Impaired antiviral response and alpha/beta interferon induction in mice lacking beta interferon

Type I interferons in regulation of mucosal immunity

The mucosal system is the first line of defense against many pathogens. It is continuously exposed to dietary and microbial antigens, and thus the host must maintain a homeostatic environment between commensal microbiota and pathogenic infections. Following infections and inflammatory events, a rapid innate immune response is evoked to dampen the inflammatory processes. Type I interferons, a family of pleiotropic cytokines and major products of the innate immune response, have a key role in these early immune events at the mucosa, as reviewed here. With the emergence of new discoveries of immune cell types in mucosal tissues and their reactions to commensal and pathogenic organisms, we also review the opportunities for exciting research in this field.

Removal of vaccinia virus genes that block interferon type I and II pathways improves adaptive and memory responses of the HIV/AIDS vaccine candidate NYVAC-C in mice

Poxviruses encode multiple inhibitors of the interferon (IFN) system, acting at different levels and blocking the induction of host defense mechanisms. Two viral gene products, B19 and B8, have been shown to act as decoy receptors of type I and type II IFNs, blocking the binding of IFN to its receptor. Since IFN plays a major role in innate immune responses, in this investigation we asked to what extent the viral inhibitors of the IFN system impact the capacity of poxvirus vectors to activate immune responses. This was tested in a mouse model with single and double deletion mutants of the vaccine candidate NYVAC-C, which expresses the HIV-1 Env, Gag, Pol, and Nef antigens. When deleted individually or in double, the type I (B19) and type II (B8) IFN binding proteins were not required for virus replication in cultured cells. Studies of immune responses in mice after DNA prime/NYVAC boost revealed that deletion of B8R and/or B19R genes improved the magnitude and quality of HIV-1-specific CD8(+) T cell adaptive immune responses and impacted their memory phase, changing the contraction, the memory differentiation, the effect magnitude, and the functionality profile. For B cell responses, deletion of the viral gene B8R and/or B19R had no effect on antibody levels to HIV-1 Env. These findings revealed that single or double deletion of viral factors (B8 and B19) targeting the IFN pathway is a useful approach in the design of improved poxvirus-based vaccines.

The nitric oxide pathway provides innate antiviral protection in conjunction with the type I interferon pathway in fibroblasts

The innate host response to virus infection is largely dominated by the production of type I interferon and interferon stimulated genes. In particular, fibroblasts respond robustly to viral infection and to recognition of viral signatures such as dsRNA with the rapid production of type I interferon; subsequently, fibroblasts are a key cell type in antiviral protection. We recently found, however, that primary fibroblasts deficient for the production of interferon, interferon stimulated genes, and other cytokines and chemokines mount a robust antiviral response against both DNA and RNA viruses following stimulation with dsRNA. Nitric oxide is a chemical compound with pleiotropic functions; its production by phagocytes in response to interferon-γ is associated with antimicrobial activity. Here we show that in response to dsRNA, nitric oxide is rapidly produced in primary fibroblasts. In the presence of an intact interferon system, nitric oxide plays a minor but significant role in antiviral protection. However, in the absence of an interferon system, nitric oxide is critical for the protection against DNA viruses. In primary fibroblasts, NF-κB and interferon regulatory factor 1 participate in the induction of inducible nitric oxide synthase expression, which subsequently produces nitric oxide. As large DNA viruses encode multiple and diverse immune modulators to disable the interferon system, it appears that the nitric oxide pathway serves as a secondary strategy to protect the host against viral infection in key cell types, such as fibroblasts, that largely rely on the type I interferon system for antiviral protection.

CD11b⁺, Ly6G⁺ cells produce type I interferon and exhibit tissue protective properties following peripheral virus infection

The goal of the innate immune system is containment of a pathogen at the site of infection prior to the initiation of an effective adaptive immune response. However, effector mechanisms must be kept in check to combat the pathogen while simultaneously limiting undesirable destruction of tissue resulting from these actions. Here we demonstrate that innate immune effector cells contain a peripheral poxvirus infection, preventing systemic spread of the virus. These innate immune effector cells are comprised primarily of CD11b⁺Ly6C⁺Ly6G^- monocytes that accumulate initially at the site of infection, and are then supplemented and eventually replaced by CD11b⁺Ly6C⁺Ly6G⁺ cells. The phenotype of the CD11b⁺Ly6C⁺Ly6G⁺ cells resembles neutrophils, but the infiltration of neutrophils typically occurs prior to, rather than following, accumulation of monocytes. Indeed, it appears that the CD11b⁺Ly6C⁺Ly6G⁺ cells that infiltrated the site of VACV infection in the ear are phenotypically distinct from the classical description of both neutrophils and monocyte/macrophages. We found that CD11b⁺Ly6C⁺Ly6G⁺ cells produce Type I interferons and large quantities of reactive oxygen species. We also observed that depletion of Ly6G⁺ cells results in a dramatic increase in tissue damage at the site of infection. Tissue damage is also increased in the absence of reactive oxygen species, although reactive oxygen species are typically thought to be damaging to tissue rather than protective. These data indicate the existence of a specialized population of CD11b⁺Ly6C⁺Ly6G⁺ cells that infiltrates a site of virus infection late and protects the infected tissue from immune-mediated damage via production of reactive oxygen species. Regulation of the action of this population of cells may provide an intervention to prevent innate immune-mediated tissue destruction.

During a natural virus infection, small doses of infectious virus are deposited at a peripheral infection site, and then a “race” ensues, in which the replicating virus attempts to “outpace” the responding immune system of the host. In the early phases of infection, the innate immune system must contain the infection prior to the development of an effective adaptive response. Here we have characterized the cells of the innate immune system that move to a site of peripheral virus infection, and we find that a subset of these cells display atypical expression of cell surface molecules, timing of infiltration, and function. These cells protect the infected tissue from damage by producing reactive oxygen molecules, which are widely accepted to increase tissue damage. Therefore our findings indicate that during a peripheral virus infection, the typical rules governing the function of the innate immune system are altered to prevent tissue damage.

Modulation of NKp30- and NKp46-mediated natural killer cell responses by poxviral hemagglutinin

Natural killer (NK) cells are an important element in the immune defense against the orthopox family members vaccinia virus (VV) and ectromelia virus (ECTV). NK cells are regulated through inhibitory and activating signaling receptors, the latter involving NKG2D and the natural cytotoxicity receptors (NCR), NKp46, NKp44 and NKp30. Here we report that VV infection results in an upregulation of ligand structures for NKp30 and NKp46 on infected cells, whereas the binding of NKp44 and NKG2D was not significantly affected. Likewise, infection with ectromelia virus (ECTV), the mousepox agent, enhanced binding of NKp30 and, to a lesser extent, NKp46. The hemagglutinin (HA) molecules from VV and ECTV, which are known virulence factors, were identified as novel ligands for NKp30 and NKp46. Using NK cells with selectively silenced NCR expression and NCR-CD3ζ reporter cells, we observed that HA present on the surface of VV-infected cells, or in the form of recombinant soluble protein, was able to block NKp30-triggered activation, whereas it stimulated the activation through NKp46. The net effect of this complex influence on NK cell activity resulted in a decreased NK lysis susceptibility of infected cells at late time points of VV infection when HA was expression was pronounced. We conclude that poxviral HA represents a conserved ligand of NCR, exerting a novel immune escape mechanism through its blocking effect on NKp30-mediated activation at a late stage of infection.

Beta interferon controls West Nile virus infection and pathogenesis in mice

Studies with mice lacking the common plasma membrane receptor for type I interferon (IFN-αβR(-)(/)(-)) have revealed that IFN signaling restricts tropism, dissemination, and lethality after infection with West Nile virus (WNV) or several other pathogenic viruses. However, the specific functions of individual IFN subtypes remain uncertain. Here, using IFN-β(-)(/)(-) mice, we defined the antiviral and immunomodulatory function of this IFN subtype in restricting viral infection. IFN-β(-)(/)(-) mice were more vulnerable to WNV infection than wild-type mice, succumbing more quickly and with greater overall mortality, although the phenotype was less severe than that of IFN-αβR(-)(/)(-) mice. The increased susceptibility of IFN-β(-)(/)(-) mice was accompanied by enhanced viral replication in different tissues. Consistent with a direct role for IFN-β in control of WNV replication, viral titers in ex vivo cultures of macrophages, dendritic cells, fibroblasts, and cerebellar granule cell neurons, but not cortical neurons, from IFN-β(-)(/)(-) mice were greater than in wild-type cells. Although detailed immunological analysis revealed no major deficits in the quality or quantity of WNV-specific antibodies or CD8(+) T cells, we observed an altered CD4(+) CD25(+) FoxP3(+) regulatory T cell response, with greater numbers after infection. Collectively, these results suggest that IFN-β controls WNV pathogenesis by restricting infection in key cell types and by modulating T cell regulatory networks.

Glycosaminoglycans mediate retention of the poxvirus type I interferon binding protein at the cell surface to locally block interferon antiviral responses

Eradication of smallpox was accomplished 30 yr ago, but poxviral infections still represent a public health concern due to the potential release of variola virus or the emergence of zoonotic poxviruses, such as monkeypox virus. A critical determinant of poxvirus virulence is the inhibition of interferons (IFNs) by the virus-encoded type I IFN-binding protein (IFNα/βBP). This immunomodulatory protein is secreted and has the unique property of interacting with the cell surface in order to prevent IFN-mediated antiviral responses. However, the mechanism of its attachment to the cell surface remains unknown. Using surface plasmon resonance and cell-binding assays, we report that the IFNα/βBP from vaccinia virus, the smallpox vaccine, interacts with cell surface glycosaminoglycans (GAGs). Analysis of the contribution of different regions of the protein to cell surface binding demonstrated that clusters of basic residues in the first immunoglobulin domain mediate GAG interactions. Furthermore, mutation of the GAG-interaction motifs does not affect its IFN-binding and -blocking capacity. Functional conservation of GAG-binding sites is demonstrated for the IFNα/βBP from variola and monkeypox viruses, extending our understanding of immune modulation by the most virulent human poxviruses. These results are relevant for the design of improved vaccines and intervention strategies.

RIG-I/MDA5/MAVS are required to signal a protective IFN response in rotavirus-infected intestinal epithelium

Rotavirus is a dsRNA virus that infects epithelial cells that line the surface of the small intestine. It causes severe diarrheal illness in children and ∼500,000 deaths per year worldwide. We studied the mechanisms by which intestinal epithelial cells (IECs) sense rotavirus infection and signal IFN-β production, and investigated the importance of IFN-β production by IECs for controlling rotavirus production by intestinal epithelium and virus excretion in the feces. In contrast with most RNA viruses, which interact with either retinoic acid-inducible gene I (RIG-I) or melanoma differentiation-associated gene 5 (MDA5) inside cells, rotavirus was sensed by both RIG-I and MDA5, alone and in combination. Rotavirus did not signal IFN-β through either of the dsRNA sensors TLR3 or dsRNA-activated protein kinase (PKR). Silencing RIG-I or MDA5, or their common adaptor protein mitochondrial antiviral signaling protein (MAVS), significantly decreased IFN-β production and increased rotavirus titers in infected IECs. Overexpression of laboratory of genetics and physiology 2, a RIG-I-like receptor that interacts with viral RNA but lacks the caspase activation and recruitment domains required for signaling through MAVS, significantly decreased IFN-β production and increased rotavirus titers in infected IECs. Rotavirus-infected mice lacking MAVS, but not those lacking TLR3, TRIF, or PKR, produced significantly less IFN-β and increased amounts of virus in the intestinal epithelium, and shed increased quantities of virus in the feces. We conclude that RIG-I or MDA5 signaling through MAVS is required for the activation of IFN-β production by rotavirus-infected IECs and has a functionally important role in determining the magnitude of rotavirus replication in the intestinal epithelium.

Fish virus-induced interferon exerts antiviral function through Stat1 pathway

Virus-induced interferons (IFNs) have been identified in various fish species and display antiviral activities similar to mammalian type I IFNs. However, apart from the mammalian IFN system, the IFN signaling pathway remains largely unknown. Using transient transfection and recombinant protein, we are reporting in this study that a crucian carp (Carassius auratus L.) IFN exhibits strong antiviral activity against grass carp hemorrhagic virus (GCHV) infection and also mediates Poly I:C-induced antiviral response, which correlates with its ability to induce a set of IFN-stimulated genes (ISGs). Strikingly, overexpression of wild-type Stat1 increases the effects of IFN on both the expression of ISGs and the inhibition of virus infection, whereas a dominant negative mutant of Stat1 (Stat1-Delta C), which lacks of the C-terminal transcriptional activation domain (TAD), inhibits the antiviral activity of IFN and reduces the expression of ISGs, demonstrating that fish IFN induces the expression of ISGs and host antiviral response through Stat1 pathway reminiscent that of mammalian IFNs. Significantly, unlike mammalian type I IFNs, recombinant fish IFN is able to upregulate IFN itself, which is enhanced by overexpression of Stat1 but impaired by knockdown of Stat1, indicating a positive feedback loop in regulation of IFN itself. These results provide strong evidence for the existence of an evolutionary conserved Stat1 pathway between fish and mammals, which is indispensable for fish virus-induced IFN antiviral response.

Viral transformation for production of personalized type I interferons

Type I interferons (IFN) are cytokines with many functions and have been widely used to treat many human diseases such as hepatitis C virus infection. Using the viral transformation and priming properties of Epstein-Barr virus, we have developed a system that can produce high levels of "personalized" IFNs, which are produced from the cells of the patient to whom the IFNs are to be administrated. We demonstrate the feasibility of the system. This seems to be the first report for the establishment of a personalized IFN-production system. The personalized IFNs could have a longer circulation time, fewer side effects but higher efficacy. We anticipate that the system can provide an improved form of IFN for medical uses.

The highly virulent variola and monkeypox viruses express secreted inhibitors of type I interferon

Variola virus (VARV) caused smallpox, one of the most devastating human diseases and the first to be eradicated, but its deliberate release represents a dangerous threat. Virulent orthopoxviruses infecting humans, such as monkeypox virus (MPXV), could fill the niche left by smallpox eradication and the cessation of vaccination. However, immunomodulatory activities and virulence determinants of VARV and MPXV remain largely unexplored. We report the molecular characterization of the VARV- and MPXV-secreted type I interferon-binding proteins, which interact with the cell surface after secretion and prevent type I interferon responses. The proteins expressed in the baculovirus system have been purified, and their interferon-binding properties characterized by surface plasmon resonance. The ability of these proteins to inhibit a broad range of interferons was investigated to identify potential adaptation to the human immune system. Furthermore, we demonstrate by Western blot and activity assays the expression of the type I interferon inhibitor during VARV and MPXV infections. These findings are relevant for the design of new vaccines and therapeutics to smallpox and emergent virulent orthopoxviruses because the type I interferon-binding protein is a major virulence factor in animal models, vaccination with this protein induces protective immunity, and its neutralization prevents disease progression.

Neutrophils responsive to endogenous IFN-beta regulate tumor angiogenesis and growth in a mouse tumor model

Angiogenesis is a hallmark of malignant neoplasias, as the formation of new blood vessels is required for tumors to acquire oxygen and nutrients essential for their continued growth and metastasis. However, the signaling pathways leading to tumor vascularization are not fully understood. Here, using a transplantable mouse tumor model, we have demonstrated that endogenous IFN-beta inhibits tumor angiogenesis through repression of genes encoding proangiogenic and homing factors in tumor-infiltrating neutrophils. We determined that IFN-beta-deficient mice injected with B16F10 melanoma or MCA205 fibrosarcoma cells developed faster-growing tumors with better-developed blood vessels than did syngeneic control mice. These tumors displayed enhanced infiltration by CD11b+Gr1+ neutrophils expressing elevated levels of the genes encoding the proangiogenic factors VEGF and MMP9 and the homing receptor CXCR4. They also expressed higher levels of the transcription factors c-myc and STAT3, known regulators of VEGF, MMP9, and CXCR4. In vitro, treatment of these tumor-infiltrating neutrophils with low levels of IFN-beta restored expression of proangiogenic factors to control levels. Moreover, depletion of these neutrophils inhibited tumor growth in both control and IFN-beta-deficient mice. We therefore suggest that constitutively produced endogenous IFN-beta is an important mediator of innate tumor surveillance. Further, we believe our data help to explain the therapeutic effect of IFN treatment during the early stages of cancer development.

Activation of an antiviral response in normal but not transformed mouse cells: a new determinant of minute virus of mice oncotropism

Parvovirus minute virus of mice (MVMp) is endowed with oncotropic properties so far ascribed only to the dependency of the virus life cycle on cellular factors expressed during S phase and/or modulated by malignant transformation. For other viruses oncotropism relies on their inability to circumvent type I interferon (IFN)-induced innate antiviral mechanisms, the first line of defense triggered by normal cells against viral infections. These agents propagate, therefore, preferentially in transformed/tumor cells, which often lack functional antiviral mechanisms. The present study aimed at investigating whether antiviral processes also contribute to MVMp oncotropism. Our results demonstrate that in contrast to MVMp-permissive transformed mouse A9 fibroblasts, freshly isolated normal counterparts (mouse embryonic fibroblasts [MEFs]) mount, through production and release of type I IFNs upon their infection, an antiviral response against MVMp lytic multiplication. Pretreatment of MEFs with a type I IFN-beta-neutralizing antibody, prior to MVMp infection, inhibits the virus-triggered antiviral response and improves the fulfillment of the MVMp life cycle. Our results also show that part of the A9 permissiveness to MVMp relies on the inability to produce type I IFNs upon parvovirus infection, a feature related either to an A9 intrinsic deficiency of this process or to an MVMp-triggered inhibitory mechanism, since stimulation of these cells by exogenous IFN-beta strongly inhibits the parvovirus life cycle. Taken together, our results demonstrate for the first time that parvovirus infection triggers an innate antiviral response in normal cells and suggest that the MVMp oncotropism depends at least in part on the failure of infected transformed cells to mount such a response.

Dynamic accumulation of plasmacytoid dendritic cells in lymph nodes is regulated by interferon-β

Plasmacytoid dendritic cells (pDCs) represent a major cellular component of our front-line defense against viruses because of their capacity to rapidly secrete type I interferon (IFN)–α and -β after infection. Constant immunosurveillance of the host requires that lymphocytes traffic through lymph nodes (LNs) to sample antigen, yet little is known about the dynamics of pDC accumulation within the secondary lymphoid organs. Here we show that pDCs readily accumulate within the secondary lymphoid organs of mice after virus infection. Interestingly, retention of pDC within LNs is enhanced in the presence of the sphingoshine-1-phosphate receptor agonist FTY720 in a manner similar to that observed for B and T lymphocytes. Ex vivo comparison of mouse pDCs with lymphocytes revealed that pDCs express sphingoshine-1-phosphate 4 and also constitutively express CD69, which is further up-regulated upon virus infection. In IFN-β−/− mice, accumulation of pDC and lymphocytes within LNs is reduced both during viral infection and under steady state conditions, and these defects can be reversed by adding recombinant IFN-β in vivo. These data suggest that pDC and lymphocytes use similar mechanisms for retention within LNs and that these processes are influenced by IFN-β even in the absence of viral infection.

The immunologic aspects of poxvirus oncolytic therapy

The concept of using replicating oncolytic viruses in cancer therapy dates to the beginning of the twentieth century. However, in the last few years, an increasing number of pre-clinical and clinical trials have been carried out with promising preliminarily results. Novel, indeed, is the suggestion that viral oncolytic therapy might not operate exclusively through an oncolysis-mediated process but additionally requires the "assistance" of the host's immune system. Originally, the host's immune response was believed to play a predominant obstructive role against viral replication, hence limiting the anti-tumor efficacy of viral vectors. Recent data, however, suggest that the immune response may also play a key role in promoting tumor destruction in association with the oncolytic process. In fact, immune effector pathways activated during oncolytic virus-induced tumor rejection seem to follow a similar pattern to those observed when the broader phenomenon of immune-mediated tissue-specific rejection occurs in other immune-related pathologies. We recently formulated the "Immunologic Constant of Rejection" hypothesis, emphasizing commonalties in transcriptional patterns observed when tissue-destruction occurs: whether with a favorable outcome, such as in tumor rejection and pathogen clearance; or a destructive one, such as in allograft rejection or autoimmunity. Here, we propose that a similar mechanism induces clearance of virally infected tumors and that such a mechanism is primarily dependent on innate immune functions.

Lactate dehydrogenase-elevating virus induces systemic lymphocyte activation via TLR7-dependent IFNalpha responses by plasmacytoid dendritic cells

BACKGROUND

Lactate dehydrogenase-elevating virus (LDV) is a natural infectious agent of mice. Like several other viruses, LDV causes widespread and very rapid but transient activation of both B cells and T cells in lymphoid tissues and the blood. The mechanism of this activation has not been fully described and is the focus of the current studies.

PRINCIPAL FINDINGS

A known inducer of early lymphocyte activation is IFNalpha, a cytokine strongly induced by LDV infection. Neutralization of IFNalpha in the plasma from infected mice ablated its ability to activate lymphocytes in vitro. Since the primary source of virus-induced IFNalpha in vivo is often plasmacytoid dendritic cells (pDC's), we depleted these cells prior to LDV infection and tested for lymphocyte activation. Depletion of pDC's in vivo eradicated both the LDV-induced IFNalpha response and lymphocyte activation. A primary receptor in pDC's for single stranded RNA viruses such as LDV is the toll-like receptor 7 (TLR7) pattern recognition receptor. Infection of TLR7-knockout mice revealed that both the IFNalpha response and lymphocyte activation were dependent on TLR7 signaling in vivo. Interestingly, virus levels in both TLR7 knockout mice and pDC-depleted mice were indistinguishable from controls indicating that LDV is largely resistant to the systemic IFNalpha response.

CONCLUSION

Results indicate that LDV-induced activation of lymphocytes is due to recognition of LDV nucleic acid by TLR7 pattern recognition receptors in pDC's that respond with a lymphocyte-inducing IFNalpha response.

Alteration of TLR3 pathways by glucocorticoids may be responsible for immunosusceptibility of human corneal epithelial cells to viral infections

PURPOSE

The toll-like receptor 3 (TLR3) recognizes viral double-stranded RNA and its synthetic analog polyriboinosinic-polyribocytidylic acid (poly(I:C)), and the activation of TLR3 is known to induce the production of type I interferon (IFN) and inflammatory cytokines/chemokines. The purpose of this study was to determine the role played by innate responses to a herpes simplex virus 1 (HSV-1) infection of the corneal epithelial cells. In addition, we determined the effects of immunosuppressive drugs on the innate responses.

METHODS

Cultured human corneal epithelial cells (HCECs) were exposed to poly(I:C), and the expressions of the mRNAs of the cytokines/chemokines macrophage-inflammatory protein 1 alpha (MIP1-alpha), macrophage-inflammatory protein 1 beta (MIP1-beta), interleukin-6 (IL-6), interleukin-8 (IL-8), regulated on activation, normal T cell expressed and secreted (RANTES), Interferon-beta (IFN-beta), and TLR3 were determined using real-time reverse transcription-polymerase chain reaction (RT-PCR). The effects of dexamethasone (DEX, 10(-6) or 10(-5) M) and cyclosporine A (CsA, 10(-6) or 10(-5) M) on the expression of these cytokines and TLR3 were also determined using real-time RT-PCR. Levels of MIP1-alpha, MIP1-beta, IL-6, IL-8, RANTES, and IFN-beta were measured using the enzyme-linked immunosorbent assay (ELISA). The activation of nuclear factor kappa B (NFkappaB) and interferon regulatory factor 3 (IRF3) in HCECs was assessed by immunohistochemical staining. The effects of DEX and CsA on HCECs exposed to HSV-1 (McKrae strain) were also examined.

RESULTS

The expressions of MIP1-alpha, MIP1-beta, IL-6, IL-8, RANTES, IFN-beta, and TLR3 were up-regulated in HCECs exposed to poly(I:C). The poly(I:C)-induced expressions of IL-6 and IL-8 were down-regulated by both DEX and CsA, while the expressions of IFN-beta and TLR3 were suppressed by DEX alone. Similarly, the poly(I:C)-induced activation of NFkappaB was decreased by both DEX and CsA, and the activation of IRF3 was reduced by DEX alone. When HCECs were inoculated with HSV-1, DEX led to a decrease in the expression of IL6, IFN-beta, and TLR3, and an extension of plaque formation.

CONCLUSION

These results indicate that DEX may increase the susceptibility of HCECs to viral infections by altering the TLR3 signaling pathways.

Inborn errors of interferon (IFN)-mediated immunity in humans: insights into the respective roles of IFN-alpha/beta, IFN-gamma, and IFN-lambda in host defense

Interferon (IFN) was originally identified as a substance 'interfering' with viral replication in vitro. The first IFNs to be identified were classified as type I IFNs (IFN-alpha/beta and related molecules), two other types have since been identified: type II IFN (IFN-gamma) and type III IFNs (IFN-lambda). Each IFN binds to one of three type-specific receptors. In the mouse model of experimental infections in vivo, IFN-alpha/beta are essential for immunity to most viruses tested, whereas IFN-gamma is important for immunity to a smaller number of viruses, together with bacteria, fungi, and parasites, consistent with IFN-gamma acting as the 'macrophage activating factor.' The precise role of IFN-lambda remains unclear. In recent years, inborn errors affecting the production of, or the response to, IFNs have been reported in human patients, shedding light onto the function of IFNs in natura. Disorders of IFN-gamma production, caused by IL12B, IL12RB1, and specific NEMO mutations, or of IFN-gamma responses, caused by IFNGR1, IFNGR2, and dominant STAT1 mutations, confer predisposition to mycobacterial disease in patients resistant to most viruses. By contrast, disorders of IFN-alpha/beta and IFN-lambda production, caused by UNC93B1 and TLR3 mutations, confer predisposition to herpes simplex encephalitis (HSE) in otherwise healthy patients. Consistently, patients with impaired responses to IFN-alpha/beta, IFN-gamma, and presumably IFN-lambda (carrying recessive mutations in STAT1), or with impaired responses to IFN-alpha/beta and impaired IFN-gamma production (carrying mutations in TYK2), or with impaired production of IFN-alpha/beta, IFN-gamma, and IFN-lambda (carrying specific mutations in NEMO), are vulnerable to mycobacterial and viral infections, including HSE. These experiments of nature suggest that the three types of IFNs play at least two different roles in host defense. IFN-gamma is essential for anti-mycobacterial immunity, whereas IFN-alpha/beta and IFN-lambda are essential for anti-viral immunity. Future studies in humans aim to define the specific roles of IFN-alpha/beta and IFN-lambda types and individual molecules in host defense in natura.

Interferons and viral infections

Interferons represent a family of cytokines, which is of central importance in the innate immune response to virus infections. All interferons act as secreted ligands of specific cell surface receptors, eliciting the transcription of hundreds of interferon-stimulated genes whose protein products have antiviral activity, as well as antimicrobial, antiproliferative/antitumor, and immunomodulatory effects. Expression of type I and III interferons is induced in virtually all cell types upon recognition of viral molecular patterns, especially nucleic acids, by cytoplasmic and endosomal receptors, whereas type II interferon is induced by cytokines such as IL-12, and its expression is restricted to immune cells such as T cells and NK cells. The effectiveness of the interferon system in counteracting viral infections is reflected by the multitude of inhibitors of interferon induction or interferon action that are encoded by many viruses, preventing their eradication and resulting in the continued coexistence of viruses and vertebrates. The unique biological functions of interferons have led to their therapeutic use in the treatment of diseases such as hepatitis, multiple sclerosis, and certain leukemias.

Differential effects of the type I interferons alpha4, beta, and epsilon on antiviral activity and vaccine efficacy

The type I IFNs exert a range of activities that include antiviral, antiproliferative, and immunomodulatory effects. To study this further, we have constructed recombinant vaccinia viruses expressing HIV or hemagglutinin (HA) Ags along with murine type I IFNs, IFN-alpha(4) (HA-VV-IFN-alpha(4)), IFN-beta (HA-VV-IFN-beta), or IFN-epsilon (HIV-VV-IFN-epsilon), a recently discovered member of this family. Our aims were to characterize IFN-epsilon functionality as a type I IFN and also to study the biological properties of these factors toward the development of safer and more effective vector-based vaccines. HIV-VV-IFN-epsilon and HA-VV-IFN-beta grew to lower titers than did their parental controls in murine cell lines. In vivo, however, HIV-VV-IFN-epsilon growth was not attenuated, while IFN-beta demonstrated potent local antiviral activity with no replication of HA-VV-IFN-beta detected. Flow cytofluorometric analysis of B lymphocytes incubated with virally encoded IFN-epsilon showed up-regulation of activation markers CD69 and CD86, while RT-PCR of IFN-epsilon-treated cells revealed that gene expression levels of antiviral proteins were elevated, indicating the induction of an antiviral state. The use of these constructs in a poxvirus prime-boost immunization regime led to robust humoral and cellular immune responses against the encoded Ags, despite the lack of replication in the case of HA-VV-IFN-beta. Thus, coexpression of these factors may be beneficial in the design of safer vector-based vaccines. Our data also indicate that while IFN-epsilon exhibits certain biological traits similar to other type I IFNs, it may also have a specific role in mucosal immune regulation that is quite distinct.

Mitochondrial localization and pro-apoptotic effects of the interferon-inducible protein ISG12a

ISG12a is one of the most highly induced genes following treatment of cells with type I interferons (IFNs). The encoded protein belongs to a family of poorly characterized, low molecular weight IFN-inducible proteins that includes 6-16 (G1P3), 1-8U (IFITM3), and 1-8D (IFITM2). Our studies demonstrate that the ISG12a protein associates with or inserts into the mitochondrial membrane. Transient expression of ISG12a led to decreased viable cell numbers and enhanced sensitivity to DNA-damage induced apoptosis, effects that were blocked by Bcl-2 co-expression or treatment with a pan-caspase inhibitor. ISG12a enhanced etoposide induced cytochrome c release, Bax activation and loss of mitochondrial membrane potential. siRNA-mediated inhibition of ectopic ISG12a protein expression prevented the sensitization to etoposide-induced apoptosis and also decreased the ability of IFN-beta pretreatment to sensitize cells to etoposide, thereby demonstrating a role for ISG12a in this process. These data suggest that ISG12a contributes to IFN-dependent perturbation of normal mitochondrial function, thus adding ISG12a to a growing list of IFN-induced proteins that impact cellular apoptosis.

Innate Immunity in the Female Reproductive Tract: Role of Sex Hormones in Regulating Uterine Epithelial Cell Protection Against Pathogens

The mucosal immune system in the upper female reproductive tract is uniquely prepared to maintain a balance between the presence of commensal bacteria, sexually transmitted bacterial and viral pathogens, allogeneic spermatozoa, and an immunologically distinct fetus. At the center of this dynamic system are the epithelial cells that line the Fallopian tubes, uterus, cervix and vagina. Epithelial cells provide a first line of defense that confers continuous protection, by providing a physical barrier as well as secretions containing bactericidal and virucidal agents. In addition to maintaining a state of ongoing protection, these cells have evolved to respond to pathogens, in part through Toll-like receptors (TLRs), to enhance innate immune protection and, when necessary, to contribute to the initiation of an adaptive immune response. Against this backdrop, epithelial cell innate and adaptive immune function is modulated to meet the constraints of procreation. The overall goal of this review is to focus on the dynamic role of epithelial cells in the upper reproductive tract, with special emphasis on the uterus, to define the unique properties of these cells as they maintain homeostasis in preparation for successful fertilization and pregnancy while at the same time confer protection against sexually transmitted infections, which threaten to compromise women's reproductive health and survival. By understanding the nature of this protection and the ways in which innate and adaptive immunity are regulated by sex hormones, these studies provide the opportunity to contribute to the foundation of information essential for ensuring reproductive health.

The orthopoxvirus type I IFN binding protein is essential for virulence and an effective target for vaccination

Nonliving antiviral vaccines traditionally target proteins expressed at the surface of the virion with the hope of inducing neutralizing antibodies. Orthopoxviruses (OPVs), such as the human smallpox virus and the mouse-equivalent ectromelia virus (ECTV; an agent of mousepox), encode immune response modifiers (IRMs) that can increase virulence by decreasing the host immune response. We show that one of these IRMs, the type I interferon (IFN) binding protein (bp) of ECTV, is essential for ECTV virulence and is a natural target of the antibody response. More strikingly, we demonstrate that immunization with recombinant type I IFN bp protects mice from lethal mousepox. Collectively, our experiments have important implications for our understanding of the role of IRMs in OPV virulence and of type I IFNs in OPV infections. Furthermore, our work provides proof of concept that effective antiviral vaccines can be made to prevent disease by targeting virulence factors as an alternative to the traditional approach that attempts to prevent infection by virus neutralization.

Distinct Signature Type I Interferon Responses are Determined by the Infecting virus and the Target Cell

Background

Type I interferons (IFN) include multiple IFN-α subtypes which exhibit considerable amino acid identity and activate the same cell-surface receptor. The promoter regions of the IFN-α genes, however, have different transcription factor binding sites, implying differential transcriptional activation. Evolutionary conservation of multiple subtypes may have resulted from external pressures associated with the crucial nature of an IFN response, namely that different viruses that are tropic for different target tissues determine the nature and extent of an IFN response, specifically the IFN-α subtype profile.

Methods

Studies were undertaken to examine inducible IFN gene expression profiles in response to infection with single-stranded RNA viruses: Sendai virus (SeV), murine hepatitis virus (MHV-1) and coxsackie virus B3 (CVB3).

Results

In vitro, distinct signature profiles of SeV and MHV-1-inducible gene expression for IFN-α2, IFN-α4 and IFN-α5 subtypes in L2 and L929 mouse fibroblast cells, in relation to the extent and kinetics of their induction, were identified. In vivo, whereas A/J mice are highly permissive for both MHV-1 and CVB3 infections and mount a poor IFN response, C57Bl/6 mice are relatively resistant to both virus infections and mount a vigorous IFN response.

Conclusions

These data suggest that the infecting virus and the target cell type dictate the extent and signature of inducible type I IFN gene expression. The extent of IFN response to viral infection influences the subsequent biological outcome: a robust IFN response prescribes a level of resistance, whereas a poor IFN response contributes towards a permissive phenotype for infection.

TLR3 increases disease morbidity and mortality from vaccinia infection

Innate immunity is required for effective control of poxvirus infections, but cellular receptors that initiate the host response to these DNA viruses remain poorly defined. Given this information and the fact that functions of TLRs in immunity to DNA viruses remain controversial, we investigated effects of TLR3 on pathogenesis of vaccinia virus, a prototype poxvirus. We used a recombinant strain Western Reserve vaccinia virus that expresses firefly luciferase to infect wild-type C57BL/6 and TLR3-/- mice through intranasal inoculation. Bioluminescence imaging showed that TLR3-/- mice had substantially lower viral replication in the respiratory tract and diminished dissemination of virus to abdominal organs. Mice lacking TLR3 had reduced disease morbidity, as measured by decreased weight loss and hypothermia after infection. Importantly, TLR3-/- mice also had improved survival relative to wild-type mice. Infected TLR3-/- mice had significantly reduced lung inflammation and recruitment of leukocytes to the lung. Mice lacking TLR3 also had lower levels of inflammatory cytokines, including IL-6, MCP-1, and TNF-alpha in serum and/or bronchoalveolar lavage fluid, but levels of IFN-beta did not differ between genotypes of mice. To our knowledge, our findings show for the first time that interactions between TLR3 and vaccinia increase viral replication and contribute to detrimental effects of the host immune response to poxviruses.

Interferon type I responses in primary and secondary infections

The mammalian host responds to a microbial infection with a rapid innate immune reaction that is dominated by type I interferon (IFN-I) release. Most cells of vertebrates can respond to microbial attack with IFN-I production, but the cell type responsible for most of the systemic IFN-I release is thought to be plasmacytoid dendritic cells (pDCs). Besides its anti-microbial and especially anti-viral properties IFN-I also exerts a regulatory role on many facets of the sequential adaptive immune response. One of these is being the recently described partial, systemic activation of the vast majority of B and T lymphocytes in mice, irrespective of antigen reactivity. The biological significance of this partial activation of lymphocytes is at present speculative. Secondary infections occurring within a short time span of a primary infection fail to elicit a similar lymphocyte activation response due to a refractory period in systemic IFN-I production. This period of exhaustion in IFN-I responses is associated with an increased susceptibility of the host to secondary infections. The latter correlates with well-established clinical observations of heightened susceptibility of patients to secondary microbial infections after viral episodes.

Modified vaccinia virus Ankara induces Toll-like receptor-independent type I interferon responses

Modified vaccinia virus Ankara (MVA) is a highly attenuated vaccinia virus strain undergoing clinical evaluation as a replication-deficient vaccine vector against various infections and tumor diseases. To analyze the basis of its high immunogenicity, we investigated the mechanism of how MVA induces type I interferon (IFN) responses. MVA stimulation of bone marrow-derived dendritic cells (DC) showed that plasmacytoid DC were main alpha IFN (IFN-alpha) producers that were triggered independently of productive infection, viral replication, or intermediate and late viral gene expression. Increased IFN-alpha levels were induced upon treatment with mildly UV-irradiated MVA, suggesting that a virus-encoded immune modulator(s) interfered with the host cytokine response. Mice devoid of Toll-like receptor 9 (TLR9), the receptor for double-stranded DNA, mounted normal IFN-alpha responses upon MVA treatment. Furthermore, mice devoid of the adaptors of TLR signaling MyD88 and TRIF and mice deficient in protein kinase R (PKR) showed IFN-alpha responses that were only slightly reduced compared to those of wild-type mice. MVA-induced IFN-alpha responses were critically dependent on autocrine/paracrine triggering of the IFN-alpha/beta receptor and were independent of IFN-beta, thus involving "one-half" of a positive-feedback loop. In conclusion, MVA-mediated type I IFN secretion was primarily triggered by non-TLR molecules, was independent of virus propagation, and critically involved IFN feedback stimulation. These data provide the basis to further improve MVA as a vaccine vector.

Inhibition of the alpha/beta interferon response by mouse hepatitis virus at multiple levels

Mouse hepatitis virus (MHV) was used as a model to study the interaction of coronaviruses with the alpha/beta interferon (IFN-alpha/beta) response. While MHV strain A59 appeared to induce IFN-beta gene transcription and low levels of nuclear translocation of the IFN-beta transcription factor interferon regulatory factor 3 (IRF-3), MHV did not induce IFN-beta protein production during the course of infection in L2 mouse fibroblast cells. In addition, MHV was able to significantly decrease the level of IFN-beta protein induced by both Newcastle disease virus (NDV) and Sendai virus infections, without targeting it for proteasomal degradation and without altering the nuclear translocation of IRF-3 or IFN-beta mRNA production or stability. These results indicate that MHV infection causes an inhibition of IFN-beta production at a posttranscriptional level, without altering RNA or protein stability. In contrast, MHV induced IFN-beta mRNA and protein production in the brains of infected animals, suggesting that the inhibitory mechanisms observed in vitro are not enough to prevent IFN-alpha/beta production in vivo. Furthermore, MHV replication is highly resistant to IFN-alpha/beta action, as indicated by unimpaired MHV replication in L2 cells pretreated with IFN-beta. However, when L2 cells were coinfected with MHV and NDV in the presence of IFN-beta, NDV, but not MHV, replication was inhibited. Thus, rather than disarming the antiviral activity induced by IFN-beta pretreatment completely, MHV may be inherently resistant to some aspects of the antiviral state induced by IFN-beta. These findings show that MHV employs unique strategies to circumvent the IFN-alpha/beta response at multiple steps.

Early production of type I interferon during West Nile virus infection: role for lymphoid tissues in IRF3-independent interferon production

Infection of cells with flaviviruses in vitro is reduced by pretreatment with small amounts of type I interferon (IFN-alpha/beta). Similarly, pretreatment of animals with IFN and experiments using mice defective in IFN signaling have indicated a role for IFN in controlling flavivirus disease in vivo. These data, along with findings that flavivirus-infected cells block IFN signaling, suggest that flavivirus infection can trigger an IFN response. To investigate IFN gene induction by the very first cells infected during in vivo infection with the flavivirus West Nile virus (WNV), we infected mice with high-titer preparations of WNV virus-like particles (VLPs), which initiate viral genome replication in cells but fail to spread. These studies demonstrated a brisk production of IFN in vivo, with peak levels of over 1,000 units/ml detected in sera between 8 and 24 h after inoculation by either the intraperitoneal or footpad route. The IFN response was dependent on genome replication, and WNV genomes and WNV antigen-positive cells were readily detected in the popliteal lymph nodes (pLN) of VLP-inoculated mice. High levels of IFN mRNA transcripts and functional IFN were also produced in VLP-inoculated IFN regulatory factor 3 null (IRF3(-/-)) mice, indicating that IFN production was independent of the IRF3 pathways to IFN gene transcription, consistent with the IFN type produced (predominantly alpha).

The chemotherapeutic agent DMXAA potently and specifically activates the TBK1-IRF-3 signaling axis

Vascular disrupting agents (VDAs) represent a novel approach to the treatment of cancer, resulting in the collapse of tumor vasculature and tumor death. 5,6-dimethylxanthenone-4-acetic acid (DMXAA) is a VDA currently in advanced phase II clinical trials, yet its precise mechanism of action is unknown despite extensive preclinical and clinical investigations. Our data demonstrate that DMXAA is a novel and specific activator of the TANK-binding kinase 1 (TBK1)–interferon (IFN) regulatory factor 3 (IRF-3) signaling pathway. DMXAA treatment of primary mouse macrophages resulted in robust IRF-3 activation and ∼750-fold increase in IFN-β mRNA, and in contrast to the potent Toll-like receptor 4 (TLR4) agonist lipopolysaccharide (LPS), signaling was independent of mitogen-activated protein kinase (MAPK) activation and elicited minimal nuclear factor κB–dependent gene expression. DMXAA-induced signaling was critically dependent on the IRF-3 kinase, TBK1, and IRF-3 but was myeloid differentiation factor 88–, Toll–interleukin 1 receptor domain–containing adaptor inducing IFN-β–, IFN promoter-stimulator 1–, and inhibitor of κB kinase–independent, thus excluding all known TLRs and cytosolic helicase receptors. DMXAA pretreatment of mouse macrophages induced a state of tolerance to LPS and vice versa. In contrast to LPS stimulation, DMXAA-induced IRF-3 dimerization and IFN-β expression were inhibited by salicylic acid. These findings detail a novel pathway for TBK1-mediated IRF-3 activation and provide new insights into the mechanism of this new class of chemotherapeutic drugs.

Human primary immunodeficiencies of type I interferons

Type I interferons (IFN-alpha/beta and related molecules) are essential for protective immunity to experimental infection by numerous viruses in the mouse model. In recent years, human primary immunodeficiencies affecting either the production of (UNC-93B deficiency) or the response to (STAT1 and TYK2 deficiencies) these IFNs have been reported. Affected patients are highly susceptible to certain viruses. Patients with STAT1 or TYK2 deficiency are susceptible to multiple viruses, including herpes simplex virus-1 (HSV-1), whereas UNC-93B-deficient patients present isolated HSV-1 encephalitis. However, these immunological defects are not limited to type I IFN-mediated immunity. Impaired type II IFN (IFN-gamma)-mediated immunity plays no more than a minor role in the pathogenesis of viral diseases in these patients, but the contribution of impaired type III IFN (IFN-lambda)-mediated immunity remains to be determined. These novel inherited disorders strongly suggest that type I IFN-mediated immunity is essential for protection against natural infections caused by several viruses in humans.

Synergistic roles of antibody and interferon in noncytolytic clearance of Sindbis virus from different regions of the central nervous system

Sindbis virus (SINV) is an alphavirus that causes infection of neurons and encephalomyelitis in adult immunocompetent mice. Recovery can occur without apparent neurological damage. To better define the factors facilitating noncytolytic clearance of SINV in different regions of the central nervous system (CNS) and the roles of innate and adaptive immune responses at different times during infection, we have characterized SINV infection and clearance in the brain, brain stem, and spinal cords of severe combined immunodeficiency (SCID) and C57BL/6 (wild-type [WT]) mice and mice deficient in beta interferon (IFN-beta) (BKO), antibody (muMT), IFN-gamma (GKO), IFN-gamma receptor (GRKO), and both antibody and IFN-gamma (muMT/GKO). WT mice cleared infectious virus by day 8, while SCID mice had persistent virus replication at all sites. For 3 days after infection, BKO mice had higher titers at all sites than WT mice, despite similar IFN-alpha production, but cleared virus similarly. GKO and GRKO mice cleared infectious virus from all sites by days 8 to 10 and, like WT mice, displayed transient reactivation at 12 to 22 days. muMT mice did not clear virus from the brain, and clearance from the brain stem and lumbar spinal cord was delayed, followed by reactivation. Eighty-one days after infection, muMT/GKO mice had not cleared virus from any site, but titers were lower than for SCID mice. These studies show that IFN-beta is independently important for early control of CNS virus replication, that antiviral antibody is critical for clearance from the brain, and that both antibody and IFN-gamma contribute to prevention of reactivation after initial clearance.

Protective role of beta interferon in host defense against influenza A virus

Type I interferon (IFN), which includes the IFN-alpha and -beta subtypes, plays an essential role in host defense against influenza A virus. However, the relative contribution of IFN-beta remains unresolved. In mice, type I IFN is effective against influenza viruses only if the IFN-induced resistance factor Mx1 is present, though most inbred mouse strains, including the recently developed IFN-beta-deficient mice, bear only defective Mx1 alleles. We therefore generated IFN-beta-deficient mice carrying functional Mx1 alleles (designated Mx-BKO) and compared them to either wild-type mice bearing functional copies of both IFN-beta and Mx1 (designated Mx-wt) or mice carrying functional Mx1 alleles but lacking functional type I IFN receptors (designated Mx-IFNAR). Influenza A virus strain SC35M (H7N7) grew to high titers and readily formed plaques in monolayers of Mx-BKO and Mx-IFNAR embryo fibroblasts which showed no spontaneous expression of Mx1. In contrast, Mx-wt embryo fibroblasts were found to constitutively express Mx1, most likely explaining why SC35M did not grow to high titers and formed no visible plaques in such cells. In vivo challenge experiments in which SC35M was applied via the intranasal route showed that the 50% lethal dose was about 20-fold lower in Mx-BKO mice than in Mx-wt mice and that virus titers in the lungs were increased in Mx-BKO mice. The resistance of Mx-BKO mice to influenza A virus strain PR/8/34 (H1N1) was also substantially reduced, demonstrating that IFN-beta plays an important role in the defense against influenza A virus that cannot be compensated for by IFN-alpha.

Contribution of Interferon-β to the Murine Macrophage Response to the Toll-like Receptor 4 Agonist, Lipopolysaccharide

Interferon-beta (IFN-beta) has been identified as the signature cytokine induced via the Toll-like receptor (TLR) 4, "MyD88-independent" signaling pathway in macrophages stimulated by Gram-negative bacterial lipopolysaccharide (LPS). In this study, we analyzed the responses of macrophages derived from wild-type (IFN-beta(+/+)) mice or mice with a targeted mutation in IFN-beta (IFN-beta(-/-)) to the prototype TLR4 agonist, Escherichia coli LPS. A comparison of basal and LPS-induced gene expression (by reverse transcription-PCR, real-time PCR, and Affymetrix microarray analyses) resulted in the identification of four distinct patterns of gene expression affected by IFN-beta deficiency. Analysis of a subset of each group of differentially regulated genes by computer-assisted promoter analysis revealed putative IFN-responsive elements in all genes examined. LPS-induced activation of intracellular signaling molecules, STAT1 Tyr-701, STAT1 Ser-727, and Akt, but not p38, JNK, and ERK MAPK proteins, was significantly diminished in IFN-beta(-/-) versus IFN-beta(+/+) macrophages. "Priming" of IFN-beta(-/-) macrophages with exogenous recombinant IFN-beta significantly increased levels of LPS-induced gene expression for induction of monocyte chemotactic protein 5, inducible nitric-oxide synthase, IP-10, and IL-12 p40 mRNA, whereas no increase or relatively small increases were observed for IL-1beta, IL-6, monocyte chemotactic protein 1, and MyD88 mRNA. Finally, IFN-beta(-/-) mice challenged in vivo with LPS exhibited increased survival when compared with wild-type IFN-beta(+/+) controls, indicating that IFN-beta contributes to LPS-induced lethality; however, not to the extent that one observes in mice with more complete pathway deficiencies (e.g. TLR4(-/-) or TRIF(-/-) mice). Collectively, these findings reveal unanticipated regulatory roles for IFN-beta in response to LPS in vitro and in vivo.

Effects of type I interferons on Friend retrovirus infection

The type I interferon (IFN) response plays an important role in the control of many viral infections. However, since there is no rodent animal model for human immunodeficiency virus, the antiviral effect of IFN-alpha and IFN-beta in retroviral infections is not well characterized. In the current study we have used the Friend virus (FV) model to determine the activity of type I interferons against a murine retrovirus. After FV infection of mice, IFN-alpha and IFN-beta could be measured between 12 and 48 h in the serum. The important role of type I IFN in the early immune defense against FV became evident when mice deficient in IFN type I receptor (IFNAR(-/-)) or IFN-beta (IFN-beta(-/-)) were infected. The levels of FV infection in plasma and in spleen were higher in both strains of knockout mice than in C57BL/6 wild-type mice. This difference was induced by an antiviral effect of IFN-alpha and IFN-beta and was most likely mediated by antiviral enzymes as well as by an effect of these IFNs on T-cell responses. Interestingly, the lack of IFNAR and IFN-beta enhanced viral loads during acute and chronic FV infection. Exogenous IFN-alpha could be used therapeutically to reduce FV replication during acute but not chronic infection. These findings indicate that type I IFN plays an important role in the immediate antiviral defense against Friend retrovirus infection.

The latent membrane protein 1 of Epstein-Barr virus (EBV) primes EBV latency cells for type I interferon production

Epstein-Barr virus (EBV) latency has been associated with a variety of human cancers. Latent membrane protein 1 (LMP-1) is one of the key viral proteins required for transformation of primary B cells in vitro and establishment of EBV latency. We have previously shown that LMP-1 induces the expression of several interferon (IFN)-stimulated genes and has antiviral effect (Zhang, J., Das, S. C., Kotalik, C., Pattnaik, A. K., and Zhang, L. (2004) J. Biol. Chem. 279, 46335-46342). In this report, a novel mechanism related to the antiviral effect of LMP-1 is identified. We show that EBV type III latency cells, in which LMP-1 is expressed, are primed to produce robust levels of endogenous IFNs upon infection of Sendai virus. The priming action is due to the expression of LMP-1 but not EBV nuclear antigen 2 (EBNA-2). The signaling events from the C-terminal activator regions of LMP-1 are essential to prime cells for high IFN production. LMP-1-mediated activation of NF-kappaB is apparently necessary and sufficient for LMP-1-mediated priming effect in DG75 cells, a human B cell line. IFN regulatory factor 7 (IRF-7) that can be activated by LMP-1 is also implicated in the priming action. Taken together, these data strongly suggest that LMP-1 may prime EBV latency cells for IFN production and that the antiviral property of LMP-1 may be an intrinsic part of EBV latency program, which may assist the establishment and/or maintenance of viral latency.

Evasion of innate immunity by vaccinia virus

Vaccinia virus, a member of the Poxviridae, expresses many proteins involved in immune evasion. In this review, we present a brief characterisation of the virus and its effects on host cells and discuss representative secreted and intracellular proteins expressed by vaccinia virus that are involved in modulation of innate immunity. These proteins target different aspects of the innate response by binding cytokines and interferons, inhibiting cytokine synthesis, opposing apoptosis or interfering with different signalling pathways, including those triggered by interferons and toll-like receptors.

Stromal cells and osteoclasts are responsible for exacerbated collagen-induced arthritis in interferon-beta-deficient mice

OBJECTIVE

Clinical trials using interferon-beta (IFNbeta) in the treatment of rheumatoid arthritis have shown conflicting results. We undertook this study to understand the mechanisms of IFNbeta in arthritis at a physiologic level.

METHODS

Collagen-induced arthritis (CIA) was induced in IFNbeta-deficient and control mice. The role of IFNbeta was investigated in both the priming and effector phases of the disease. The effect of IFNbeta deficiency on synovial cells, macrophages, and fibroblasts from preimmunized mice was analyzed by flow cytometry, immunohistochemistry, and enzyme-linked immunosorbent assay. Differences in osteoclast maturation were determined in situ by histology of arthritic and naive paws and by in vitro maturation studies of naive bone marrow cells. The importance of IFNbeta-producing fibroblasts was determined by transferring fibroblasts into mice at the time of CIA immunization.

RESULTS

Mice lacking IFNbeta had a prolonged disease with a higher incidence compared with control mice. IFNbeta deficiency was found to influence the effector phase, but not the priming phase, of arthritis. Compared with control mice, IFNbeta-deficient mice had greater infiltration of CD11b+ cells and greater production of tumor necrosis factor alpha in vivo, and their macrophages and fibroblasts were both more activated in vitro. Moreover, IFNbeta-deficient mice generated a greater number of osteoclasts in vitro, and mice immunized to induce arthritis, but not naive mice, had a greater number of osteoclasts in vivo compared with control mice. Importantly, IFNbeta-competent fibroblasts were able to ameliorate arthritis in IFNbeta-deficient recipients.

CONCLUSION

Our data indicate that IFNbeta is involved in regulating the activation state of osteoclasts and stromal cells, including macrophages and fibroblasts, but that it has little effect on T cells.

Reciprocal immunomodulation in a schistosome and hepatotropic virus coinfection model

Human coinfection with the helminth parasite Schistosoma mansoni and hepatitis B and hepatitis C viruses is associated with increased hepatic viral burdens and severe liver pathology. In this study we developed a murine S. mansoni/lymphocytic choriomeningitis virus (LCMV) coinfection model that reproduces the enhanced viral replication and liver pathology observed in human coinfections, and used this model to explore the mechanisms involved. Viral coinfection during the Th2-dominated granulomatous phase of the schistosome infection resulted in induction of a strong LCMV-specific T cell response, with infiltration of high numbers of LCMV-specific IFN-gamma-producing CD8+ cells into the liver. This was associated with suppression of production of the Th2 cytokines dominant during S. mansoni infection and a rapid increase in morbidity, linked to hepatotoxicity. Interestingly, the liver of coinfected mice was extremely susceptible to viral replication. This correlated with a reduced intrahepatic type I IFN response following virus infection. Schistosome egg Ags were found to suppress the type I IFN response induced in murine bone marrow-derived dendritic cells by polyinosinic-polycytidylic acid. These results suggest that suppression of the antiviral type I IFN response by schistosome egg Ags in vivo predisposes the liver to enhanced viral replication with ensuing immunopathological consequences, findings that may be paralleled in human schistosome/hepatotropic virus coinfections.

Interferons and viruses: signaling for supremacy

Interferon (IFN)-alpha and IFN-beta are critical mediators of host defense against microbial challenges, directly interfering with viral infection and influencing both the innate and adaptive immune responses. IFNs exert their effects in target cells through the activation of a cell-surface receptor, leading to a cascade of signaling events that determine transcriptional and translation regulation. Understanding the circuitry associated with IFN-mediated signal transduction that leads to a specific biological outcome has been a major focus of our laboratory. Through the efforts of graduate students, postdoctoral fellows, a skilled research technologist, and important collaborations with investigators elsewhere, we have provided some insights into the complexity of the IFN system-and the elegance and simplicity of how protein-protein interactions define biological function.

Toll-like receptor 3 agonist poly(I:C)-induced antiviral response in human corneal epithelial cells

The objective of this study was to examine the expression of Toll-like receptor 3 (TLR3) by human corneal epithelial cells (HCECs) and to determine whether exposure to the TLR3 agonist polyinosinic-polycytidylic acid [poly(I:C)] induces an antiviral response in these cells. Fluorescence-activated cell sorter (FACS) analysis revealed TLR3 to be constitutively expressed and distributed intracellularly in HCECs. Stimulation of HCECs with the TLR3 agonist poly(I:C) induced the activation of nuclear factor (NF)-kappaB and production of the proinflammatory cytokine interleukin (IL)-6 and the chemokine IL-8. Upon exposure to poly(I:C), HCECs initiated a potent antiviral response resulting in an increase of interferon (IFN)-beta mRNA expression (7-fold). Poly(I:C) stimulation also up-regulated mRNA expression of the antiviral chemokine IFN-gamma inducible protein 10 (IP10), myxovirus resistance gene A and 2',5'-oligoadenylate synthetase (5-, 10- and 9-fold, respectively), and secretion of IP10. These responses were also induced by exogenously added type 1 IFNs, but could not be blocked by pretreatment of the cells with anti-TLR3 monoclonal antibody, suggesting that the receptor was not expressed on the cell surface. Furthermore, incubation of HCECs with an endosomal acidification inhibitor, chloroquine, markedly inhibited poly(I:C)-mediated IFN-beta expression in HCECs. These results suggest that corneal epithelial cells are important sentinels of the corneal innate immune system against viral infection, and that stimulation of TLR3 can induce the expression of key proinflammatory cytokines and chemokines and antiviral genes that help in the defence of the cornea against viral infection.

Type I interferons trigger systemic, partial lymphocyte activation in response to viral infection

The vast majority of both T and B cells in mice were found to up-regulate cell surface expression of the early activation markers CD69 and CD86, but not CD25, within 24 h of infection with Semliki Forest virus. Kinetics and magnitude of activation marker expression was dependent on live virus, dose, and correlated with strain virulence. Activation marker expression declined to baseline levels over the next 96 h. This very early "activation" of such a high percentage of lymphocytes required the presence of type I IFN receptor genes, was inducible with poly(I:C), and correlated with IFN-I levels in serum. We conclude that virus-induced IFN-I release systemically affects most of the hosts T and B cells by triggering them rapidly and independently of Ag-reactivity into a semiactivated state.

Organization and promoter analysis of the zebrafish (Danio rerio) interferon gene

Interferon plays important roles in confronting viral infections as the first line of defense. For the purpose of understanding the molecular mechanism which controls transcription of the interferon gene, we cloned and sequenced the interferon promoter region of the zebrafish interferon gene and characterized its activity using firefly luciferase transient transfection expression assays. Different fragments of the zebrafish interferon 5'-flanking region were transfected into ZFL cells. In these cell lines, maximum promoter activity was located in 2.2 kb of the zebrafish interferon 5' flanking region of the ZFL cell line. In this study, we investigated whether the viral replicative intermediate double-stranded RNA (herein we used synthetic polyinosinic-polycytidylic acid [poly(I):poly(C)] modifies the effects of interferon on gene expression. For this purpose, all zebrafish interferon promoter fragments were treated with either 1, 10, or 100 microg/ml poly(I):poly(C). The results showed that after treatment with 10 microg/ml poly(I):poly(C), high promoter activity was observed in the -2.2-kb interferon promoter fragment. Several putative transcription factors were shown in the promoter region, including IRF-1, C/EBP, NFkappaB, and GATA-1. Further study of the in vivo expression of the interferon promoter during development was carried out in transgenic zebrafish expressing an interferon promoter-driven green fluorescent protein (GFP) encoding the GFP cDNA transgene. Morphological studies of transgenic zebrafish indicated that the interferon promoter-driven GFP transcripts appeared in the yolk, head, and lymphoid organs. These results indicate that the interferon promoter is active in a tissue-specific manner, and suggest that the interferon promoter plays an important role in virus resistance during teleost growth.

Review: Milstein Award lecture: interferons and cancer: where from here?

Interferons (IFNs) remain the most broadly active cytokines for cancer treatment, yet ones for which the full potential is not reached. IFNs have impacted positively on both quality and quantity of life for hundreds of thousands of cancer patients with chronic leukemia, lymphoma, bladder carcinoma, melanoma, and renal carcinoma. The role of the IFN system in malignant pathogenesis continues to enhance understanding of how the IFN system may be modulated for therapeutic advantage. Reaching the full potential of IFNs as therapeutics for cancer will also result from additional understanding of the genes underlying apoptosis induction, angiogenesis inhibition, and influence on immunologic function. Food and Drug Administration (FDA) approval of IFNs occurred less than 20 years ago; after 40 years, third-generation products of early cytotoxics, such as 5- fluorouracil (5FU), are beginning to reach clinical approval. Thus, substantial potential exists for additional application of IFNs and IFN inducers as anticancer therapeutics, particularly when one considers that their pleiotropic cellular and molecular effects have yet to be fully defined.

Immune responses to dsRNA: implications for gene silencing technologies

Nucleic acid-induced gene silencing, such as RNA interference (RNAi), induces a multitude of responses in addition to the knockdown of a gene. This is best understood in the context of the antiviral immune response, from which the processes of RNAi are thought to be derived. Viral challenge of a vertebrate host leads to an intricate series of responses that orchestrate antiviral immunity. The success of this multifaceted system in overcoming viral encounters hinges on complex pathogen-host interactions. One aspect of these interactions, the nucleic acid-based immune response, is key to the successful resolution of a viral challenge. In particular, dsRNA, a nucleic acid associated with viral replication, is involved in numerous interactions contributing to induction, activation and regulation of antiviral mechanisms. Specifically, dsRNA is responsible for stimulating important protective responses, such as the activation of dicer-related antiviral pathways, induction of type 1 IFN, and stimulation of dsRNA-activated protein kinase and oligoadenylate synthetase. Furthermore, the modulation and shaping of this overall immune response is facilitated through nucleic acid interactions with pattern recognition receptors such as toll-like receptor 3. These diverse dsRNA-induced antiviral responses have implications for biotechnologies that use dsRNA to harness one arm of the host antiviral machinery for silencing a specific target gene. The interlinked nature of these response elements means that it may be difficult to completely isolate one element from the other arms of the antiviral response program of an organism. Thus, it is beneficial to understand all aspects of the immune response to dsRNA in order to manipulate these systems and minimize unwanted non-specific effects.

Transformation of mouse fibroblasts alters the induction pattern of type I IFNs after virus infection

Type I interferons (IFNs) have been shown to be involved in many immune defence and inflammatory responses. We here show that IFN-beta plays an absolute essential role in the efficient induction of all type I IFNs after infection of primary embryonic as well as primary adult fibroblasts with Sendai virus. In contrast, after immortalization of such fibroblasts with SV40 large T antigen, IFN-alpha4 can be induced independently of IFN-beta. However, efficient secretion of type I IFNs even in immortalized fibroblasts is only found when the complete signalling loop is induced by IFN-beta.

Inhibition of Beta interferon induction by severe acute respiratory syndrome coronavirus suggests a two-step model for activation of interferon regulatory factor 3

Severe acute respiratory syndrome (SARS) is caused by a novel coronavirus termed SARS-CoV. We and others have previously shown that the replication of SARS-CoV can be suppressed by exogenously added interferon (IFN), a cytokine which is normally synthesized by cells as a reaction to virus infection. Here, we demonstrate that SARS-CoV escapes IFN-mediated growth inhibition by preventing the induction of IFN-beta. In SARS-CoV-infected cells, no endogenous IFN-beta transcripts and no IFN-beta promoter activity were detected. Nevertheless, the transcription factor interferon regulatory factor 3 (IRF-3), which is essential for IFN-beta promoter activity, was transported from the cytoplasm to the nucleus early after infection with SARS-CoV. However, at a later time point in infection, IRF-3 was again localized in the cytoplasm. By contrast, IRF-3 remained in the nucleus of cells infected with the IFN-inducing control virus Bunyamwera delNSs. Other signs of IRF-3 activation such as hyperphosphorylation, homodimer formation, and recruitment of the coactivator CREB-binding protein (CBP) were found late after infection with the control virus but not with SARS-CoV. Our data suggest that nuclear transport of IRF-3 is an immediate-early reaction to virus infection and may precede its hyperphosphorylation, homodimer formation, and binding to CBP. In order to escape activation of the IFN system, SARS-CoV appears to block a step after the early nuclear transport of IRF-3.