Different relative activities of human cell-derived interferon-alpha subtypes: IFN-alpha 8 has very high antiviral potency

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.

Functional Interfaces, Biological Pathways, and Regulations of Interferon-Related DNA Damage Resistance Signature (IRDS) Genes

Interferon (IFN)-related DNA damage resistant signature (IRDS) genes are a subgroup of interferon-stimulated genes (ISGs) found upregulated in different cancer types, which promotes resistance to DNA damaging chemotherapy and radiotherapy. Along with briefly discussing IFNs and signalling in this review, we highlighted how different IRDS genes are affected by viruses. On the contrary, different strategies adopted to suppress a set of IRDS genes (STAT1, IRF7, OAS family, and BST2) to induce (chemo- and radiotherapy) sensitivity were deliberated. Significant biological pathways that comprise these genes were classified, along with their frequently associated genes (IFIT1/3, IFITM1, IRF7, ISG15, MX1/2 and OAS1/3/L). Major upstream regulators from the IRDS genes were identified, and different IFN types regulating these genes were outlined. Functional interfaces of IRDS proteins with DNA/RNA/ATP/GTP/NADP biomolecules featured a well-defined pharmacophore model for STAT1/IRF7-dsDNA and OAS1/OAS3/IFIH1-dsRNA complexes, as well as for the genes binding to GDP or NADP+. The Lys amino acid was found commonly interacting with the ATP phosphate group from OAS1/EIF2AK2/IFIH1 genes. Considering the premise that targeting IRDS genes mediated resistance offers an efficient strategy to resensitize tumour cells and enhances the outcome of anti-cancer treatment, this review can add some novel insights to the field.

Shared and Unique Features of Human Interferon-Beta and Interferon-Alpha Subtypes

Type I interferons (IFN-I) were first discovered as an antiviral factor by Isaacs and Lindenmann in 1957, but they are now known to also modulate innate and adaptive immunity and suppress proliferation of cancer cells. While much has been revealed about IFN-I, it remains a mystery as to why there are 16 different IFN-I gene products, including IFNβ, IFNω, and 12 subtypes of IFNα. Here, we discuss shared and unique aspects of these IFN-I in the context of their evolution, expression patterns, and signaling through their shared heterodimeric receptor. We propose that rather than investigating responses to individual IFN-I, these contexts can serve as an alternative approach toward investigating roles for IFNα subtypes. Finally, we review uses of IFNα and IFNβ as therapeutic agents to suppress chronic viral infections or to treat multiple sclerosis.

Immunopathogenesis of infectious bronchitis virus Q1 in specific pathogen free chicks

The immunopathogenesis of avian coronavirus, infectious bronchitis virus (IBV) Q1, was investigated in specific pathogen free chicks. Following infection, chicks exhibited respiratory clinical signs and reduced body weight. Oropharyngeal (OP) and cloacal (CL) swabs were collected at intervals and found to be RT-PCR positive, with a greater number of partial-S1 amino acid changes noted in CL swabs compared to OP swabs. In tissue samples, IBV viral load peaked 9 days post infection (dpi) in the trachea and kidneys, and 14 dpi in the proventriculus. At 28 dpi, ELISA data showed that 63% of infected chicks seroconverted. There was significantly higher mRNA up-regulation of IFN-α, TLR3, MDA5, LITAF, IL-1β and IL-6 in the trachea compared to the kidneys. Findings presented here demonstrate that this Q1 isolate induces greater lesions and host innate immune responses in chickens' tracheas compared to the kidneys.

Evaluation of a single amino acid substitution at position 79 of human IFN-α2b in interferon-receptor assembly and activity

Type I interferons (IFNs) are homologous cytokines that bind to a cell surface receptor and establish signaling pathways that motivate immune responses. The purpose of the current study is to assess the activity of a novel-engineered IFN-α2b. The crystallographic structure of IFN-α2b and its receptors was acquired from Protein Data Bank. Various amino acid substitutions were designed based on structural properties and other biological characteristics of residues to find the most effective amino acid on IFN affinity to advanced activities. The IFN-α2b mutants and receptors have been modeled and the interactions between two proteins have been studied as in silico by protein-protein docking for both mutants and native forms. The proper nucleic acid sequence IFN-α2 (T79Q) has been prepared based on the selected mutant. The modified IFN gene was cloned in pcDNA 3.1(-) and introduced to Chinese Hamster Ovary (CHO) cell line. Antiviral and antiproliferative assays of native and IFN-α2 (T79Q) proteins were performed in vitro. The results showed two-fold increasing in IFN-α2 (T79Q) activity (antiviral and antiproliferative activity) in comparison to native IFN-α2b. This engineered IFN-α2b may have significant novel therapeutic applications and in silico studies can be an influential method for practical research function and structure of these molecules.

Dose-Dependent Differences in HIV Inhibition by Different Interferon Alpha Subtypes While Having Overall Similar Biologic Effects

Elucidating the functional role of the IFN-α subtypes is of particular importance for the development of efficacious therapies using exogenous IFN-α. Specifically, this will help define whether IFN therapy should be based on the use of pathogen-dependent IFN subtypes or, rather, IFN mutants with optimized IFNAR binding properties.

Type I interferons (IFNs) are key players in the antiviral immune response. Interferon alpha (IFN-α) belongs to this class of IFNs and comprises 12 subtypes that differ from each other in their binding affinities for a common receptor and, thus, in their signaling potencies. Recent data suggest that IFN-α6 and -α14 are the most potent IFN-α subtypes in restricting HIV replication when applied exogenously. However, in the context of antiviral therapy, IFNs are administered at high doses, which may compensate for differences in potency seen between IFN-α subtypes. In this study, we reexamined whether IFN-α subtypes induce different biological activities, with a focus on how IFN-α treatment dose affects cellular responses to HIV in primary CD4⁺ T cells, peripheral blood mononuclear cells (PBMCs), and macrophages. We found that the subtypes’ antiviral activities were dose dependent, with >90% inhibition of HIV replication at a high dose of all IFN-αs except the weak IFN-α/β receptor (IFNAR) binder, IFN-α1. The quality of the responses engendered by IFN-α1, -α2, -α6, and -α14 was highly comparable, with essentially the same set of genes induced by all four subtypes. Hierarchal cluster analysis revealed that the individual donors were stronger determinants for the IFN-stimulated-gene (ISG) responses than the specific IFN-α subtype used for stimulation. Notably, IFN-α2-derived mutants with substantially reduced IFNAR2 binding still inhibited HIV replication efficiently, whereas mutants with increased IFNAR1 binding potentiated antiviral activity. Overall, our results support the idea that IFN-α subtypes do not induce different biological responses, given that each subtype is exogenously applied at bioequivalent doses.

IMPORTANCE Elucidating the functional role of the IFN-α subtypes is of particular importance for the development of efficacious therapies using exogenous IFN-α. Specifically, this will help define whether IFN therapy should be based on the use of pathogen-dependent IFN subtypes or, rather, IFN mutants with optimized IFNAR binding properties.

TLR3 agonism re-establishes CNS immune competence during α4-integrin deficiency

OBJECTIVE

Natalizumab blocks α4-integrin-mediated leukocyte migration into the central nervous system (CNS). It diminishes disease activity in multiple sclerosis (MS), but carries a high risk of progressive multifocal encephalopathy (PML), an opportunistic infection with JV virus that may be prompted by diminished CNS immune surveillance. The initial host response to viral infections entails the synthesis of type I interferons (IFN) upon engagement of TLR3 receptors. We hypothesized that TLR3 agonism reestablishes CNS immune competence in the setting of α4-integrin deficiency.

METHOD

We generated the conditional knock out mouse strain Mx1.Cre+ α4-integrinfl/fl, in which the α4-integrin gene is ablated upon treatment with the TLR3 agonist poly I:C. Adoptive transfer of purified lymphocytes from poly I:C-treated Mx1.Cre+ α4-integrinfl/fl donors into naive recipients recapitulates immunosuppression under natalizumab. Active experimental autoimmune encephalomyelitis (EAE) in Mx1.Cre+ α4-integrinfl/fl mice treated with poly I:C represents immune-reconstitution.

RESULTS

Adoptive transfer of T cells from poly I:C treated Mx1.Cre+ α4-integrinfl/fl mice causes minimal EAE. The in vitro migratory capability of CD45+ splenocytes from these mice is reduced. In contrast, actively-induced EAE after poly I:C treatment results in full disease susceptibility of Mx1.Cre+ α4-integrinfl/fl mice, and the number and composition of CNS leukocytes is similar to controls. Extravasation of Evans Blue indicates a compromised blood-brain barrier. Poly I:C treatment results in a 2-fold increase in IFN β transcription in the spinal cord.

INTERPRETATION

Our data suggest that TLR3 agonism in the setting of relative α4-integrin deficiency can reestablish CNS immune surveillance in an experimental model. This pathway may present a feasible treatment strategy to treat and prevent PML under natalizumab therapy and should be considered for further experimental evaluation in a controlled setting.

Double-Stranded Ribonucleic Acid-Mediated Antiviral Response Against Low Pathogenic Avian Influenza Virus Infection

Toll-like receptor (TLR)3 signaling pathway is known to induce type 1 interferons (IFNs) and proinflammatory mediators leading to antiviral response against many viral infections. Double-stranded ribonucleic acid (dsRNA) has been shown to act as a ligand for TLR3 and, as such, has been a focus as a potential antiviral agent in many host-viral infection models. Yet, its effectiveness and involved mechanisms as a mediator against low pathogenic avian influenza virus (LPAIV) have not been investigated adequately. In this study, we used avian fibroblasts to verify whether dsRNA induces antiviral response against H₄N₆ LPAIV and clarify whether type 1 IFNs and proinflammatory mediators such as interleukin (IL)-1β are contributing to the dsRNA-mediated antiviral response against H₄N₆ LPAIV. We found that dsRNA induces antiviral response in avian fibroblasts against H₄N₆ LPAIV infection. The treatment of avian fibroblasts with dsRNA increases the expressions of TLR3, IFN-α, IFN-β, and IL-1β. We also confirmed that this antiviral response elicited against H₄N₆ LPAIV infection correlates, but is not attributable to type 1 IFNs or IL-1β. Our findings imply that the TLR3 ligand, dsRNA, can elicit antiviral response in avian fibroblasts against LPAIV infection, highlighting potential value of dsRNA as an antiviral agent against LPAIV infections. However, further investigations are required to determine the potential role of other innate immune mediators or combination of the tested cytokines in the dsRNA-mediated antiviral response against H₄N₆ LPAIV infection.

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.

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.

The kinetics and protection of the antiviral state induced by recombinant iIFN1a in rainbow trout against infectious hematopoietic necrosis virus

The iIFN1a (intracellular IFN-a1), that is one of the IFN-a1 variants, was shown to be functional intracellularly and act as a novel defense against an infectious hematopoietic necrosis virus (IHNV). To determine its antiviral properties, a recombinant iIFN1a was generated in Escherichia coli. Its antiviral activity against IHNV was 1.69×10(7)U/mg in CHSE-214 cells. Additionally, iIFN1a was capable of inducing comparable levels of IRF-1, IRF-2, IFN-I, IFN-γ and Mx transcription in head kidney, spleen and liver tissues at an early time point (6h), that was followed by a rapid decline 24h after induction. The recombinant protein also elicited protection against IHNV in vivo. At 6 and 24h after induction there was 100% protection against the virus, however, at 48 and 72h the protection decreased to 57 and 40%, respectively. The in vivo protection kinetics correlated with the kinetics of gene expression. The results of this study provide details of the antiviral state that was induced by iIFN1a in vivo for the first time. Additionally, this information will facilitate the development of this recombinant protein as a potential anti-viral treatment and/or adjuvant.

Interferon-α Subtypes in an Ex Vivo Model of Acute HIV-1 Infection: Expression, Potency and Effector Mechanisms

HIV-1 is transmitted primarily across mucosal surfaces and rapidly spreads within the intestinal mucosa during acute infection. The type I interferons (IFNs) likely serve as a first line of defense, but the relative expression and antiviral properties of the 12 IFNα subtypes against HIV-1 infection of mucosal tissues remain unknown. Here, we evaluated the expression of all IFNα subtypes in HIV-1-exposed plasmacytoid dendritic cells by next-generation sequencing. We then determined the relative antiviral potency of each IFNα subtype ex vivo using the human intestinal Lamina Propria Aggregate Culture model. IFNα subtype transcripts from the centromeric half of the IFNA gene complex were highly expressed in pDCs following HIV-1 exposure. There was an inverse relationship between IFNA subtype expression and potency. IFNα8, IFNα6 and IFNα14 were the most potent in restricting HIV-1 infection. IFNα2, the clinically-approved subtype, and IFNα1 were both highly expressed but exhibited relatively weak antiviral activity. The relative potencies correlated with binding affinity to the type I IFN receptor and the induction levels of HIV-1 restriction factors Mx2 and Tetherin/BST-2 but not APOBEC3G, F and D. However, despite the lack of APOBEC3 transcriptional induction, the higher relative potency of IFNα8 and IFNα14 correlated with stronger inhibition of virion infectivity, which is linked to deaminase-independent APOBEC3 restriction activity. By contrast, both potent (IFNα8) and weak (IFNα1) subtypes significantly induced HIV-1 GG-to-AG hypermutation. The results unravel non-redundant functions of the IFNα subtypes against HIV-1 infection, with strong implications for HIV-1 mucosal immunity, viral evolution and IFNα-based functional cure strategies.

The type I interferons: Basic concepts and clinical relevance in immune-mediated inflammatory diseases

There is increasing scientific and clinical interest in elucidating the biology of type I Interferons, which began approximately 60 years ago with the concept of "viral interference", a property that reduces the ability of a virus to infect cells. Although our understanding of the multiple cellular and molecular functions of interferons has advanced significantly, much remains to be learned and type I Interferons remain an active and fascinating area of inquiry. In this review, we cover some general aspects of type I interferon genes, with emphasis on interferon-alpha, and various aspects of molecular mechanisms triggered by type I interferons and toll-like receptor signaling by the Janus activated kinase/signal transducer activation of transcription (JAK-STAT) pathway and interferon regulatory factor pathway. We will also describe the role of type I interferons in autoimmune and inflammatory diseases, and its potential use as therapeutic agent.

Characterization of bovine interferon α1: expression in yeast Pichia pastoris, biological activities, and physicochemical characteristics

A bovine interferon α (BoIFNα) gene that included signal sequence was amplified from bovine liver genomic DNA. The gene was named BoIFN-α1 according to the position at which the encoded gene of the bovine IFN was located in the bovine genome. The sequence included a 23-amino-acid signal peptide and a 166-amino-acid mature peptide. The structural characteristics and phylogenetic relationships of the BoIFN-α1 gene were analyzed. A recombinant mature BoIFN-α1 (rBoIFN-α1) was expressed in the yeast Pichia pastoris. Physicochemical characteristics and antiviral activity were determined in vitro. Recombinant BoIFN-α1 was found to be highly sensitive to trypsin and stable at pH 2.0 or 65°C. It also exhibited antiviral activity, which was neutralized by a rabbit anti-rBoIFNα polyclonal antibody. This study revealed that rBoIFN-α1 has the typical characteristics of IFNα and can be used for both research and industrial application.

Expression of human interferon-α8 synthetic gene under P(BAD) promoter

Recombinant human interferon-α8 (rhIFN-α8) was obtained by synthesizing a codon-optimized gene in a two-step polymerase chain reaction (PCR) and expressing it in Escherichia coli. The gene encoding human IFN-α8 shows a high content of rare codons. These were replaced based on E. coli codon usage and balancing TA-GC ratio contents of the entire gene. The two-step PCR was performed using long (45-60 nucleotides) overlapped primers and two Taq polymerases (pfu clone and GC-rich system) and resulted in a DNA band of 504 base pairs (bp) corresponding to the calculated size of the IFN-α8 coding sequence; the pfu clone failed to amplify the gene in the correct size without unspecific bands. The full gene was cloned into the pBAD-TOPO expression vector. After cloning, the gene was reoriented by NcoI restriction digestion and religation. The ligated pBAD-TOPO-IFN-α8 (pBAD-IFNα8) plasmid carried the IFN-α8 gene under transcriptional control of the L-arabinose-inducible P(BAD) promoter. IFN-α8 expression was optimized with respect to L-arabinose concentration, temperature, and time of induction in shake flask cultures to maximize the yield of soluble IFN-α8. The produced IFN-α8 was characterized by polyacrylamide gel electrophoresis and immunoassays. After purification on DEAE-Sepharose, the yield was 100 mg/liter. The antiviral and anticancer activities of the IFN-α8 were evaluated in comparison with IFN-α2a, and the results are discussed.

The differential antiviral activities of chicken interferon α (ChIFN-α) and ChIFN-β are related to distinct interferon-stimulated gene expression

Chicken interferon α (ChIFN-α) and ChIFN-β are type I IFNs that are important antiviral cytokines in the innate immune system. In the present study, we identified the virus-induced expression of ChIFN-α and ChIFN-β in chicken fibroblast DF-1 cells and systematically evaluated the antiviral activities of recombinant ChIFN-α and ChIFN-β by cytopathic-effect (CPE) inhibition assays. We found that ChIFN-α exhibited stronger antiviral activity than ChIFN-β in terms of inhibiting the replication of vesicular stomatitis virus, Newcastle disease virus and avian influenza virus, respectively. To elucidate the mechanism of differential antiviral activities between the two ChIFNs, we measured the relative mRNA levels of IFN-stimulated genes (ISGs) in IFN-treated DF-1 cells by real-time PCR. ChIFN-α displayed greater induction potency than ChIFN-β on several ISGs encoding antiviral proteins and MHC-I, whereas ChIFN-α was less potent than ChIFN-β for inducing ISGs involved in signaling pathways. In conclusion, ChIFN-α and ChIFN-β presented differential induction potency on various sets of ISGs, and the stronger antiviral activity of ChIFN-α is likely attributed to the greater expression levels of downstream antiviral ISGs.

[Population genetics and human immunity: the interferon paradigm]

The evolutionary genetics dissection of immunity-related genes provides insights into immunological defence mechanisms and highlight host pathways playing an important role in pathogen resistance. Recent population genetic data have increased knowledge of the biological relevance of human interferons (IFN), cytokines released by host cells in response to pathogen presence or tumour cells. Some IFN-α subtypes as well as IFN-γ are strongly evolutionarily constrained, suggesting that the functions they fulfil are essential and non redundant. Other IFN, the most extreme cases being IFN-α10 and IFN-ε, can accumulate missense or nonsense mutations at high population frequencies, suggesting higher redundancy. Furthermore, genetic variation at some IFN genes can be advantageous for the host and increase in frequency by positive selection. This has been shown for type III IFN, where mutations at IL28A, IL28B and IL29 have been positively selected in Europeans and Asians, most likely by increasing resistance to viral infection. This review uses the IFN paradigm to illustrate the value of the evolutionary approach in highlighting important determinants of host immune responsiveness in the natural setting.

Expression profiles of human interferon-alpha and interferon-lambda subtypes are ligand- and cell-dependent

Recent genome-wide association studies suggest distinct roles for 12 human interferon-alpha (IFN-α) and 3 IFN-λ subtypes that may be elucidated by defining the expression patterns of these sets of genes. To overcome the impediment of high homology among each of the sets, we designed a quantitative real-time PCR assay that incorporates the use of molecular beacon and locked nucleic acid (LNA) probes, and in some instances, LNA oligonucleotide inhibitors. We then measured IFN subtype expression by human peripheral blood mononuclear cells and by purified monocytes, myeloid dendritic cells (mDC), plasmacytoid dendritic cells (pDC), and monocyte-derived macrophages (MDM), and -dendritic cells (MDDC) in response to poly I:C, lipopolysaccharide (LPS), imiquimod and CpG oligonucleotides. We found that in response to poly I:C and LPS, monocytes, MDM and MDDC express a subtype pattern restricted primarily to IFN-β and IFN-λ1. In addition, while CpG elicited expression of all type I IFN subtypes by pDC, imiquimod did not. Furthermore, MDM and mDC highly express IFN-λ, and the subtypes of IFN-λ are expressed hierarchically in the order IFN-λ1 followed by IFN-λ2, and then IFN-λ3. These data support a model of coordinated cell- and ligand-specific expression of types I and III IFN. Defining IFN subtype expression profiles in a variety of contexts may elucidate specific roles for IFN subtypes as protective, therapeutic or pathogenic mediators.

High-throughput quantitative real-time polymerase chain reaction array for absolute and relative quantification of rhesus macaque types I, II, and III interferon and their subtypes

Rhesus macaques provide a valuable research and preclinical model for cancer and infectious diseases, as nonhuman primates share immune pathways with humans. Interferons (IFNs) are key cytokines in both innate and adaptive immunity, so a detailed analysis of gene expression in peripheral blood and tissues may shed insight into immune responses. Macaques have 18 IFN genes, of which 14 encode for 13 distinct IFN-α subtypes, and one for IFN-β. Here, we developed a high-throughput array to evaluate each of the IFN-α subtypes, as well as IFN-β, IFN-γ and 2 subtypes of IFN-λ. With this array, expression of each IFN species may be quantified as relative to a reference (housekeeping) gene (ΔCq) or fitted to its own 4-point standard curve for absolute quantification (copy number per mass unit RNA). After validating the assay with IFN complementary DNA, we determined the IFN expression profile of peripheral blood mononuclear cells from 3 rhesus macaques in response to TLR agonists, and demonstrated that the profiles are consistent among animals. Furthermore, because the IFN expression profiles differ depending on the TLR stimuli, they suggest different biological functions for many of the IFN species measured, including individual subtypes of IFN-α.

Reduced interferon (IFN)-α conditioned by IFNA2 (-173) and IFNA8 (-884) haplotypes is associated with enhanced susceptibility to severe malarial anemia and longitudinal all-cause mortality

Severe malarial anemia (SMA) is a leading cause of pediatric morbidity and mortality in holoendemic Plasmodium falciparum transmission areas. Although dysregulation in cytokine production is an important etiology of SMA, the role of IFN-α in SMA has not been reported. As such, we investigated the relationship between IFN-α promoter polymorphisms [i.e., IFNA2 (A-173T) and IFNA8 (T-884A)], SMA, and functional changes in IFN-α production in children (n = 663; <36 months) residing in a holoendemic P. falciparum transmission region of Kenya. Children with SMA had lower circulating IFN-α than malaria-infected children without severe anemia (P = 0.025). Multivariate logistic regression analyses revealed that heterozygosity at -884 (TA) was associated with an increased risk of SMA [OR 2.80 (95 % CI 1.22-6.43); P = 0.015] and reduced IFN-α relative to wild type (TT; P = 0.038). Additional analyses demonstrated that carriage of the -173T/-884A (TA) haplotype was associated with increased susceptibility to SMA [OR 3.98 (95 % CI 1.17-13.52); P = 0.026] and lower IFN-α (P = 0.031). Follow-up of these children for 36 months revealed that carriers of TA haplotype had greater all-cause mortality than non-carriers (P < 0.001). Generation of reporter constructs showed that the IFNA8 wild-type -884TT exhibited higher levels of luciferase expression than the variant alleles (P < 0.001). Analyses of malaria-associated inflammatory mediators demonstrated that carriers of TA haplotype had altered production of IL-1β, MIG, and IL-13 compared to non-carriers (P < 0.050). Thus, variation at IFNA2 -173 and IFNA8 -884 conditions reduced IFN-α production, and increased susceptibility to SMA and mortality.

Evolutionary genetic dissection of human interferons

As revealed by population genetic analyses, different human interferon genes evolved under distinct selective constraints and signatures of positive selection vary according to geographic region, suggesting that some sequence changes may have conferred an advantage by increasing resistance to viral infection.

Interferons (IFNs) are cytokines that play a key role in innate and adaptive immune responses. Despite the large number of immunological studies of these molecules, the relative contributions of the numerous IFNs to human survival remain largely unknown. Here, we evaluated the extent to which natural selection has targeted the human IFNs and their receptors, to provide insight into the mechanisms that govern host defense in the natural setting. We found that some IFN-α subtypes, such as IFN-α6, IFN-α8, IFN-α13, and IFN-α14, as well as the type II IFN-γ, have evolved under strong purifying selection, attesting to their essential and nonredundant function in immunity to infection. Conversely, selective constraints have been relaxed for other type I IFNs, particularly for IFN-α10 and IFN-ε, which have accumulated missense or nonsense mutations at high frequencies within the population, suggesting redundancy in host defense. Finally, type III IFNs display geographically restricted signatures of positive selection in European and Asian populations, indicating that genetic variation at these genes has conferred a selective advantage to the host, most likely by increasing resistance to viral infection. Our population genetic analyses show that IFNs differ widely in their biological relevance, and highlight evolutionarily important determinants of host immune responsiveness.

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.

Positive selection of the bat interferon alpha gene family

Type I interferons (IFNs) are produced by leukocytes in reaction to pathogenic infection and function as positive mediators in antiviral pathways. Among IFNs, IFN alpha (IFNA) has the largest number of family members and plays an important role against the invasion of pathogens. Bats are putative and proven vectors for numerous viruses; however, the evolution of the IFNA family in bats has not been addressed. Here, we construct a phylogeny of IFNA families, including one fruit bat (Dobsonia viridis), with other vertebrates as references. Site-model estimation reveals that positive selection has shaped bat IFNA genes, showing that positive selection drives the evolution of bat IFNA genes.

Type I interferons: crucial participants in disease amplification in autoimmunity

A significant body of data implicates the type I interferon (IFN) pathway in the pathogenesis of autoimmune rheumatic diseases. In these disorders, a self-reinforcing cycle of IFN production can contribute to immunopathology through multiple mechanisms. Type I IFN cytokines are pleiotropic in their effects, mediating antiviral and antitumor activities, and possess numerous immunomodulatory functions for both the innate and adaptive immune responses. A key principle of the type I IFN system is rapid induction and amplification of the signaling pathway, which generates a feed-forward loop of IFN production, ensuring that a vigorous antiviral immune response is mounted. Although such feed-forward pathways are highly adaptive when it comes to rapid and effective virus eradication, this amplification can be maladaptive in immune responses directed against host tissues. Such feed-forward loops, however, create special opportunities for therapy.

IFN-alpha expression and antiviral effects are subtype and cell type specific in the cardiac response to viral infection

The interferon-beta (IFN-beta) response is critical for protection against viral myocarditis in several mouse models, and IFN-alpha or -beta treatment is beneficial against human viral myocarditis. The IFN-beta response in cardiac myocytes and cardiac fibroblasts forms an integrated network for organ protection; however, the different IFN-alpha subtypes have not been studied in cardiac cells. We developed a quantitative RT-PCR assay that distinguishes between 13 highly conserved IFN-alpha subtypes and found that reovirus T3D induces five IFN-alpha subtypes in primary cardiac myocyte and fibroblast cultures: IFN-alpha1, -alpha2, -alpha4, -alpha5, and -alpha8/6. Murine IFN-alpha1, -alpha2, -alpha4, or -alpha5 treatment induced IRF7 and ISG56 and inhibited reovirus T3D replication in both cell types. This first investigation of IFN-alpha subtypes in cardiac cells for any virus demonstrates that IFN-alpha is induced in cardiac cells, that it is both subtype and cell type specific, and that it is likely important in the antiviral cardiac response.

Enhanced anti-HCV activity of interferon alpha 17 subtype

BACKGROUND

Pegylated interferon alpha 2 (a or b) plus ribavirin is the most effective treatment of chronic hepatitis C but a large proportion of patients do not respond to therapy. So, it is interesting to improve the treatment efficacy. Interferon alpha is a type I interferon composed of 12 different subtypes. Each subtype signals by the Jak-Stat pathway but modulations in the antiviral activity was previously described.

METHODS

Using the hepatitis C virus (HCV) culture system, we have tested the anti-HCV activity of each interferon alpha subtypes. We have analyzed the effect of each subtype on the HCV multiplication and the cell-signaling pathway for some subtypes.

RESULTS

There were divergent effects of IFN alpha subtypes against HCV. We have found that IFN alpha 17 was three times more efficient than IFN alpha 2a on HCV. This efficiency was related to a stronger stimulation of the Jak-Stat pathway.

CONCLUSION

We suggest that IFN alpha17 should be tested therapeutically with a view to improving treatment efficacy.

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.

Anti-retroviral effects of type I IFN subtypes in vivo

Type I IFN play a very important role in immunity against viral infections. Murine type I IFN belongs to a multigene family including 14 IFN-alpha subtypes but the biological functions of IFN-alpha subtypes in retroviral infections are unknown. We have used the Friend retrovirus model to determine the anti-viral effects of IFN-alpha subtypes in vitro and in vivo. IFN-alpha subtypes alpha1, alpha4, alpha6 or alpha9 suppressed Friend virus (FV) replication in vitro, but differed greatly in their anti-viral efficacy in vivo. Treatment of FV-infected mice with the IFN-alpha subtypes alpha1, alpha4 or alpha9, but not alpha6 led to a significant reduction in viral loads. Decreased splenic viral load after IFN-alpha1 treatment correlated with an expansion of activated FV-specific CD8(+) T cells and NK cells into the spleen, whereas in IFN-alpha4- and -alpha9-treated mice it exclusively correlated with the activation of NK cells. The results demonstrate the distinct anti-retroviral effects of different IFN-alpha subtypes, which may be relevant for new therapeutic approaches.

Severe acute respiratory syndrome coronavirus elicits a weak interferon response compared to traditional interferon-inducing viruses

The aim of the present study is to investigate changes of interferon (IFN) production occurring over the first 48 h after infection of peripheral blood mononuclear cells (PBMCs) with severe acute respiratory syndrome (SARS) coronavirus (CoV) and to compare these changes to those induced by well-established IFN-inducing viruses, such as vesicular stomatitis (VSV) and Newcastle viruses (NDV). Experiments have been carried out using PBMCs of 10 different healthy donors. The results showed that the antiviral activity of IFN contained in the supernatant of SARS-CoV-infected PBMCs was lower than those induced by VSV and NDV. Consequently, SARS-CoV induces a lower synthesis of IFN-alpha, -beta and -gamma compared to VSV and NDV. Characterization of the profile of IFN-alpha subtypes genes expression in SARS-CoV-infected PBMCs demonstrated that the level of IFN-alpha2 and -6 subtypes were higher compared to other IFN-alpha subtypes namely, IFN-alpha5, -8, -10, -13/1, -17, and -21. In conclusion, SARS-CoV induces IFNs to a less extent compared to VSV and NDV, thus suggesting that the IFN system does play a limited role in early host defense against SARS-CoV infection.

Maturation-dependent responses of human neuronal cells to western equine encephalitis virus infection and type I interferons

Innate cell-autonomous antiviral responses are essential first lines of defense against central nervous system infections but may also contribute to neuropathogenesis. We investigated the relationships between innate immunity and neuronal differentiation using an in vitro culture system with human cell lines to analyze cellular responses to the neurotropic alphavirus western equine encephalitis virus. Human neuronal cells displayed a maturation-dependent reduction in virus-induced cytopathology that was independent of autocrine interferon alpha or beta activity. In addition, maturation was associated with enhanced responsiveness to exogenous stimuli, such that differentiated neurons required five- to ten-fold less type I interferon to suppress viral replication or virus-induced cytopathology compared to immature cells, although this enhanced responsiveness extended to only a subset of unique type I interferons. These results demonstrate that maturation-dependent changes in human neuronal cells may be key determinants in the innate immune response to infections with neurotropic alphaviruses.

Similar effects of recombinant interferon-alpha-2b and natural interferon-alpha when combined with intra-arterial 5-fluorouracil for the treatment of advanced hepatocellular carcinoma

AIM

Intra-arterial 5-fluorouracil (5-FU) plus interferon (IFN) combination therapy is effective against advanced hepatocellular carcinoma (HCC) with portal vein tumour thrombosis. In this study, we compared the efficiency and safety of recombinant IFN-alpha-2b with natural IFN-alpha as components of the combination therapy.

METHODS

Consecutive HCC patients (n=31) with portal vein tumour thrombosis were enrolled in this prospective study. They received combination therapy of 5-FU and either recombinant IFN-alpha-2b (R group, n=15) or natural IFN-alpha (N group, n=16). We compared the two groups for the early response rate, adverse reactions, time to progression (TTP) and survival rates. In addition, we assessed the cost-effectiveness of each protocol.

RESULTS

The early response rate (R: 26.7%, N: 31.2%), median TTP (R: 5.8 months, N: 5.6 months) and median survival time (R: 7.5 months, N: 6.5 months) were not significantly different between the R and N groups. There were no differences in adverse reactions between the two groups. The estimated cost-effectiveness ratio of recombinant IFN-alpha-2b was better than natural IFN-alpha.

CONCLUSIONS

In our protocol of combination therapy, there were no significant differences between recombinant IFN-alpha-2b and natural IFN-alpha with regard to early response to therapy, adverse effects, TTP and survival rates. 5-FU could be combined with either recombinant IFN-alpha-2b or natural IFN-alpha, although the cost-effectiveness of the former warrants its use clinically.

The combination of IFN-alpha2 and IFN-alpha8 exhibits synergistic antiproliferative activity on renal cell carcinoma (RCC) cell lines through increased binding affinity for IFNAR-2

Although there are at least 13 interferon-alpha (IFN-alpha) subtypes in humans, interactions between the subtypes remain unknown. To understand IFN-alpha interactions, we examined the antiproliferative activities and the receptor binding affinities of different combinations of IFN-alpha2 and IFN-alpha8 using six renal cell carcinoma (RCC) cell lines. Although IFN-alpha8 was the more potent subtype, synergistic and antagonistic antiproliferative effects were also observed in certain combinations of IFN-alpha2 and IFN-alpha8. To analyze the interactions between IFN-alpha2 and IFN-alpha8, the receptor-binding kinetics of different combinations of IFN-alpha2 and IFN- alpha8 to the IFN-alpha receptors, IFNAR-1 or IFNAR-2, were measured using a surface plasmon resonance-based biosensor. Unexpectedly, the receptor binding kinetics to IFNAR-2 but not to IFNAR-1 were mutually related to antiproliferative activity and increase in the binding speed (K(a)) for IFNAR-2. Moreover, we observed the increased fluorescence intensity (FI) of biotin-labeled IFN-alpha8 to IFNAR-2 by receptor binding inhibition assay with unlabeled IFN-alpha2 but not the other combinations. These findings indicate that the binding manner of IFN-alpha8 for IFNAR-2 is different from that of IFN-alpha2, suggesting that binding of IFN-alpha8 rather than binding of IFN-alpha2 to IFNAR-2 leads to activation and subsequent antiproliferative activity despite the same antiviral activity in RCC.

Suppression of innate immune cytokines and interferon regulatory factor-1 by endogenous interferon-alpha in response to respiratory syncytial virus in neonate mononuclear cells

Respiratory syncytial virus (RSV) infections are extremely common in early childhood but are most severe in infants in the first few months of life. Unresponsive adaptive immunity and hyporesponsive innate immunity were previously found to be the typical responses of neonate mononuclear cells (MCs) to live RSV. Investigating the mechanism of innate immune hyporesponsiveness in neonate MCs to live RSV revealed that in contrast to the previously reported low expression of interferon (IFN)-gamma, IFN-alpha expression in response to live RSV was significantly greater than that observed in adult MCs. Inhibition of live RSV-induced IFN-alpha with anti-IFN-alpha antibodies in neonate MCs led to significant increases in innate cytokine [IFN-gamma, interleukin (IL)-12, IL-18 and tumor necrosis factor (TNF)-alpha] but not adaptive immune cytokine [IL-2] production. Although MCs from adults responded to live RSV with upregulation of interferon regulatory factor-1 (IRF-1) mRNA, IRF-1 mRNA in RSV-treated neonate MCs was not detectable. However, in the presence of anti-IFN-alpha antibodies, live RSV induced detectable IRF-1 mRNA expression in neonate MCs. These data support the possibility that the severity of early life RSV-induced illnesses may occur via a mechanism in which live RSV induces IFN-alpha that in turn leads to innate immune suppression in neonate MCs.

Gene cloning, sequencing, expression and biological activity of giant panda (Ailuropoda melanoleuca) interferon-alpha

The giant panda (Ailuropoda melanoleuca) is an endangered species and indigenous to China. In mammals, multiple subtypes of interferon-alpha (IFN-alpha) exist, most of which possess antiviral activity. Little is known about giant panda IFN-alpha genes and the role they may play in giant panda immunological responses to viruses. We have cloned genes encoding 12 giant panda IFN-alpha (AmIFN-alpha or AmIFNA) subtypes that share from 90 to 99% amino acid sequence identity. AmIFN-alpha12 has one additional amino acid at position 57, which is not present in other subtypes. Sequence identity of the AmIFN-alpha proteins encoded by the 12 genes compared to human IFN-alpha2 is approximately 58%. Unlike most of the human subtypes, each of the 12 giant panda IFN sequences has an N-glycosylation recognition site. Expression of all 12 AmIFN-alpha subtypes in 293 cells was confirmed by SDS-PAGE and Western blotting analysis. The antiviral activity and antiproliferative activity of each AmIFN-alpha subtype produced in transiently transfected 293 cell cultures were tested in vitro. All AmIFN-alpha subtypes were found to be stable at pH 2 or 65 degrees C and to exhibit antiviral activity. Some IFN subtypes (AmIFN-alpha8 and AmIFN-alpha4) showed higher biological activity levels than others, whereas AmIFN-alpha11 exhibited lower activity. AmIFN-alpha had various antiproliferative activities to different target cells. To B16 cells, AmIFN-alpha3, AmIFN-alpha4, AmIFN-alpha8 had the highest activities, while to K562 cells, AmIFN-alpha3, AmIFN-alpha7, AmIFN-alpha10 had the highest activities. The various IFN-alpha subtypes displayed a good correlation between their antiviral and antiproliferative potencies.

Chemiluminescent imaging analysis of interferon alpha in serum samples

Enzyme-linked immunosorbent assay (ELISA), horseradish peroxidase (HRP)-catalyzed fluorescent reaction, and oxalate chemiluminescence imaging analysis have been combined to develop a sensitive, simple, and rapid method for analysis of interferon alpha (alpha-IFN) in human serum samples. A typical "sandwich type" immunoassay was used. Reaction of o-phenylenediamine (OPD) with hydrogen peroxide (H(2)O(2)), catalyzed by HRP, produced 2,3-diaminophenazine (PDA), which was detected by chemiluminescence imaging analysis with the bis(2,4,6-trichlorophenyl)oxalate (TCPO)-H(2)O(2)-glyoxaline-PDA chemiluminescent system. The TCPO chemiluminescent imaging system is more sensitive and the chemiluminescence quantum yield is at least five times higher than for the luminol-H(2)O(2)-HRP-PIP (p-iodophenol) chemiluminescent imaging system. The results showed there was a very good linear correlation between response and amount of alpha-IFN in the range 1.3-156.0 pg mL(-1) (R = 0.9991) and the detection limit was 0.8 pg mL(-1) (S/N=3). The relative standard deviation (n = 9) was 4.7%. The proposed method has been used for successful analysis of the amount of alpha-IFN in human serum. The results obtained compared well with those obtained by conventional colorimetric ELISA and luminol chemiluminescent ELISA.

Hepatitis C Virus (HCV) Core Protein-Induced, Monocyte-Mediated Mechanisms of Reduced IFN-α and Plasmacytoid Dendritic Cell Loss in Chronic HCV Infection

IFN-alpha production by plasmacytoid dendritic cells (PDCs) is critical in antiviral immunity. In the present study, we evaluated the IFN-alpha-producing capacity of PDCs of patients with chronic hepatitis C virus (HCV) infection in treatment-naive, sustained responder, and nonresponder patients. IFN-alpha production was tested in PBMCs or isolated PDCs after TLR9 stimulation. Treatment-naive patients with chronic HCV infection had reduced frequency of circulating PDCs due to increased apoptosis and showed diminished IFN-alpha production after stimulation with TLR9 ligands. These PDC defects correlated with the presence of HCV and were in contrast with normal PDC functions of sustained responders. HCV core protein, which was detectable in the plasma of infected patients, reduced TLR9-triggered IFN-alpha and increased TNF-alpha and IL-10 production in PBMCs but not in isolated PDCs, suggesting HCV core induced PDC defects. Indeed, addition of rTNF-alpha and IL-10 induced apoptosis and inhibited IFN-alpha production in PDCs. Neutralization of TNF-alpha and/or IL-10 prevented HCV core-induced inhibition of IFN-alpha production. We identified CD14+ monocytes as the source of TNF-alpha and IL-10 in the HCV core-induced inhibition of PDC IFN-alpha production. Anti-TLR2-, not anti-TLR4-, blocking Ab prevented the HCV core-induced inhibition of IFN-alpha production. In conclusion, our results suggest that HCV interferes with antiviral immunity through TLR2-mediated monocyte activation triggered by the HCV core protein to induce cytokines that in turn lead to PDC apoptosis and inhibit IFN-alpha production. These mechanisms are likely to contribute to HCV viral escape from immune responses.

Growth inhibitory effects of interferon-alpha subtypes vary according to human liver cancer cell lines

BACKGROUND

Interferon (IFN)-alpha preparations used in the treatment of viral and neoplastic disease consist of single or multiple IFN-alpha subtypes that may possess different biological activity, but there are no data on liver cancer cells.

METHODS

Antiproliferative effects and the mechanisms of growth inhibition of five IFN-alpha subtypes (alpha1, alpha2, alpha5, alpha8 and alpha10) were examined in vitro using 13 human liver cancer cell lines.

RESULTS

The antiproliferative effect of each IFN-alpha subtype was different in each cell line. The 50% growth inhibitory concentration (IC50) on an antiviral unit basis showed that alpha5 presented the most potent antiproliferative effects in 11 of the 13 cell lines, and alpha8 in two cell lines. On average, the antiproliferative effects were strong in descending order from alpha5, alpha8, alpha10, alpha2 to alpha1. On weight basis, the most potent antiproliferative effect was shown by alpha8 in nine of the 13 cell lines, alpha5 in four cell lines, and the potency of the effects on average in descending order was alpha8, alpha5, alpha10, alpha2 and alpha1. No significant difference was observed between natural and recombinant alpha2. The mechanism of growth inhibition of each subtype in HAK-1B and KMCH-1 cell lines were apoptosis and S-phase arrest, and their induction levels were related to a certain degree to the antiproliferative effects.

CONCLUSIONS

Our findings show that the antiproliferative effect of each IFN-alpha subtype varies according to the cell line, but that the cells are relatively or absolutely responsive to alpha5 and alpha8 subtypes.

Complex Modulation of Cell Type-Specific Signaling in Response to Type I Interferons

The type I interferons (IFNs) are pleiotropic cytokines that regulate many different cellular functions. The major signaling pathway activated by type I IFNs involves sequential phosphorylation of the tyrosine residues of the Janus kinase (JAK) and signal transducers and activators of transcription (STAT) proteins, providing the primary mechanism through which gene expression is induced. Recent work has shown that the responses are quite complex, as shown by different responses to specific subtypes of type I IFN, activation of kinases in addition to JAKs, patterns of activation of all seven STATs in different cells, and activation of transcription factors other than STATs. The type I IFNs use this complexity to regulate many different biological functions in different types of cells, by activating different specific signals and patterns of gene expression.

Attenuating mutations in the P/C gene of human parainfluenza virus type 1 (HPIV1) vaccine candidates abrogate the inhibition of both induction and signaling of type I interferon (IFN) by wild-type HPIV1

Recombinant human parainfluenza virus type 1 (HPIV1) and mutants containing point and deletion (Delta) mutations in the P/C gene (r-CDelta10-15HNT553A, r-CR84G, r-CF170S and r-CDelta170), which have previously been evaluated as HPIV1 vaccine candidates, were evaluated for their effect on the type I interferon (IFN) response in vitro. HPIV1 wt infection inhibited the IFN response by inhibiting IFN regulatory factor-3 (IRF-3) activation and IFN production in A549 cells and IFN signaling in Vero cells. In contrast, r-CR84G, r-CF170S and r-CDelta170 were defective for inhibition of IRF-3 activation and IFN production and r-CF170S and r-CDelta170 did not inhibit IFN signaling. Thus, HPIV1 antagonizes the IFN response at both the level of induction and signaling, and antagonism at both levels was disrupted by mutations in the P/C gene. Because CF170S affects C and not P, the anti-IFN function can be attributed to the C proteins. These data, in the context of previous in vivo studies, suggest that the loss of antagonism of the IFN response at both the level of induction and signaling, observed with the P/C mutants, r-CF170S and r-CDelta170, was necessary for significant attenuation in African green monkeys (AGMs).

Variations in the unstructured C-terminal tail of interferons contribute to differential receptor binding and biological activity

Type I interferons (IFNs) elicit antiviral, antiproliferative and immunomodulatory properties in cells. All of them bind to the same receptor proteins, IFNAR1 and IFNAR2, with different affinities. While the 13 known IFNalphas are highly conserved, the C-terminal unstructured tail was found to have large variation in its net charge, from neutral to +4. This led us to speculate that the tail may have a role in modulation of the IFN biological activity, through fine-tuning the binding to IFNAR2. To evaluate this hypothesis, we replaced the tail of IFNalpha2 with that of IFNalpha8 and IFNbeta tails, or deleted the last five residues of this segment. Mutations to the more positively charged tail of IFNalpha8 resulted in a 20-fold higher affinity to IFNAR2, which results in a higher antiviral and antiproliferative activity. Double and multiple mutant cycle analysis placed the tail near a negatively charged loop on IFNAR2, comprising of residues Glu 132-134. Deleting the tail resulted in only twofold reduction in binding compared to the wild-type. Next, we modeled the location of the tail using a two-step procedure: first we generated 200 models of the tail docked on IFNAR2 using HADDOCK, second the models were scored according to the fit between experimentally determined rates of association of nine mutant complexes, and their calculated rates using the PARE software. From the results we suggest that the unstructured tail of IFNalpha is gaining a specific structure in the bound state, binding to a groove below the 132-134 loop in IFNAR2.

Alternative and accessory pathways in the regulation of IFN-beta-mediated gene expression

Type I interferons (IFNs) induce the transcription of IFN-stimulated genes (ISGs) through activation of the Jak-Stat pathway. Although some determinants of specificity are dictated by the Jak-Stat components, recent observations indicate that the system incorporates other components for selectivity and flexibility, whose mechanisms remain to be defined. We identified a gene, beta-R1, which was induced relatively selectively by IFN-beta as compared with numerous IFN-alpha subtypes. Because all type I IFNs equally activate Jak-Stat signaling to IFN-stimulated gene factor 3 (ISGF3), this observation implied the existence of accessory signals for IFN-induced gene expression. We have used beta-R1 as a model system to examine this accessory signaling. In addition to Jak-Stat signaling for mediating IFN-induced cellular responses, p38 mitogen-activated protein kinase (p38 MAPK), phosphoinositol 3-kinase (PI3K), the IkappaB kinases (IKKs), and nuclear factor-kappaB (NF-kappaB) are some of the accessory components identified as required for the induction of certain IFN-beta-induced genes. This review focuses on the roles of accessory components in IFN-beta-mediated signaling, mechanisms of accessory signal generation, and how they modulate gene induction.

Antiproliferative effects of 5-fluorouracil and interferon-alpha in combination on a hepatocellular carcinoma cell line in vitro and in vivo

BACKGROUND AND AIM

We investigated the antiproliferative effects of interferon-alpha (IFN-alpha) and 5-fluorouracil (5-FU) in combination on a hepatocellular carcinoma (HCC) cell line.

METHOD

In the in vitro study, IFN-alpha and/or 5-FU was added to the culture of the poorly differentiated-type HCC cell line, HAK-1B, and their antiproliferative effects and additional or synergic effects in combination treatment were examined. In the in vivo study, HAK-1B cells were transplanted into nude mice and the changes in tumor volume and weight, apoptosis, BrdU and cyclin A positive cells, and artery-like blood vessels were investigated. Expressions of angiogenesis factors and IFN-alpha receptor (IFNAR-2) were examined in the developed tumors.

RESULTS

In vitro growth of HAK-1B cells was suppressed dose-dependently to 5-FU, but the addition of IFN-alpha did not induce additional or synergic effects. In vivo growth in terms of tumor diameter and weight was suppressed at most in the IFN-alpha + 5-FU (combination) group, that is, the tumor volume became 29.3% and the tumor weight became 54.7% of the control. In the combination group, numbers of BrdU-positive S-phase cells and cyclin A positive cells increased together with the increase in apoptotic cells, but there was no significant relation between the tumor shrinkage effects and angiogenesis factors or artery-like blood vessels. In the combination group, INFAR-2 decreased significantly in comparison to the other groups.

CONCLUSION

The synergic growth-suppression effects in the current in vivo study using the combination treatment are attributable to the enhanced induction of S-phase arrest and of apoptosis.

Ability of Orally Administered IFN-α-Containing Transgenic Potato Extracts to InhibitListeria monocytogenesInfection

Type I interferons (IFN-alpha/beta) were originally thought to be antiviral cytokines, but it has recently been reported that they also play an important role in potentiating innate and adaptive immune responses. Moreover, several studies have shown that the oral administration of type I IFN ameliorates various biologic activities. Here, we studied the ability of orally administered IFN-alpha to protect mice from systemic Listeria monocytogenes infection. Daily oral administration of purified natural IFN-alpha at a concentration of 1000 international units (IU)/20 microl reduced the bacterial burden in infected organs. We also examined the protective effect of IFN-alpha expressed in transgenic potato plants. A much lower concentration of IFN-alpha (20 IU/ 20 microl) in the plant extracts was almost as protective as much higher concentrations of purified natural IFN-alpha. Our observations indicate that transgenic cytokine-expressing plants can be used prophylactically as edible pharmaceuticals to enhance systemic defense responses in humans and animals.

In vitro susceptibility of 10 clinical isolates of SARS coronavirus to selected antiviral compounds

Effective antiviral agents are urgently needed to combat the possible return of severe acute respiratory syndrome (SARS). Commercial antiviral agents and pure chemical compounds extracted from traditional Chinese medicinal herbs were screened against 10 clinical isolates of SARS coronavirus by neutralisation tests with confirmation by plaque reduction assays. Interferon-beta-1a, leukocytic interferon-alpha, ribavirin, lopinavir, rimantadine, baicalin and glycyrrhizin showed antiviral activity. The two interferons were only active if the cell lines were pre-incubated with the drugs 16 h before viral inoculation. Results were confirmed by plaque reduction assays. Antiviral activity varied with the use of different cell lines. Checkerboard assays for synergy were performed showing combinations of interferon beta-1a or leukocytic interferon-alpha with ribavirin are synergistic. Since the clinical and toxicity profiles of these agents are well known, they should be considered either singly or in combination for prophylaxis or treatment of SARS in randomised placebo controlled trials in future epidemics.