A new member of the interleukin 10-related cytokine family encoded by a poxvirus

Poxvirus Vaccines: Past, Present, and Future

Smallpox was a significant cause of mortality for over three thousand years, amounting to 10% of deaths yearly. Edward Jenner discovered smallpox vaccination in 1796, which rapidly became a smallpox infection preventive practice throughout the world and eradicated smallpox infection by 1980. After smallpox eradication, monkeypox vaccines have been used primarily in research and in outbreaks in Africa, where the disease is endemic. In the present, the vaccines are being used for people who work with animals or in high-risk areas, as well as for healthcare workers treating patients with monkeypox. Among all orthopoxviruses (OPXV), monkeypox viral (MPXV) infection occurs mainly in cynomolgus monkeys, natural reservoirs, and occasionally causes severe multi-organ infection in humans, who were the incidental hosts. The first case of the present epidemic of MXPV was identified on May 7, 2022, and rapidly increased the number of cases. In this regard, the WHO declared the outbreak, an international public health emergency on July 23, 2022. The first monkeypox vaccine was developed in the 1960s by the US Army and was based on the vaccinia virus, which is also used in smallpox vaccines. In recent years, newer monkeypox vaccines have been developed based on other viruses such as Modified Vaccinia Ankara (MVA). These newer vaccines are safer and can provide longer-lasting immunity with fewer side effects. For the future, there is ongoing research to improve the current vaccines and to develop new ones. One notable advance has been the development of a recombinant vaccine that uses a genetically modified vaccinia virus to express monkeypox antigens. This vaccine has shown promising results in pre-clinical trials and is currently undergoing further testing in clinical trials. Another recent development has been the use of a DNA vaccine, which delivers genetic material encoding monkeypox antigens directly into cells. This type of vaccine has shown effectiveness in animal studies and is also undergoing clinical testing in humans. Overall, these recent advances in monkeypox vaccine development hold promise for protecting individuals against this potentially serious disease.

Protein kinase R is an innate immune sensor of proteotoxic stress via accumulation of cytoplasmic IL-24

Proteasome dysfunction can lead to autoinflammatory disease associated with elevated type I interferon (IFN-αβ) and NF-κB signaling; however, the innate immune pathway driving this is currently unknown. Here, we identified protein kinase R (PKR) as an innate immune sensor for proteotoxic stress. PKR activation was observed in cellular models of decreased proteasome function and in multiple cell types from patients with proteasome-associated autoinflammatory disease (PRAAS). Furthermore, genetic deletion or small-molecule inhibition of PKR in vitro ameliorated inflammation driven by proteasome deficiency. In vivo, proteasome inhibitor-induced inflammatory gene transcription was blunted in PKR-deficient mice compared with littermate controls. PKR also acted as a rheostat for proteotoxic stress by triggering phosphorylation of eIF2α, which can prevent the translation of new proteins to restore homeostasis. Although traditionally known as a sensor of RNA, under conditions of proteasome dysfunction, PKR sensed the cytoplasmic accumulation of a known interactor, interleukin-24 (IL-24). When misfolded IL-24 egress into the cytosol was blocked by inhibition of the endoplasmic reticulum-associated degradation pathway, PKR activation and subsequent inflammatory signaling were blunted. Cytokines such as IL-24 are normally secreted from cells; therefore, cytoplasmic accumulation of IL-24 represents an internal danger-associated molecular pattern. Thus, we have identified a mechanism by which proteotoxic stress is detected, causing inflammation observed in the disease PRAAS.

Locally Produced IL-10 Limits Cutaneous Vaccinia Virus Spread

Skin infection with the poxvirus vaccinia (VV) elicits a powerful, inflammatory cellular response that clears virus infection in a coordinated, spatially organized manner. Given the high concentration of pro-inflammatory effectors at areas of viral infection, it is unclear how tissue pathology is limited while virus-infected cells are being eliminated. To better understand the spatial dynamics of the anti-inflammatory response to a cutaneous viral infection, we first screened cytokine mRNA expression levels after epicutaneous (ec.) VV infection and found a large increase the anti-inflammatory cytokine IL-10. Ex vivo analyses revealed that T cells in the skin were the primary IL-10-producing cells. To understand the distribution of IL-10-producing T cells in vivo, we performed multiphoton intravital microscopy (MPM) of VV-infected mice, assessing the location and dynamic behavior of IL-10 producing cells. Although virus-specific T cells were distributed throughout areas of the inflamed skin lacking overt virus-infection, IL-10+ cells closely associated with large keratinocytic foci of virus replication where they exhibited similar motility patterns to bulk antigen-specific CD8+ T cells. Paradoxically, neutralizing secreted IL-10 in vivo with an anti-IL-10 antibody increased viral lesion size and viral replication. Additional analyses demonstrated that IL-10 antibody administration decreased recruitment of CCR2+ inflammatory monocytes, which were important for reducing viral burden in the infected skin. Based upon these findings, we conclude that spatially concentrated IL-10 production limits cutaneous viral replication and dissemination, likely through modulation of the innate immune repertoire at the site of viral growth.

Lister strain vaccinia virus with thymidine kinase gene deletion is a tractable platform for development of a new generation of oncolytic virus

Vaccinia virus (VV) has many attractive characteristics as a potential cancer therapeutic. There are several strains of VV. The nonvaccine strain Western Reserve VV with deletion of both the thymidine kinase and the viral growth factor genes (known as WRDD) has been reported as the most potent tumor-targeted oncolytic VV. Other strains, such as the European vaccine Lister strain, are largely untested. This study evaluated the antitumor potency and biodistribution of different VV strains using in vitro and in vivo models of cancer. Lister strain virus with thymidine kinase gene deletion (VVΔTK) demonstrated superior antitumor potency and cancer-selective replication in vitro and in vivo, compared with WRDD, especially in human cancer cell lines and immune-competent hosts. Further investigation of functional mechanisms revealed that Lister VVΔTK presented favorable viral biodistribution within the tumors, with lower levels of proinflammatory cytokines compared with WRDD, suggesting that Lister strain may induce a diminished host inflammatory response. This study indicates that the Lister strain VVΔTK may be a particularly promising VV strain for the development of the next generation of tumor-targeted oncolytic therapeutics.

The Therapeutic Potential of Anti-Interleukin-20 Monoclonal Antibody

Interleukin (IL)-20, a member of the IL-10 family of cytokines, was discovered in 2001. IL-20 acts on multiple cell types by activating on a heterodimer receptor complex of either IL-20R1–IL-20R2 or IL-22R1–IL-20R2. Recent evidence indicates that IL-20's interaction with its receptors might have proinflammatory effects on chronic inflammatory diseases, particularly rheumatoid arthritis (RA), osteoporosis, and breast cancer. Updated information about IL-20, such as its identification, expression, receptors, signaling, and biological activities, is illustrated in this review based on our research and the data available in the literature. IL-20 is a pleiotropic cytokine, which promotes inflammation, angiogenesis, and chemotaxis. IL-20 also regulates osteoclast differentiation by altering the receptor activator of NF-κB (RANK) and RANK ligand (RANKL) axis. Inflammation, angiogenesis, and osteoclastogenesis are critical for the pathogenesis of RA, osteoporosis, and breast cancer-induced osteolysis. Based on the in vitro and in vivo data and clinical samples, we demonstrated that IL-20 plays pivotal roles in these three diseases. In experimental models, anti-IL-20 monoclonal antibody ameliorates arthritis severity, protects against ovariectomized-induced bone loss, and inhibits breast tumor-induced osteolysis. This review presents the clinical implications of IL-20, which will lead to a better understanding of the biological functions of IL-20 in these diseases and provide new therapeutic options in the future.

IL-10 encoded by viruses: a remarkable example of independent acquisition of a cellular gene by viruses and its subsequent evolution in the viral genome

Many viruses have evolved strategies to deregulate the host immune system. These strategies include mechanisms to subvert or recruit the host cytokine network. IL-10 is a pleiotropic cytokine that has both immunostimulatory and immunosuppressive properties. However, its key features relate mainly to its capacity to exert potent immunosuppressive effects. Several viruses have been shown to upregulate the expression of cellular IL-10 (cIL-10) with, in some cases, enhancement of infection by suppression of immune functions. Other viruses encode functional orthologues of cIL-10, called viral IL-10s (vIL-10s). The present review is devoted to these virokines. To date, vIL-10 orthologues have been reported for 12 members of the family Herpesviridae, two members of the family Alloherpesviridae and seven members of the family Poxviridae. Study of vIL-10s demonstrated several interesting aspects on the origin and the evolution of these viral genes, e.g. the existence of multiple (potentially up to nine) independent gene acquisition events at different times during evolution, viral gene acquisition resulting from recombination with cellular genomic DNA or cDNA derived from cellular mRNA and the evolution of cellular sequence in the viral genome to restrict the biological activities of the viral orthologues to those beneficial for the virus life cycle. Here, various aspects of the vIL-10s described to date are reviewed, including their genetic organization, protein structure, origin, evolution, biological properties and potential in applied research.

Horizontal transfer and the evolution of host-pathogen interactions

Horizontal gene transfer has been long known in viruses and prokaryotes, but its importance in eukaryotes has been only acknowledged recently. Close contact between organisms, as it occurs between pathogens and their hosts, facilitates the occurrence of DNA transfer events. Once inserted in a foreign genome, DNA sequences have sometimes been coopted by pathogens to improve their survival or infectivity, or by hosts to protect themselves against the harm of pathogens. Hence, horizontal transfer constitutes a source of novel sequences that can be adopted to change the host-pathogen interactions. Therefore, horizontal transfer can have an important impact on the coevolution of pathogens and their hosts.

Cowpox virus induces interleukin-10 both in vitro and in vivo

Cowpox virus infection induces interleukin-10 (IL-10) production from mouse bone marrow-derived dendritic cells (BMDCs) or cells of the mouse macrophage line (RAW264.7) at about 1800 pg/ml, whereas infections with vaccinia virus (strains WR or MVA) induced much less IL-10. Similarly, in vivo, IL-10 levels in bronchoalveolar lavage fluids of mice infected with cowpox virus were significantly higher than those after vaccinia virus infection. However, after intranasal cowpox virus infection, although dendritic and T-cell accumulations in the lungs of IL-10 deficient mice were greater than those in wild-type mice, weight-loss and viral burdens were not significantly different. IL-10 deficient mice were more susceptible than wild-type mice to re-infection with cowpox virus even though titers of neutralizing antibodies and virus-specific CD8 T cells were similar between IL-10 deficient and wild-type mice. Greater bronchopneumonia in IL-10 deficient mice than wild-type mice suggests that IL-10 contributes to the suppression of immunopathology in the lungs.

Contribution of cytokines to pathology and protection in virus infection

Acute and chronic viral infections greatly contribute to global health burden. While concerted action of multiple elements of the immune system help the host cope with most viruses, some infections lead to host damage or death. Cytokines are central drivers and controllers of both immune-mediated virus elimination and of immunopathology. Here, we review recent progress in understanding the protective and damaging roles in viral infections of cytokines and chemokines associated with innate, regulatory, and Th1, Th2 and Th17 responses.

Cytokine-induced paracrystals prolong the activity of signal transducers and activators of transcription (STAT) and provide a model for the regulation of protein solubility by small ubiquitin-like modifier (SUMO)

The biological effects of cytokines are mediated by STAT proteins, a family of dimeric transcription factors. In order to elicit transcriptional activity, the STATs require activation by phosphorylation of a single tyrosine residue. Our experiments revealed that fully tyrosine-phosphorylated STAT dimers polymerize via Tyr(P)-Src homology 2 domain interactions and assemble into paracrystalline arrays in the nucleus of cytokine-stimulated cells. Paracrystals are demonstrated to be dynamic reservoirs that protect STATs from dephosphorylation. Activated STAT3 forms such paracrystals in acute phase liver cells. Activated STAT1, in contrast, does not normally form paracrystals. By reversing the abilities of STAT1 and STAT3 to be sumoylated, we show that this is due to the unique ability of STAT1 among the STATs to conjugate to small ubiquitin-like modifier (SUMO). Sumoylation had one direct effect; it obstructed proximal tyrosine phosphorylation, which led to semiphosphorylated STAT dimers. These competed with their fully phosphorylated counterparts and interfered with their polymerization into paracrystals. Consequently, sumoylation, by preventing paracrystal formation, profoundly curtailed signal duration and reporter gene activation in response to cytokine stimulation of cells. The study thus identifies polymerization of activated STAT transcription factors as a positive regulatory mechanism in cytokine signaling. It provides a unifying explanation for the different subnuclear distributions of STAT transcription factors and reconciles the conflicting results as to the role of SUMO modification in STAT1 functioning. We present a generally applicable system in which protein solubility is maintained by a disproportionately small SUMO-modified fraction, whereby modification by SUMO partially prevents formation of polymerization interfaces, thus generating competitive polymerization inhibitors.

Interleukin-19: multiple roles in immune regulation and disease

First reported in 1999, IL-19 remains a mystery in many ways. Despite appearing in many genome scans and candidate gene studies, and having been searched for specifically as part of the IL-10 family, its function is still to be defined. Nonetheless, a pattern of Th2 promotion is coalescing from this nebulous body of work, supported by increasing evidence for a role in asthma. Similarly, a clear but less intuitive role as a subtle immunomodulator is emerging in psoriasis and chronic inflammatory disorders in general. Indeed, several human diseases and their animal models have highlighted a role for IL-19. Key questions remain, relating to the nature of its receptor, its function (if any) on leukocytes and how its effects are distinguished by the cell from those of IL-20 and IL-24. In this review, I shall attempt to bring together a summary of the known work - disparate as it may be - as well as presenting a picture of these two important clinical disorders and the potential involvement of this somewhat enigmatic cytokine.

Distinct roles of IL-22 in human psoriasis and inflammatory bowel disease

IL-22, an IL-10 family cytokine, is produced by different leukocyte subsets, including T cells, NK cells and lymphoid tissue inducer (LTi) cells. IL-22 mediates the crosstalk between leukocytes and tissue epithelia because its receptor is preferentially expressed on various tissue epithelial cells. IL-22 is essential for host defense against infections of extracellular pathogens, such as bacteria and yeasts, by eliciting various innate defensive mechanisms from tissue epithelial cells and promoting wound-healing responses. In autoimmune diseases, however, diverse tissue microenvironments and underlying pathogenic mechanisms may result in opposing contributions of IL-22 in disease progression. For example, in psoriasis, IL-22 can synergize with other proinflammatory cytokines to induce many of the pathogenic phenotypes from keratinocytes and exacerbate disease progression. In contrast, IL-22 plays a beneficial role in IBD by enhancing barrier integrity and epithelial innate immunity of intestinal tract.

The evolutionary biology of poxviruses

The poxviruses (family Poxviridae) are a family of double-stranded viruses including several species that infect humans and their domestic animals, most notably Variola virus (VARV), the causative agent of smallpox. The evolutionary biology of these viruses poses numerous questions, for which we have only partial answers at present. Here we review evidence regarding the origin of poxviruses, the frequency of host transfer in poxvirus history, horizontal transfer of host genes to poxviruses, and the population processes accounting for patterns of nucleotide sequence polymorphism.

A method for the generation of ectromelia virus (ECTV) recombinants: in vivo analysis of ECTV vCD30 deletion mutants

BACKGROUND

Ectromelia virus (ECTV) is the causative agent of mousepox, a lethal disease of mice with similarities to human smallpox. Mousepox progression involves replication at the initial site of infection, usually the skin, followed by a rapid spread to the secondary replicative organs, spleen and liver, and finally a dissemination to the skin, where the typical rash associated with this and other orthopoxviral induced diseases appears. Case fatality rate is genetically determined and reaches up to 100% in susceptible mice strains. Like other poxviruses, ECTV encodes a number of proteins with immunomodulatory potential, whose role in mousepox progression remains largely undescribed. Amongst these is a secreted homologue of the cellular tumour necrosis factor receptor superfamily member CD30 which has been proposed to modulate a Th1 immune response in vivo.

METHODOLOGY/PRINCIPAL FINDINGS

To evaluate the contribution of viral CD30 (vCD30) to virus pathogenesis in the infected host, we have adapted a novel transient dominant method for the selection of recombinant ECTVs. Using this method, we have generated an ECTV vCD30 deletion mutant, its corresponding revertant control virus as well as a virus encoding the extracellular domain of murine CD30. These viruses contain no exogenous marker DNA sequences in their genomes, as opposed to other ECTVs reported up to date.

CONCLUSIONS/SIGNIFICANCE

We show that the vCD30 is expressed as a secreted disulfide linked trimer and that the absence of vCD30 does not impair mousepox induced fatality in vivo. Replacement of vCD30 by a secreted version of mouse CD30 caused limited attenuation of ECTV. The recombinant viruses generated may be of use in the study of the role of the cellular CD30-CD30L interaction in the development of the immune response. The method developed might be useful for the construction of ECTV mutants for the study of additional genes.

Differential signaling of cmvIL-10 through common variants of the IL-10 receptor 1

Human IL-10 (hIL-10) signaling is mediated by receptors consisting of two subunits, IL-10 receptor 1 (IL-10R1) and IL-10 receptor 2. Two common variants of the IL-10R1 (Ser 138 Gly (single-nucleotide polymorphism 3, SNP3) and Gly 330 Arg (SNP4)) are associated with diverse disease phenotypes. Viral homologs to hIL-10, such as cmvIL-10, utilize the same IL-10 receptor complex as part of viral immune evasion strategies. For the present study we hypothesized that IL-10R1 variants alter the ability of viral IL-10 to utilize the IL-10R1 signaling pathway. HeLa cell clones expressing different IL-10R1 haplotypes (WT or any variant) were incubated with hIL-10 or cmvIL-10. In cells expressing IL-10R1-WT, cmvIL-10 (both non-glycosylated- and HeLa-expressed) resulted in equal or slightly stronger STAT3 phosphorylation compared with hIL-10. In clones expressing IL-10R1-SNP3, IL-10R1-SNP4 or IL-10R1-SNP3+4, the cmvIL-10 showed significantly less STAT3 phosphorylation, especially when HeLa-expressed cytokines were used. Time course experiments demonstrated a slower kinetic of cmvIL-10 STAT3 activation through the variant IL-10R1. Similarly, IL-10R1 variants decreased the cmvIL-10-induced SOCS3 and signaling lymphocytic activation molecule mRNA expression. These data suggest that the IL-10R1 variants differentially reduce the signaling activity of cmvIL-10 and thereby may affect CMV's ability to escape from the host's immune surveillance.

Vaccinia virus protein C16 acts intracellularly to modulate the host response and promote virulence

The vaccinia virus (VACV) strain Western Reserve C16 protein has been characterized and its effects on virus replication and virulence have been determined. The C16L gene is present in the inverted terminal repeat and so is one of the few VACV genes that are diploid. The C16 protein is highly conserved between different VACV strains, and also in the orthopoxviruses variola virus, ectromelia virus, horsepox virus and cowpox virus. C16 is a 37.5 kDa protein, which is expressed early during infection and localizes to the cell nucleus and cytoplasm of infected and transfected cells. The loss of the C16L gene had no effect on virus growth kinetics but did reduce plaque size slightly. Furthermore, the virulence of a virus lacking C16L (vDeltaC16) was reduced in a murine intranasal model compared with control viruses and there were reduced virus titres from 4 days post-infection. In the absence of C16, the recruitment of inflammatory cells in the lung and bronchoalveolar lavage was increased early after infection (day 3) and more CD4(+) and CD8(+) T cells expressed the CD69 activation marker. Conversely, late after infection with vDeltaC16 (day 10) there were fewer T cells remaining, indicating more rapid clearance of infection. Collectively, these data indicate that C16 diminishes the immune response and is an intracellular immunomodulator.

Inflammation et virus: déclenchement,contournements et détournements de la réponse inflammatoire au cours des infections virales

The inflammatory process aims at opposing an early responseto the viral infections. Inflammation is supposed to delay or limit viral multiplication and dissemination until a specific immune response can be raised. This review introduces the basis of virus-induced inflammation and presents various strategies that are used by viruses to circumvent or exploit inflammation for their own benefit.

Genus Parapoxvirus

Highly contagious pustular skin infections of sheep, goats and cattle that were unwittingly transmitted to humans from close contact with infected animals, have been the scourge of shepherds, herdsmen and dairy farmers for centuries. In more recent times we recognise that these proliferative pustular lesions are likely to be caused by a group of zoonotic viruses that are classified as parapoxviruses. In addition to infecting the above ungulates, parapoxviruses have more recently been isolated from seals, camels, red deer and reindeer and most have been shown to infect man. The parapoxviruses have one of the smallest genomes of the poxvirus family (140 kb) yet share over 70% of their genes with the most virulent members. Like other poxviruses, the central core of the genomes encode factors for virus transcription and replication, and structural proteins, whereas the terminal regions encode accessory factors that give the parapoxvirus group many of its unique features. Several genes of parapoxviruses are unique to this genus and encode factors that target inflammation, the innate immune responses and the development of acquired immunity. These factors include a homologue of mammalian interleukin (IL)-10, a chemokine binding protein and a granulocyte-macrophage colony stimulating factor /IL-2 binding protein. The ability of this group to reinfect their hosts, even though a cell-mediated memory response is induced during primary infection, may be related to their epitheliotropic niche and the immunomodulators they produce. In this highly localised environment, the secreted immunomodulators only interfere with the local immune response and thus do not compromise the host’s immune system. The discovery of a vascular endothelial growth factor-like gene may explain the highly vascular nature of parapoxvirus lesions. There are many genes of parapoxviruses which do not encode polypeptides with significant matches with protein sequences in public databases, separating this genus from most other mammalian poxviruses. These genes appear to be involved in inhibiting apoptosis, manipulating cell cycle progression and degradation of cellular proteins that may be involved in the stress response, thus allowing the virus to subvert intracellular antiviral mechanisms and enhance the availability of cellular molecules required for replication. Parapoxviruses in common with Molluscum contagiosum virus lack a number of genes that are highly conserved in other poxviruses, including factors for nucleotide metabolism, serine protease inhibitors and kelch-like proteins. It is apparent that parapoxviruses have evolved a unique repertoire of genes that have allowed adaptation to the highly specialised environment of the epidermis.

Structural studies of the interleukin-19 subfamily of cytokines

The interleukin-19 (IL-19) subfamily of cytokines is part of a larger family of homologs of IL-10 that includes two groups of proteins: five viral cytokines, and eight cellular cytokines, having quite different biological activities. Among proteins of the latter group, IL-19, IL-20, IL-22, and IL-24 were suggested to form a structurally unique IL-19 subfamily characterized by their structural features and aggregation state as monomers. IFN-lambda1, IFN-lambda2, and IFN-lambda3 are likely to belong to this subfamily, and it is still not clear whether IL-26 belongs to it or not. In spite of their differences in biological function, all cellular homologs of IL-10 used for signaling a set of five overlapping membrane-bound receptors: three long receptor chains (IL-20R1, IL-22R1, and IFN-lambdaR) and two short receptor chains (IL-20R2 and IL-10R2). Signal transduction is initiated when a cytokine binds two receptor chains, one long and one short, forming a ternary complex. Crystal structures of IL-19 and IL-22 showed that these cytokines consist of seven amphipathic helices of different length organized in helical bundle, covering an extensive hydrophobic core. Based on the similarity of the structures with the structure of a single domain of IL-10, and with the crystal structure of a binary IL-10/IL-10R1 complex, putative receptor binding sites on the surface of IL-19 and IL-22 were identified. This chapter summarizes the available structural data on the IL-19 subfamily of cytokines and their putative ligand/receptor complexes.

Yaba-like disease virus chemokine receptor 7L, a CCR8 orthologue

Yaba-like disease virus (YLDV) gene 7L encodes a seven-transmembrane G protein-coupled receptor with 53 % amino acid identity to human CC chemokine receptor 8 (CCR8). Initial characterization of 7L showed that this 56 kDa cell-surface glycoprotein binds human CCL1 with high affinity (Kd=0.6 nM) and induces signal transduction by activation of heterotrimeric G proteins and downstream protein kinases. Further characterization of YLDV 7L is presented here and shows that murine CC chemokines can induce G-protein activation via the 7L receptor, despite having a low binding affinity for this receptor. In addition, when expressed by recombinant vaccinia virus (VACV), YLDV 7L was found on the outer envelope of VACV extracellular enveloped virus. The contribution of 7L to poxvirus pathogenesis was investigated by infection of mice with a recombinant VACV expressing 7L (vDeltaB8R-7L) and was compared with the outcome of infection by parental and revertant control viruses. In both intranasal and intradermal models, expression of 7L caused attenuation of VACV. The role of this protein in viral virulence is discussed.

Viral strategies for evading antiviral cellular immune responses of the host

The host invariably responds to infecting viruses by activating its innate immune system and mounting virus-specific humoral and cellular immune responses. These responses are aimed at controlling viral replication and eliminating the infecting virus from the host. However, viruses have evolved numerous strategies to counter and evade host's antiviral responses. Providing specific examples from the published literature, we discuss in this review article various strategies that viruses have developed to evade antiviral cellular responses of the host. Unraveling these viral strategies allows a better understanding of the host-pathogen interactions and their coevolution. This knowledge is important for identifying novel molecular targets for developing antiviral reagents. Finally, it may also help devise new knowledge-based strategies for developing antiviral vaccines.

Murine interferon lambdas (type III interferons) exhibit potent antiviral activity in vivo in a poxvirus infection model

Human interferon lambdas (IFN-lambdas) (type III IFNs) exhibit antiviral activity in vitro by binding to a receptor complex distinct from that used by type I and type II IFNs, and subsequent signalling through the Janus kinase signal transducers and activators of transcription (STAT) pathway. However, evidence for a function of type III IFNs during virus infection in vivo is lacking. Here, the expression of murine IFN-lambdas by recombinant vaccinia virus (VACV) is described and these proteins are shown to have potent antiviral activity in vivo. VACV expressing murine IFN-lambda2 (vIFN-lambda2) and IFN-lambda3 (vIFN-lambda3) showed normal growth in tissue culture and expressed N-glycosylated IFN-lambda in infected cell extracts and culture supernatants. The role that murine IFN-lambdas play during virus infection was assessed in two different mouse models. vIFN-lambda2 and vIFN-lambda3 were avirulent for mice infected intranasally and induced no signs of illness or weight loss, in contrast to control viruses. Attenuation of vIFN-lambda2 was associated with increases in lymphocytes in bronchial alveolar lavages and CD4+ T cells in total-lung lymphocyte preparations. In addition, vIFN-lambda2 was cleared more rapidly from infected lungs and, in contrast to control viruses, did not disseminate to the brain. Expression of IFN-lambda2 also attenuated VACV in an intradermal-infection model, characterized by a delay in lesion onset and reduced lesion size. Thus, by characterizing murine IFN-lambdas within a mouse infection model, the potent antiviral and immunostimulatory activity of IFN-lambdas in response to poxvirus infection has been demonstrated.