Participation of endogenous tumour necrosis factor alpha in host resistance to cytomegalovirus infection

CD4 T Cell-Mediated Immune Control of Cytomegalovirus Infection in Murine Salivary Glands

CD4 T cells are well known for their supportive role in CD8 T cell and B cell responses during viral infection. However, during murine cytomegalovirus (MCMV) infection in the salivary glands (SGs), CD4 T cells exhibit direct antiviral effector functions to control the infection. In this mucosal organ, opposed to other infected tissues, MCMV establishes a sustained lytic replication that lasts for several weeks. While the protective function of CD4 T cells is exerted through the production of the pro-inflammatory cytokines interferon gamma (IFNγ) and tumor necrosis factor alpha (TNF), the reasons for their markedly delayed control of lytic MCMV infection remain elusive. Here, we review the current knowledge on the dynamics and mechanisms of the CD4 T cell-mediated control of MCMV-infected SGs, including their localization in the SG in relation to MCMV infected cells and other immune cells, their mode of action, and their regulation.

TNF Decoy Receptors Encoded by Poxviruses

Tumour necrosis factor (TNF) is an inflammatory cytokine produced in response to viral infections that promotes the recruitment and activation of leukocytes to sites of infection. This TNF-based host response is essential to limit virus spreading, thus poxviruses have evolutionarily adopted diverse molecular mechanisms to counteract TNF antiviral action. These include the expression of poxvirus-encoded soluble receptors or proteins able to bind and neutralize TNF and other members of the TNF ligand superfamily, acting as decoy receptors. This article reviews in detail the various TNF decoy receptors identified to date in the genomes from different poxvirus species, with a special focus on their impact on poxvirus pathogenesis and their potential use as therapeutic molecules.

TNF controls a speed-accuracy tradeoff in the cell death decision to restrict viral spread

Rapid death of infected cells is an important antiviral strategy. However, fast decisions that are based on limited evidence can be erroneous and cause unnecessary cell death and subsequent tissue damage. How cells optimize their death decision making strategy to maximize both speed and accuracy is unclear. Here, we show that exposure to TNF, which is secreted by macrophages during viral infection, causes cells to change their decision strategy from "slow and accurate" to "fast and error-prone". Mathematical modeling combined with experiments in cell culture and whole organ culture show that the regulation of the cell death decision strategy is critical to prevent HSV-1 spread. These findings demonstrate that immune regulation of cellular cognitive processes dynamically changes a tissues' tolerance for self-damage, which is required to protect against viral spread.

How to Train Your Dragon: Harnessing Gamma Delta T Cells Antiviral Functions and Trained Immunity in a Pandemic Era

The emergence of viruses with pandemic potential such as the SARS-CoV-2 coronavirus causing COVID-19 poses a global health challenge. There is remarkable progress in vaccine technology in response to this threat, but their design often overlooks the innate arm of immunity. Gamma Delta (γδ) T cells are a subset of T cells with unique features that gives them a key role in the innate immune response to a variety of homeostatic alterations, from cancer to microbial infections. In the context of viral infection, a growing body of evidence shows that γδ T cells are particularly equipped for early virus detection, which triggers their subsequent activation, expansion and the fast deployment of antiviral functions such as direct cytotoxic pathways, secretion of cytokines, recruitment and activation of other immune cells and mobilization of a trained immunity memory program. As such, γδ T cells represent an attractive target to stimulate for a rapid and effective resolution of viral infections. Here, we review the known aspects of γδ T cells that make them crucial component of the immune response to viruses, and the ways that their antiviral potential can be harnessed to prevent or treat viral infection.

The IκB Kinases Restrict Human Cytomegalovirus Infection

Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus that causes disease in immunosuppressed populations. HCMV has a complex relationship with innate immune signaling pathways. Specifically, HCMV has been found to block some aspects of inflammatory signaling while benefiting from others. Through analysis of knockout cell lines targeting the NF-κB regulatory kinases IκB kinase α (IKKα) and IKKβ, we find that the IKKs are host restriction factors that contribute to cytokine-mediated resistance to viral infection, limit the initiation of HCMV infection, and attenuate viral cell-to-cell spread. The HCMV UL26 protein is a viral immune modulator important for HCMV infection that has been shown to inhibit host cell NF-κB signaling, yet it has remained unclear how UL26-mediated NF-κB modulation contributes to infection. Here, we find that UL26 modulation of NF-κB signaling is separable from its contribution to high-titer viral replication. However, we find that IKKβ is required for the induction of cytokine expression associated with ΔUL26 infection. Collectively, our data indicate that the IKKs restrict infection but HCMV targets their signaling to modulate the cellular inflammatory environment.IMPORTANCE Innate immune signaling is a critical defense against viral infection and represents a central host-virus interaction that frequently determines the outcomes of infections. NF-κB signaling is an essential component of innate immunity that is extensively modulated by HCMV, a significant cause of morbidity in neonates and immunosuppressed individuals. However, the roles that various facets of NF-κB signaling play during HCMV infection have remained elusive. We find that the two major regulatory kinases in this pathway, IKKα and IKKβ, limit the initiation of infection, viral replication, and cell-to-cell spread. In addition, our results indicate that these kinases contribute differently to the host cell response to infection in the absence of a virally encoded NF-κB inhibitor, UL26. Given the importance of NF-κB in viral infection, elucidating the contributions of various NF-κB constituents to infection is an essential first step toward the possibility of targeting this pathway therapeutically.

Tissue-specific control of latent CMV reactivation by regulatory T cells

Cytomegalovirus (CMV) causes a persistent, lifelong infection. CMV persists in a latent state and undergoes intermittent subclinical viral reactivation that is quelled by ongoing T cell responses. While T cells are critical to maintain control of infection, the immunological factors that promote CMV persistence remain unclear. Here, we investigated the role of regulatory T cells (Treg) in a mouse model of latent CMV infection using Foxp3-diphtheria toxin receptor (Foxp3-DTR) mice. Eight months after infection, MCMV had established latency in the spleen, salivary gland, lung, and pancreas, which was accompanied by an increased frequency of Treg. Administration of diphtheria toxin (DT) after establishment of latency efficiently depleted Treg and drove a significant increase in the numbers of functional MCMV-specific CD4+ and CD8+ T cells. Strikingly, Treg depletion decreased the number of animals with reactivatable latent MCMV in the spleen. Unexpectedly, in the same animals, ablation of Treg drove a significant increase in viral reactivation in the salivary gland that was accompanied with augmented local IL-10 production by Foxp3-CD4+T cells. Further, neutralization of IL-10 after Treg depletion significantly decreased viral load in the salivary gland. Combined, these data show that Treg have divergent control of MCMV infection depending upon the tissue. In the spleen, Treg antagonize CD8+ effector function and promote viral persistence while in the salivary gland Treg prevent IL-10 production and limit viral reactivation and replication. These data provide new insights into the organ-specific roles of Treg in controlling the reactivation of latent MCMV infection.

Cytomegalovirus (CMV) infection in both mice and humans is normally initially contained by a vigorous adaptive immune response that drives the virus into latency in multiple tissues. However, the immunologic mechanisms that control latency are not well understood. In this report, we have examined the role of regulatory T cells (Treg) in a mouse model of CMV infection. Interestingly, depletion of regulatory T cells had profound consequences on MCMV latent infection, depending upon the tissue. In the spleen, Treg depletion enhanced CD8+ T cell responses and reduced reactivatable latent infection from the spleen. In striking contrast, in the salivary gland, Treg depletion enhanced the production of IL-10 from CD4+ T cells as well as viral reactivation. Thus, Treg play divergent and tissue specific roles in controlling MCMV reactivation from latency.

Tumor Necrosis Factor Alpha-Induced Recruitment of Inflammatory Mononuclear Cells Leads to Inflammation and Altered Brain Development in Murine Cytomegalovirus-Infected Newborn Mice

Congenital human cytomegalovirus (HCMV) infection is a significant cause of abnormal neurodevelopment and long-term neurological sequelae in infants and children. Resident cell populations of the developing brain have been suggested to be more susceptible to virus-induced cytopathology, a pathway thought to contribute to the clinical outcomes following intrauterine HCMV infection. However, recent findings in a newborn mouse model of the infection in the developing brain have indicated that elevated levels of proinflammatory mediators leading to mononuclear cell activation and recruitment could underlie the abnormal neurodevelopment. In this study, we demonstrate that treatment with tumor necrosis factor alpha (TNF-α)-neutralizing antibodies decreased the frequency of CD45⁺ Ly6C^hi CD11b⁺ CCR2⁺ activated myeloid mononuclear cells (MMCs) and the levels of proinflammatory cytokines in the blood and the brains of murine CMV-infected mice. This treatment also normalized neurodevelopment in infected mice without significantly impacting the level of virus replication. These results indicate that TNF-α is a major component of the inflammatory response associated with altered neurodevelopment that follows murine CMV infection of the developing brain and that a subset of peripheral blood myeloid mononuclear cells represent a key effector cell population in this model of virus-induced inflammatory disease of the developing brain.IMPORTANCE Congenital human cytomegalovirus (HCMV) infection is the most common viral infection of the developing human fetus and can result in neurodevelopmental sequelae. Mechanisms of disease leading to neurodevelopmental deficits in infected infants remain undefined, but postulated pathways include loss of neuronal progenitor cells, damage to the developing vascular system of the brain, and altered cellular positioning. Direct virus-mediated cytopathic effects cannot explain the phenotypes of brain damage in most infected infants. Using a mouse model that recapitulates characteristics of the brain infection described in human infants, we have shown that TNF-α plays a key role in brain inflammation, including recruitment of inflammatory mononuclear cells. Neutralization of TNF-α normalized neurodevelopmental abnormalities in infected mice, providing evidence that virus-induced inflammation is a major component of disease in the developing brain. These results suggest that interventions limiting inflammation associated with the infection could potentially improve the neurologic outcome of infants infected in utero with HCMV.

MAPKAP kinase 2 regulates IL-10 expression and prevents formation of intrahepatic myeloid cell aggregates during cytomegalovirus infections

BACKGROUND & AIMS

The kinase p38(MAPK) and its downstream target MAPKAP kinase (MK) 2 are critical regulators of inflammatory responses towards pathogens. To date, the relevance of MK2 for regulating IL-10 expression and other cytokine responses towards cytomegalovirus (CMV) infection and the impact of this pathway on viral replication in vitro and in vivo is unknown and the subject of this study.

METHODS

The effect of MK2, interferon-α receptor (IFNAR)1, tristetraprolin (TTP) and IL-10 on mouse (M)CMV virus titres, cytokine expression, signal transduction, transcript stability, liver enzymes release, immune cell recruitment and aggregation in response to MCMV infection were studied ex vivo in hepatocytes and macrophages, as well as in vivo.

RESULTS

MK2 is critical for MCMV-induced production of IL-10, IFN-α2 and 4, IFN-β, IL-6, and TNF-α but not for IFN-γ. The MCMV-induced IL-10 production requires activation of IFNAR1 and is further regulated by MK2 and TTP-dependent stabilization of IL-10 transcripts. MK2(-/-) mice are able to control acute MCMV replication, despite deregulated cytokine production. This may be related to the observation that MCMV-infected MK2(-/-) mice show enhanced formation of focal intrahepatic lymphocyte infiltrates resembling intrahepatic myeloid cell aggregates of T cell expansion (iMATEs), which were also observed in MCMV-infected IL-10(-/-) mice but are almost absent in MCMV-infected wild-type controls.

CONCLUSIONS

The data suggest that MK2 is critical for regulating cytokine responses towards acute MCMV infection, including that of IL-10 via IFNARI-mediated circuits. MCMV stimulates expression of MK2-dependent cytokines, in particular IL-10 and thereby prevents enhanced formation of intrahepatic iMATE-like cellular aggregates.

BK virus infection activates the TNFα/TNF receptor system in Polyomavirus-associated nephropathy

Polyomavirus-associated nephropathy due to BK virus infection (BKVAN) is recognized as an important cause of significant kidney transplant dysfunction often leading to renal graft loss. The activation of innate immune defense mechanisms during BKVAN is still poorly understood and an altered regulation of inflammatory mediators by resident kidney cells upon viral infection can be expected to contribute to the onset and progression of disease. TNFα interacting with its receptors, TNF receptor 1 (TNFR1) and TNF receptor 2 (TNFR2), is largely accepted to be involved in viral responses, exhibiting both proinflammatory and immunosuppressive effects. Our aim was to examine the expressions of TNFα and TNFR1 and 2 in human collecting duct epithelial cells (HCDC) after infection with BKV as well as to study the effect of TNFα and poly(I:C), a synthetic analog of viral RNA, on the expressions of TNF receptors and proinflammatory cytokines and chemokines in HCDC. Quantitative RT-PCR analyses showed a downregulation of TNFα and an upregulation of both TNFR1 and 2 upon exposure of HCDC to the BK virus. TNFα stimulation induced the expressions of IL-6, IL-8, RANTES, and TNFR2. Poly(I:C) upregulated the expressions of both TNFR1 and TNFR2, a response that could be effectively blocked by siRNA to TLR3 and RIG-I, two double-stranded (ds) RNA receptors of the innate immune system. Poly(I:C)-dependent expression of TNFR2 but not TNFR1 was enhanced by TNFα. Taken together, our results suggest an involvement of TNF/TNFR system in virus-associated nephropathy.

Nanocomplexes for gene therapy of respiratory diseases: Targeting and overcoming the mucus barrier

Gene therapy, i.e. the delivery and expression of therapeutic genes, holds great promise for congenital and acquired respiratory diseases. Non-viral vectors are less toxic and immunogenic than viral vectors, although they are characterized by lower efficiency. However, they have to overcome many barriers, including inflammatory and immune mediators and cells. The respiratory and airway epithelial cells, the main target of these vectors, are coated with a layer of mucus, which hampers the effective reaching of gene therapy vectors carrying either plasmid DNA or small interfering RNA. This barrier is thicker in many lung diseases, such as cystic fibrosis. This review summarizes the most important advancements in the field of non-viral vectors that have been achieved with the use of nanoparticulate (NP) systems, composed either of polymers or lipids, in the lung gene delivery. In particular, different strategies of targeting of respiratory and airway lung cells will be described. Then, we will focus on the two approaches that attempt to overcome the mucus barrier: coating of the nanoparticulate system with poly(ethylene glycol) and treatment with mucolytics. Our conclusions are: 1) Ligand and physical targeting can direct therapeutic gene expression in specific cell types in the respiratory tract; 2) Mucopenetrating NPs are endowed with promising features to be useful in treating respiratory diseases and should be now advanced in pre-clinical trials. Finally, we discuss the development of such polymer- and lipid-based NPs in the context of in vitro and in vivo disease models, such as lung cancer, as well as in clinical trials.

The human cytomegalovirus UL26 protein antagonizes NF-κB activation

Viral infection frequently triggers activation of host innate immune pathways that attempt to limit viral spread. The NF-κB pathway is a critical component that governs this response. We have found that the human cytomegalovirus (HCMV) U(L)26 protein antagonizes NF-κB activation. Upon infection, an HCMV strain lacking the U(L)26 gene (ΔU(L)26) induced the nuclear translocation of the NF-κB RelB subunit and activated expression and secretion of interleukin-6 (IL-6), an NF-κB target gene. The ΔU(L)26 mutant was also more sensitive to challenge with tumor necrosis factor alpha (TNF-α), a canonical NF-κB inducer. Further, expression of U(L)26 in the absence of other viral proteins blocked NF-κB activation induced by either TNF-α treatment or infection with Sendai virus (SeV). Our results indicate that U(L)26 expression is sufficient to block TNF-α-induced NF-κB nuclear translocation and IκB degradation. Last, U(L)26 blocks TNF-α-induced IκB-kinase (IKK) phosphorylation, a key step in NF-κB activation. Combined, our results indicate that U(L)26 is part of a viral program to antagonize innate immunity through modulation of NF-κB signaling.

IMPORTANCE

The NF-κB signaling pathway regulates innate immunity, an integral host process that limits viral pathogenesis. Viruses have evolved mechanisms to modulate NF-κB signaling to ensure their replication. HCMV is a major cause of birth defects and disease in immunosuppressed populations. HCMV is known to actively target the NF-κB pathway, which is important for HCMV infection. Our results indicate that the HCMV U(L)26 gene is a key modulator of NF-κB pathway activity. We find the U(L)26 gene is both necessary and sufficient to block NF-κB activation upon challenge with antiviral cytokines. Further, U(L)26 attenuates the phosphorylation and activation of a key NF-κB activating kinase complex, IKK. Our study provides new insight into how HCMV targets the NF-κB pathway. Given its importance to viral infection, the mechanisms through which viruses target the NF-κB pathway highlight areas of vulnerability that could be therapeutically targeted to attenuate viral replication.

Recent approaches and strategies in the generation of antihuman cytomegalovirus vaccines

The development of prophylactic and to lesser extent therapeutic vaccines for the prevention of disease associated with human cytomegalovirus (HCMV) infections has received considerable attention from biomedical researchers and pharmaceutical companies over the previous 15 years, even though attempts to produce such vaccines have been described in the literature for over 40 years. Studies of the natural history of congenital HCMV infection and infection in allograft recipients have suggested that prophylaxis of disease associated with HCMV infection could be possible, particularly in hosts at risk for more severe disease secondary to the lack of preexisting immunity. Provided a substantial understanding of immune response to HCMV together with several animal models that faithfully recapitulate aspects of human infection and immunity, investigators seem well positioned to design and test candidate vaccines. Yet more recent studies of the role of a maternal immunity in the natural history of congenital HCMV infection, including the recognition that reinfection of previously immune women by genetically distinct strains of HCMV occur in populations with a high seroprevalence, have raised several questions about the nature of protective immunity in maternal populations. This finding coupled with observations that have documented a significant incidence of damaging congenital infections in offspring of women with immunity to HCMV prior to conception has suggested that vaccine development based on conventional paradigms of adaptive immunity to viral infections may be of limited value in the prevention of damaging congenital HCMV infections. Perhaps a more achievable goal will be prophylactic vaccines to modify HCMV associated disease in allograft transplant recipients. Although recent descriptions of the results from vaccine trials have been heralded as evidence of an emerging success in the quest for a HCMV vaccine, careful analyses of these studies have also revealed that major hurdles remain to be addressed by current strategies.

CD4 T cell responses in latent and chronic viral infections

The spectrum of tasks which is fulfilled by CD4 T cells in the setting of viral infections is large, ranging from support of CD8 T cells and humoral immunity to exertion of direct antiviral effector functions. While our knowledge about the differentiation pathways, plasticity, and memory of CD4 T cell responses upon acute infections or immunizations has significantly increased during the past years, much less is still known about CD4 T cell differentiation and their beneficial or pathological functions during persistent viral infections. In this review we summarize current knowledge about the differentiation, direct or indirect antiviral effector functions, and the regulation of virus-specific CD4 T cells in the setting of persistent latent or active chronic viral infections with a particular emphasis on herpes virus infections for the former and chronic lymphocytic choriomeningitis virus infection for the latter.

Antiviral T cell response triggers cytomegalovirus hepatitis in mice

One common sign of human cytomegalovirus infection is altered liver function. Murine cytomegalovirus strain v70 induces a rapid and severe hepatitis in immunocompetent mice that requires the presence of T cells in order to develop. v70 exhibits approximately 10-fold-greater virulence than the commonly used strain K181, resulting in a more severe, sustained, and lethal hepatitis but not dramatically higher viral replication levels. Hepatitis and death are markedly delayed in immunodeficient SCID compared to immunocompetent BALB/c mice. Transfer of BALB/c splenocytes to SCID mice conferred rapid disease following infection, and depletion of either CD4 or CD8 T cells in BALB/c mice reduced virus-induced hepatitis. The frequency of CD8 T cells producing gamma interferon and tumor necrosis factor in response to viral antigen was higher in settings where more severe disease occurred. Thus, virus-specific effector CD8 T cells appear to contribute to lethal virus-induced hepatitis, contrasting their protective role during sublethal infection. This study reveals how protection and disease during cytomegalovirus infection depend on viral strain and dose, as well as the quality of the T cell response.

Innate immunity regulates adaptive immune response: lessons learned from studying the interplay between NK and CD8+ T cells during MCMV infection

Natural killer (NK) cells play a crucial role in early immune response against cytomegalovirus infection. A large and mounting body of data indicate that these cells are involved in the regulation of the adaptive immune response as well. By using mouse cytomegalovirus (MCMV) as a model, several groups provided novel insights into the role of NK cells in the development and kinetics of antiviral CD8(+) T cell response. Depending on infection conditions, virus strain and the genetic background of mice used, NK cells are either positive or negative regulators of the CD8(+) T cell response. At present, there is no unique explanation for the observed differences between various experimental systems used. In this review we discuss the mechanisms involved in the interplay between NK and CD8(+) T cells in the early control of MCMV infection.

Polyfunctional CD8(+) T cells are associated with the vaccination-induced control of a novel recombinant influenza virus expressing an HCV epitope

In hepatitis C virus (HCV) infection, CD8(+) T cell responses have been shown to be important in viral clearance. Examining the efficacy of CD8(+) T cell vaccines against HCV has been limited by the lack of an HCV infectious model in mice and the differences between MHC restriction in humans and mice. Using HLA-A2 transgenic HHD mice, we demonstrate that intranasally delivered Pam2Cys-based lipopeptides containing HLA-A2-restricted HCV epitopes can induce polyfunctional CD8(+) T cell responses in several organs including the liver. To examine the activity of these responses in an infectious context, we developed a recombinant influenza virus that expresses the NS5B(2594-2602) epitope from non-structural protein 5B of hepatitis C virus (PR8-HCV(NS5B)). We showed that mice inoculated with a lipopeptide containing the NS5B epitope had reduced viral loads following challenge with the PR8-HCV(NS5B) virus. This reduction was associated with the induction of NS5B(2594-2602)-specific IFN-γ and TNF-α co-producing CD8(+) T cells. The T cell receptor usage in the NS5B(2594-2602) response was found to exhibit a Vβ8.1/8.2 bias that was characterized by a narrow repertoire and a common CDR3β motif. This work has identified CD8(+) T cell functions induced by lipopeptides that are associated with viral control and demonstrate the potential of lipopeptide-based vaccines as candidates for treatment of HCV infection.

Paradoxical response to prophylactic Didox (N-3, 4 trihydroxybenzamide) treatment in murine cytomegalovirus-infected mice

BACKGROUND

In this study, we investigated the effect of Didox (DX) on the pathogenicity of and host responses to murine cytomegalovirus (MCMV) infection.

METHODS

In vitro efficacy of DX against MCMV was determined using plaque reduction assays. For in vivo studies, mice infected with a sublethal dose (10(4) PFU) of MCMV were treated daily with DX (200 mg/kg) using either a prophylactic or delayed protocol. At predetermined intervals, target organs were removed for histopathology. Cytokine transcription and viral load were performed using real-time PCR. Serum cytokine levels were determined by ELISA, and T-cell markers by real-time PCR.

RESULTS

DX (0.5-50 μM) inhibited MCMV plaque formation in vitro. However, in vivo, prophylactic DX treatment did not decrease viral load and prolonged hepatic proinflammatory cytokine transcription at days 3 and 5 post-infection, which corresponded with more severe histopathological changes observed in the liver. Significant CD8(+) T-cell marker suppression was seen, in accordance with DX-induced inhibition of lymphocyte proliferation observed in vitro. DX prolonged the recovery of MCMV-infected mice when given after infection was established.

CONCLUSIONS

Despite promising MCMV inhibition in vitro, DX had no beneficial effect on MCMV disease in our model and paradoxically had adverse effects when administered prophylactically. The lack of correlation between in vitro activity and in vivo efficacy emphasizes the importance of selecting appropriate antiviral targets and of using animal models when testing new drugs.

Treatment of TNF mediated diseases by selective inhibition of soluble TNF or TNFR1

The TNF signaling pathway is a valuable target in the therapy of autoimmune diseases, and anti-TNF drugs are successfully used to treat diseases such as rheumatoid arthritis, Crohn's disease and psoriasis. By their ability to interfere with inflammatory processes at multiple levels, these TNF blockers have become invaluable tools to inhibit the inflammation induced damage and allow recovery of the affected tissues. Unfortunately this therapy has some drawbacks, including increased risk of infection and malignancy, and remarkably, the onset of new auto-immune diseases. Some of these effects are caused by the unwanted abrogation of beneficial TNF signaling. More specific targeting of the pathological TNF-induced signaling might lead to broader applicability and improved safety. Specificity might be increased by inhibiting the soluble TNF/TNFR1 axis while leaving the often beneficial transmembrane TNF/TNFR2 signaling untouched. This approach looks promising because it inhibits the pathological effects of TNF and reduces the side effects, and it opens the way for the treatment of other diseases in which TNFR2 inhibition is detrimental. In this review we give an overview of in vivo mouse studies of TNF mediated pathologies demonstrating that the blockade or genetic deletion of sTNF or TNFR1 is preferable over total TNF blockade.

Absence of cross-presenting cells in the salivary gland and viral immune evasion confine cytomegalovirus immune control to effector CD4 T cells

Horizontal transmission of cytomegaloviruses (CMV) occurs via prolonged excretion from mucosal surfaces. We used murine CMV (MCMV) infection to investigate the mechanisms of immune control in secretory organs. CD4 T cells were crucial to cease MCMV replication in the salivary gland (SG) via direct secretion of IFNγ that initiated antiviral signaling on non-hematopoietic cells. In contrast, CD4 T cell helper functions for CD8 T cells or B cells were dispensable. Despite SG-resident MCMV-specific CD8 T cells being able to produce IFNγ, the absence of MHC class I molecules on infected acinar glandular epithelial cells due to viral immune evasion, and the paucity of cross-presenting antigen presenting cells (APCs) prevented their local activation. Thus, local activation of MCMV-specific T cells is confined to the CD4 subset due to exclusive presentation of MCMV-derived antigens by MHC class II molecules on bystander APCs, resulting in IFNγ secretion interfering with viral replication in cells of non-hematopoietic origin.

Cytomegaloviruses (CMVs) infect 50 to 90 % of the world's population and cause severe clinical complication in immunosuppressed individuals. An important tissue for horizontal transmission is the salivary gland (SG). CD4 T cells are crucial for viral control in this organ. However, how CD4 T cells control MCMV and why CD8 T cells, important effector cells in other organs, are inefficient in the SG, remains unclear. Here we show that CD4 T cells exert direct antiviral effector rather than helper functions by secretion of IFNγ acting on non-hematopoietic cells. Although SG-resident CD8 T cells were able to produce IFNγ and outnumbered CD4 T cells, absence of MHC class I expression on infected cells due to CMV-encoded immune evasion genes and concomitant absence of cross-presenting antigen presenting cells prohibited antigen recognition by CD8 T cells. Deletion of CMV-encoded immune evasion genes enabled CD8 T cells to control MCMV replication in the SG in absence of CD4 T cells. Hence, CMV control depends on direct antiviral functions of CD4 T cells because of exclusive MHC class II-restricted CMV antigen presentation by bystander APCs in the SG, exemplifying a strategy of effective immune evasion by which CMVs to promote their own transmission.

Tumour necrosis factor alpha (TNF-alpha) stimulation of cells with established dengue virus type 2 infection induces cell death that is accompanied by a reduced ability of TNF-alpha to activate nuclear factor kappaB and reduced sphingosine kinase-1 activity

Tumor necrosis factor alpha (TNF-α) has an antiviral role in some infections but in dengue virus (DENV) infection it is linked to severe pathology. We have previously shown that TNF-α stimulation cannot activate nuclear factor κB (NF-κB) to the fullest extent in DENV-2-infected cells. Here, we investigate further responses of DENV-2-infected cells to TNF-α, focussing particularly on cell death and pro-survival signals. TNF-α stimulation of productively DENV-2-infected monocyte-derived macrophages or HEK-293 cells induced caspase-3-mediated cell death. While TNF-α induced comparable degradation of the inhibitor of NF-κB alpha (IκB-α) and NF-κB activation in mock-infected and DENV-2-infected cells early in infection, later in infection and coinciding with TNF-α-induced cell death, TNF-α-stimulated IκB-α degradation and NF-κB activation was reduced. This was associated with reduced levels of sphingosine kinase-1 (SphK1) activity in DENV-2-infected cells; SphK1 being a known mediator of TNF-α-stimulated survival signals. Transfection experiments demonstrated inhibition of TNF-α-stimulated NF-κB activation by expression of DENV-2 capsid (CA) but enhancement by DENV-2 NS5 protein. DENV-2 CA alone, however, did not induce TNF-α-stimulated cell death or inhibit SphK1 activity. Thus, productively DENV-2-infected cells have compromised TNF-α-stimulated survival pathways and show enhanced susceptibility to TNF-α-stimulated cell death, suggesting a role for TNF-α in the killing of healthy productively DENV-2-infected cells. Additionally, the altered ability of TNF-α to activate NF-κB as infection progresses is reflected by the opposing actions of DENV-2 CA and NS5 proteins on TNF-α-stimulated NF-κB activation and could have important consequences for NF-κB-driven release of inflammatory cytokines.

The salivary glands as a privileged site of cytomegalovirus immune evasion and persistence

The salivary glands (SG) provide a haven for persistent cytomegalovirus replication, and in this regard are a privileged site of virus immune evasion. The murine cytomegalovirus (MCMV) model has provided insight into the immunological environment of the SG and the unqiue virus-host relationship of this organ. In response to MCMV infection, a robust T cell-mediated immune response is elicited, comprised predominantly of CD8+ T cells that phenotypically and functionally appear activated. However, they fail to clear virus by an unknown evasion mechanism that is independent of inhibitory NKG2A- or Programmed Death 1-mediated signaling. Virus is eventually eliminated from the SG by effector CD4+ T cells expressing antiviral cytokines. However, this mechanism is severely dampened by high levels of the immunosuppressive cytokine IL-10, selectively expressed by SG CD4+ T cells.

Subconjunctival antisense oligonucleotides targeting TNF-alpha influence immunopathology and viral replication in murine HSV-1 retinitis

BACKGROUND

To investigate the role of tumor necrosis factor-alpha (TNF-alpha) in immunopathology and viral replication in the contralateral eye in the von Szily model of herpes simplex virus (HSV)-1 acute retinitis.

METHODS

In vivo distribution was analyzed after subconjunctival injection of FITC-labeled antisense oligonucleotides (ASON). After HSV-1 (KOS) was injected in the right anterior chamber (AC) in BALB/c mice, the course of the contralateral retinitis was evaluated. The left eyes were treated with either TNF-alpha ASON, sequence-unspecific control (CON), or buffer. The ocular TNF-alpha content was quantified by ELISA. The delayed-type hypersensitivity (DTH) reaction, uptake of [3H]thymidine from regional lymph nodes (rln)- and spleen cells, serum-neutralizing antibodies, and viral titer in the eyes were evaluated.

RESULTS

After subconjunctival injection, FITC-labeled ASON were found in the choroid and retina. In the TNF-alpha ASON-treated eyes, TNF-alpha expression and the incidence and severity of retinitis were reduced on day 8 postinfection (PI) (p < 0.05). On day 10 PI, higher viral titers were only seen in the eyes of the TNF-alpha ASON group (p < 0.05), and retinitis was slightly more severe on day 12 PI. While the HSV-1 specific [3H]thymidine uptake from rln cells was higher in the TNF-alpha ASON mice (p < 0.05), the [3H]thymidine uptake from spleen cells, the DTH response, and the neutralizing-antibody titers did not differ between the groups.

CONCLUSIONS

After regional blockade of TNF-alpha in experimental HSV-1 retinitis TNF-alpha seems to possess an antiviral capacity against HSV-1 in the contralateral eye and participates in the immunopathology of HSV-1-induced acute retinitis.

Cytomegalovirus M45 cell death suppression requires receptor-interacting protein (RIP) homotypic interaction motif (RHIM)-dependent interaction with RIP1

Herpesviruses such as cytomegaloviruses encode functions that modulate the innate response in diverse ways to counteract host sensing and delay host clearance during infection. The murine cytomegalovirus M45 protein interacts with receptor-interacting protein (RIP) 1 and RIP3 via a RIP homotypic interaction motif. Cell death suppression by M45 requires RIP homotypic interaction motif-dependent interaction with RIP1. This interaction also underlies the cell tropism role of M45 in preventing premature death of endothelial cells during murine cytomegalovirus infection. Thus, M45 is a viral inhibitor of RIP activation that provides a direct cell type-dependent replication benefit to the virus while modulating other biological processes signaling via the RIP1 adaptor such as activation of Toll-like receptor (TLR)3 as well as other mediators of cell death.

Upregulation of CD94/NKG2A receptors and Qa-1b ligand during murine cytomegalovirus infection of salivary glands

Following acute infection, murine cytomegalovirus (MCMV) replicates persistently in the salivary glands, despite the vigorous response of activated CD8 T cells that infiltrate this gland. Virus-specific CD8 T lymphocytes isolated from this organ were found to express the inhibitory CD94/NKG2A receptor that, in some virus models, confers an inhibitory response to cytotoxic T lymphocytes (CTLs). In response to MCMV infection, expression of the CD94/NKG2A ligand, Qa-1b, increased dramatically in the submandibular gland (SMG) prior to upregulation of H-2Dd. However, there was no net negative impact on virus-specific T-cell function, as virus titres were similar in CD94- and CD94+ mice. CD94/NKG2A expression, also known to inhibit apoptosis, did not influence the numbers of accumulated T, NK and NK T cells. These data indicate that expression of inhibitory CD94/NKG2A receptors does not account for the failure of MCMV-specific CTLs to clear the SMG of infection.

Dengue virus (DV) replication in monocyte-derived macrophages is not affected by tumor necrosis factor alpha (TNF-alpha), and DV infection induces altered responsiveness to TNF-alpha stimulation

Tumor necrosis factor alpha (TNF-alpha) is believed to play a significant role in the pathogenesis of dengue virus (DV) infection, with elevated levels of TNF-alpha in the sera of DV-infected patients paralleling the severity of disease and TNF-alpha release being coincident with the peak of DV production from infected monocyte-derived macrophages (MDM) in vitro. Since macrophages are a primary cell target in vivo for DV infection, we investigated the potential antiviral role of TNF-alpha in regulating DV replication in MDM. While pretreatment of MDM with TNF-alpha had a minor inhibitory effect, addition of TNF-alpha to MDM with established DV infection had no effect on DV replication as measured by DV RNA levels or progeny virus production. Blocking endogenous TNF-alpha using short interfering RNA or inhibitory TNF-alpha antibodies also had no effect on infectious DV production or viral RNA synthesis. Together, these results demonstrate that DV replication in MDM is not affected by TNF-alpha. Additionally, normal cellular TNF-alpha signaling, measured by quantitation of TNF-alpha-induced stimulation of transcription from an NF-kappaB-responsive reporter plasmid or NF-kappaB protein nuclear translocation, was blocked in DV-infected MDM and Huh7 cells. Thus, DV replication in MDM is not affected by TNF-alpha, and infected cells do not respond normally to TNF-alpha stimulation. It is therefore unlikely that the increased production of TNF-alpha seen in DV infection directly effects DV clearance by reducing DV replication, and the ability of DV to alter TNF-alpha responsiveness highlights another example of viral subversion of cellular functions.

Vgamma9Vdelta2 T cell-mediated non-cytolytic antiviral mechanisms and their potential for cell-based therapy

In healthy adult Homo sapiens, the most frequent circulating gammadelta T cells (Vgamma9Vdelta2) respond to pyrophosphomonoesters, alkylamines (together referred to as non-peptidic antigens, NpAgs) and nitrogen-containing bisphosphonates. The seemingly very low toxicity of bisphosphonate and pyrophosphomonoester drugs in vivo, may allow novel approaches to the immunotherapy of viral infections. For example, these drugs can be used to stimulate Vgamma9Vdelta2 T cells to release antiviral molecules that directly suppress virus replication without destroying the virus-replicating cells. In addition, the soluble molecules released by gammadelta T cells could boost the antiviral potency of cytotoxic T lymphocytes (CTLs) and promote antigen presentation. The relative therapeutic value of drug-induced direct antiviral and immunoregulatory activities may depend on the infecting virus as well as on the nature of protective immune responses.

Use of quantitative real-time PCR (qRT-PCR) to measure cytokine transcription and viral load in murine cytomegalovirus infection

A quantitative real-time PCR (qRT-PCR) assay was developed to measure cytokine transcription profiles and viral load during sub-clinical and clinical infection with murine cytomegalovirus (MCMV). Primers/fluorogenic probes specific for mouse cytokines and for the immediate early gene 1 (IE1) of MCMV were used to quantitate cytokine responses and viral load in various organs of MCMV infected mice. Increased mRNA levels of TNF-alpha, INF-gamma and IL-10 were detected in the spleens, lungs and livers of clinically infected mice at 5 days post-infection. Transcription of these cytokines was 2-5-fold lower (p=0.07 for each cytokine) in the spleens and 10-100-fold lower in the lungs (p=0.03 for INFgamma, not significant for IL-10 and TNFalpha) and livers (p<0.05 for each cytokine) of sub-clinically infected mice. Clinical MCMV infection induced high levels of IL-6 in the lungs and spleens of infected animals, while no significant transcription of IL-6 was detected in any organ during sub-clinical infection (p<0.05). The timing of peak amounts of INF-gamma, IL-10 and IL-6 observed in the spleens of clinically infected mice correlated with high viral loads in these organs. Cytokine expression rose in the salivary glands later, at day 15, corresponding to the increase in salivary gland viral load. The qRT-PCR demonstrates that infection with MCMV induces an organ-specific cytokine response characterized by the production of TNF-alpha, INF-gamma, IL-6 and IL-10 which correlates with severity of the disease (sub-clinical versus clinical) and with viral load. In summary, qRT-PCR is a sensitive and accurate method to study MCMV infection and host responses to the virus.

Inhibition by TNF-alpha and IL-4 of cationic lipid mediated gene transfer in cystic fibrosis tracheal gland cells

BACKGROUND

In vivo, tracheal gland serous cells highly express the cystic fibrosis transmembrane conductance regulator (cftr) gene. This gene is mutated in the lethal monogenic disease cystic fibrosis (CF). Clinical trials in which the human CFTR cDNA was delivered to the respiratory epithelia of CF patients have resulted in weak and transient gene expression.

METHODS AND RESULTS

As CF is characterized by mucus inspissation, airway infection, and severe inflammation, we tested the hypothesis that inflammation and especially two cytokines involved in the Th1/Th2 inflammatory response, interleukin 4 (IL-4) and TNFalpha, could inhibit gene transfer efficiency using a model of human CF tracheal gland cells (CF-KM4) and Lipofectamine reagent as a transfection reagent. The specific secretory defects of CF-KM4 cells were corrected by Lipofectamine-mediated human CFTR gene transfer. However, this was altered when cells were pre-treated with IL-4 and TNFalpha. Inhibition of luciferase reporter gene expression by IL-4 and TNFalpha pre-treated CF-KM4 cells was measured by activity and real-time RT-PCR. Both cytokines induced similar and synergistic inhibition of transgene expression and activity. This cytokine-mediated inhibition could be prevented by anti-inflammatory agents such as glucocorticoids but not by non-steroidal (NSAI) agents.

CONCLUSIONS

This data suggests that an inflammatory context generated by IL-4 and TNFalpha can inhibit human CFTR gene transfer in CF tracheal gland cells and that glucocorticoids may have a protecting action.

IL-12 Protects against Coxsackievirus B3-Induced Myocarditis by Increasing IFN-γ and Macrophage and Neutrophil Populations in the Heart

Th1-type immune responses, mediated by IL-12-induced IFN-gamma, are believed to exacerbate certain autoimmune diseases. We recently found that signaling via IL-12Rbeta1 increases coxsackievirus B3 (CVB3)-induced myocarditis. In this study, we examined the role of IL-12 on the development of CVB3-induced myocarditis using mice deficient in IL-12p35 that lack IL-12p70. We found that IL-12 deficiency did not prevent myocarditis, but viral replication was significantly increased. Although there were no changes in the total percentage of inflammatory cells in IL-12-deficient hearts compared with wild-type BALB/c controls by FACS analysis, macrophage and neutrophil populations were decreased. This decrease corresponded to reduced TNF-alpha and IFN-gamma levels in the heart, suggesting that macrophage and/or neutrophil populations may be a primary source of TNF-alpha and IFN-gamma during acute CVB3 myocarditis. Increased viral replication in IL-12-deficient mice was not mediated by reduced TNFRp55 signaling, because viral replication was unaltered in TNFRp55-deficient mice. However, STAT4 or IFN-gamma deficiency resulted in significantly increased viral replication and significantly reduced TNF-alpha and IFN-gamma levels in the heart, similar to IL-12 deficiency, indicating that the IL-12/STAT4 pathway of IFN-gamma production is important in limiting CVB3 replication. Furthermore, STAT4 or IFN-gamma deficiency also increased chronic CVB3 myocarditis, indicating that therapeutic strategies aimed at reducing Th1-mediated autoimmune diseases may exacerbate common viral infections such as CVB3 and increase chronic inflammatory heart disease.

Intracerebral infection with murine cytomegalovirus induces CXCL10 and is restricted by adoptive transfer of splenocytes

The brain's intrinsic immune system consists of glial cells that produce cytokines and chemokines in response to stimulation with cytomegalovirus (CMV). The present experiments were undertaken to determine whether this intrinsic glial cell response alone is sufficient to control CMV infection of the central nervous system (CNS) or whether effector cells from the somatic immune system are also required. Following stereotactic, intracerebroventricular (icv), injection of murine cytomegalovirus (MCMV) into immunocompetent (C.B-17) mice, viral spread in the brain was limited to the cells of the ventricular walls and the infection was resolved by 10 days post infection (p.i.). In contrast, icv infection of immunodeficient (C.B-17 SCID/bg) mice resulted in viral spread from the ventricles throughout the brain parenchyma and these mice succumbed to lethal disease. Adoptive transfer of total splenocytes from major histocompatibility complex (MHC)-matched, MCMV-primed animals restricted intracerebral viral infection to the periventricular cells and reduced levels of reporter gene expression from the viral genome. Peripheral immune cell transfer also protected immunodeficient animals from lethal disease. Depletion of Thy 1.2(+) cells from MCMV-primed splenocytes abolished the protective effect of adoptive transfer. Viral expression was found to be fourfold greater in the brains of animals given Thy 1.2-depleted splenocytes than from those receiving total undepleted cells. As MCMV infection proceeded in the brains of immunodeficient mice, levels of the T-cell chemoattractants CXCL10 and CCL2 remained elevated, whereas CXCL10 levels waned in the brains of animals receiving transferred splenocytes. Taken together, these results demonstrate the ability of T lymphocytes to restrict intracerebral viral spread and indicate that intrinsic glial cell responses alone are insufficient to control MCMV brain infection.

Pathogenesis of murine cytomegalovirus infection

Infection of mice with murine cytomegalovirus (MCMV) is an established model for studying human cytomegalovirus (HCMV) infection. Similarly to HCMV infection, pathological changes and disease manifestations during MCMV infection are mainly dependent on the immune status of the mouse host. This review focuses mainly on the pathogenesis of MCMV infection in immunocompetent and immunodeficient and/or immature mice and discusses the principles of immunosurveillance of infection and the mechanisms by which this virus evades immune control.

Murine cytomegalovirus infection inhibits tumor necrosis factor alpha responses in primary macrophages

Despite robust host immune responses the betaherpesvirus murine cytomegalovirus (MCMV) is able to establish lifelong infection. This capacity is due at least in part to the virus utilizing multiple immune evasion mechanisms to blunt host responses. Macrophages are an important cell for MCMV infection, dissemination, and latency despite expression in the host of multiple cytokines, including tumor necrosis factor alpha (TNF-alpha), that can induce an antiviral state in macrophages or other cells. In this study, we found that MCMV infection of bone marrow-derived macrophages inhibited TNF-alpha-induced ICAM-1 surface expression and mRNA expression in infected cells via expression of immediate early and/or early viral genes. MCMV infection blocked TNF-alpha-induced nuclear translocation of NF-kappaB. This inhibition of TNF-alpha signaling was explained by a decrease in TNF receptor 1 (TNFR1) and TNFR2 that was due to decreased mRNA for the latter. These findings provide a mechanism by which MCMV can evade the effects of an important host cytokine in macrophages.

Simian-human immunodeficiency virus SHIV89.6-induced protection against intravaginal challenge with pathogenic SIVmac239 is independent of the route of immunization and is associated with a combination of cytotoxic T-lymphocyte and alpha interferon responses

Attenuated primate lentivirus vaccines provide the most consistent protection against challenge with pathogenic simian immunodeficiency virus (SIV). Thus, they provide an excellent model to examine the influence of the route of immunization on challenge outcome and to study vaccine-induced protective anti-SIV immune responses. In the present study, rhesus macaques were immunized with live nonpathogenic simian-human immunodeficiency virus (SHIV) 89.6 either intravenously or mucosally (intranasally or intravaginally) and then challenged intravaginally with pathogenic SIVmac239. The route of immunization did not affect mucosal challenge outcome after a prolonged period of systemic infection with the nonpathogenic vaccine virus. Further, protection from the SIV challenge was associated with the induction of multiple host immune effector mechanisms. A comparison of immune responses in vaccinated-protected and vaccinated-unprotected animals revealed that vaccinated-protected animals had higher frequencies of SIV Gag-specific cytotoxic T lymphocytes and gamma interferon (IFN-gamma)-secreting cells during the acute phase postchallenge. Vaccinated-protected animals also had a more pronounced increase in peripheral blood mononuclear cell IFN-alpha mRNA levels than did the vaccinated-unprotected animals in the first few weeks after challenge. Thus, innate as well as cellular anti-SIV immune responses appeared to contribute to the SHIV89.6-induced protection against intravaginal challenge with pathogenic SIVmac239.

Vigorous innate and virus-specific cytotoxic T-lymphocyte responses to murine cytomegalovirus in the submaxillary salivary gland

To better understand the immunological mechanisms that permit prolonged shedding of murine cytomegalovirus (MCMV) from the salivary gland, the phenotypic and functional characteristics of leukocytes infiltrating the submaxillary gland (SMG) were analyzed in infected BALB/c mice. A robust innate immune response, comprised of CD11c+ major histocompatibility complex class II+ CD11b- CD8alpha+ dendritic cells and gamma/delta T-cell receptor-bearing CD3+ T cells was prominent through at least 28 days postinfection. Concurrently, a dramatic increase in pan-NK (DX5+) CD3+ and CD8+ T cells was observed, while CD4+ T cells, known to be essential for viral clearance from this tissue, increased slightly. The expression particularly of gamma interferon but also of interleukin-10 and CC chemokines was extraordinarily high in the SMG in response to MCMV infection. The gamma interferon was produced primarily by CD4+ and CD8+ T lymphocytes and DX5+ CD3+ T cells. The SMG CD8+ T cells were highly cytolytic ex vivo, and a significant proportion of these cells were specific to an immunodominant MCMV peptide. These peptide-specific clones were not exhausted by the presence of high virus titers, which persisted in the SMG despite the strength of the cell-mediated responses. In contrast, MCMV replication was efficiently cleared from the draining cervical and periglandular lymph nodes, a tissue displaying a substantially weaker antiviral response. Our data indicated that vigorous innate and acquired immune responses are elicited, activated, and retained in response to mucosal inflammation from persistent MCMV infection of the submaxillary gland.

Fatal attraction: cytomegalovirus-encoded chemokine homologs

Members of the cytomegalovirus (CMV) subfamily of betaherpesviruses infecting primates and rodents encode divergent proteins with sequence characteristics and activities of chemokines, a class of small, secreted proteins that control leukocyte migration and trafficking behavior. Human CMV genes UL146 and UL147 encode proteins with sequence characteristics of CXC chemokines, whereas, murine CMV encodes a CC chemokine homolog (MCK-2). Human CMV UL146 encodes a neutrophil-attracting chemokine denoted viral CXC chemokine-1 (vCXCL1) that is as potent as host IL-8 and functions via the CXCR2 receptor, one of two human IL-8 receptors. Murine CMV MCK-2 is composed of a chemokine domain derived from open reading frame (ORF) m131 (and denoted MCK-1) as well as a domain derived from m129 that does not have sequence similarity to any known class of proteins. A synthetic version of murine CMV m131 (MCK-1) protein carries out many of the activities of a positive-acting chemokine, including transient release of intracellular calcium stores and cell adhesion of peritoneal macrophage populations. In the context of the viral genome and infection of the mouse host, the m131-m129 (MCK-2) gene product confers increased inflammation, higher levels of viremia, and higher titers of virus in salivary glands, consistent with a role in promoting dissemination by attracting an important mononuclear leukocyte population. Other characterized primate CMVs, but not other primate betaherpesviruses, encode gene products similar to human UL146 and UL147. Other characterized rodent CMVs encode a gene product similar to the murine CMV chemokine homolog, although not as a spliced gene product. Thus chemokines, like viral proteins that downmodulate MHC class I expression or have sequence homology to host MHC class I proteins, have evolved in primate and rodent CMVs to carry out an analogous set of immunomodulatory functions during infection of the host even though they arise from distinct origins.

Virus-cell interactions regulating induction of tumor necrosis factor alpha production in macrophages infected with herpes simplex virus

Macrophages respond to virus infections by rapidly secreting proinflammatory cytokines, which play an important role in the first line of defense. Tumor necrosis factor alpha (TNF-alpha) is one of the major macrophage-produced cytokines. In this study we have investigated the virus-cell interactions responsible for induction of TNF-alpha expression in herpes simplex virus (HSV)-infected macrophages. Both HSV type 1 (HSV-1) and HSV-2 induced TNF-alpha expression in macrophages activated with gamma interferon (IFN-gamma). This induction was to some extent sensitive to UV treatment of the virus. Virus particles unable to enter the cells displayed reduced capacity to stimulate TNF-alpha expression but retained a significant portion which was abolished by HSV-specific antibodies. Recombinant HSV-1 glycoprotein D was able to trigger TNF-alpha secretion in concert with IFN-gamma. Sugar moieties of HSV glycoproteins have been reported to be involved in induction of IFN-alpha but did not contribute to TNF-alpha expression in macrophages. Moreover, the entry-dependent portion of the TNF-alpha induction was investigated with HSV-1 mutants and found to be independent of the tegument proteins VP16 and UL13 and partly dependent on nuclear translocation of the viral DNA. Finally, we found that macrophages expressing an inactive mutant of the double-stranded RNA (dsRNA)-activated protein kinase (PKR) produced less TNF-alpha in response to infectious HSV infection than the empty-vector control cell line but displayed the same responsiveness to UV-inactivated virus. These results indicate that HSV induces TNF-alpha expression in macrophages through mechanisms involving (i) viral glycoproteins, (ii) early postentry events occurring prior to nuclear translocation of viral DNA, and (iii) viral dsRNA-PKR.

Susceptibility to cytomegalovirus infection may be dependent on the cytokine response to the virus

BACKGROUND

Cytomegalovirus (CMV) infection is an important cause of morbidity and mortality in an immunocompromised host. Pulmonary infection with CMV results in an inflammatory response, which includes the local production of cytokines. Cytokine production stimulated by CMV infection serves to activate a series of immunologic responses involved in viral clearance. Previous work has demonstrated that different mouse strains express variable sensitivity to CMV infection.

METHODS

Using mouse strains that express sensitive (BALB/cj) and resistant (C57BL/6) CMV phenotypes, we asked whether the differences in susceptibility to infection were caused by differences in pulmonary cytokine production after intraperitoneal infection with CMV.

RESULTS

C57 mice demonstrated a higher total bronchoalveolar lavage (BAL) and BAL lymphocyte count at 3 and 7 days after intraperitoneal infection compared with BALB mice. There were no differences in BAL cytokine production; however, we were able to demonstrate differences in CMV DNA load in the lungs of BALB mice compared with that of C57 mice. In addition, there appeared to be increased whole-lung production of the TH2 cytokine IL-10 in the BALB mice versus the C57 mice.

CONCLUSIONS

This observation suggests that the genetic susceptibility to CMV infection may, in part, be regulated by differences in cytokines production within the local environment.

Expression of TNF-alpha by herpes simplex virus-infected macrophages is regulated by a dual mechanism: transcriptional regulation by NF-kappa B and activating transcription factor 2/Jun and translational regulation through the AU-rich region of the 3' untranslated region

Here we have investigated the regulation of TNF-alpha expression in macrophages during HSV-2 infection. Despite a low basal level of TNF-alpha mRNA present in resting macrophages, no TNF-alpha protein is detectable. HSV-2 infection marginally increases the level of TNF-alpha mRNA and protein in resting macrophages, whereas a strong increase is observed in IFN-gamma-activated cells infected with the virus. By reporter gene assay it was found that HSV infection augments TNF-alpha promoter activity. Moreover, treatment of the cells with actinomycin D, which totally blocked mRNA synthesis, only partially prevented accumulation of TNF-alpha protein, indicating that the infection lifts a block on translation of TNF-alpha mRNA. EMSA analysis showed that specific binding to the kappaB#3 site of the murine TNF-alpha promoter was induced within 1 h after infection and persisted beyond 5 h where TNF-alpha expression is down-modulated. Binding to the cAMP responsive element site was also induced but more transiently with kinetics closely following activation of the TNF-alpha promoter. Inhibitors against either NF-kappaB activation or the activating transcription factor 2 kinase p38 abrogated TNF-alpha expression, showing a requirement for both signals for activation of the promoter. This observation was corroborated by reporter gene assays. As to the translational regulation of TNF-alpha, the AU-rich sequence in the 3' untranslated region of the mRNA was found to be responsible for this control because deletion of this region renders mRNA constitutively translationable. These results show that TNF-alpha production is induced by HSV-2 in macrophages through both transcriptional and translational regulation.

Noncytolytic control of viral infections by the innate and adaptive immune response

This review describes the contribution of noncytolytic mechanisms to the control of viral infections with a particular emphasis on the role of cytokines in these processes. It has long been known that most cell types in the body respond to an incoming viral infection by rapidly secreting antiviral cytokines such as interferon alpha/beta (IFN-alpha/beta). After binding to specific receptors on the surface of infected cells, IFN-alpha/beta has the potential to trigger the activation of multiple noncytolytic intracellular antiviral pathways that can target many steps in the viral life cycle, thereby limiting the amplification and spread of the virus and attenuating the infection. Clearance of established viral infections, however, requires additional functions of the immune response. The accepted dogma is that complete clearance of intracellular viruses by the immune response depends on the destruction of infected cells by the effector cells of the innate and adaptive immune system [natural killer (NK) cells and cytotoxic T cells (CTLs)]. This notion, however, has been recently challenged by experimental evidence showing that much of the antiviral potential of these cells reflects their ability to produce antiviral cytokines such as IFN-gamma and tumor necrosis factor (TNF)-alpha at the site of the infection. Indeed, these cytokines can purge viruses from infected cells noncytopathically as long as the cell is able to activate antiviral mechanisms and the virus is sensitive to them. Importantly, the same cytokines also control viral infections indirectly, by modulating the induction, amplification, recruitment, and effector functions of the immune response and by upregulating antigen processing and display of viral epitopes at the surface of infected cells. In keeping with these concepts, it is not surprising that a number of viruses encode proteins that have the potential to inhibit the antiviral activity of cytokines.

Reactivation of latent human cytomegalovirus in CD14(+) monocytes is differentiation dependent

We have previously demonstrated reactivation of latent human cytomegalovirus (HCMV) in myeloid lineage cells obtained from healthy donors. Virus was obtained from allogenically stimulated monocyte-derived macrophages (Allo-MDM), but not from macrophages differentiated by mitogenic stimulation (ConA-MDM). In the present study, the cellular and cytokine components essential for HCMV replication and reactivation were examined in Allo-MDM. The importance of both CD4(+) and CD8(+) T cells in the generation of HCMV-permissive Allo-MDM was demonstrated by negative selection or blocking experiments using antibodies directed against both HLA class I and HLA class II molecules. Interestingly, contact of monocytes with CD4 or CD8 T cells was not essential for reactivation of HCMV, since virus was observed in macrophages derived from CD14(+) monocytes stimulated by supernatants produced by allogeneic stimulation of peripheral blood mononuclear cells. Examination of the cytokines produced in Allo-MDM and ConA-MDM cultures indicated a significant difference in the kinetics of production and quantity of these factors. Further examination of the cytokines essential for the generation of HCMV-permissive Allo-MDM identified gamma interferon (IFN-gamma) but not interleukin-1 or -2, tumor necrosis factor alpha, or granulocyte-macrophage colony-stimulating factor as critical components in the generation of these macrophages. In addition, although IFN-gamma was crucial for reactivation of latent HCMV, addition of IFN-gamma to unstimulated macrophage cultures was insufficient to reactivate virus. Thus, this study characterizes two distinct monocyte-derived cell types which can be distinguished by their ability to reactivate and support HCMV replication and identifies the critical importance of IFN-gamma in the reactivation of HCMV.

Cytomegalovirus induces cytokine and chemokine production differentially in microglia and astrocytes: antiviral implications

Glial cells function as sensors for infection within the brain and produce cytokines to limit viral replication and spread. We examined both cytokine (TNF-alpha, IL-1beta, and IL-6) and chemokine (MCP-1, MIP-1alpha, RANTES, and IL-8) production by primary human glial cells in response to cytomegalovirus (CMV). Although CMV-infected astrocytes did not produce antiviral cytokines, they generated significant quantities of the chemokines MCP-1 and IL-8 in response to viral infection. On the other hand, supernatants from CMV-stimulated purified microglial cell cultures showed a marked increase in the production of TNF-alpha and IL-6, as well as chemokines. Supernatants from CMV-infected astrocyte cultures induced the migration of microglia towards chemotactic signals generated from infected astrocytes. Antibodies to MCP-1, but not to MIP-1alpha, RANTES, or IL-8, inhibited this migratory activity. These findings suggest that infected astrocytes may use MCP-1 to recruit antiviral cytokine-producing microglial cells to foci of infection. To test this hypothesis, cocultures of astrocytes and microglial cells were infected with CMV. Viral gene expression in these cocultures was 60% lower than in CMV infected purified astrocyte cultures lacking microglia. These results support the hypothesis that microglia play an important antiviral role in defense of the brain against CMV. The host defense function of microglial cells may be directed in part by chemokines, such as MCP-1, produced by infected astrocytes.

CD4(+) lymphocyte-mediated suppression of cytomegalovirus expression in human astrocytes

Cytomegalovirus-stimulated CD4(+) lymphocytes from seropositive but not seronegative donors suppressed viral gene expression in primary human astrocytes. This suppressive activity was mediated through soluble factors. These findings suggest that CD4(+) lymphocytes play a role in defense of the brain against cytomegalovirus.

Tumor necrosis factor (TNF)-alpha and TNF receptors in viral pathogenesis

Tumor necrosis factor-alpha (TNF-alpha) and TNF receptors (TNFR) are members of the growing TNF ligand and receptor families that are involved in immune regulation. The present report will focus on the role of the prototypic ligand TNF and its two receptors, TNFR1 and TNFR2, in viral pathogenesis. Although TNF was reported years ago to modulate viral infections, recent findings on the molecular pathways involved in TNFR signaling have allowed a better understanding of the molecular interactions between cellular and viral factors within the infected cell. The interactions of viral proteins with intracellular components downstream of the TNFR have highlighted at the molecular level how viruses can manipulate the cellular machinery to escape the immune response and to favor the spread of the infection. We will review here the role of TNF and TNFR in immune response and the role of TNF and TNFR signaling in viral pathogenesis.

Pathogenesis, natural history, treatment, and prevention of hepatitis C

Approximately 4 million persons in the United States and probably more than 100 million persons worldwide are infected with hepatitis C virus. The virus has the unique ability to cause persistent infection in susceptible hosts after parenteral or percutaneous transmission, and its underlying mechanisms are not well understood. The immunologic correlates of protection and viral clearance and the pathogenesis of liver injury are yet to be defined, but recent studies suggest the importance of cell-mediated immune responses. Although 70% to 80% of infected persons become chronic carriers, most have relatively mild disease with slow progression. However, chronic and progressive hepatitis C carries significant morbidity and mortality and is a major cause of cirrhosis, end-stage liver disease, and liver cancer. Development of an effective hepatitis C virus vaccine is not imminent, but recent advances in technology and basic knowledge of molecular virology and immunology have engendered novel approaches to the fundamental problems encountered in vaccine development. Current therapy for hepatitis C, although effective in some patients, is problematic and still evolving. Advances in modern biology and immunology promise new therapies for this important disease.

Decreased cytomegalovirus expression following proinflammatory cytokine treatment of primary human astrocytes

Understanding the influence of immune effector mechanisms on CMV infection of the CNS may facilitate the development of immunotherapies for viral encephalitis. Using cultures of highly purified, fully permissive primary human astrocytes, proinflammatory cytokines, but not antiinflammatory cytokines or beta-chemokines, were found to inhibit CMV expression, DNA synthesis, and replication. Treatment with certain proinflammatory cytokines 24 h before CMV infection markedly suppressed viral expression in astrocytes. TNF-alpha, IL-1beta, and IFN-gamma all inhibited CMV expression (70 +/- 4.2%, 65 +/- 3.4%, and 82 +/- 3.6% inhibition of viral expression, respectively, n = 5). In contrast, no viral suppression was observed following IL-6 treatment. Suppressive activity was dependent on the addition of cytokines before CMV infection. Cytokine pretreatment did not affect CMV entry into primary astrocytes, and the observed cytokine-induced suppressive activity was not affected by the NO synthase inhibitor NG-monomethyl- -arginine (NGMA). Instead, the suppressive effect appeared to be mediated through a mechanism involving inhibition of CMV major immediate early promoter activity. These results support the hypothesis that proinflammatory cytokines possess anti-CMV activity in brain cells and may lead to new interventions for CMV encephalitis based upon immunotherapy.

Replication of murine cytomegalovirus in differentiated macrophages as a determinant of viral pathogenesis

Blood monocytes or tissue macrophages play a pivotal role in the pathogenesis of murine cytomegalovirus (MCMV) infection, providing functions beneficial to both the virus and the host. In vitro and in vivo studies have indicated that differentiated macrophages support MCMV replication, are target cells for MCMV infection within tissues, and harbor latent MCMV DNA. However, this cell type presumably initiates early, antiviral immune responses as well. In addressing this paradoxical role of macrophages, we provide evidence that the proficiency of MCMV replication in macrophages positively correlates with virulence in vivo. An MCMV mutant from which the open reading frames M139, M140, and M141 had been deleted (RV10) was defective in its ability to replicate in macrophages in vitro and was highly attenuated for growth in vivo. However, depletion of splenic macrophages significantly enhanced, rather than deterred, replication of both wild-type (WT) virus and RV10 in the spleen. The ability of RV10 to replicate in intact or macrophage-depleted spleens was independent of cytokine production, as this mutant virus was a poor inducer of cytokines compared to WT virus in both intact organs and macrophage-depleted organs. Macrophages were, however, a major contributor to the production of tumor necrosis factor alpha and gamma interferon in response to WT virus infection. Thus, the data indicate that tissue macrophages serve a net protective role and may function as "filters" in protecting other highly permissive cell types from MCMV infection. The magnitude of virus replication in tissue macrophages may dictate the amount of virus accessible to the other cells. Concomitantly, infection of this cell type initiates the production of antiviral immune responses to guarantee efficient clearance of acute MCMV infection.

Immunity to rotavirus infection in mice

Recent findings from our laboratory regarding the immune response of mice to rotavirus (a mucosal pathogen) show that although in most situations an acquired (T or B cell or both) response is necessary for elimination of primary rotavirus infection, unidentified innate mechanisms can also play a role in some mouse strains. Similar to what is seen with many other viruses, CD8+ T cells appear to provide the first but not the exclusive mechanism that mediates clearance of a primary rotavirus infection. Antibodies are the critical mediators of prevention against rotavirus reinfection. Nonneutralizing IgA monoclonal antibodies directed against VP6 (an internal structural rotavirus protein) can mediate immunity against rotaviruses in vivo. Rotavirus-specific CD8+ T cells can mediate their antiviral effect in the absence of perforin, fas, or interferon-gamma and are preferentially represented in the subset that expresses high levels of the enteric mucosal homing receptor alpha4beta7.

Endogenous Glucocorticoids Protect Against Cytokine-Mediated Lethality During Viral Infection

Certain cytokines activate the hypothalamic-pituitary-adrenal axis for glucocorticoid release, and these hormones can protect against cytokine-mediated pathologies. However, endogenous activation of such a pathway has not been established during infections. A prominent glucocorticoid response peaks 36 h following murine CMV (MCMV) infection, coincident with circulating levels of the cytokines IL-12, IFN-γ, TNF, and IL-6, and dependent on IL-6 for maximal release. These studies examined functions of the hormone induction. Mice rendered glucocorticoid deficient by adrenalectomy were more susceptible than intact mice to MCMV-induced lethality, and the increased sensitivity was reversed by hormone replacement. Lack of endogenous glucocorticoids resulted in increases in IL-12, IFN-γ, TNF, and IL-6 production, as well as in mRNA expression for a wider range of cytokines, also including IL-1α and IL-1β. Viral burdens did not increase, and actually decreased, in the livers of glucocorticoid-deficient mice. TNF, but not IFN-γ, was required for increased lethality in the absence of endogenous hormone. These results conclusively demonstrate the importance of induced endogenous glucocorticoids in protection against life-threatening effects resulting from infection-elicited cytokine responses. Taken together with the dependence on induced IL-6, they document existence of an immune system-hypothalamic-pituitary-adrenal axis pathway for regulating endogenous responses to viral infections.