Synergistic antiviral activity of human interferon combinations in the hepatitis C virus replicon system.

The use of type I interferon (IFN), in combination with ribvirin, to treat chronic hepatitis C virus (HCV) infection has many drawbacks that prevent widespread application, ultimately leading to a significant unmet clinical need. Potential improvements in IFN therapy through targeted delivery, molecular alteration, and combination with other agents are ongoing in an attempt to decrease adverse effects and increase efficacy. In this report, the HCV replicon cell culture system was used to assess potential synergistic antiviral effects of multiple IFN species when administered in combination. Quantitative analysis of HCV replicon RNA by TaqMan (PE Applied Biosystems, Foster City, CA) and qualitative analysis of HCV protein expression were used to measure the antiviral efficacy of individual and combination IFN treatments, and synergistic responses of IFN combinations were determined through statistical analysis of the TaqMan results. We found that when administered simultaneously, type I/II IFN combinations (IFN-alpha2b + IFN-gamma or IFN-beta + IFN-gamma) resulted in dramatic antiviral synergy, whereas a type I/I combination (IFN-alpha2b + IFN-beta) demonstrated a slightly antagonistic profile. The synergistic effect is likely due to differential cell surface receptors and signaling pathways employed by types I and II IFNs. Conversely, all type I IFN species bind the same receptor and signal through similar pathways, possibly accounting for the nearly additive response observed. In support of this hypothesis, IFN treatment resulted in differential induction of Stat1 phosphorylation at Tyr 701. In conclusion, simultaneous type I/II IFN combination treatment may allow an overall decreased effective IFN dose, which may reduce the side effect profiles that hinder current therapy.     

Activation of endogenous type I IFN signaling contributes to persistent HCV infection

HCV infection is a major world health problem, leading to both end‐stage liver disease and primary liver cancer. Great efforts have been made in developing new therapies for HCV infection; however, combination therapy with pegylated IFN‐α and ribavirin (pegIFN‐RBV) remains the first choice of treatment for chronic HCV infection in most countries. The treatment response to pegIFN‐RBV remains relatively low. Understanding the molecular mechanisms of persistent HCV infection and pegIFN‐RBV resistance will suggest ways of improving the current standard of care and offers new antiviral therapies for both HCV and other viral infections. Recent data suggest that increased expression of hepatic IFN‐stimulated genes (ISGs) before treatment is associated with treatment nonresponse in patients chronically infected with HCV. Although ISGs are generally antiviral in nature, in the case of HCV, the virus may exploit some of them to its benefit. This is not unique to HCV: Blockade of type I IFN signaling has been shown to control persistent LCMV infection. Thus, in certain viral infections, preactivation or overactivation of type I IFN signaling may contribute to viral persistence. In this review, we briefly summarize the findings from high‐throughput gene expression profiling from patients chronically infected with HCV, then focus on a novel ubiquitin‐like signaling pathway (ISG15/USP18) and its potential role in HCV persistence. Finally, the role of activation of endogenous type I IFN signaling in persistent HCV infection will be discussed in the context of recent studies indicating that blocking IFN signaling controls persistent LCMV infection. Copyright © 2014 John Wiley & Sons, Ltd.     

Viruses and the type I interferon antiviral system: induction and evasion

The type I interferon (IFN) system responds to viral infection and induces an "antiviral state" in cells, providing an important first line of defense against virus infection. Interaction of type I IFNs (IFN alpha and IFN beta) with their receptor induces hundreds of cellular genes. Of the proteins induced by IFN, the antiviral function of only a few is known, and their mechanisms of action are only partly understood. Additionally, although viral-encoded mechanisms that counteract specific components of the type I IFN response have been known for some time, it has recently become clear that many (if not most) viruses encode some form of IFN-antagonist. Understanding the interplay between viral-encoded IFN antagonists and the interferon response will be essential if the therapeutic potential of IFNs is to be fully exploited.     

Emerging roles of interferon-stimulated genes in the innate immune response to hepatitis C virus infection

Infection with hepatitis C virus (HCV), a major viral cause of chronic liver disease, frequently progresses to steatosis and cirrhosis, which can lead to hepatocellular carcinoma. HCV infection strongly induces host responses, such as the activation of the unfolded protein response, autophagy and the innate immune response. Upon HCV infection, the host induces the interferon (IFN)-mediated frontline defense to limit virus replication. Conversely, HCV employs diverse strategies to escape host innate immune surveillance. Type I IFN elicits its antiviral actions by inducing a wide array of IFN-stimulated genes (ISGs). Nevertheless, the mechanisms by which these ISGs participate in IFN-mediated anti-HCV actions remain largely unknown. In this review, we first outline the signaling pathways known to be involved in the production of type I IFN and ISGs and the tactics that HCV uses to subvert innate immunity. Then, we summarize the effector mechanisms of scaffold ISGs known to modulate IFN function in HCV replication. We also highlight the potential functions of emerging ISGs, which were identified from genome-wide siRNA screens, in HCV replication. Finally, we discuss the functions of several cellular determinants critical for regulating host immunity in HCV replication. This review will provide a basis for understanding the complexity and functionality of the pleiotropic IFN system in HCV infection. Elucidation of the specificity and the mode of action of these emerging ISGs will also help to identify novel cellular targets against which effective HCV therapeutics can be developed.     

Proteasome activator and antigen-processing aminopeptidases are regulated by virus-induced type I interferon in the hepatitis C virus-infected liver.

Many components of the class I antigen-processing pathway are thought to be regulated solely by interferon-gamma (IFN-gamma). Herein, we report type I IFN-mediated induction of proteasome activator (PA28) subunits alpha and beta, endoplasmic reticulum aminopeptidase 1 (ERAP1), ERAP2, and leucine aminopeptidase (LAP). This mechanism was initiated by either synthetic RNA (poly(I-C)) or by hepatitis C virus (HCV) RNA-mediated induction of type I IFN and abrogated by blocking of type I IFN. In serial liver biopsies of chimpanzees with acute HCV infection, increases in PA28 subunit and aminopeptidase mRNA levels correlated with intrahepatic type I IFN responses and preceded intrahepatic IFN-gamma responses by several weeks. Thus, viral RNA-induced type I IFN regulates the antigen-processing machinery early during viral infection and prior to IFN-gamma response. This mechanism may contribute to the high effectiveness of type I IFN-based therapies if administered early during acute HCV infection.     

VIRUSES AND THE TYPE I INTERFERON ANTIVIRAL SYSTEM: INDUCTION AND EVASION

The type I interferon (IFN) system responds to viral infection and induces an "antiviral state" in cells, providing an important first line of defense against virus infection. Interaction of type I IFNs (IFNα and IFNβ) with their receptor induces hundreds of cellular genes. Of the proteins induced by IFN, the antiviral function of only a few is known, and their mechanisms of action are only partly understood. Additionally, although viral-encoded mechanisms that counteract specific components of the type I IFN response have been known for some time, it has recently become clear that many (if not most) viruses encode some form of IFN-antagonist. Understanding the interplay between viral-encoded IFN antagonists and the interferon response will be essential if the therapeutic potential of IFNs is to be fully exploited.     

Lack of a role for type I and type II interferons in the resolution of rotavirus-induced diarrhea and infection in mice.

Rotavirus infects the intestinal epithelium of most mammalian species and causes diarrhea in infants. Previously, we have shown that both type I and II human interferons (IFNs) have potent and mechanistically discreet antiviral effects in vitro against rotavirus. We have also shown that adult IFN-gamma knockout (-/-) mice have no alteration in clearance of primary rotavirus infection. In the present studies, we wished to determine the importance of both IFN types in modulation of degree and duration of disease and infection in mice. Immunocompetent suckling mice were treated orally (5,000 IU) or parenterally (500 IU) with type I and II murine IFNs before and after challenge with virulent murine rotavirus. Treated animals developed diarrhea indistinguishable from that observed in untreated control mice. In other experiments, type I IFN receptor -/- suckling mice and IFN-gamma-/- suckling mice developed diarrhea of similar characteristics and duration and had comparable quantities of viral antigen in their intestines as did immunocompetent mice. Furthermore, type I IFN receptor -/- adult mice infected with rotavirus shed equivalent quantities of viral antigen and with similar kinetics as the control mice. Thus, IFNs do not seem to be major inhibitors of rotavirus diarrhea or replication in mice.     

Intronless and intron-containing type I IFN genes coexist in amphibian Xenopus tropicalis: Insights into the origin and evolution of type I IFNs in vertebrates

Type I IFNs are considered to be the core IFN species in vertebrates because of their predominant antiviral effects. But, a puzzling question remains to be answered, as to how intronless type I IFN genes in amniotes might have evolved from intron-containing type I IFN genes in fish and amphibians. In this study, intronless and intron-containing type I IFNs were found in the amphibian model, Xenopus tropicalis, with a total of sixteen and five genes, respectively. The intronless IFNs can be divided into three subgroups, and the intron-containing ones into two subgroups, implying that a retroposition event might have occurred in amphibians, resulting in the generation of intronless type I IFN genes. Two models were tentatively proposed to explain the evolution of type I IFNs in vertebrates: in model A, fish should possess the most primitive multi-exon-containing type I IFNs, and intronless type I IFN genes in amphibians are the ancestor of modern intronless type I IFNs in amniotes; in model B, intronless type I IFN genes in X. tropicalis may just represent an independent bifurcation in this species or probably in amphibians, and intronless type I IFN genes in amniotes may have arisen from another retroposition event occurred in a transition period even when reptiles were diverged from amphibians. It is considered that the model B can reflect the current knowledge on the occurrence of intronless and intron-containing type I IFN genes in vertebrate lineages. This study thus contributes to a better understanding of the origin and evolution of type I IFNs in vertebrates, and of the occurrence of intronless I IFNs in higher vertebrates.     

Interferons induce an antiviral state in human pancreatic islet cells

Enterovirus infections, in particular those with Coxsackieviruses, have been linked to the development of type 1 diabetes (T1D). Although animal models have demonstrated that interferons (IFNs) regulate virus-induced T1D by acting directly on the beta cell, little is known on the human pancreatic islet response to IFNs. Here we show that human islet cells respond to IFNs by expressing signature genes of antiviral defense. We also demonstrate that they express three intracellular sensors for viral RNA, the toll like receptor 3 (TLR3) gene, the retinoic acid-inducible gene I (RIG-I) and the melanoma differentiation-associated gene-5 (MDA-5), which induce type I IFN production in infected cells. Finally, we show for the first time that the IFN-induced antiviral state provides human islets with a powerful protection from the replication of Coxsackievirus. This may be critical for beta cell survival and protection from virus-induced T1D in humans.     

Fish interferon-stimulated genes: The antiviral effectors

Type I interferons (IFN) are the cornerstone cytokine of innate antiviral immunity. In response to a viral infection, IFN signaling results in the expression of a diverse group of genes known as interferon-stimulated genes (ISGs). These ISGs are responsible for interfering with viral replication and infectivity, helping to limit viral infection within a cell. In mammals, many antiviral effector ISGs have been identified and the antiviral mechanisms are at least partially elucidated. In fish fewer ISGs have been identified and while there is evidence they limit viral infection, almost nothing is known of their respective antiviral mechanisms. This review discusses seven ISGs common to mammals and fish and three ISGs that are unique to fish. The lack of understanding regarding fish ISG's antiviral effector functions is highlighted and draws attention to the need for research in this aspect of aquatic innate immunity.     

Autoimmunity is a type I interferon-deficiency syndrome corrected by ingested type I IFN via the GALT system.

Type I interferons (IFN-alpha/beta), products of the innate immune system, can modulate immune function whereas proinflammatory IFN-gamma (type II IFN), a product of the acquired immune system upregulates inflammation and enhances cell mediated immunity. We have proposed a unifying hypothesis of the origin of autoimmunity as a type I IFN immunodeficiency syndrome involving inadequate regulation of the acquired immune system product IFN-gamma by the IFN-alpha/beta innate immune system. The common theme of ingested type I IFNs in autoimmunity is inhibition of proinflammatory type II IFN systemically or at the target organ. In multiple sclerosis (MS) and insulin-dependent diabetes mellitus (IDDM) at the target organ, and in rheumatoid arthritis (RA) as a regulator of other proinflammatory cytokines, IFN-gamma is the nexus of inflammation in autoimmunity. Ingested type I IFNs counteract type II IFN, overcome the relative lack of type I IFN activity, and ameliorate autoimmunity. The administration of type I IFNs (IFN-alpha/beta) via the gut offers an exciting alternative to systemic application for overcoming the type I IFN immunodeficiency in autoimmunity. Successful use of ingested type I IFN in three separate prototypical autoimmune diseases suggests a broad antiinflammatory therapeutic profile for this technology.