of the type I interferon receptor subunits as well as intact, fully functional signaling complexes in living cells are achieved by this method.

Two-Dimensional Trap for Ultrasensitive Quantification of Transient Protein Interactions

We present an ultrasensitive technique for quantitative protein-protein interaction analysis in a two-dimensional format based on phase-separated, micropatterned membranes. Interactions between proteins captured to lipid probes via an affinity tag trigger partitioning into the liquid-ordered phase, which is readily quantified by fluorescence imaging. Based on a calibration with well-defined low-affinity protein-protein interactions, equilibrium dissociation constants >1 mM were quantified. Direct capturing of proteins from mammalian cell lysates enabled us to detect homo- and heterodimerization of signal transducer and activator of transcription proteins. Using the epidermal growth factor receptor (EGFR) as a model system, quantification of low-affinity interactions between different receptor domains contributing to EGFR dimerization was achieved. By exploitation of specific features of the membrane-based assay, the regulation of EGFR dimerization by lipids was demonstrated.

High efficiency cell-specific targeting of cytokine activity

Systemic toxicity currently prevents exploiting the huge potential of many cytokines for medical applications. Here we present a novel strategy to engineer immunocytokines with very high targeting efficacies. The method lies in the use of mutants of toxic cytokines that markedly reduce their receptor-binding affinities, and that are thus rendered essentially inactive. Upon fusion to nanobodies specifically binding to marker proteins, activity of these cytokines is selectively restored for cell populations expressing this marker. This 'activity-by-targeting' concept was validated for type I interferons and leptin. In the case of interferon, activity can be directed to target cells in vitro and to selected cell populations in mice, with up to 1,000-fold increased specific activity. This targeting strategy holds promise to revitalize the clinical potential of many cytokines.

Cloning, identification of the two cytokine receptor family B subunits CRFB1 and CRFB5 from grass carp (Ctenopharyngodon idella)

Similar to the mammalian counterparts, fish type I interferon (IFN) performs its potential biological activities via binding to the corresponding receptor on target cell membrane. Fish type I IFN receptor, a kind of enzyme-linked receptor, consists of two subunits and belongs to the class II cytokine receptor family B (CRFB). In the present study, we cloned and identified two putative grass carp (Ctenopharyngodon idella) type I interferon receptor subunits (termed CiCRFB1 and CiCRFB5) by homology cloning techniques. Phylogenetic tree analysis suggested that CiCRFB1 and CiCRFB5 shared highly homology to Danio rerio CRFB1 and CRFB5 respectively. CiCRFB1 and CiCRFB5 were up-regulated after the stimulation with Grass Carp Hemorrhagic Virus (GCHV) and Polyinosinic-polycytidylic acid (Poly I:C), indicating that they are related to the intracellular antiviral activity. In order to know more about the roles of CiCRFB1 and CiCRFB5 in the process, the extracellular domains of CiCRFB1 (CiCRFB1-EC) and CiCRFB5 (CiCRFB5-EC), as well as grass carp type I IFN (CiIFN) were expressed in Escherichia coli BL21, and purified by affinity chromatography with the Ni-NTA His-Bind resin. Cross-linking reactions were employed to analyze the affinity of the ligand (CiIFN) with the two putative receptor subunits (CiCRFB1-EC and CiCRFB5-EC). The result suggested the formation of (CiCRFB5)2 homodimer was more easily than that of (CiCRFB1)2 under the induction of CiIFN in vitro. However, CiIFN was inclined to bind to (CiCRFB1)2 homodimer. Interestingly, although CiIFN seemed unable to facilitate the formation of (CiCRFB1 + CiCRFB5) heterodimer in the absence of DSS cross linker, however it can bind to the heterodimer in the presence of DSS. This indicated that the homodimer and the heterodimer were the potential receptor for CiIFN.

Receptor dimerization dynamics as a regulatory valve for plasticity of type I interferon signaling

Type I interferons (IFNs) activate differential cellular responses through a shared cell surface receptor composed of the two subunits, IFNAR1 and IFNAR2. We propose here a mechanistic model for how IFN receptor plasticity is regulated on the level of receptor dimerization. Quantitative single-molecule imaging of receptor assembly in the plasma membrane of living cells clearly identified IFN-induced dimerization of IFNAR1 and IFNAR2. The negative feedback regulator ubiquitin-specific protease 18 (USP18) potently interferes with the recruitment of IFNAR1 into the ternary complex, probably by impeding complex stabilization related to the associated Janus kinases. Thus, the responsiveness to IFNα2 is potently down-regulated after the first wave of gene induction, while IFNβ, due to its ∼100-fold higher binding affinity, is still able to efficiently recruit IFNAR1. Consistent with functional data, this novel regulatory mechanism at the level of receptor assembly explains how signaling by IFNβ is maintained over longer times compared with IFNα2 as a temporally encoded cause of functional receptor plasticity.

Dimerization dictates the message

Feedback regulation of receptor dimerization determines the cell’s response to different interferons.

Structural Insights into the Neutralization Properties of the Fully Human, Anti-interferon Monoclonal Antibody Sifalimumab

We report the three-dimensional structure of human interferon α-2A (IFN-α2A) bound to the Fab fragment of a therapeutic monoclonal antibody (sifalimumab; IgG1/κ). The structure of the corresponding complex was solved at a resolution of 3.0 Å using molecular replacement and constitutes the first reported structure of a human type I IFN bound to a therapeutic antibody. This study revealed the major contribution made by the first complementarity-determining region in each of sifalimumab light and heavy chains. These data also provided the molecular basis for sifalimumab mechanism of action. We propose that its interferon-neutralizing properties are the result of direct competition for IFN-α2A binding to the IFN receptor subunit 1 (IFNAR1) and do not involve inhibiting IFN-α2A binding to the IFN receptor subunit 2 (IFNAR2).

Immunosensor for trace penicillin G detection in milk based on supported bilayer lipid membrane modified with gold nanoparticles

In this work, we developed an immunosensor for electrochemical detection of penicillin G at trace level. The biosensor was fabricated by immobilizing anti-penicillin G in a supported bilayer lipid membrane (s-BLM) modified with gold nanoparticles, and the modified electrodes were characterized by the scanning electron microscope (SEM), cyclic voltammetry and electrochemical impedance spectroscopy. The biosensor was able to detect penicillin G with a linear correlation ranging from 3.34×10(-3)ng/L to 3.34×10(3)ng/L and a detection limit of 2.7×10(-4)ng/L, much lower than the maximum residue limit (MRL) of penicillin G in milk (4ppb, equal to 4×10(3)ng/L) set out by the European Union. The mean coefficient variation (CV) of the intra-assays and the inter-assays were 5.4% and 7.7%, respectively. In addition, the concentration of penicillin G in milk samples determined by this biosensor was in good agreement with that determined by high performance liquid chromatography (HPLC) assay.

Impairment of type I but not type III IFN signaling by hepatitis C virus infection influences antiviral responses in primary human hepatocytes

Peginterferon lambda-1a (Lambda), a type III interferon (IFN), acts through a unique receptor complex with limited cellular expression outside the liver which may result in a differentiated tolerability profile compared to peginterferon alfa (alfa). In Phase 2b clinical studies, Lambda administered in combination with ribavirin (RBV) was efficacious in patients with hepatitis C virus (HCV) infection representing genotypes 1 through 4, and was associated with more rapid declines in HCV RNA compared to alfa plus RBV. To gain insights into potential mechanisms for this finding, we investigated the effects of HCV replication on IFN signaling in primary human hepatocytes (PHH) and in induced hepatocyte-like cells (iHLCs). HCV infection resulted in rapid down-regulation of the type I IFN-α receptor subunit 1 (IFNAR1) transcript in hepatocytes while the transcriptional level of the unique IFN-λ receptor subunit IL28RA was transiently increased. In line with this observation, IFN signaling was selectively impaired in infected cells upon stimulation with alfa but not in response to Lambda. Importantly, in contrast to alfa, Lambda was able to induce IFN-stimulated gene (ISG) expression in HCV-infected hepatocytes, reflecting the onset of innate responses. Moreover, global transcriptome analysis in hepatocytes indicated that Lambda stimulation prolonged the expression of various ISGs that are potentially beneficial to antiviral defense mechanisms. Collectively, these observed effects of HCV infection on IFN receptor expression and signaling within infected hepatocytes provide a possible explanation for the more pronounced early virologic responses observed in patients treated with Lambda compared to alfa.

Live cell micropatterning reveals the dynamics of signaling complexes at the plasma membrane

The use of micropatterned surfaces that bind HaloTag fusion proteins allows spatial organization of plasma membrane proteins for efficient visualization and quantification of protein–protein interactions in live cells.

Interactions of proteins in the plasma membrane are notoriously challenging to study under physiological conditions. We report in this paper a generic approach for spatial organization of plasma membrane proteins into micropatterns as a tool for visualizing and quantifying interactions with extracellular, intracellular, and transmembrane proteins in live cells. Based on a protein-repellent poly(ethylene glycol) polymer brush, micropatterned surface functionalization with the HaloTag ligand for capturing HaloTag fusion proteins and RGD peptides promoting cell adhesion was devised. Efficient micropatterning of the type I interferon (IFN) receptor subunit IFNAR2 fused to the HaloTag was achieved, and highly specific IFN binding to the receptor was detected. The dynamics of this interaction could be quantified on the single molecule level, and IFN-induced receptor dimerization in micropatterns could be monitored. Assembly of active signaling complexes was confirmed by immunostaining of phosphorylated Janus family kinases, and the interaction dynamics of cytosolic effector proteins recruited to the receptor complex were unambiguously quantified by fluorescence recovery after photobleaching.

Rapid transfer of transmembrane proteins for single molecule dimerization assays in polymer-supported membranes

Dimerization of transmembrane receptors is a key regulatory factor in cellular communication, which has remained challenging to study under well-defined conditions in vitro. We developed a novel strategy to explore membrane protein interactions in a controlled lipid environment requiring minute sample quantities. By rapid transfer of transmembrane proteins from mammalian cells into polymer-supported membranes, membrane proteins could be efficiently fluorescence labeled and reconstituted with very low background. Thus, differential ligand-induced dimerization of the type I interferon (IFN) receptor subunits IFNAR1 and IFNAR2 could be probed quantitatively at physiologically relevant concentrations by single molecule imaging. These measurements clearly support a regulatory role of the affinity of IFNs toward IFNAR1 for controlling the level of receptor dimerization.

Anti-CD138-targeted interferon is a potent therapeutic against multiple myeloma

Multiple myeloma (MM), a plasma cell malignancy, is the second most prevalent hematologic malignancy in the US. Although much effort has been made trying to understand the etiology and the complexities of this disease with the hope of developing effective therapies, MM remains incurable at this time. Because of their antiproliferative and proapoptotic activities, interferons (IFNs) have been used to treat various malignancies, including MM. Although some success has been observed, the inherent toxicities of IFNs limit their efficacy. To address this problem, we produced anti-CD138 antibody fusion proteins containing either IFNα2 or a mutant IFNα2 (IFNα2(YNS)) with the goal of targeting IFN to CD138-expressing cells, thereby achieving effective IFN concentrations at the site of the tumor in the absence of toxicity. The fusion proteins inhibited the proliferation and induced apoptosis of U266, ANBL-6, NCI-H929, and MM1-144 MM cell lines. The fusion proteins decreased the expression of IFN regulatory factor 4 (IRF4) in U266. In addition, the fusion proteins were effective against primary cells from MM patients, and treatment with fusion proteins prolonged survival in the U266 murine model of MM. These studies show that IFNα antibody fusion proteins can be effective novel therapeutics for the treatment of MM.

Unraveling the convoluted biological roles of type I interferons in infection and immunity: a way forward for therapeutics and vaccine design

It has been well-established that type I interferons (IFN-Is) have pleiotropic effects and play an early central role in the control of many acute viral infections. However, their pleiotropic effects are not always beneficial to the host and in fact several reports suggest that the induction of IFN-Is exacerbate disease outcomes against some bacterial and chronic viral infections. In this brief review, we probe into this mystery and try to develop answers based on past and recent studies evaluating the roles of IFN-Is in infection and immunity as this is vital for developing effective IFN-Is based therapeutics and vaccines. We also discuss the biological roles of an emerging IFN-I, namely IFN-ε, and discuss its potential use as a mucosal therapeutic and/or vaccine adjuvant. Overall, we anticipate the discussions generated in this review will provide new insights for better exploiting the biological functions of IFN-Is in developing efficacious therapeutics and vaccines in the future.

Multifaceted activities of type I interferon are revealed by a receptor antagonist

Type I interferons (IFNs), including various IFN-α isoforms and IFN-β, are a family of homologous, multifunctional cytokines. IFNs activate different cellular responses by binding to a common receptor that consists of two subunits, IFNAR1 and IFNAR2. In addition to stimulating antiviral responses, they also inhibit cell proliferation and modulate other immune responses. We characterized various IFNs, including a mutant IFN-α2 (IFN-1ant) that bound tightly to IFNAR2 but had markedly reduced binding to IFNAR1. Whereas IFN-1ant stimulated antiviral activity in a range of cell lines, it failed to elicit immunomodulatory and antiproliferative activities. The antiviral activities of the various IFNs tested depended on a set of IFN-sensitive genes (the "robust" genes) that were controlled by canonical IFN response elements and responded at low concentrations of IFNs. Conversely, these elements were not found in the promoters of genes required for the antiproliferative responses of IFNs (the "tunable" genes). The extent of expression of tunable genes was cell type-specific and correlated with the magnitude of the antiproliferative effects of the various IFNs. Although IFN-1ant induced the expression of robust genes similarly in five different cell lines, its antiviral activity was virus- and cell type-specific. Our findings suggest that IFN-1ant may be a therapeutic candidate for the treatment of specific viral infections without inducing the immunomodulatory and antiproliferative functions of wild-type IFN.

Soluble IFN receptor potentiates in vivo type I IFN signaling and exacerbates TLR4-mediated septic shock

Circulating levels of a soluble type I IFNR are elevated in diseases, such as chronic inflammation, infections, and cancer, but whether it functions as an antagonist, agonist, or transporter is unknown. In this study, we elucidate the in vivo importance of the soluble type I IFNAR, soluble (s)IFNAR2a, which is generated by alternative splicing of the Ifnar2 gene. A transgenic mouse model was established to mimic the 10-15-fold elevated expression of sIFNAR2a observed in some human diseases. We generated transgenic mouse lines, designated SolOX, in which the transgene mRNA and protein-expression patterns mirrored the expression patterns of the endogenous gene. SolOX were demonstrated to be more susceptible to LPS-mediated septic shock, a disease model in which type I IFN plays a crucial role. This effect was independent of "classical" proinflammatory cytokines, such as TNF-α and IL-6, whose levels were unchanged. Because the increased levels of sIFNAR2a did not affect the kinetics of the increased interferonemia, this soluble receptor does not potentiate its ligand signaling by improving IFN pharmacokinetics. Mechanistically, increased levels of sIFNAR2a are likely to facilitate IFN signaling, as demonstrated in spleen cells overexpressing sIFNAR2a, which displayed quicker, higher, and more sustained activation of STAT1 and STAT3. Thus, the soluble IFNR is an important agonist of endogenous IFN actions in pathophysiological processes and also is likely to modulate the therapeutic efficacy of clinically administered IFNs.

Multifarious determinants of cytokine receptor signaling specificity

Cytokines play crucial roles in regulating immune homeostasis. Two important characteristics of most cytokines are pleiotropy, defined as the ability of one cytokine to exhibit diverse functionalities, and redundancy, defined as the ability of multiple cytokines to exert overlapping activities. Identifying the determinants for unique cellular responses to cytokines in the face of shared receptor usage, pleiotropy, and redundancy will be essential in order to harness the potential of cytokines as therapeutics. Here, we discuss the biophysical (ligand-receptor geometry and affinity) and cellular (receptor trafficking and intracellular abundance of signaling molecules) parameters that contribute to the specificity of cytokine bioactivities. Whereas the role of extracellular ternary complex geometry in cytokine-induced signaling is still not completely elucidated, cytokine-receptor affinity is known to impact signaling through modulation of the stability and kinetics of ternary complex formation. Receptor trafficking also plays an important and likely underappreciated role in the diversification of cytokine bioactivities but it has been challenging to experimentally probe trafficking effects. We also review recent efforts to quantify levels of intracellular signaling components, as second messenger abundance can affect cytokine-induced bioactivities both quantitatively and qualitatively. We conclude by discussing the application of protein engineering to develop therapeutically relevant cytokines with reduced pleiotropy and redirected biological functionalities.

Anti-CD20-interferon-β fusion protein therapy of murine B-cell lymphomas

Type I interferons (IFNα/β) are cytokines with a broad spectrum of antitumor activities including antiproliferative, proapoptotic, and immunostimulatory effects, and are potentially useful in the treatment of B-cell malignancies and other cancers. To improve antitumor potency and diminish the systemic side effects of IFN, we recently developed anti-CD20-IFNα fusion proteins with in vitro and in vivo efficacy against both mouse and human lymphomas expressing CD20. As IFNβ binds more tightly to the IFNα/β receptor (IFNAR) and has more potent antitumor activities, we have now constructed an anti-CD20 fusion protein with murine IFNβ (mIFNβ). Anti-CD20-mIFNβ was more potent than recombinant mIFNβ and anti-CD20-mIFNα in inhibiting the proliferation of a mouse B-cell lymphoma expressing human CD20 (38C13-huCD20). Growth inhibition was accompanied by caspase-independent apoptosis and DNA fragmentation. The efficacy of anti-CD20-mIFNβ required the physical linkage of mIFNβ to anti-CD20 antibody. Importantly, anti-CD20-mIFNβ was active against tumor cells expressing low levels of IFNAR (38C13-huCD20 IFNAR). In vivo, established 38C13-huCD20 tumors were largely insensitive to rituximab or a nontargeted mIFNβ fusion protein, yet treatment with anti-CD20-mIFNβ eradicated 83% of tumors. Anti-CD20-mIFNβ was also more potent in vivo against 38C13-huCD20 than anti-CD20-mIFNα, curing 75% versus 25% of tumors (P=0.001). Importantly, although anti-CD20-mIFNα could not eradicate 38C13-huCD20 IFNAR tumors, anti-CD20-mIFNβ treatment prolonged survival (P=0.0003), and some animals remained tumor-free. Thus, antibody fusion proteins targeting mIFNβ to tumors show promise as therapeutic agents, especially for use against tumors resistant to the effects of mIFNα.

Induction and control of the type I interferon pathway by Bluetongue virus

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A general review describing the current knowledge on the type I IFN pathway.

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Description of several mechanisms evolved by viruses to counteract this antiviral response.

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An up-to-date review on the interaction of BTV and the type I IFN pathway in vivo and in vitro.

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Description of the cellular sensors involved in the induction of IFN-α/β synthesis upon BTV infection in haematopoietic and non-haematopoietic cells.

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Description of the strategies evolved by BTV to counteract this cellular antiviral response.

The innate immune response is the first line of defence against viruses, involving the production of type I IFN (IFN-α/β) and other pro-inflammatory cytokines that control the infection. It also shapes the adaptive immune response generated by both T and B cells. Production of type I IFN occurs both in vivo and in vitro in response to Bluetongue virus (BTV), an arthropod-borne virus. However, the mechanisms responsible for the production of IFN-β in response to BTV remained unknown until recently and are still not completely understood. In this review, we describe the recent advances in the identification of cellular sensors and signalling pathways involved in this process. The RNA helicases retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) were shown to be involved in the expression of IFN-β as well as in the control of BTV infection in non-haematopoietic cells. In contrast, induction of IFN-α/β synthesis in sheep primary plasmacytoid dendritic cells (pDCs) required the MyD88 adaptor independently of the Toll-like receptor 7 (TLR7), as well as the kinases dsRNA-activated protein kinase (PKR) and stress-activated protein kinase (SAPK)/Jun N-terminal protein kinase (JNK). As type I IFN is essential for the establishment of an antiviral cellular response, most of viruses have elaborated counteracting mechanisms to hinder its action. This review also addresses the ability of BTV to interfere with IFN-β synthesis and the recent findings describing the non-structural viral protein NS3 as a powerful antagonist of the host cellular response.

Ligand-independent interaction of the type I interferon receptor complex is necessary to observe its biological activity

Ectopic coexpression of the two chains of the Type I and Type III interferon (IFN) receptor complexes (IFN-αR1 and IFN-αR2c, or IFN-λR1 and IL-10R2) yielded sensitivity to IFN-alpha or IFN-lambda in only some cells. We found that IFN-αR1 and IFN-αR2c exhibit FRET only when expressed at equivalent and low levels. Expanded clonal cell lines expressing both IFN-αR1 and IFN-αR2c were sensitive to IFN-alpha only when IFN-αR1 and IFN-αR2c exhibited FRET in the absence of human IFN-alpha. Coexpression of RACK-1 or Jak1 enhanced the affinity of the interaction between IFN-αR1 and IFN-αR2c. Both IFN-αR1 and IFN-αR2c exhibited FRET with Jak1 and Tyk2. Together with data showing that disruption of the preassociation between the IFN-gamma receptor chains inhibited its biological activity, we propose that biologically active IFN receptors require ligand-independent juxtaposition of IFN receptor chains assisted by their associated cytosolic proteins.