Interferons play key roles in mediating antiviral and antigrowth responses and in modulating immune response. The main signaling pathways are rapid and direct. They involve tyrosine phosphorylation and activation of signal transducers and activators of transcription factors by Janus tyrosine kinases at the cell membrane, followed by release of signal transducers and activators of transcription and their migration to the nucleus, where they induce the expression of the many gene products that determine the responses. Ancillary pathways are also activated by the interferons, but their effects on cell physiology are less clear. The Janus kinases and signal transducers and activators of transcription, and many of the interferon-induced proteins, play important alternative roles in cells, raising interesting questions as to how the responses to the interferons intersect with more general aspects of cellular physiology and how the specificity of cytokine responses is maintained.

http://www3.uah.es/farmamol/Public/AnnReviews/PDF/Biochemistry/Interferons.pdf

How cells respond to interferons

Interferon-gamma (IFN-gamma) coordinates a diverse array of cellular programs through transcriptional regulation of immunologically relevant genes. This article reviews the current understanding of IFN-gamma ligand, receptor, signal transduction, and cellular effects with a focus on macrophage responses and to a lesser extent, responses from other cell types that influence macrophage function during infection. The current model for IFN-gamma signal transduction is discussed, as well as signal regulation and factors conferring signal specificity. Cellular effects of IFN-gamma are described, including up-regulation of pathogen recognition, antigen processing and presentation, the antiviral state, inhibition of cellular proliferation and effects on apoptosis, activation of microbicidal effector functions, immunomodulation, and leukocyte trafficking. In addition, integration of signaling and response with other cytokines and pathogen-associated molecular patterns, such as tumor necrosis factor-alpha, interleukin-4, type I IFNs, and lipopolysaccharide are discussed.

https://jlb.onlinelibrary.wiley.com/doi/epdf/10.1189/jlb.0603252

Interferon-γ: an overview of signals, mechanisms and functions

Interferons are cytokines that have antiviral, antiproliferative and immunomodulatory effects. Because of these important properties, in the past two decades, major research efforts have been undertaken to understand the signalling mechanisms through which these cytokines induce their effects. Since the original discovery of the classical JAK (Janus activated kinase)-STAT (signal transducer and activator of transcription) pathway of signalling, it has become clear that the coordination and cooperation of multiple distinct signalling cascades - including the mitogen-activated protein kinase p38 cascade and the phosphatidylinositol 3-kinase cascade - are required for the generation of responses to interferons. It is anticipated that an increased understanding of the contributions of these recently identified pathways will advance our current thinking about how interferons work.

/pdf/mechanisms-of-type-i-and-type-ii-interferon-mediated-14ljx2ig3n.pdf

Mechanisms of type-I- and type-II-interferon-mediated signalling.

Tremendous progress has been made in understanding the molecular basis of the antiviral actions of interferons (IFNs), as well as strategies evolved by viruses to antagonize the actions of IFNs. Furthermore, advances made while elucidating the IFN system have contributed significantly to our understanding in multiple areas of virology and molecular cell biology, ranging from pathways of signal transduction to the biochemical mechanisms of transcriptional and translational control to the molecular basis of viral pathogenesis. IFNs are approved therapeutics and have moved from the basic research laboratory to the clinic. Among the IFN-induced proteins important in the antiviral actions of IFNs are the RNA-dependent protein kinase (PKR), the 2',5'-oligoadenylate synthetase (OAS) and RNase L, and the Mx protein GTPases. Double-stranded RNA plays a central role in modulating protein phosphorylation and RNA degradation catalyzed by the IFN-inducible PKR kinase and the 2'-5'-oligoadenylate-dependent RNase L, respectively, and also in RNA editing by the IFN-inducible RNA-specific adenosine deaminase (ADAR1). IFN also induces a form of inducible nitric oxide synthase (iNOS2) and the major histocompatibility complex class I and II proteins, all of which play important roles in immune response to infections. Several additional genes whose expression profiles are altered in response to IFN treatment and virus infection have been identified by microarray analyses. The availability of cDNA and genomic clones for many of the components of the IFN system, including IFN-alpha, IFN-beta, and IFN-gamma, their receptors, Jak and Stat and IRF signal transduction components, and proteins such as PKR, 2',5'-OAS, Mx, and ADAR, whose expression is regulated by IFNs, has permitted the generation of mutant proteins, cells that overexpress different forms of the proteins, and animals in which their expression has been disrupted by targeted gene disruption. The use of these IFN system reagents, both in cell culture and in whole animals, continues to provide important contributions to our understanding of the virus-host interaction and cellular antiviral response.

Antiviral Actions of Interferons

Summary: The innate immune system constitutes the first line of defense against invading microbial pathogens and relies on a large family of pattern recognition receptors (PRRs), which detect distinct evolutionarily conserved structures on pathogens, termed pathogen-associated molecular patterns (PAMPs). Among the PRRs, the Toll-like receptors have been studied most extensively. Upon PAMP engagement, PRRs trigger intracellular signaling cascades ultimately culminating in the expression of a variety of proinflammatory molecules, which together orchestrate the early host response to infection, and also is a prerequisite for the subsequent activation and shaping of adaptive immunity. In order to avoid immunopathology, this system is tightly regulated by a number of endogenous molecules that limit the magnitude and duration of the inflammatory response. Moreover, pathogenic microbes have developed sophisticated molecular strategies to subvert host defenses by interfering with molecules involved in inflammatory signaling. This review presents current knowledge on pathogen recognition through different families of PRRs and the increasingly complex signaling pathways responsible for activation of an inflammatory and antimicrobial response. Moreover, medical implications are discussed, including the role of PRRs in primary immunodeficiencies and in the pathogenesis of infectious and autoimmune diseases, as well as the possibilities for translation into clinical and therapeutic applications.

Pathogen Recognition and Inflammatory Signaling in Innate Immune Defenses

During a study of the interference produced by heat-inactivated influenza virus with the growth of live virus in fragments of chick chorio-allantoic membrane it was found that following incubation of heated virus with membrane a new factor was released. This factor, recognized by its ability to induce interference in fresh pieces of chorio-allantoic membrane, was called interferon. Following a lag phase interferon was first detected in the membranes after 3 h incubation and thereafter it was released into the surrounding fluid.

Virus interference. I The interferon

Mx protein: Constitutive expression in 3T3 cells transformed with cloned Mx cDNA confers selective resistance to influenza virus

Interferon could be titrated by the amount of interference induced in fragments of chorioallantoic membranes challenged with influenza A virus. Over a ten-fold range, inverse proportion between interferon concentration and haemagglutinin titre reached by the challenge virus was observed. Interferon proved stable at 2 degrees C for 2 weeks. Marked inactivation took place after 1 h at 60 degrees C. Interferon was not measurably sedimented by 100 000 g for $\frac{1}{2}$ $\text{h}$. It was held back by gradocol filters of a.p.d. $0.6\mu $. It was not dialyzable. Interferon was active against influenza A, Sendai, Newcastle disease and vaccinia viruses. It was not neutralized by anti-MEL rabbit serum and only slightly inhibited by pooled human serum rich in complement-fixing antibody to influenza A soluble antigen.

Virus interference. II. Some properties of interferon.

Resistance of mice to mouse-adapted influenza A virus.

The genetically determined resistance towards orthomyxoviruses exhibited by mice homozygous (A2G) or heterozygous (A2G X A/J) for the gene Mx was abolished or greatly diminished by treatment with anti-interferon globulin (AIF). AIF induced increased susceptibility to challenge with hepatotropic, neurotropic, and pneumotropic strains of influenza A virus. Hepatotropic virus titers in blood and livers of AIF-treated, Mx-bearing mice were higher by a factor of 10(3)--10(6) than those in untreated mice of the same genotype, and were comparable to those in genetically susceptible (untreated or AIF-treated) mice. Peritoneal macrophages from Mx-bearing untreated mice were resistant to challenge with a macrophage-adapted strain of influenza A virus even in the presence of AIF. However, when macrophages were taken from resistant mice injected with AIF and also cultivated in the presence of AIF, they were as susceptible to the virus as macrophages taken from susceptible mice. We conclude that interferons is an important factor in resistance to orthomyxoviruses governed by the gene Mx.

/pdf/genetically-determined-interferon-dependent-resistance-to-2t458xtyz4.pdf

Jean Lindenmann

Papers

Virus interference. I The interferon

Mx protein: Constitutive expression in 3T3 cells transformed with cloned Mx cDNA confers selective resistance to influenza virus

Virus interference. II. Some properties of interferon.

Resistance of mice to mouse-adapted influenza A virus.

Genetically determined, interferon-dependent resistance to influenza virus in mice.