Tumour necrosis factors alpha and beta inhibit virus replication and synergize with interferons

Highly pathogenic porcine reproductive and respiratory syndrome virus impairs LPS- and poly(I:C)-stimulated tumor necrosis factor-alpha release by inhibiting ERK signaling pathway

Atypical porcine reproductive and respiratory syndrome (PRRS) characterized by high morbidity and mortality emerged in China in 2006. The causative agent was confirmed to be a highly pathogenic PRRS virus (HP-PRRSV). However, the pathogenesis of HP-PRRSV is still uncertain. Here, the ability of the highly pathogenic strains (HV and JX) to induce tumor necrosis factor alpha (TNF-α) was studied. Our results showed that HV and JX were weaker inducers of TNF-α than the conventional strain CH-1a. Moreover, HV infection was demonstrated to suppress extracellular signal-regulated kinase (ERK) phosphorylation at the early time points. Pharmacologic inhibition or activation of ERK revealed that TNF-α production in HV-infected macrophages was associated with the activation status of ERK. Furthermore, HV- and JX-infection could potently impair lipopolysaccharide (LPS)- and poly(I:C)-stimulated TNF-α release in a dose dependent manner whereas synergistic effects were observed at mRNA level. The observation suggested the involvement of posttranslational impact of HP-PRRSV on TNF-α production, which might be attributed to the reduced ERK1/2 phosphorylation in response to toll-like receptor (TLR)-ligation. Taken together, our results indicated that HP-PRRSV infection could impair TNF-α production by inhibiting ERK signaling pathway, which might partially contribute to the pathogenesis of HP-PRRSV.

Hepatitis B virus (HBV) reactivation in patients receiving tumor necrosis factor (TNF)-targeted therapy: analysis of 257 cases

The emergence of tumor necrosis factor-α (TNF-α)-targeted therapies as a key therapeutic option for patients with rheumatic, digestive, and dermatologic autoimmune diseases has been associated with increasing reports of liver damage in patients with hepatitis B virus (HBV) infection. We studied the current evidence on the use of anti-TNF agents in patients with HBV through a systematic analysis of cases reported in the MEDLINE and EMBASE databases using the MeSH term "hepatitis B virus" combined with the terms "infliximab," "etanercept," "adalimumab," "certolizumab," "golimumab," and "anti-TNF agents," and summarize the results here. We analyzed 257 patients with positive HBV markers who received anti-TNF therapy (255 identified in the search strategy and 2 new cases), 89 HBsAg+ carriers, and 168 anti-HBc+ persons. HBV reactivation was reported in 35 (39%) HBsAg+ carriers. The percentage of reactivation was higher in patients previously treated with immunosuppressive agents (96% vs. 70%, p=0.033) and lower in those who received antiviral prophylaxis (23% vs. 62%, p=0.003). Acute liver failure was reported in 5 patients, 4 of whom died. Infliximab was associated with a higher rate of induced liver disease (raised transaminase levels, clinical signs, viral reactivation, and acute liver failure) compared with etanercept. In anti-HBc+ persons, reactivation was reported in 9 (5%) cases, including 1 patient who died due to fulminant liver failure.In summary, our search of the current evidence identified 257 reported HBV+ patients treated with anti-TNF agents, with a significant percentage of liver damage in HBsAg+ carriers, including raised transaminase levels (42%), signs and symptoms of liver disease (16%), reappearance of serum HBV-DNA (39%), and death related to liver failure (5%). The rate of reactivation in anti-HBc+ persons was 7-fold lower than in HBsAg+ carriers. The increasing number of reported cases of HBV reactivation following TNF-targeted therapies and the associated morbidity and mortality demand specific preventive strategies.

Receptor-ligand requirements for increased NK cell polyfunctional potential in slow progressors infected with HIV-1 coexpressing KIR3DL1*h/*y and HLA-B*57

Carriage of the natural killer (NK) receptor genotype KIR3DL1*h/*y with its HLA-B*57 ligand (*h/*y+B*57) is associated with slow time to AIDS and low viral load (VL). To provide a functional basis for these epidemiological observations, we assessed whether HIV-1-infected slow progressors (SP) carrying the *h/*y+B*57 compound genotype would have increased NK cell polyfunctional potential in comparison to SP with other killer immunoglobulin-like receptor (KIR)/HLA compound genotypes and whether this enhanced polyfunctionality was dependent upon the coexpression of both KIR3DL1*h/*y and HLA-B*57. The functional potential of NK cells was investigated by stimulating peripheral blood mononuclear cells with HLA-devoid targets or single HLA transfectants. Multiparametric flow cytometry was used to detect NK cells with seven functional profiles representing all permutations of CD107a expression and gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) secretion. NK cells from individuals carrying KIR3DL1 receptor-HLA-Bw4 ligand pairs had greater trifunctional responses than those from KIR3DL1 homozygotes (hmz), who were Bw6 homozygotes. NK cells from subjects carrying the *h/*y+B*57 genotypes exhibited the highest trifunctional potential, and this was dependent on cocarriage of the NK receptor and its ligand. Trifunctional cells secreted more of each function tested on a per-cell basis than each corresponding monofunctional NK subset. Although VL influenced NK functionality, individuals with defined KIR/HLA genotypes exhibited differences in NK cell polyfunctionality that could not be accounted for by VL alone. The protective effect of HLA-B*57 on slow progression to AIDS and low VL may be mediated through its interaction with KIR3DL1 alleles to educate NK cells for potent activity upon stimulation.

Liver diseases associated with anti-tumor necrosis factor-alpha (TNF-α) use for inflammatory bowel disease

The conventional treatment of inflammatory bowel disease (IBD) has focused on nonspecifically targeting mucosal inflammation. In the last decade, with the advent of novel biological agents that directly inhibit proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-α), rapid progress has been made in clinical management of complex and challenging patients with IBD. However, there remain many unanswered questions about the short and long-term side effects; this article focuses on hepatic complications. This review aims to provide a concise update to gastroenterologists on the well-known, as well as the potential rare consequences of anti-TNFα therapy on the liver and recommendations for clinical management. We performed a focused literature review for reports of the effect of anti-TNF therapy on preexisting liver disease as well as de novo hepatitis and drug-induced hepatotoxicity. Search terms used included anti-TNF therapy, biologics, liver disease, inflammatory bowel disease, hepatitis, hepatotoxicity, opportunistic infections,, and hepatitis virus reactivation. There are multiple potential effects of anti-TNF therapy on the liver during treatment of patients with IBD. Often treatment may be complicated by preexisting chronic liver disease. Clinicians should be aware of potential hepatic side effects and appropriate management options.

A synthetic adjuvant to enhance and expand immune responses to influenza vaccines

Safe, effective adjuvants that enhance vaccine potency, including induction of neutralizing Abs against a broad range of variant strains, is an important strategy for the development of seasonal influenza vaccines which can provide optimal protection, even during seasons when available vaccines are not well matched to circulating viruses. We investigated the safety and ability of Glucopyranosyl Lipid Adjuvant-Stable Emulsion (GLA-SE), a synthetic Toll-like receptor (TLR)4 agonist formulation, to adjuvant Fluzone® in mice and non-human primates. The GLA-SE adjuvanted Fluzone vaccine caused no adverse reactions, increased the induction of T helper type 1 (T(H)1)-biased cytokines such as IFNγ, TNF and IL-2, and broadened serological responses against drifted A/H1N1 and A/H3N2 influenza variants. These results suggest that synthetic TLR4 adjuvants can enhance the magnitude and quality of protective immunity induced by influenza vaccines.

HIV-1 infection inhibits cytokine production in human thymic macrophages

OBJECTIVE

The thymus serves as a critical site of T-lymphocyte ontogeny and selection. Thymic infection by HIV-1 is known to disrupt thymocyte maturation by both direct and indirect means; however, the mechanism behind these effects remains poorly defined. Macrophages represent one of the most important peripheral targets of HIV-1 infection, are resident in the thymic stroma, and play a central role in thymocyte maturation.

MATERIALS AND METHODS

Studies presented here define three primary features and outcomes of thymic macrophages (TM) and HIV-1 infection: (1) The distinctive TM phenotype (surface markers and cytokine production measured by immunofluorescence, fluorescence-activated cell sorting, and reverse transcriptase polymerase chain reaction) relative to macrophages from other sources (blood [monocyte-derived macrophages] and bone marrow); (2) infection of TM by different HIV-1 subtypes (X4, R5, and X4/R5) measured by enzyme-linked immunosorbent assay and polymerase chain reaction; and (3) consequences of HIV-1 infection on cytokine production by TM measured by reverse transcriptase polymerase chain reaction.

RESULTS

The results demonstrate that TM display a distinctive phenotype of HIV-1 receptors (CD4(lo), CXCR4(lo), CCR5(med), CCR3(hi)), chemokine production (macrophage inflammatory protein-1α(+); regulated on activation, normal T expressed and secreted(+); macrophage inflammatory protein-1b(-); stromal cell-derived factor -1(-)); and cytokine production (tumor necrosis factor-α(+), interleukin-8(+), macrophage colony-stimulating factor(+), interleukin-6(-)) relative to either monocyte-derived macrophages or bone marrow. TM were infected in vitro with R5 and X4/R5-tropic HIV-1 subtypes, and developed syncytia formation during long-term X4/R5 culture. In contrast, TM supported only transient replication of X4-tropic HIV-1. Lastly, infection of TM with HIV-1 abolished the production of all cytokines tested in long-term in vitro cultures.

CONCLUSIONS

Taken together, these results indicate that TM are a potential direct target of in situ HIV-1 infection, and that this infection may result in the disruption of macrophage functions that govern normal thymocyte maturation.

Porcine reproductive and respiratory syndrome virus non-structural protein 1 suppresses tumor necrosis factor-alpha promoter activation by inhibiting NF-κB and Sp1

The objective of this study was to identify porcine reproductive and respiratory syndrome virus (PRRSV)-encoded proteins that are responsible for the inhibition of TNF-α expression and the mechanism(s) involved in this phenomenon. Using a TNF-α promoter reporter system, the non-structural protein 1 (Nsp1) was found to strongly suppress the TNF-α promoter activity. Such inhibition takes place especially at the promoter's proximal region. Both Nsp1α and Nsp1β, the two proteolytic fragments of Nsp1, were shown to be involved in TNF-α promoter suppression. Furthermore, using reporter plasmids specific for transcription factors (TFs) that bind to TNF-α promoter, Nsp1α and Nsp1β were demonstrated to inhibit the activity of the TFs that bind CRE-κB(3) and Sp1 elements respectively. Subsequent analyses showed that Nsp1α moderately inhibits NF-κB activation and that Nsp1β completely abrogates the Sp1 transactivation. These findings reveal one of the important mechanisms underlying the innate immune evasion by PRRSV during infection.

Prevalence of reactivation of hepatitis B virus replication in rheumatoid arthritis patients

Reactivation of hepatitis B involves the reappearance of active necroinflammatory liver disease after an inactive hepatitis B surface antigen (HBsAg) carrier state or resolved hepatitis B, occurring during or after immunosuppression therapy or chemotherapy. We prospectively investigated the reactivation rate for hepatitis B virus (HBV) DNA replication in cases of rheumatoid arthritis (RA) with resolved hepatitis B. HBV markers were evaluated in 428 RA patients. Patients with positive findings of HBsAg or HBV DNA at enrolment were excluded. The study population comprised 422 RA patients, with resolved hepatitis B diagnosed in 135 patients based on HBsAg-negative and antihepatitis B core antibody/antihepatitis B surface antibody-positive results. HBV DNA was measured every 3 months in this group, and if HBV DNA became positive after enrolment, measurement was repeated every month. HBV DNA became positive (≥3.64 log copies/mL) in 7 of 135 patients for 12 months. Use of biologic agents was significantly more frequent in patients who developed reactivation of HBV DNA replication (85.7%) than in patients who did not (36.0%, p = 0.008). Hazard ratios for use of biologic agents and etanercept were 10.9 (p = 0.008) and 6.9 (p = 0.001), respectively. RA patients with resolved hepatitis B need careful monitoring when receiving biologic agents, regardless of HBV DNA levels.

Cytotoxic T lymphocytes established by seasonal human influenza cross-react against 2009 pandemic H1N1 influenza virus

While few children and young adults have cross-protective antibodies to the pandemic H1N1 2009 (pdmH1N1) virus, the illness remains mild. The biological reasons for these epidemiological observations are unclear. In this study, we demonstrate that the bulk memory cytotoxic T lymphocytes (CTLs) established by seasonal influenza viruses from healthy individuals who have not been exposed to pdmH1N1 can directly lyse pdmH1N1-infected target cells and produce gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha). Using influenza A virus matrix protein 1 (M1(58-66)) epitope-specific CTLs isolated from healthy HLA-A2(+) individuals, we further found that M1(58-66) epitope-specific CTLs efficiently killed both M1(58-66) peptide-pulsed and pdmH1N1-infected target cells ex vivo. These M1(58-66)-specific CTLs showed an effector memory phenotype and expressed CXCR3 and CCR5 chemokine receptors. Of 94 influenza A virus CD8 T-cell epitopes obtained from the Immune Epitope Database (IEDB), 17 epitopes are conserved in pdmH1N1, and more than half of these conserved epitopes are derived from M1 protein. In addition, 65% (11/17) of these epitopes were 100% conserved in seasonal influenza vaccine H1N1 strains during the last 20 years. Importantly, seasonal influenza vaccination could expand the functional M1(58-66) epitope-specific CTLs in 20% (4/20) of HLA-A2(+) individuals. Our results indicated that memory CTLs established by seasonal influenza A viruses or vaccines had cross-reactivity against pdmH1N1. These might explain, at least in part, the unexpected mild pdmH1N1 illness in the community and also might provide some valuable insights for the future design of broadly protective vaccines to prevent influenza, especially pandemic influenza.

Indolent infectious tenosynovitis afflicting rheumatoid patients treated with tumor necrosis factor inhibitors: case report

Tumor necrosis factor (TNF) is a cytokine associated with the pathogenesis of rheumatoid arthritis. Tumor necrosis factor inhibitors have become important biological treatments that favorably alter the natural history of rheumatoid disease. Side effects include an increased risk of malignancy and infection, particularly tuberculosis. We present 2 patients with rheumatoid arthritis on TNF inhibitors in whom flares of wrist tenosynovitis, initially diagnosed as rheumatoid disease exacerbations, were caused by infections with uncommon opportunistic pathogens. Diagnostic and treatment recommendations for this subset of rheumatoid patients are discussed.

Characterization of synergistic induction of CX3CL1/fractalkine by TNF-alpha and IFN-gamma in vascular endothelial cells: an essential role for TNF-alpha in post-transcriptional regulation of CX3CL1

CX3CL1/fractalkine, a chemokine specific to monocytes and NK cells, is induced synergistically by TNF-alpha and IFN-gamma in vascular endothelial cells. However, the mechanism for this synergism remains unclear. This study explored the hypothesis that the CX3CL1 expression is regulated at a posttranscriptional level, which may responsible for the synergism between TNF-alpha and IFN-gamma. Brief exposure of HUVECs to TNF-alpha led to a robust increase in IFN-gamma-induced CX3CL1 production. We found that TNF-alpha stabilized CX3CL1 mRNA in HUVECs stimulated with IFN-gamma. Cloning of 3' untranslated region (UTR) of CX3CL1 mRNA revealed the presence of a single copy of nonametric AU-rich element in its 3'UTR, and a luciferase reporter assay showed that a single AU-rich element is a crucial cis-element in the posttranscriptional regulation of CX3CL1. TNF-alpha treatment resulted in the phosphorylation of p38 MAPK and its downstream target, MAPK-activated protein kinase-2, but IFN-gamma did not affect the levels of MAPK and MAPK-activated protein kinase-2 phosphorylation induced by TNF-alpha. Treatment of the cells with an inhibitor of p38 MAPK accelerated the decay of CX3CL1 mRNA induced by TNF-alpha or the combination of TNF-alpha and IFN-gamma. Immunoprecipitation assay revealed that mRNA stabilizer HuR directly binds to 3'UTR of CX3CL1 mRNA. CX3CL1 expression is under control of posttranscriptional regulation, which is involved in the synergistic induction of CX3CL1 in response to the combined stimulation with TNF-alpha and IFN-gamma.

A novel H1N1 virus causes the first pandemic of the 21st century

A novel H1N1 virus of swine origin (H1N1v ) is currently spreading in humans, giving rise to the first pandemic in 40 years. The disease is of moderate severity but has notable differences from seasonal influenza. In contrast to seasonal influenza, those over 60 years are relatively spared, a likely consequence of the presence of H1N1v cross-neutralizing antibody in this age group. Most patients appear to have mild influenza-like illness and many of the complications leading to hospitalization and mortality occur in those with underlying disease conditions or pregnancy. Studies in animal models suggest that the novel H1N1v pandemic virus causes a more severe illness and appears to have a greater predilection for the alveolar epithelium than seasonal influenza viruses. As there are as yet little data on the pathogenesis and immunology of H1N1v infection in humans, we have reviewed relevant data from past pandemics, from seasonal influenza and avian influenza H5N1 to highlight key issues pertaining to pathogenesis and immunology.

Transcriptional control of the TNF gene

The cytokine TNF is a critical mediator of immune and inflammatory responses. The TNF gene is an immediate early gene, rapidly transcribed in a variety of cell types following exposure to a broad range of pathogens and signals of inflammation and stress. Regulation of TNF gene expression at the transcriptional level is cell type- and stimulus-specific, involving the recruitment of distinct sets of transcription factors to a compact and modular promoter region. In this review, we describe our current understanding of the mechanisms through which TNF transcription is specifically activated by a variety of extracellular stimuli in multiple cell types, including T cells, B cells, macrophages, mast cells, dendritic cells, and fibroblasts. We discuss the role of nuclear factor of activated T cells and other transcription factors and coactivators in enhanceosome formation, as well as the contradictory evidence for a role for nuclear factor kappaB as a classical activator of the TNF gene. We describe the impact of evolutionarily conserved cis-regulatory DNA motifs in the TNF locus upon TNF gene transcription, in contrast to the neutral effect of single nucleotide polymorphisms. We also assess the regulatory role of chromatin organization, epigenetic modifications, and long-range chromosomal interactions at the TNF locus.

HIV protective KIR3DL1 and HLA-B genotypes influence NK cell function following stimulation with HLA-devoid cells

Epidemiological studies in humans have implicated carriage of combinations of genes encoding certain KIR3DL1 (killer Ig-like receptor 3DL1) alleles and their HLA-Bw4 ligands in slower progression to AIDS, lower viral load and protection from infection. Given that the KIR3DL1*h/*y/HLA-B*57 genetic combination is strongly associated with favorable HIV outcomes, we measured responses from NK cells isolated from these individuals by multiparametric flow cytometry for cytokine secretion and degranulation in response to stimulation with HLA-devoid cells to assess whether the KIR/HLA compound genotypes linked to better HIV outcome favor increased NK cell functional potential. Our results indicate that NK cells from these individuals had increased functional potential, particularly in the KIR3DL1(+) NK cell subset. These results support a link between KIR/HLA genotypes and NK cell function and could provide an explanation for the observation that some KIR/HLA combinations are associated protective phenotypes in the context of host-HIV interactions.

Review article: chronic viral infection in the anti-tumour necrosis factor therapy era in inflammatory bowel disease

BACKGROUND

Anti-tumour necrosis factor (TNF) therapy is now well established in the treatment of inflammatory bowel disease and the risk of opportunistic infection is recognized. However, specific considerations regarding screening, detection, prevention and treatment of chronic viral infections in the context of anti-TNF therapy in inflammatory bowel disease are not widely adopted in practice.

AIM

To provide a detailed and comprehensive review of the relevance of chronic viral infections in the context of anti-TNF therapy in inflammatory bowel disease.

METHODS

Literature search was conducted using Medline, Pubmed and Embase using the terms viral infection, hepatitis, herpes, CMV, EBV, HPV, anti-TNF, infliximab, adalimumab, certolizumab pegol and etanercept. Hepatitis B and C and HIV had the largest literature associated and these have been summarized in Tables.

RESULTS

Particular risks are associated with the use of anti-TNF drugs in patients with hepatitis B infection, in whom reactivation is common unless anti-viral prophylaxis is used. Reactivation of herpes zoster is the most common viral problem associated with anti-TNF treatment, and may be particularly severe. Primary varicella infection may present with atypical features in patients on anti-TNF.

CONCLUSION

Appreciation of risks of chronic viral disease associated with anti-TNF therapy may permit early recognition, prophylaxis and treatment.

Reactivation of hepatitis B viral infection in inactive HBsAg carriers following anti-tumor necrosis factor-alpha therapy

OBJECTIVE

To investigate whether anti-tumor necrosis factor-alpha (TNF-alpha) therapy can influence the reactivation of hepatitis B virus (HBV) infection in inactive HBsAg carriers.

METHODS

The medical records of 103 patients [59 with ankylosing spondylitis (AS), 41 with rheumatoid arthritis (RA), 2 with juvenile RA, and 1 with psoriatic arthritis] who had been treated with anti-TNF-alpha therapy were reviewed retrospectively. Data on seropositivity of HBV, HBV load, and serum aminotransferases prior to and after initiation of anti-TNF-alpha therapy were obtained.

RESULTS

Eight patients were inactive HBsAg carriers, and all of them had normal liver function and undetectable HBV load prior to anti-TNF-alpha therapy. Reactivation of hepatitis B occurred in 1 patient during the course of anti-TNF-alpha therapy. After the third infusion of infliximab 5 mg/kg at Week 6, a blood test showed that the patient had normal liver function. When the patient returned for the fourth infusion of infliximab at Week 14, a blood test showed markedly elevated aspartate aminotransferase (AST)/alanine aminotransferase (ALT) levels (457 and 1054 IU/l, respectively) and increased viral DNA by HBV polymerase chain reaction (PCR). The fourth infliximab infusion was canceled, and entecavir 0.5 mg/day was prescribed. Then AST/ALT levels began to decrease and returned to normal range after 3 months. Followup HBV PCR showed negative results.

CONCLUSION

We found 1 HBV reactivation case among 8 inactive HBsAg carriers following anti-TNF-alpha therapy. This finding supports the prophylactic use of antiviral agents in HBV carriers, even if they have normal liver function or an undetectable viral load.

Cytokine determinants of viral tropism

The specificity of a given virus for a cell type, tissue or species - collectively known as viral tropism - is an important factor in determining the outcome of viral infection in any particular host. Owing to the increased prevalence of zoonotic infections and the threat of emerging and re-emerging pathogens, gaining a better understanding of the factors that determine viral tropism has become particularly important. In this Review, we summarize our current understanding of the central role of antiviral and pro-inflammatory cytokines, particularly the interferons and tumour necrosis factor, in dictating viral tropism and how these cytokine pathways can be exploited therapeutically for cancer treatment and to better counter future threats from emerging zoonotic pathogens.

HERPES SIMPLEX VIRUS INFECTION AND APOPTOSIS

Consequences of human herpes simplex virus (HSV) infection include the induction of apoptosis and the concomitant synthesis of proteins which act to block this process from killing the infected cell. Recent data has clarified our current understanding of the mechanisms of induction and prevention of apoptosis by HSV. These findings emphasize the fact that modulation of apoptosis by HSV during infection is a multicomponent phenomenon. We review recent evidence showing how this important human pathogen modulates the fundamental cell death process.

Inhibition of intrahepatic gamma interferon production by hepatitis C virus nonstructural protein 5A in transgenic mice

Hepatitis C virus (HCV) utilizes strategies to suppress or evade the host immune response for establishment of persistent infection. We have shown previously that HCV nonstructural protein 5A (NS5A) impairs tumor necrosis factor alpha (TNF-alpha)-mediated apoptosis. In this study, we have examined the immunomodulatory role of HCV NS5A protein in transgenic mouse (NS5A-Tg) liver when mice were challenged with an unrelated hepatotropic adenovirus as a nonspecific stimulus. Hepatotropic adenovirus was introduced intravenously into NS5A-Tg mice and control mice, and virus clearance from liver was compared over a time course of 3 weeks. The differential mRNA expression levels of 84 cytokine-related genes, signal pathway molecules, transcription factors, and cell surface molecules were determined using real-time reverse transcription-PCR array. NS5A-Tg mice failed to clear adenovirus from liver up to 3 weeks postinfection while control mice cleared virus within 1 to 2 weeks. Subsequent study revealed that gamma interferon (IFN-gamma) expression is inhibited at both the mRNA and protein levels in NS5A-Tg mice, and an inverse expression of transcription factors Gata-3 and Tbx21 is observed. However, TNF-alpha mRNA and protein expression were elevated in both NS5A-Tg and control mice. Together, our results suggested that HCV NS5A acts as an immunomodulator by inhibiting IFN-gamma production and may play an important role toward establishment of chronic HCV infection.

The implications of anti-tumour necrosis factor therapy for viral infection in patients with inflammatory bowel disease

INTRODUCTION

Anti-tumour necrosis factor (TNF) therapy is increasingly used in the management of inflammatory bowel disease; however, concerns have been raised regarding risk of infection with such drugs. Little is known about their effect upon viral infection.

SOURCES OF DATA

A search of PubMed using the terms 'infliximab', 'etanercept', 'adalimumab' or 'anti-TNF therapy' combined with the names of specific viruses was performed. A search of cited papers was used to identify further relevant reports.

AREAS OF AGREEMENT

Numerous reports of the use of anti-TNF in patients with chronic or latent viral infection appear in the literature. Specific problems related to hepatitis B virus and varicella zoster virus may exist. The safety profile of anti-TNF in chronic viral infection is generally reassuring.

AREAS OF CONTROVERSY

Numerous consensus statements relating to pre-treatment serology or vaccination have recently appeared; however, significant variation exists in their recommendations.

GROWING POINTS

Increasing awareness of the implications of anti-TNF therapy on viral infection may allow safer use of such drugs.

AREAS TIMELY FOR DEVELOPING RESEARCH

The clinical and cost-effectiveness of screening for viral infections prior to anti-TNF requires further study.

The risk of infections with biologic therapies for rheumatoid arthritis

OBJECTIVES

To assess the risk of serious and nonserious bacterial and viral infections associated with the use of biologic therapy (abatacept, adalimumab, anakinra, etanercept, infliximab, and rituximab) in patients with rheumatoid arthritis (RA).

METHODS

Information was derived from PubMed, EMBASE, and the Cochrane clinical trials register and database of systematic reviews and relevant congress abstracts up to and including February 2008.

RESULTS

Compared with the general population, patients with RA have a heightened risk of infection, including tuberculosis. Long-term clinical trials and postmarketing studies indicate that anakinra and the tumor necrosis factor (TNF) inhibitors are associated with an increased risk of infections versus conventional disease-modifying antirheumatic drugs (DMARDs), especially early in the course of treatment. The most common sites of infection are the respiratory tract (including pneumonia), skin and soft tissue, and the urinary tract. The risk of tuberculosis also appears higher with TNF inhibitors (in particular, infliximab) versus DMARDs, although this can be reduced by screening and prophylaxis. TNF inhibitors do not appear to significantly increase the risk of reactivating chronic viral infections. Influenza and pneumococcal vaccinations are generally effective in the face of TNF inhibitors or abatacept. Available data suggest that the risk of infections and serious infections with abatacept and rituximab may be similar to that of the TNF inhibitors. To date, there have been no reports from clinical trials of increased tuberculosis or opportunistic infections with abatacept or rituximab.

CONCLUSIONS

All marketed TNF inhibitors for compared to control RA appear to increase the risk of serious and nonserious infections compared with DMARDs. Although suggestive, data for abatacept and rituximab are less definitive and longer periods of patient exposure to these agents are needed before an assessment of their risks can be made.

Atypical infectious mononucleosis in a patient receiving tumor necrosis factor alpha inhibitory treatment

The objective is to report a case of atypical acute infectious mononucleosis in a juvenile ankylosing spondylitis patient who was treated with infliximab. A 20-year-old man was hospitalized for the evaluation of lymphadenopathy and systemic symptoms. His symptoms developed at the eighth week of the infliximab treatment and he required hospitalization. Lymph node biopsy was performed and he was diagnosed as atypical infectious mononucleosis (absence of fever, pharyngitis, lymphocytosis and negative atypical lymphocytosis on blood smear). Infections have become major concerns in patients treated with TNF-blocking agents. In theoretical base, it is not surprising as TNF-alpha has a crucial role in the body's defense against both bacterial and viral invasion. Blocking the action of TNF may also change the course of the disease and could lead to a delay in the diagnosis. TNF-alpha-blocking treatment may mask the typical symptoms of infectious mononucleosis and atypical cases should be included in the differential diagnosis of lymphadenopathy in patients receiving anti-TNF-alpha agents.

The addition of tumor necrosis factor plus beta interferon induces a novel synergistic antiviral state against poxviruses in primary human fibroblasts

Tumor necrosis factor (TNF) and members of the interferon (IFN) family have been shown to independently inhibit the replication of a variety of viruses. In addition, previous reports have shown that treatment with various combinations of these antiviral cytokines induces a synergistic antiviral state that can be significantly more potent than addition of any of these cytokines alone. The mechanism of this cytokine synergy and its effects on global gene expression, however, are not well characterized. Here, we use DNA microarray analysis to demonstrate that treatment of uninfected primary human fibroblasts with TNF plus IFN-beta induces a distinct synergistic state characterized by significant perturbations of several hundred genes which are coinduced by the individual cytokines alone, as well as the induction of more than 850 novel host cell genes. This synergy is mediated directly by the two ligands, not by intermediate secreted factors, and is necessary and sufficient to completely block the productive replication and spread of myxoma virus in human fibroblasts. In contrast, the replication of two other poxviruses, vaccinia virus and tanapox virus, are only partially inhibited in these cells by the synergistic antiviral state, whereas the spread of both of these viruses to neighboring cells was efficiently blocked. Taken together, our data indicate that the combination of TNF and IFN-beta induces a novel synergistic antiviral state that is highly distinct from that induced by either cytokine alone.

Restricted Semliki Forest virus replication in perforin and Fas-ligand double-deficient mice

Previously, we have shown that mice defective in granule exocytosis and/or Fas.L/Fas-mediated cytolytic pathways are significantly more resistant to alphavirus, Semliki Forest virus (SFV), infection compared with wild-type mice. Here, we evaluated SFV replication in different tissues of mice defective in both cytolytic pathways (perf−/−xgld) relative to that in wild-type counterparts and found that viral replication in perf−/−xgld mice is remarkably restricted. Although the mechanism responsible for this observation is yet to be established, the lower virus titres found in these mice indicate that the role of cytolytic effector molecules in antiviral immunity needs to be re-evaluated.

RIG-I mediates the co-induction of tumor necrosis factor and type I interferon elicited by myxoma virus in primary human macrophages

The sensing of pathogen infection and subsequent triggering of innate immunity are key to controlling zoonotic infections. Myxoma virus (MV) is a cytoplasmic DNA poxvirus that in nature infects only rabbits. Our previous studies have shown that MV infection of primary mouse cells is restricted by virus-induced type I interferon (IFN). However, little is known about the innate sensor(s) involved in activating signaling pathways leading to cellular defense responses in primary human immune cells. Here, we show that the complete restriction of MV infection in the primary human fibroblasts requires both tumor necrosis factor (TNF) and type I IFN. We also demonstrate that MV infection of primary human macrophages (pHMs) activates the cytoplasmic RNA sensor called retinoic acid inducible gene I (RIG-I), which coordinately induces the production of both TNF and type I IFN. Of note, RIG-I sensing of MV infection in pHMs initiates a sustained TNF induction through the sequential involvement of the downstream IFN-regulatory factors 3 and 7 (IRF3 and IRF7). Thus, RIG-I-mediated co-induction of TNF and type I IFN by virus-infected pHMs represents a novel innate defense mechanism to restrict viral infection in human cells. These results also reveal a new regulatory mechanism for TNF induction following viral infection.

[Infliximab in ankylosing spondylitis associated with chronic hepatitis B infection. Role of Lamivudine therapy]

Anti-tumor necrosis factor-a (TNF) therapy has been associated with reactivation of hepatitis B virus infection. Case reports have suggested the concomitant need of lamivudine treatment in patients with HBV infection treated with antiTNFa agents. We describe a case of ankylosing spondylitis with positive HBV surface antigen (HBsAg) treated with infliximab and lamivudine. Clinical response was excellent but when lamivudine therapy was stopped, reactivation of replication viral occurred. After the reintroduction of lamivudine, viral replication was controlled and liver function tests were normalized. Preventive long-term lamivudine therapy is mandatory when anti-TNFa therapy is maintained in patients with chronic HBV infection.

Tumor necrosis factor and interferon: cytokines in harmony

Individually, tumor necrosis factor (TNF) and the various interferons frequently display strong antiviral activities. Certain combinations of these cytokines, however, induce a synergistic antiviral state which is distinct from that induced by either one alone. This novel synergistic antiviral state likely occurs through several possible mechanisms, involves multiple signaling pathways, and inhibits a wider range of viruses than the individual cytokines alone. While underappreciated when first discovered, this synergistic phenomenon is proving to be of a much broader scope than initially thought. More work is needed to refine our understanding of this observation and its physiological implications for anti-pathogen responses.

Blockade of virus infection by human CD4+ T cells via a cytokine relay network

CD4(+) T cells directly participate in bacterial clearance through secretion of proinflammatory cytokines. Although viral clearance relies heavily on CD8(+) T cell functions, we sought to determine whether human CD4(+) T cells could also directly influence viral clearance through cytokine secretion. We found that IFN-gamma and TNF-alpha, secreted by IL-12-polarized Th1 cells, displayed potent antiviral effects against a variety of viruses. IFN-gamma and TNF-alpha acted directly to inhibit hepatitis C virus replication in an in vitro replicon system, and neutralization of both cytokines was required to block the antiviral activity that was secreted by Th1 cells. IFN-gamma and TNF-alpha also exerted antiviral effects against vesicular stomatitis virus infection, but in this case, functional type I IFN receptor activity was required. Thus, in cases of vesicular stomatitis virus infection, the combination of IFN-gamma and TNF-alpha secreted by human Th1 cells acted indirectly through the IFN-alpha/beta receptor. These results highlight the importance of CD4(+) T cells in directly regulating antiviral responses through proinflammatory cytokines acting in both a direct and indirect manner.

Cytomegalovirus colitis in a patient with Behcet’s disease receiving tumor necrosis factor alpha inhibitory treatment

Anti-tumor necrosis factor alpha (TNF-α) inhibitors are effective in the treatment of various inflammatory rheumatic conditions. Increased risks of serious infections are the major issues concerning the long-term safety of these agents. We present a case of a young male Behcet’s patient whose disease was complicated by cytomegalovirus (CMV) colitis. Colitis started 10 d after the third Infliximab dose and responded to the cessation of TNF blocking treatment and administration of ganciclovir. Tumor necrosis factor alpha and interferon gamma act at several levels in combating viral infections. CMV infections should be kept in mind and included in the differential diagnosis of severe gastrointestinal symptoms in patients receiving anti-TNF agents.

Physiological responses to cachectin

Mammals infected with parasitic, bacterial or viral organisms or bearing tumours characteristically display a catabolic state and weight loss which can advance to cachexia (or wasting), shock and death. Although the phenomenon is commonly observed in many parasitic diseases its mechanism is not understood. We have identified and isolated a macrophage protein, cachectin, as the molecule that may be responsible for cachexia and shock. Cachectin is produced by macrophages in response to endotoxin or a number of other bacterial or protozoal products. The released cachectin acts as a hormone, binding to specific high affinity receptors and eliciting biological responses. In the adipocyte anabolic enzymes such as lipoprotein lipase are suppressed through the selective inhibition of mRNA production. An intriguing aspect of cachectin is its pivotal role in the pathogenesis of endotoxin-induced shock. Cachectin causes fever and anorexia and can induce lethal shock and tissue injury in experimental animals. During its chemical characterization cachectin was shown to be identical to tumour necrosis factor (TNF), a macrophage protein that kills tumour cells. This finding emphasizes the extensive range of effects associated with this protein. Cachectin has many properties in common with interleukin 1 but binds to a different receptor and lacks structural homology. Presumably, low levels of cachectin help the host in its battle to remove invasive pathogens, but extensive production of cachectin can lead to shock and catabolic stress hormone responses. These findings have added a new dimension to the biological properties of cachectin, its production, and its role in cachexia and shock.

Human tumour necrosis factors: structure and receptor interactions

Activation of lymphoid and myeloid cells causes the production of factors cytotoxic to various tumour cell types in vitro and in vivo. We have investigated the biochemistry, molecular biology and mechanism of action of two such factors. The factor derived from a myeloid cell line was named TNF-alpha (previously referred to as TNF) and that derived from lymphoid cells named TNF-beta (previously called lymphotoxin). Both proteins were purified from the conditioned media of the human cell lines and sequenced. Structural information revealed that TNF-alpha is 157 amino acid residues long and contains one disulphide bond. TNF-beta is a glycoprotein of 171 amino acids that contains no cysteine residues. Protein sequence information was used to isolate and characterize cDNAs for TNF-alpha and TNF-beta by recombinant DNA methods. The expression of the cDNAs in Escherichia coli made available large quantities of these proteins for biological studies. The two proteins are 31% identical and 52% homologous to each other. The genes for both cytokines are approximately three kilobases in size and are closely linked on human chromosome six. TNF-alpha and TNF-beta both bind to various cell types via a single class of high affinity receptors. On most cells the same receptor is recognized by both cytokines. The receptors for TNF-alpha can be up-regulated by both interferons and lectins. Up-regulation of receptors by interferons is accompanied by synergistic enhancement of the biological response whereas up-regulation by lectins results in an antagonistic response. Besides antiproliferative effects, both cytokines exhibit direct antiviral effects on infection by both DNA and RNA viruses.

Antiparasitic effects of tumour necrosis factor in vivo and in vitro

Early experiments in mice suggested that tumour necrosis factor (TNF) might be cytotoxic to asexual blood-stage malaria parasites. This was based on the striking activity of tumour necrosis serum (TNS) on the parasite both in vitro and in vivo, and the inability to separate by physical means the parasite-killing and tumour-killing components. However, recombinant TNF does not have this cytotoxic effect in vitro, while its antiparasitic activity in vivo, though significant, is not as strong as that of an equivalent amount of TNS. Thus it appears that TNS contains another cytotoxic molecule and that TNF itself may act indirectly in vivo, perhaps by activating an effector cell. An example of this has been found in murine schistosomiasis, where macrophage-derived TNF is able to activate eosinophils to attack the infecting worms. One mechanism of schistosomule damage is by eosinophil cationic proteins, and these have also been found to be cytotoxic to blood-stage malaria. There may therefore be a pathway of TNF activity common to both parasites. In a similar way, the crisis-forming factor (CFF) found in the serum of certain immune Sudanese adults is clearly distinct from TNF, since CFF-containing sera do not kill TNF-susceptible tumour cells and rTNF does not kill Plasmodium falciparum in vitro. This confirms that there are other cytotoxic molecules, still to be identified, with a role in immunity to malaria and perhaps other parasites. TNF is also active against intracellular Trypanosoma cruzi and against some viruses but in both cases this appears to be an interferon-like mediatory effect and not direct cytotoxicity. It is not yet clear whether these antiparasitic activities are part of the biological role of TNF.

Granzyme B production distinguishes recently activated CD8(+) memory cells from resting memory cells

For immune diagnostic purposes it would be critical to be able to distinguish between ongoing immune processes, such as active infections, and long-term immune memory, for example imprinted by infections that have been cleared a long time ago or by vaccinations. We tested the hypothesis that the secretion of granzyme B, as detected in ex vivo ELISPOT assays, permits this distinction. We studied EBV-, flu- and CMV-specific CD8(+) cells in healthy individuals, Vaccinia virus-reactive CD8(+) cells in the course of vaccination, and HIV-specific CD8(+) cells in HIV-infected individuals. Antigen-specific ex vivo GzB production was detected only transiently after Vaccinia immunization, and in HIV-infected individuals. Our data suggest that ex vivo ELISPOT measurements of granzyme B permit the identification of actively ongoing CD8(+) cell responses-a notion that is pertinent to the immune diagnostic of infections, transplantation, allergies, autoimmune diseases, tumors and vaccine development.

The RNA binding domain of influenza A virus NS1 protein affects secretion of tumor necrosis factor alpha, interleukin-6, and interferon in primary murine tracheal epithelial cells

Primary differentiated respiratory epithelial cell cultures closely model the in vivo environment and allow for studies of innate immune responses generated specifically by epithelial cells, the primary cell type infected by human influenza A virus strains. We used primary murine tracheal epithelial cell (mTEC) cultures to investigate antiviral and cytokine responses to influenza A virus infection, focusing on the contribution of the RNA binding domain of the NS1 protein. rWSN NS1 R38A replication is attenuated in mTEC cultures; however, viral antigen is detected predominantly in ciliated cells, similar to wild-type virus. NS1 and NS1 R38A proteins display a primarily cytoplasmic localization in infected mTEC cultures. Increased production of tumor necrosis factor alpha, interleukin-6, and beta interferon is observed during rWSN NS1 R38A infection, and cytokines are secreted in a directional manner. Cytokine pretreatment of mTEC cultures and Vero cells suggest that rWSN NS1 R38A is more sensitive to the presence of antiviral/inflammatory cytokines than wild-type virus. Our results demonstrate that the RNA binding domain is a critical regulator of both cytokine production and cytokine sensitivity during influenza A virus infection of primary tracheal epithelial cells.

Molecular cloning, sequencing and phylogenetic analysis of inflammatory cytokines of swamp type buffalo contrasting with other bubaline breeds

The current research concerned in the cloning, sequencing and phylogenetic analysis of inflammatory cytokine (IL-1alpha, IL-1beta, IL-6 and TNF-alpha) genes from swamp buffalo and two bubaline breeds, CB (cross between swamp and riverine type buffalo) and the Bulgarian Murrah buffalo. Multiple sequence comparison showed a high homology between the bubaline breeds, which ranged from 99.3% to 100.0% similarity, whereas from 98.6% to 99.0% compared to cattle. The phylogenetic analysis had confirmed and justified the degree of relationship between these bubaline species and their distinctness to each other by the bootstrap value (%) generated. These findings were discussed with particular attention to the diversity of the inflammatory cytokine proteins within closely related species. The result of this study concluded that a small difference in the cytokine structures might be the reason behind or has a contributory factor on the previous reports about the existence of disease resistance. However, in-depth study is necessary to further qualify these findings.

CD8(+) T cell-mediated immune responses in West Nile virus (Sarafend strain) encephalitis are independent of gamma interferon

The flavivirus West Nile virus (WNV) can cause fatal encephalitis in humans and mice. It has recently been demonstrated, in an experimental model using WNV strain Sarafend and C57BL/6 mice, that both virus- and immune-mediated pathology is involved in WNV encephalitis, with CD8(+) T cells being the dominant subpopulation of lymphocyte infiltrates in the brain. Here, the role of activated WNV-immune CD8(+) T cells in mouse WNV encephalitis was investigated further. Passive transfer of WNV-immune CD8(+) T cells reduced mortality significantly and prolonged survival times of mice infected with WNV. Early infiltration of WNV-immune CD8(+) T cells into infected brains is shown, suggesting a beneficial contribution of these lymphocytes to recovery from encephalitis. This antiviral function was not markedly mediated by gamma interferon (IFN-gamma), as a deficiency in IFN-gamma did not affect mortality to two strains of WNV (Sarafend and Kunjin) or brain virus titres significantly. The cytolytic potential, as well as precursor frequency, of WNV-immune CD8(+) T cells were not altered by the absence of IFN-gamma. This was reflected in transfer experiments of WNV-immune CD8(+) T cells from IFN-gamma(-/-) mice into WNV-infected wild-type mice, which showed that IFN-gamma-deficient T cells were as effective as those from WNV-immune wild-type mice in ameliorating disease outcome. It is speculated here that one of the pleiotropic functions of IFN-gamma is mimicked by WNV-Sarafend-mediated upregulation of cell-surface expression of major histocompatibility complex antigens, which may explain the lack of phenotype of IFN-gamma(-/-) mice in response to WNV.

Interferon: The pathways of discovery

This historical account covers 50 years of seminal research work on interferon done since its discovery in 1957. Topics related to molecular structure, production and action of interferons are considered from the viewpoint of how our insights have expanded and deepened within the context of evolving tools and general knowledge in cellular and molecular biology. Lines of thought that linked each discovery to the next are expounded.

Relationships between hepatitis C virus replication and CXCL-8 production in vitro

The chemokine CXCL-8 (interleukin-8) is induced by many viruses, including hepatitis C virus (HCV). In the current study, we examined CXCL-8 levels in the context of acute and chronic HCV replication in vitro. Two different small interfering RNAs were used to silence CXCL-8 mRNA and protein expression in Huh7 and BB7 replicon cells. HCV RNA synthesis in BB7 cells was inhibited by CXCL-8 knockdown. Furthermore, antibody neutralization of endogenous CXCL-8 activity inhibited HCV replication, while addition of recombinant human CXCL-8 stimulated NS5A protein expression. Moreover, CXCL-8 protein levels correlated positively with HCV RNA levels in four independent subgenomic and genomic replicon lines (R = 0.41, P = 0.0013). However, CXCL-8 mRNA levels correlated inversely with CXCL-8 protein and HCV RNA levels in all replicon lines and in Huh7 cells. Transient replication assays with strongly permissive and weakly permissive Huh7 cells and three independent subgenomic replicons with various replicative capacities revealed that CXCL-8 protein levels were higher in weakly than in strongly permissive cells. The JFH-1 subgenomic replicon, which replicated to high levels in both strongly and weakly permissive Huh7 cells, induced CXCL-8 protein to high levels in both cell types. The data indicate that in the replicon system, CXCL-8 protein levels are positively associated with chronic HCV replication and that CXCL-8 removal inhibits HCV replication. During acute HCV replication, CXCL-8 production may be inhibitory to viruses with low replicative capacity. The data underscore the complex regulation of CXCL-8 mRNA and protein expression and further suggest that in addition to contributing to HCV pathology via proinflammatory actions, CXCL-8 may have opposing antiviral and proviral effects depending on the level of HCV replication, the cellular context, and whether the infection is acute or chronic.

Rapid pathogenesis induced by a vesicular stomatitis virus matrix protein mutant: viral pathogenesis is linked to induction of tumor necrosis factor alpha

Vesicular stomatitis virus (VSV) matrix (M) protein blocks host mRNA export from the nucleus and thereby inhibits interferon induction in infected cells. M mutants with mutations of methionine 51 (M51) lack this shutoff function. We examined pathogenesis of a VSV M mutant with a deletion of M51 (VSVDeltaM51) after intranasal infection of BALB/c mice and found an unexpected phenotype. Mice that received VSVDeltaM51 experienced a more rapid but overall less severe weight loss than mice that received the recombinant wild-type VSV (rwtVSV). Rapid weight loss was not explained by faster initial replication because VSVDeltaM51 replication was controlled faster than rwtVSV replication in the lungs and did not spread systemically like rwtVSV. This faster control of VSVDeltaM51 correlated with a more rapid induction of interferon in the lung. Because tumor necrosis factor alpha (TNF-alpha) is associated with weight loss, we examined TNF-alpha induction in mice infected with rwtVSV or VSVDeltaM51. We found more-rapid induction of TNF-alpha by the mutant at early times after infection, while rwtVSV induced more TNF-alpha later in infection. This result suggested that TNF-alpha induction might explain both the rapid weight loss caused by the mutant and the overall greater weight loss caused by the rwtVSV. Using TNF-alpha knockout mice (C57BL/6 background), we showed that weight loss following rwtVSV infection was greatly reduced in the absence of TNF-alpha. Although the rapid weight loss caused by VSVDeltaM51 was less pronounced in C57BL/6 mice, it was eliminated in the absence of TNF-alpha. These results indicate a role for TNF-alpha in the pathogenesis of VSV.

Restraint stress decreases virus-induced pro-inflammatory cytokine mRNA expression during acute Theiler's virus infection

Stressful life events have been associated with the onset and/or exacerbation of multiple sclerosis (MS). Our previous studies have indicated that restraint stress (RS) reduces inflammation and virus-induced chemokine expression in the Theiler's virus-induced demyelination (TVID) model of MS. Here we report that RS significantly reduced the virus-induced interferon-gamma mRNA levels in the brain. Additionally, mRNA levels of lymphotoxin-beta, tumor necrosis factor-alpha, and interferon-gamma in the brain were negatively correlated with viral titers in the brain. These results indicated an immunosuppressive effect of stress during early TVID causing impaired viral clearance, which may be a potential exacerbating factor for later demyelination.

Pathogenesis of herpes simplex hepatitis in macrophage-depleted mice: possible involvement of tumor necrosis factor-alpha and inducible nitric oxide synthase in massive apoptosis

Massive liver cell death provoked in silica-treated mice subsequently infected with herpes simplex virus (HSV)-1 is very similar pathohistologically to the cell death observed in human fulminant hepatitis. Previously, we have shown this liver cell death to be extensive apoptosis. In the present study, we examined various factors related to liver damage patho- and immunologically, as well as by reverse transcription-polymerase chain reaction. Tumor necrosis factor (TNF)-alpha, inducible nitric oxide synthase (iNOS), interferon (IFN)-alpha, and interleukin-6 mRNAs were detected to a much greater extent in silica-treated mice compared with control mice after HSV-1 infection, and excessive expression of iNOS mRNA and cytokine mRNAs in the liver may be closely related to massive liver cell apoptosis. The apoptosis was less related to the fas ligand than to TNF-alpha. Silica blockage of macrophages makes the liver cell extremely vulnerable to HSV-1 infection, and it induced expression of E-selectin and neutrophil margination in the liver. Subsequent HSV-1 infection induced excessive production of iNOS and cytokines, particularly TNF-alpha, but administration of anti-TNF-alpha antibody or NG-monomethyl-L-arginine was not completely efficacious for the survival of the mice. Overproduction of free radicals in combination with cytokines, such as TNF-alpha, IL-6 and IFN-alpha, may result in hepatic cell apoptosis.