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

Evidence that deficient IFN-gamma production is a biological basis of herpes simplex virus type-2 neurovirulence

Although immune response control of herpes simplex virus (HSV) has been well demonstrated, numerous HSV-2 strains are neurovirulent in immunocompetent mice. Using an RNase protection assay and an ELISA, we found that HSV-2-infected mice exhibited a deficient IFN-gamma response, an inability to clear virus, and eventual death. An HSV-based amplicon vector expressing mouse IFN-gamma was constructed and packaged into HSV-1-helper virus (HSV(pIFN-gamma)). In mice treated with HSV(pIFN-gamma), (i) the LD50 of HSV-2(G) increased 5000-fold, (ii) intracerebral IFN-gamma expression increased 10-fold, and (iii) HSV titer rapidly decreased. We suggest that the deficient IFN-gamma response is a basis for HSV-2 neurovirulence in mice.

Characterizing immunodominant and protective influenza hemagglutinin epitopes by functional activity and relative binding to major histocompatibility complex class II sites

In the present study the analysis of functional activity and major histocompatibility complex (MHC) binding of two adjacent MHC class II-restricted epitopes, located in the C-terminal 306-329 region of human influenza A virus hemagglutinin 1 subunit (HA1) conserved with subtype sequences and not affected by antigenic drift, was undertaken to explore the hierarchy of local immunodominance. The functional activity of two T cell hybridomas of the memory/effector Th1 phenotype in combination with in vivo immunization studies provided a good tool for investigating the functional characteristics of the T cell response. The in vitro binding assays performed with a series of overlapping, N-terminal biotinylated peptides covering the 306-341 sequence enabled us to compare the relative binding efficiency of peptides, comprising two distinct epitopes of this region, to I-Ed expressed on living antigen-presenting cells. Our studies revealed that (i) immunization of BALB/c mice with the 306-329 H1 or H2 peptides resulted in the activation and proliferation of T cells recognizing both the 306-318 and the 317-329 epitopes, while the 306-329 H3 peptide elicits predominantly 306-318-specific T cells, (ii) the 317-329 HA1 epitope of the H1 and H2 but not the H3 sequence is recognized by T cells and is available for recognition not only in the 317-329 peptide but also in the extended 306-329 or 306-341 peptides, (iii) the 306-318 and the 317-329 hemagglutinin peptides encompassing the H1, H2 but not the H3 sequence bind with an apparently similar affinity to and therefore compete for I-Ed binding sites, and (iv) the 317-341, the 317-329 peptides and their truncated analogs show subtype-dependent differences in MHC binding and those with lower binding capacity represent the H3 subtype sequences. These results demonstrate that differences in the binding capacity of peptides comprising two non-overlapping epitopes located in the C-terminal 306-329 region of HA1 of all three subtype-specific sequences to MHC class II provide a rationale for the local and also for the previously observed in vivo immunodominance of the 306-318 region over the 317-329 epitope in the H3 but not in the H1 or H2 sequences. In good correlation with the results of the binding and functional inhibition assays, these data demonstrate that in the H1 and H2 subtypes both regions are available for T cell recognition, they compete for the same restriction element with an apparently similar binding efficiency and, therefore, function as co-dominant epitopes. Due to the stabilizing effect of the fusion peptide, peptides comprising the 306-341 or 317-341 H1 sequences are highly immunogenic and elicit a protective immune response which involves the production of antibodies and interleukin-2 and tumor necrosis factor producing effector Th1 cells both directed against the 317-329 region. Based on the similarity of the I-Ed and HLA-DR1 peptide binding grooves and motifs, these results suggest that amino acid substitutions inserted to the H3 subtype sequence during viral evolution can modify the relative MHC binding capacity and invert the local hierarchy of immunodominance of two closely situated epitopes that are able to bind to the same MHC class II molecule.

Promoter attenuation in gene therapy: interferon-gamma and tumor necrosis factor-alpha inhibit transgene expression

One of the major limitations to current gene therapy is the low-level and transient vector gene expression due to poorly defined mechanisms, possibly including promoter attenuation or extinction. Because the application of gene therapy vectors in vivo induces cytokine production through specific or nonspecific immune responses, we hypothesized that cytokine-mediated signals may alter vector gene expression. Our data indicate that the cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) inhibit transgene expression from certain widely used viral promoters/enhancers (cytomegalovirus, Rous sarcoma virus, simian virus 40, Moloney murine leukemia virus long terminal repeat) delivered by adenoviral, retroviral or plasmid vectors in vitro. A constitutive cellular promoter (beta-actin) is less sensitive to these cytokine effects. Inhibition is at the mRNA level and cytokines do not cause vector DNA degradation, inhibit total cellular protein synthesis, or kill infected/transfected cells. Administration of neutralizing anti-IFN-gamma monoclonal antibody results in enhanced transgene expression in vivo. Thus, standard gene therapy vectors in current use may be improved by altering cytokine-responsive regulatory elements. Determination of the mechanisms involved in cytokine-regulated vector gene expression may improve the understanding of the cellular disposition of vectors for gene transfer and gene therapy.

Antiviral activity of tumor necrosis factor (TNF) is mediated via p55 and p75 TNF receptors

The antiviral nature of tumor necrosis factor (TNF) is generally well accepted. TNF appears to induce multiple antiviral mechanisms, and to synergize with interferon (IFN)-gamma in promoting antiviral activities. We infected TNF receptor (TNFR)-deficient mice with the virulent murine pathogen, ectromelia virus (EV), and observed that otherwise resistant mice were susceptible to lethal infection. To study the molecular basis of the antiviral action of TNF, mice were infected with a recombinant vaccinia virus encoding murine TNF (VV-HA-TNF). In normal mice, the replication of VV-HA-TNF was highly attenuated. In contrast, mice in which the TNFR type 1 (p55) or the TNFR type 2 (p75) were genetically disrupted showed a moderate defect in their capacity to clear the TNF-encoding virus. The contribution of both TNF receptors to the control of VV-HA-TNF was confirmed by the enhanced replication of VV-HA-TNF in mice deficient for both p55 and p75. These observations were corroborated by infecting TNFR-deficient mice with EV. For both infections, the p55 and p75 TNFRs were necessary to maintain normal levels of resistance. Thus, the antiviral activity of TNF is mediated via both TNFRs in vivo. Furthermore, these studies establish that TNF is an important component of the host response to a natural virus infection.

Bovine herpesvirus 4 BORFE2 protein inhibits Fas- and tumor necrosis factor receptor 1-induced apoptosis and contains death effector domains shared with other gamma-2 herpesviruses

Fas- and tumor necrosis factor receptor 1 (TNFR1)-induced apoptosis is mediated by the interaction of FADD with caspase-8. Here, we report that the bovine herpesvirus 4 (BHV4) BORFE2 gene encodes a protein that inhibits Fas- and TNFR1-induced apoptosis and contains death effector domains (DEDs). Using the yeast two-hybrid system, we found that the BORFE2 protein interacts with the prodomain of caspase-8. Furthermore, we show that BHV4 BORFE2 is a member of a family of DED-containing proteins that includes other gamma-2 herpesviruses, such as Kaposi's sarcoma-associated herpesvirus and herpesvirus saimiri.

Cytokines and immunity to viral infections

In this review, we discuss two broad approaches we have taken to study the role of cytokines and chemokines in antiviral immunity. Firstly, recombinant vaccinia viruses were engineered to express genes encoding cytokines and chemokines of interest. Potent antiviral activity was mediated by many of these encoded factors, including IL-2, IL-12, IFN-gamma, TNF-alpha, CD40L, Mig and Crg-2. In some cases, host defense mechanisms were induced (IL-2, IL-12, Mig and Crg-2), whilst for others, a direct antiviral effect was demonstrated (IFN-gamma, TNF-alpha and CD40L). In sharp contrast, vector-directed expression of IL-4, a type 2 factor, greatly increased virus virulence, due to a downregulation of host type 1 immune responses. Our second experimental approach involved the use of strains of mice deficient for the production of particular cytokines or their receptors, often in combination with our engineered viruses. Mice deficient in either IFN-gamma, IFN-gamma R, IFN-alpha/beta R, TNFRs, CD40 or IL-6 were, in general, highly susceptible to poxvirus infection. Surprisingly, not only the TNFR1, but also the TNFR2, was able to mediate the antiviral effects of TNF-alpha in vivo, whilst the antiviral activity observed following CD40-CD40L interaction is a newly defined function which may involve apoptosis of infected cells. Through the use of perforin-deficient mice, we were able to demonstrate a requirement for this molecule in the clearance of some viruses, such as ectromelia virus, whilst for others, such as vaccinia virus, perforin was less important but IFN-gamma was essential.

Tumour necrosis factor and associated cytokines in the host's response to malaria

Tumour Necrosis Factor (TNF) is produced at the initiation of malaria infections (pre-erythrocytic phase), as demonstrated by the release of bioactive TNF by peripheral blood mononuclear cells from individuals residing in endemic areas after stimulation with stage specific sporozoite antigens. During the erythrocytic phase, TNF production is greatly augmented by parasite antigens at the time of schizont rupture and merozoite release from infected erythrocytes. Some of the strongest inducers of TNF synthesis and release are malaria toxins, e.g. glycosylphosphatidylinositol moieties and malaria pigment. Because of TNF's well-known cytotoxic activity it was originally hypothesized that it alone was responsible for killing parasites directly or within host cells. Though earlier reports of the capability of serum containing TNF to kill plasmodia supported this idea, later experiments with recombinant TNF showed a lack of significant parasiticidal activity. Recent studies investigating related factors showed that they were involved with TNF in the control of infection. These factors included -ther cytokines, such as interleukin (IL)-1, IL-6, IL-12, interferon-gamma (IFN gamma) as well as nitric oxide intermediates (NOI) and reactive oxygen intermediates (ROI). This positioned TNF as a key regulator of the immune response against the malaria parasite. However, it must be noted that TNF and its associated factors are also responsible for the fever, aches and pains of acute illness, as well as the hypoglycemia, shock, bleeding and reversible coma of severe malaria seen in approximately 1 percent of individuals with malaria. Therein lies the rub; factors important in the control of malaria also appear to have detrimental properties. Research presented in this review characterizes TNF and associated cytokines' importance in the immune response to malaria.

Tumor necrosis factor alpha plays a central role in immune-mediated clearance of adenoviral vectors

Adenovirus (Ad) gene transfer vectors are rapidly cleared from infected hepatocytes in mice. To determine which effector mechanisms are responsible for elimination of the Ad vectors, we infected mice that were genetically compromised in immune effector pathways [perforin, Fas, or tumor necrosis factor alpha (TNF-alpha)] with the Ad vector, Ad5-chloramphenicol acetyl transferase (CAT). Mice were sacrificed at 7-60 days postinfection, and the levels of CAT expression in the liver determined by a quantitative enzymatic assay. When the livers of infected mice were harvested 28 days postinfection, the levels of CAT expression revealed that the effectors most important for the elimination of the Ad vector were TNF-alpha > Fas > perforin. TNF-alpha did not have a curative effect on infected hepatocytes, as the administration of TNF-alpha to infected severe combined immunodeficient mice or to infected cultures in vitro had no specific effect on virus persistence. However, TNF-alpha-deficient mice demonstrated a striking reduction in the leukocytic infiltration early on in the infection, suggesting that TNF-alpha deficiency resulted in impaired recruitment of inflammatory cells to the site of inflammation. In addition, the TNF-deficient mice had a significantly reduced humoral immune response to virus infection. These results demonstrate a dominant role of TNF-alpha in elimination of Ad gene transfer vectors. This result is particularly important because viral proteins that disable TNF-alpha function have been removed from most Ad vectors, rendering them highly susceptible to TNF-alpha-mediated elimination.

T cell therapy of human CMV and EBV infection in immunocompromised hosts

Acute virus infections in normal hosts are typically controlled by the development of a host immune response that includes MHC-restricted virus-specific T cells. Many viruses have developed methods to evade T cell recognition to facilitate initial infection and the establishment of a persistent infection in the host. Human cytomegalovirus (CMV) and Epstein-Barr virus (EBV) are ubiquitous human pathogens that utilise novel strategies to evade immune elimination. Despite these evasion methods, CD4(+) and CD8(+) T cells expressing alphabeta T cell receptors have been shown to play a pivotal role in controlling initial infection and in maintaining CMV and EBV in a latent state. However, in settings of iatrogenic or acquired T cell deficiency, primary infection or reactivation of CMV and EBV frequently progresses to cause life threatening disease. In this article the role of MHC-restricted CD8(+) and CD4(+) T cell responses in controlling CMV and EBV infections in healthy individuals and the development of novel strategies to restore protective T cell immunity to deficient hosts by the adoptive transfer of virus-specific T cells is reviewed. Copyright 1997 John Wiley & Sons, Ltd.

Evidence for a deficiency of interferon response in mononuclear cells from hepatitis C viremic patients

BACKGROUND/AIMS

The pathophysiology of chronic hepatitis C and the mechanisms of resistance to interferon alpha are poorly understood. The aim of this work was to assess the influence of HCV infection and the viral genotype on lymphocyte production of 2',5' oligo-adenylate synthetase activity and monocyte production of TNF alpha and IL1 beta.

METHODS

Mononuclear cells from 50 consecutive patients were studied after 6 months of interferon treatment. Patients with persistent viremia (PCR-positive, elevated ALT, n = 39) were compared with the PCR-negative patients with normal ALT activity (n = 11) of similar age and sex ratio.

RESULTS

Cells from the viremic patients showed lower basal and stimulated 2',5' oligo-adenylate synthetase activity, and a lower in vitro response capacity to human recombinant interferon. In contrast, no difference was observed in basal and stimulated TNF alpha or IL1 beta production between the two groups. In the PCR-positive patients the viral genotype had no significant influence on the response of mononuclear cells to interferon or endotoxin.

CONCLUSIONS

These results show that the presence of HCV in blood is associated with an elective defect in interferon system activation, independently of the viral genotype.

Constitutive and induced cytokine production by human placenta and amniotic membrane at term

Results of our previous study on the immunity of human placenta and amniotic membranes revealed that in majority of cases these organs present constitutive non-specific antiviral immunity in the organ culture (OC) system. It is possible that interferons (IFNs), tumour necrosis factors (TNFs) and interleukin 6 (IL-6) may be responsible for the antiviral effect. Here, the constitutive and lipopolysaccharide (LPS)-induced production of these cytokines and, additionally, interleukin 10 (IL-10) were determined in OC of chorionic villi, decidua and amniotic membranes. Significant amounts of constitutive TNF-alpha (2-64 U/ml), IL-6 (200-12,000 U/ml) and IL-10 (1-70 ng/ml) were detected in the maternal decidua and chorionic villi of placenta. Amniotic membranes produced lower concentrations of the cytokines. LPS increased the production of cytokines from two- to eightfold. In contrast, activity of IFN released spontaneously was found only in four of 50 placentae and amniotic membranes. LPS and Newcastle disease virus (NDV) induced IFN production in the OC system. However, the increase of IFN after induction was also very small (up to 32 U/ml). Individual differentiation in the cytokines production was observed among placentas and amniotic membranes. TNF was identified as type alpha with addition TNF-beta, IFN as type alpha, beta and gamma.

Effect of adenovirus 2 on cellular gene activation in blood-derived monocytes and macrophages

We have investigated the effect of adenovirus 2 (Ad2) infection on human monocytes and monocyte-derived macrophages with regard to expression of TNF-alpha and IL-1 beta. In monocytes, the virus was bound to the surface without being internalized. On the other hand, Ad2 was internalized by macrophages. No virus replication and no transcription of the Ad2 early genes was observed in either of the cells. Ad2 infection induced transient increase in the mRNA levels for TNF-alpha and IL-1 beta in both monocytes and in macrophages, although the kinetics of the transcription was slightly different. The production of both cytokines, measured by ELISA tests, was enhanced in monocytes. In macrophages, a slight enhancement of TNF-alpha production was seen, whereas IL-1 beta was not detected. The data indicate that cellular genes might be activated by Ad2 virus infection in nonpermissive cells where no viral gene products could be detected.

The roles of tumour necrosis factor-alpha, interleukin-1 and interleukin-12 in murine cytomegalovirus infection

The roles of the inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) and IL-12, in murine cytomegalovirus (MCMV) disease were investigated in susceptible BALB/c and resistant C57BL/6 mice. MCMV infection induced IL-1 and TNF-alpha production by peritoneal cells from BALB/c mice, as demonstrated previously in C57BL/6 mice. Overt ill-health and viral replication in the spleens of BALB/c mice were increased by in vivo treatment with soluble TNF-alpha receptors to inhibit the activity of this cytokine, whilst antibodies to IL-12 had a similar but more restricted effect C57BL/6 mice were not affected by either treatment, suggesting TNF-alpha and IL-12 are not critical for natural killer cell-mediated restriction of viral replication in the spleen. Soluble TNF-alpha receptors and antibodies to IL-12 also enhanced MCMV titres and numbers of viral antigen-positive cells in the livers of BALB/c mice and TNF-alpha receptors have similar effects in C57BL/6 livers. In contrast, IL-1 receptors improved the health of MCMV-infected BALB/c mice and reduced viral replication and hepatitis at some time-points. Mechanisms which may underlie these changes are discussed.

Human lymphotoxin mutein lacks hypotensive activity but has higher in vivo antitumor activity than lymphotoxin or tumor necrosis factor

A serious drawback of tumor necrosis factor alpha (TNF) as a clinical antitumor agent is that it also has hypotensive activity. To overcome this problem, derivatives of its sister cytokine lymphotoxin (TNF-beta or LT) were prepared. One of them, mutein 2 (Mut2) has a deletion of amino acids 1-7 but contains substituted amino acids, Met-Phe-Pro at positions 8-10 of the mature human LT. This mutein has no hypotensive activity at the maximum dose (10 mg/kg) tested on rats. In contrast, a much lower dose (1 mg/kg) of TNF and LT caused a significant blood pressure drop. In vivo studies revealed that Mut2 was more effective than TNF or LT against MethA (a mouse tumor line) as judged by the therapeutic ratio [calculated as LD50 (dose that kills 50% of the animals)/ED50 (dose that reduces the tumor size by 50%)]. With five other different mouse tumors and two different human tumors, Mut2 was also effective and the effectiveness was comparable or superior to that of TNF or LT. These results suggest the possibility that this derivative may be usable as a clinical antitumor agent without the serious side effects associated with TNF.

Characterization of the cellular and cytokine response in the central nervous system following Semliki Forest virus infection

Cytokines are important mediators in the pathogenesis of central nervous system (CNS) inflammatory diseases including multiple sclerosis (MS), experimental allergic encephalomyelitis (EAE), viral encephalitis and virus induced demyelinating diseases. We have used immunohistochemical techniques to characterize the mononuclear cell infiltrate and cytokine profiles in the CNS following infection of mice with the demyelinating A7(74) strain of Semliki Forest virus (SFV), an important viral model of MS. Mononuclear cell infiltrates in the CNS, first observed at 3 days and maximal during clearance of infectious virus, were comprised predominantly of CD8+ lymphocytes. F4/80+ macrophage/microglia and CD45/B220+ B lymphocytes were most numerous during the subsequent phase of demyelination. CD4+ T-lymphocytes were observed at low levels throughout infection. By immunostaining MHC class I, IL-1beta , IL-3 and TGF beta1 were constitutively expressed in normal mice and were upregulated following infection. MHC class II, IL-1alpha, IL-2, IL-2R, TNF-alpha and IL-6 were strongly upregulated in the CNS of SFV-infected mice and mice with chronic relapsing EAE. The spatial and temporal distribution of these cytokines during the course of disease was analysed. Whereas IL-1alpha, IL-1beta, IL-10, and TGF beta1 were observed on day 3 following infection GMCSF, IL-2 and TNF alpha were first apparent at day 7 when the cellular infiltration in the CNS was most intense. In contrast IFN gamma and IL-6 were first observed on day 10 prior to the demyelination phase of disease. Cytokines in the lesions of demyelination suggest a role in the pathogeneisis of myelin damage. Based on cytokine profiles no clear bias of either a Th1 or Th2 response was observed in the CNS during infection.

Effect of morphine on lipopolysaccharide-induced tumor necrosis factor-alpha production in vivo: involvement of the sympathetic nervous system

Morphine treatment modulates a variety of immunological parameters, including tumor necrosis factor-alpha (TNF-alpha) production by activated macrophages in vitro. The aim of our study was to clarify the effect of morphine on lipopolysaccharide (LPS)-induced TNF-alpha production in vivo. Plasma TNF-alpha levels of mice were determined by ELISA. Subcutaneous injection of morphine decreased LPS-induced TNF-alpha production throughout the response, an effect that was dose-dependent and reversible by naloxone. Blockade of the sympathetic transmission by chlorisondamine prevented the inhibitory effect of morphine on TNF-alpha production. It is concluded that (i) systemic administration of morphine inhibits LPS-induced TNF-alpha production in vivo via 'classic' opioid receptors; (ii) this effect requires intact sympathetic outflow. Since the increased incidence of bacterial and viral infections in opioid addicts is well documented, it is suggested that the inhibitory effect of morphine on TNF-alpha production might play a substantial role in the increased vulnerability of these individuals to certain infections.

Death effector domain-containing herpesvirus and poxvirus proteins inhibit both Fas- and TNFR1-induced apoptosis

To identify novel antiapoptotic proteins encoded by DNA viruses, we searched viral genomes for proteins that might interfere with Fas and TNFR1 apoptotic signaling pathways. We report here that equine herpesvirus type 2 E8 protein and molluscum contagiosum virus MC159 protein both show sequence similarity to the death effector domains (DEDs) of the Fas/TNFR1 signaling components FADD and caspase-8. Yeast two-hybrid analysis revealed that E8 protein interacted with the caspase-8 prodomain whereas MC159 protein interacted with FADD. Furthermore, expression of either E8 protein or MC159 protein protected cells from Fas- and TNFR1-induced apoptosis indicating that certain herpesviruses and poxviruses use DED-mediated interactions to interfere with apoptotic signaling pathways. These findings identify a novel control point exploited by viruses to regulate Fas- and TNFR1-mediated apoptosis.

Altered susceptibility to tumor necrosis factor alpha-induced apoptosis of mouse cells expressing polyomavirus middle and small T antigens

Infection with some virus types induces susceptibility to the cytotoxic effect of tumor necrosis factor alpha (TNF-alpha). To investigate whether expression of polyomavirus proteins has this effect on cells, the TNF-alpha sensitivity of C127 and L929 mouse cells transfected with viral DNA was analyzed. Expression of all three polyomavirus early proteins, the tumor (T) antigens, had no apparent effect. In contrast, middle T antigen by itself induced hypersensitivity to TNF-alpha. This effect was reversed by retransfection of the cells with DNA encoding small T antigen. Expression of this polypeptide also decreased the sensitivity of bovine papillomavirus type 1-transformed cells to TNF-alpha, showing that the protective function of the polyomavirus small T antigen was not strictly linked to a middle-T-antigen-induced event. Mouse and human TNF-alpha had the same effect on normal and transformed mouse cells, suggesting that this effect was mediated by TNF receptor 1. Consistent with this conclusion, all cell clones used in the experiments expressed TNF receptor 1 at similar levels, while we failed to detect TNF receptor 2. The amount of receptor on the cells was not influenced by binding of the ligand. Addition of TNF-alpha at cytotoxic concentrations to cells expressing middle T antigen by itself resulted in significant fragmentation of chromosomal DNA after only a few hours, indicating induction of apoptosis. Addition of the cytokine to these cells also leads to release of arachidonic acid, showing that phospholipase A2 was activated. However, production of arachidonic acid did not appear to significantly precede loss of cell viability.

Cytokines released by human peripheral blood mononuclear cells inhibit the production of early and late cytomegalovirus proteins

Cytomegalovirus-infected human fibroblasts are susceptible to lysis by natural killer cells and cytotoxic T cells. The purpose of this study was to determine whether non-lytic mechanisms might also contribute to the control of cytomegalovirus infection. The appearance of cytomegalovirus proteins in infected fibroblasts was determined by flow cytometry. Infected fibroblasts incubated with peripheral blood mononuclear cells for 3 days expressed less early and late proteins than fibroblasts incubated without peripheral blood mononuclear cells. Supernatants generated by the cocultivation of peripheral blood mononuclear cells with cytomegalovirus-infected fibroblasts inhibited the production of cytomegalovirus early and late proteins. The soluble factors in supernatants which contributed to the inhibitory effect were identified as interferons alpha, beta and gamma, and tumor necrosis factors alpha and beta. The ability of supernatants to inhibit the production of cytomegalovirus early protein was mimicked by combinations of corresponding recombinant cytokines. The inhibition of cytomegalovirus protein production by cytokines produced by peripheral blood mononuclear cells may contribute to early containment of cytomegalovirus infection.

M-T2: a poxvirus TNF receptor homologue with dual activities

Poxviruses are experts at manipulating and evading the host's immune response. They have acquired a number of open reading frames which specifically confer direct anti-immune properties, either by mimicking cytokine receptors and growth factors or by disarming cytokine regulatory cascades. The Myxoma T2 protein (M-T2), a TNF receptor homologue, is secreted from virus infected cells and can bind TNF-alpha with high affinity, and thereby inhibit TNF-alpha-mediated cytotoxicity. M-T2 also acts to inhibit virus-induced lymphocyte apoptosis by an as yet undefined mechanism. As such, T2 constitutes a significant virulence factor for poxviruses, influencing the outcome of infection, both in vitro and in vivo.

Herpes simplex virus type 2 inhibition of Fas ligand expression

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) are common human pathogens. In this report we demonstrate the capacity of HSV-2, but not HSV-1, to inhibit the activity and cell surface expression of Fas ligand, an important molecule involved in T-cell apoptosis and cell-mediated cytotoxicity. Cells infected with HSV-2 retained Fas ligand intracellularly instead of expressing it on the cell surface. Addition of anti-Fas antibodies markedly inhibited HSV-2 viral production, suggesting that the capacity of the virus to regulate Fas ligand expression, and thereby programmed cell death, may represent a powerful mechanism for the virus to enhance viral replication.

Molecular basis of immune evasion strategies by adenoviruses

Human adenoviruses have provided valuable insights into virus-host interactions at the clinical and experimental levels. In addition to the medical importance of adenoviruses in acute infections and the ability of the virus to persist in the host, adenovirus-based recombinants are being developed as potential vaccine vectors. It is now clear that adenoviruses employ various strategies to modulate the innate and the adaptive host immune defences. Adenovirus genome-coded products that interact with the immune response of the host have been identified, and to a large extent the molecular mechanisms of their functions have been revealed. Such knowledge will no doubt influence our approach to the areas of viral pathogenesis, vaccine development and immune modulation for disease management.

Down-regulation of human tumor necrosis factor-beta gene expression by cells with suppressive activity

Human TNF-beta (lymphotoxin) gene expression is down-regulated by immunosuppression. Induction of TNF-beta mRNA in lymphoid cells is greatly enhanced by gamma-irradiation, cyclophosphamide and cimetidine, agents that each inhibit activation of suppressive cells. The level of TNF-beta mRNA expressed in response to stimulation, whether by mitogen or antigen, is reduced strongly by concomitant activation of suppressive cell subsets. Removal of CD8 or CD11b cells leads to a pronounced superinduction of TNF-beta mRNA in the depleted cell population. Induction of TNF-beta mRNA precedes appearance of suppressive cell activity, allowing for temporary expression. The TNF-beta gene is as sensitive as IFN-gamma and IL-2 genes to suppression. Hence, three genes characteristically expressed in Th1 cells, encoding IL-2, IFN-gamma, and TNF-beta, are similarly regulated by cell-mediated suppression. Actual levels of TNF-beta during an immune response are determined by the balance between activities of expressing and suppressing cell subsets, both transiently manifested.

Evasion of apoptosis by DNA viruses

Apoptosis is a form of cell death distinct from necrosis which plays an important role in processes such as homoeostasis and the elimination of damaged cells. It can be triggered by a variety of stimuli including DNA damage and cytotoxic T lymphocyte activity, both of which may be induced in the course of a viral infection. Initially, induction of apoptosis may occur through pathways which have also been shown to be activated on disturbance of the cell cycle or damage to cellular DNA. At later time points during the course of infection, apoptosis can also be triggered by cytokines and immune effector cells. Apoptosis of the host cell before the completion of the viral replication cycle may limit the number of progeny and the spread of infection. The importance of apoptosis as an antiviral defence is illustrated by the presence of multiple pathways for apoptosis induction and inhibition in both the host and virus. In this review, the inhibition of apoptosis is described in adenovirus and poxvirus infection. These examples illustrate two of the divergent paths by which viruses may avoid the apoptotic response.

Tumor necrosis factor alpha induces the adenovirus early 3 promoter by activation of NF-kappaB

The early transcription unit 3 (E3) of human adenoviruses encodes proteins which appear to subvert host defense mechanisms. For example, the E3/19K protein inhibits the transport of major histocompatibility complex (MHC) class I molecules to the cell surface and thereby prevents cell lysis by cytotoxic T cells. Tumor necrosis factor alpha (TNF) stimulates expression of MHC molecules on the cell surface of normal cells but not of E3(+) cells, rather, a further reduction of MHC expression is evident. This was attributed to the increased expression of E3/19K upon TNF treatment, an effect also observed for other E3 proteins. We investigated the mechanism of the TNF-mediated up-regulation of E3 products. We show that TNF stimulates expression of a luciferase reporter gene driven by the E3 promoter. Mutation of individual transcription factor binding sites within the E3 promoter reveals the importance of the NF-kappaB binding site kappa2 for TNF inducibility. Electrophoretic mobility shift assays using antibodies directed against various members of the NF-kappaB family demonstrate that stimulation by TNF is mediated by the p50-p65 NF-kappaB complex. TNF inducibility does not depend on coexpression of E1A and can be observed during infection. Interestingly, the E3 promoter seems to be the only early promoter responsive to TNF and the only adenovirus promoter containing an NF-kappaB site. The implications of this regulatory mechanism for the adenovirus life cycle and its pathogenesis are discussed.

Tumor necrosis factor alpha inhibits entry of human immunodeficiency virus type 1 into primary human macrophages: a selective role for the 75-kilodalton receptor

The proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) is readily detected after human immunodeficiency virus type 1 (HIV-1) infection of primary macrophages in vitro and is present in plasma and tissues of patients with AIDS. Previous studies have shown that human recombinant TNFalpha (hrTNFalpha) enhances HIV replication in both chronically infected promonocytic and T-lymphoid cell lines in vitro. We report here that in contrast to untreated tissue culture-differentiated macrophages (TCDM), in which the proviral long terminal repeat (LTR) could be detected as soon as 8 h postinfection by a PCR assay, TCDM pretreatment for 3 days by hrTNFalpha markedly delayed its appearance until 72 h after infection with the HIV-1 Ada monocytotropic strain. Moreover the inhibition of formation of the proviral LTR in HIV-1-infected TCDM was directly proportional to the concentration of hrTNFalpha used. To determine if the inhibition of LTR formation results from blockade of viral entry, we performed a reverse transcription PCR assay to detect intracellular genomic viral RNA as early as 2 h after infection. Pretreatment of primary TCDM by hrTNFalpha for 3 days and even for only 2 h inhibits 75% of the viral entry into the cells. The inhibition of viral entry by hrTNFalpha was totally abolished by the use of anti-human TNFalpha monoclonal antibody. By using TNFalpha mutants specific for each human TNFalpha receptor, we showed that the inhibition of HIV-1 entry into TCDM was mediated not through the 55-kDa TNF receptor but through the 75-kDa TNF receptor. Although prolonged (1 to 5 days) TNFalpha treatment can downregulate CD4 expression in primary human TCDM, surface CD4 levels were not reduced by 2 h of treatment and was therefore not a limiting step for HIV-1 entry. In contrast to the inhibition of viral entry into primary TCDM, pretreatment with hrTNFalpha did not modify HIV-1 entry into phytohemagglutinin A-activated peripheral blood lymphocytes. TNFalpha-pretreatment inhibited HIV-1 replication in primary TCDM but not in phytohemagglutinin A-activated peripheral blood lymphocytes as assessed by decreased reverse transcriptase activity in culture supernatants. These results demonstrate that TNFalpha is able to enhance host cellular resistance to HIV-1 infection and that selective inhibition of HIV-1 entry into primary TCDM by TNFalpha involves the 75-kDa TNF receptor but not the 55-kDa TNF receptor.

A hydrophobic region within the adenovirus E1B 19 kDa protein is necessary for the transient inhibition of NF-kappaB activated by different stimuli

The early transcribed adenovirus proteins E1A and E1B display a variety of functions in the transformation of primary rodent cells and the regulation of apoptosis and transcription. We have recently shown recently that the E1B 19 kDa protein from Adenovirus 5 (Ad 5) can functionally antagonize the stimulatory effect of E1A 13S on the human transcription factor NF-kappaB. Here we show that expression of E1B 19 kDa negatively interfered with the activation of NF-kappaB by different stimuli, such as the E1A 13S protein, and treatment with phorbol ester and tumor necrosis factor alpha. This suggests that E1B 19 kDa acts on a common upstream signaling event. Band shift experiments showed that expression of E1B 19 kDa impaired the generation of the nuclear, DNA-binding form of NF-kappaB. Domain mapping experiments employing various E1B 19 kDa mutants revealed the necessity of a hydrophobic Bcl-2 homology region between amino acids 90 and 96 for NF-kappaB inhibition. Co-transfection experiments showed that the inhibitory effect of E1B 19 kDa on E1A 13S-activated NF-kappaB transcription was gradually lost in the course of time. Thus the continuous stimulatory action of E1A 13S can finally override the antagonistic effects of E1B 19 kDa on NF-kappaB activity. In contrast to E1B 19 kDa, expression of the E1B 55 kDa protein did not result in a de novo activation of NF-kappaB, but co-stimulated the transcriptional potential of activated NF-kappaB.

Different roles for cytotoxic T cells in the control of infections with cytopathic versus noncytopathic viruses

The assessment of the role of T-cell-mediated cytotoxicity in immunity to viral infections has been difficult to address directly and therefore has been controversial. Recent experiments with perforin-deficient mice have shown that cytotoxicity is crucial for the resolution of infection with lymphocytic choriomeningitis virus but not for the resolution of infection with vaccinia, vesicular stomatitis, Semliki Forest or influenza virus. These findings may reflect the general pattern that T-cell-mediated cytotoxicity is crucial only for the resolution of infections with noncytopathic viruses, whereas infections with cytopathic viruses are mainly controlled by soluble mediators such as antibodies and interferons.

The adenovirus E3-14.7K protein and the E3-10.4K/14.5K complex of proteins, which independently inhibit tumor necrosis factor (TNF)-induced apoptosis, also independently inhibit TNF-induced release of arachidonic acid

Tumor necrosis factor (TNF) is an inflammatory cytokine that inhibits the replication of many viruses in cultured cells. We have reported that adenovirus (Ad) infection of TNF-resistant mouse cells renders them susceptible to lysis by TNF and that two sets of proteins encoded by the E3 transcription unit block TNF cytolysis. The E3 protein sets are named E3-14.7K (14,700 kDa) and E3-10.4K/14.5K (a complex of two proteins of 10,400 and 14,500 kDa). TNF activation of the 85-kDa cytosolic phospholipase A2 (cPLA2) is thought to be essential for TNF cytolysis (i.e.,TNF-induced apoptosis). Here we provide evidence that cPLA2 is important in the response of Ad-infected cells to TNF and that the mechanism by which E3-14.7K and E3-10.4K/14.5K inhibit TNF cytolysis is by inhibiting TNF activation of cPLA2. cPLA2 cleaves arachidonic acid (AA) specifically from membrane phospholipids; therefore, cPLA2 activity was measured by the release of 3H-AA from cells prelabeled with 3H-AA. Uninfected cells or cells infected with wild-type Ad were not lysed and did not release 3H-AA in response to TNF. In contrast, TNF treatment induced cytolysis and 3H-AA release in uninfected cells sensitized to TNF by treatment with cycloheximide and also in infected cells sensitized to TNF by expression of E1A. In C127 cells, in which either E3-14.7K or E3-10.4K/14.5K inhibits TNF cytolysis, either set of proteins inhibited TNF-induced release of 3H-AA. In C3HA cells, in which E3-14.7K but not E3-10.4K/14.5K prevents TNF cytolysis, E3-14.7K but not E3-10.4K/14.5K prevented TNF-induced release of 3H-AA. When five virus mutants with lesions in E3-14.7K were examined, there was a perfect correlation between a mutant's ability to inhibit both TNF-induced cytolysis and release of 3H-AA. E3-14.7K expressed in two stably transfected C127 cell lines prevented both TNF-cycloheximide-induced cytolysis and release of 3H-AA. The E3 proteins also prevented TNF-induced cytolysis and release of 3H-AA in mouse L929 cells, which are spontaneously sensitive to TNF. TNF cytolysis was blocked by dexamethasone, an inhibitor of PLA2 activity, and by nordihydroquaiaretic acid, which inhibits the metabolism of AA to the leukotrienes. Indomethacin, which blocks the formation of prostaglandins from AA, did not inhibit TNF cytolysis. The leukotrienes and prostaglandins are amplifiers of the inflammatory response. We propose that E3-14.7K and E3-10.4K/14.5K function independently in Ad infection to inhibit both cytolysis and inflammation induced by TNF.

To kill or to cure: options in host defense against viral infection

It is generally thought that viral clearance is mediated primarily by antigen-specific T cell responses that destroy infected cells. This assumption may not be true for all viruses. Recent studies using a transgenic mouse model of hepatitis B virus infection have shown that adoptively transferred, virus-specific cytotoxic T cells can abolish hepatitis B virus gene expression and replication in the liver without killing the hepatocytes. This effect is mediated by interferon-gamma and tumor necrosis factor-alpha, which are secreted by the cytotoxic T lymphocytes following antigen recognition. Similar noncytopathic cytokine-dependent 'curative' processes also occur in this model during an unrelated infection of the liver. Intracellular viral inactivation mechanisms such as these could greatly amplify the protective effects of the immune response. Research has also been carried out to clarify the relevance of curative versus destructive mechanisms of viral clearance in other models of viral infection.

Bleb formation and F-actin distribution during mitosis and tumor necrosis factor-induced apoptosis

The murine cell line C3HA has been used extensively in studies of the cytopathology that accompanies TNF-induced cytolysis. This cell line undergoes an apoptic form of cell death characterized by plasma membrane blebbing and cytoplasmic boiling. Since plasma membrane blebs also appear on C3HA cells during mitosis, in this report we have compared these blebs with those that appear during apoptosis to determine whether they represent related structures. Our results reveal several differences. During mitosis, the blebs that appear are smaller and more heterogeneous in size than are those that appear during apoptosis. In addition, during mitosis bleb formation is preceded by the appearance of microvilli on the cell surface. No microvilli are observed during apoptosis. The staining pattern with rhodamine phalloidin also differed between mitotic and apoptic blebs, indicating a difference in their content of f-actin. The blebs that form during mitosis stained in a bright, uniform manner, suggesting an association with f-actin. In contrast, apoptic blebs were stained only at their base, the bleb itself being devoid of f-actin-associated staining. This difference may help explain why mitotic blebs are reintegrated into the cell surface, while the blebs that form during apoptosis are not.

Myxoma virus T2 protein, a tumor necrosis factor (TNF) receptor homolog, is secreted as a monomer and dimer that each bind rabbit TNFalpha, but the dimer is a more potent TNF inhibitor

The myxoma virus T2 (M-T2) gene expresses a secreted protein that contains significant sequence similarity to the ligand binding domains of the cellular tumor necrosis factor (TNF) receptors, specifically inhibits the cytolytic activity of rabbit TNFalpha and is an important virulence factor for myxoma virus infection in rabbits. M-T2 protein was overexpressed from vaccinia virus vectors, purified to apparent homogeneity, and found to specifically protect mouse and rabbit cells from lysis by rabbit TNFalpha at molar ratios comparable with the soluble versions of the host tumor necrosis factor receptors. M-T2 secreted from virus-infected cells is detected as both a monomer and a disulfide-linked dimer, both of which were shown by Scatchard analysis to bind rabbit TNFalpha (Kd values of 170 pM and 195 pM, respectively), values that are comparable with the affinities of mammalian TNFs with their receptors. In contrast to the rabbit ligand, M-T2 interacts with mouse TNFalpha with a much lower affinity, Kd of 1.7 nM, and was unable to inhibit the cytolytic activity of this ligand on mouse cells. Although both monomeric and dimeric forms bound rabbit TNFalpha with comparable affinity, the dimeric M-T2 protein was a far more potent inhibitor of rabbit TNFalpha, presumably because it can more effectively prevent dimerization of TNF receptors than can the M-T2 monomer.

Viral cross talk: intracellular inactivation of the hepatitis B virus during an unrelated viral infection of the liver

Hepatitis B virus (HBV) infection is thought to be controlled by virus-specific cytotoxic T lymphocytes (CTL). We have recently shown that HBV-specific CTL can abolish HBV replication noncytopathically in the liver of transgenic mice by secreting tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) after antigen recognition. We now demonstrate that hepatocellular HBV replication is also abolished noncytopathically during lymphocytic choriomeningitis virus (LCMV) infection, and we show that this process is mediated by TNF-alpha and IFN-alpha/beta produced by LCMV-infected hepatic macrophages. These results confirm the ability of these inflammatory cytokines to abolish HBV replication; they elucidate the mechanism likely to be responsible for clearance of HBV in chronically infected patients who become superinfected by other hepatotropic viruses; they suggest that pharmacological activation of intrahepatic macrophages may have therapeutic value in chronic HBV infection; and they raise the possibility that conceptually similar events may be operative in other viral infections as well.

Protective Role of TNF-alpha in respiratory syncytial virus infection in vitro and in vivo

Respiratory syncytial virus (RSV) infection causes substantial morbidity in young children and immunocompromised adults, yet its pathogenesis is poorly understood. Because the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) may be important in host response to viral infection, HEp-2 cells were treated with TNF-alpha and mice were given TNF-alpha antibody before RSV infection. Pretreatment of HEp-2 cells with TNF-alpha inhibited RSV replication as determined by cytopathic effect. Respiratory syncytial virus-infected BALB/c mice treated with antibody to TNF-alpha had greater maximal weight loss and slower recovery time than control mice. These results suggest a protective role for TNF-alpha in RSV infection.

Anti-human cytomegalovirus activity of cytokines produced by CD4+ T-cell clones specifically activated by IE1 peptides in vitro

The control of latent cytomegalovirus (CMV) infections by the immune system is poorly understood. We have previously shown that CD4+ T cells specific for the human CMV major regulatory protein IE1 are frequent in latently infected healthy blood donors. In order to learn about the possible role of these cells, we have developed IE1-specific CD4+ T-cell clones and, in this study, analyzed their epitope specificity and function in vitro. We measured their cytokine production when stimulated with specific IE1 peptides or whole recombinant IE1 protein. Their cytokine profiles, as deduced from gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and interleukin-4 (IL-4) and IL-6 production, were of the Th0- and Th1-like phenotypes. Supernatants from IE1-specific clones producing IFN-gamma and TNF-alpha were shown to inhibit CMV replication in U373 MG cells. This effect was due, as found by using cytokine-specific neutralizing antibodies, mostly to IFN-gamma, which was secreted at higher levels than TNF-alpha. To better assess the anti-CMV activity of cytokines, recombinant IFN-gamma and TNF-alpha were used and shown to have a synergistic effect on the inhibition of CMV replication and protein expression. Thus, IE1-specific CD4+ T cells display in vitro anti-CMV activity through cytokine secretion and may play a role in the control of in vivo latent infections.

Molecular mechanisms of lymphocyte-mediated cytotoxicity and their role in immunological protection and pathogenesis in vivo

Studies with perforin-deficient mice have demonstrated that two independent mechanisms account for T cell-mediated cytotoxicity: A main pathway is mediated by the secretion of the pore-forming protein perforin by the cytotoxic T cell, whereas an alternative nonsecretory pathway relies on the interaction of the Fas ligand that is upregulated during T cell activation with the apoptosis-inducing Fas molecule on the target cell. NK cells use the former pathway exclusively. The protective role of the perforin-dependent pathway has been shown for infection with the noncytopathic lymphocytic choriomeningitis virus, for infection with Listeria monocytogenes, and for the elimination of tumor cells by T cells and NK cells. In contrast, perforin-dependent cytotoxicity is not involved in protection against the cytopathic vaccinia virus and vesicular stomatitis virus. LCMV-induced immunopathology and autoimmune diabetes have been found to require perforin-expression. A contribution of perforin-dependent cytotoxicity to the rejection of MHC class I-disparate heart grafts has also been observed. Its absence is efficiently compensated in rejection of fully allogeneic organ or skin grafts. So far, evidence for a role of Fas-dependent cytotoxicity as a T cell effector mechanism in vivo is lacking. Current data suggest that the main function of Fas may be in regulation of the immune response and apparently less at the level of an effector mechanism in host defense. Further analysis is necessary, however, to settle this point finally.

The role of human adenovirus early region 3 proteins (gp19K, 10.4K, 14.5K, and 14.7K) in a murine pneumonia model

Products of human adenovirus (Ad) early region 3 (E3) inhibit both specific (cytotoxic T lymphocytes [CTLs]) and innate (tumor necrosis factor alpha [TNF-alpha]) immune responses in vitro. The E3 gp19K protein prevents CTL recognition of Ad-infected fibroblasts by sequestering major histocompatibility complex class I proteins in the endoplasmic reticulum. E3 proteins 10.4K, 14.5K, and 14.7K function to protect infected cells from TNF-alpha cytolysis. To address the in vivo functions of these proteins, Ad mutants that lack the E3 genes encoding these proteins were inoculated intranasally into C57BL/10SnJ (H-2b) mice. Mutants that lack the gp19K gene failed to alter CTL generation or to affect Ad-induced pulmonary infiltrates. Since gamma interferon (IFN-gamma) is capable of overcoming gp19K suppression of CTL lysis in vitro, mice were depleted of IFN-gamma and inoculated with gp19K mutants. Even when IFN-gamma was depleted, gp19K was incapable of altering pulmonary lesions. These resuls are not in accord with the function of gp19K in vitro and suggest that gp19K does not affect immune recognition in vivo during an acute virus infection, yet they do not exclude the possibility that gp19K blocks immune recognition of Ad during a persistent infection. In contrast, when mice were inoculated with Ad mutants that lack the TNF resistance genes (14.7K and either 10.4K or 14.5K), there was a marked increase in alveolar infiltration and no change in the amounts of perivascular/peribronchiolar infiltration compared with wild-type-Ad-induced pathology. These findings demonstrate the importance of TNF susceptibility and TNF by-products for recruiting inflammatory cells into the lungs during Ad infections.

The effect of exclusive breastfeeding on development and incidence of infection in infants

Of 145 normal fullterm infants studied during the first year after birth, those exclusively breastfed for the first four months differed significantly from those not exclusively breastfed in physical and behavioral development, and resistance to infection. At four months of age, the mean weight of the exclusively breastfed group was higher (p < 0.05). At one year, the exclusively breastfed group showed more advanced. Personal-Social (p = 0.05) and gross Motor development (p < 0.05) on the Denver Developmental Screening TEst, and lesser cumulative incidence of infectious diseases (p < 0.05). This study demonstrated the beneficial effects of breastfeeding on development and resistance to infection in infants.

IL-1 beta and TNF-alpha produced by peripheral blood mononuclear cells before and during interferon therapy in patients with chronic hepatitis C

We investigated the spontaneous and phytohemagglutinin-stimulated production of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) by peripheral blood mononuclear cells in patients with chronic hepatitis C during treatment with interferon-alpha (IFN-alpha). Spontaneous productions of these were significantly higher in patients with chronic hepatitis C than in healthy subjects. For patients prescribed interferon, stimulated production of TNF-alpha was significantly higher in complete responders than in partial responders, but the differences were small between the other cytokine levels and outcome of IFN treatment. Spontaneous production of these cytokines was higher in patients with genotype III with complete response than in genotype III patients with a partial response, but this was not the case in patients with genotype II. There was a negative correlation between these cytokines and histological activity index. Spontaneous production of cytokines was decreased only in complete responders after the administration of interferon. These data suggest that the elevated production of cytokines in patients with chronic hepatitis C may be due to host response to the virus, and monitoring cytokines along with alanine aminotransferase and hepatitis C virus RNA during treatment may provide more precise information of the effectiveness of therapy.

Value of the determination of TNF-alpha in the plasma of patients with non-Hodgkins lymphoma

The present report describes the value of the plasma determination of TNF-alpha, at diagnosis, in 43 patients with non-Hodgkin's lymphoma (NHL), related to their clinical presentation and the new International Prognosis Index (IPI). We also compare the levels of TNF-alpha with those of LDH, beta-2-microglobulin (beta-2-m), and ferritin. At diagnosis, the mean values of the quotients between the marker values and the maximum value of normal (ratio:r-) are placed 7 times higher than normal for r-TNF-alpha, whereas those of r-beta-2-m and r-LDH are 2,4 and 1,4 times more respectively. We found a relationship between the value of r-TNF-alpha and the ECOG, Ann Arbor stage, the number of affected extranodal sites, and between the values of r-beta-2-m with r-LDH. The best correlation was obtained between the values of r-TNF-alpha and r-beta-2-m and IPI, however r-TNF-alpha best stratify the four risk groups in this prognosis index.

O-glycosylated species of natural human tumor-necrosis factor-alpha

Tumor-necrosis factor-alpha, produced by human B-cell lymphoblastoid cell line BALL-1, was expressed as four protein bands on SDS/PAGE analysis. It may have been glycosylated, based on the fact that the heavier two of the four bands disappeared after neuraminidase treatment. Sugar composition analyses revealed that the tumor necrosis factor-alpha contained galactose, N-acetylgalactosamine and N-acetylneuraminic acid as sugar components. To prepare sugar chains, tumor necrosis factor-alpha was treated with alkaline borodeuteride and the oligosaccharide-alditols liberated were fractionated by gel-filtration chromatography on a Bio-Gel P-4 column, followed by normal-phase HPLC. Three oligosaccharide-alditols were obtained, and the structures of two of them were identified by methylation analysis and exoglycosidase digestion. The structures of these oligosaccharide-alditols were Gal beta 1-3(NeuAc alpha 2-6)GalNAcol and Gal beta 1-3GalNAcol (GalNAcol, N-acetylgalactosaminitol). The structure of the remaining oligosaccharide-alditol was determined to be NeuAc alpha 2-3Gal1-3GalNAcol by composition and methylation analyses. About 20% of tumor necrosis factor-alpha was found to be 0-glycosylated, based on the results of the sugar composition and structure analyses. An amino acid sequence analysis of the glycosylated peptides was performed after Staphylococcus aureus V8 protease digestion of tumor necrosis factor-alpha had been completed, and it was proved that the 0-glycosylation site of tumor necrosis factor-alpha was Ser 4.

Modulation of immune-associated surface markers and cytokine production by murine retinal glial cells

Murine retinal glia are normally negative for major histocompatibility complex (MHC) Class II antigens and express low levels of MHC Class I and intercellular adhesion molecule-1 (ICAM-1) as detected by avidin-biotin-peroxidase immunohistochemistry. These surface molecules associated with immune function were either induced (Class II) or upregulated (Class I and ICAM-1) on cultured retinal glial cells in a dose- and time-dependent manner following exposure to recombinant interferon-gamma (rIFN-gamma). MHC Class I and II expression by passaged and primary cells was maximal (> 90% positive) after incubation with 100 U/m1 of rIFN-gamma for 48 h. ICAM-1 expression by primary and passaged cells tripled between 48 and 72 h after exposure to 25 or 50 U/m1 of rIFN-gamma. By 72 h after exposure to 100 U/m1 of rIFN-gamma, 62% of the retinal glia were positive for ICAM-1, whereas under normal culture conditions these molecules were detected on < 3% of the retinal glia. Bacterial lipopolysaccharide (LPS), a known stimulator of central nervous system (CNS) astrocytes, increased ICAM-1 expression only 3-fold to 9% of cells staining positively, but neither MHC Class I nor Class II expression was altered from baseline levels. Surface expression of ICAM-1, MHC Class I, and MHC Class II was unaffected by exposure to either rTNF-alpha (1000 U/m1) or rIL-6 (100 U/m1) for 24 h. Under normal culture conditions, intracellular interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were detected immunohistochemically. Exposure to either rIFN-gamma or LPS induced more intense staining which correlated with increased secreted levels of both cytokines in culture supernatants. Levels of secreted TNF-alpha increased 6-fold after stimulation with LPS for 24 h, while secreted IL-6 increased over 9-fold. These results support the hypothesis that retinal glia may participate in intraretinal immune processes following stimulation during inflammatory and infections processes via either cell surface-or soluble mediator-dependent mechanisms or a combination of both.

Antisense manganese superoxide dismutase mRNA inhibits the antiviral action of interferon-gamma and interferon-alpha

Manganese superoxide dismutase (MnSOD) is induced by interferon-gamma (IFN-gamma) in various cell lines. To determine whether MnSOD plays a role in the antiviral action of IFN-gamma, we employed an antisense strategy to inhibit the expression of MnSOD in the human melanoma cell line, A375. Three antisense-containing clones that exhibited reduced induction of MnSOD were investigated with respect to their response to the antiviral protective effects of IFN-gamma and IFN-alpha. We observed a striking decrease in the ability of IFN-gamma to protect antisense clones from vesicular stomatitis virus infection (VSV). The IFN-alpha induced antiviral state was also impaired, but to a lesser degree than was observed with IFN-gamma. We excluded the possibility that these effects were caused by a higher sensitivity of the antisense cells to VSV itself and found that the antisense clones actually were less sensitive to VSV. Therefore, we conclude that MnSOD is involved in the establishment of the IFN-gamma-induced antiviral state and to a lesser degree in the antiviral actions of IFN-gamma.

The adenoviral transcription factor, E1A 13S, trans-activates the human tumor necrosis factor-alpha promoter

The 1311 bp TNF-alpha promoter region fused to a luciferase reporter vector was used in a transient transfection system to study the regulation of TNF-alpha promoter activity by E1A 13S in the U937 macrophage cell line and the MLA 144 T cell line. Co-transfections of the TNF-alpha promoter with an E1A expression vector resulted in a strong trans-activation of the promoter in both cell lines. Sequential truncation of the promoter mapped the E1A responsive region to sequences contained between -120 bp and the transcription start site. Truncation to -95 bp caused a dramatic 87% reduction of E1A activation in MLA 144 cells and further truncation to -36 bp caused a complete loss of E1A activation. In U937 cells, each truncation lowered E1A responsiveness but activity was never completely abolished. Site-directed mutagenesis of putative cis-acting sequences in the TNF-alpha promoter identified the AP-1 site as important for E1A trans-activation in the U937 cell line; the AP-2 and CRE sites also appeared to contribute to a lesser degree. In contrast, only the CRE mutation caused a reduction in E1A induced activity in the MLA 144 cell line. Co-transfection of the E1A expression vector with expression vectors for the cellular transcription factors AP-1, AP-2 and CREB indicated that none of these transcription factors showed any co-operativity with E1A. Thus, cis-acting sequences which contribute to E1A trans-activation of the TNF-alpha promoter have been delineated.

Induction of susceptibility to tumor necrosis factor by E1A is dependent on binding to either p300 or p105-Rb and induction of DNA synthesis

The introduction of the adenovirus early region 1A (E1A) gene products into normal cells sensitizes these cells to the cytotoxic effects of tumor necrosis factor (TNF). Previous studies have shown that the region of E1A responsible for susceptibility is CR1, a conserved region within E1A which binds the cellular proteins p300 and p105-Rb at nonoverlapping sites. Binding of these and other cellular proteins by E1A results in the induction of E1A-associated activities such as transformation, immortalization, DNA synthesis, and apoptosis. To investigate the mechanism by which E1A induces susceptibility to TNF, the NIH 3T3 mouse fibroblast cell line was infected with viruses containing mutations within E1A which abrogate binding of some or all of the cellular proteins to E1A. The results show that TNF susceptibility is induced by E1A binding to either p300 or p105-Rb. E1A mutants that bind neither p300 nor p105-Rb do not induce susceptibility to TNF. Experiments with stable cell lines created by transfection with either wild-type or mutant E1A lead to these same conclusions. In addition, a correlation between induction of DNA synthesis and induction of TNF sensitivity is seen. Only viruses which induce DNA synthesis can induce TNF sensitivity. Those viruses which do not induce DNA synthesis also do not induce TNF sensitivity. These data suggest that the mechanisms underlying induction of susceptibility to TNF by E1A are intimately connected to E1A's capacity to override cell cycle controls.

Stimulation of natural interferon-alpha/beta-producing cells by Staphylococcus aureus

Human peripheral blood mononuclear cells (PBMCs) produced high levels of antiviral activity, as determined by bioassay, when stimulated by Staphylococcus aureus Cowan I (SAC) and E. coli. Specific immunoassays demonstrated the presence of both IFN-alpha and gamma and, for SAC, also low levels of IFN-beta. The frequencies of SAC-induced IF N-alpha-producing cells (IPCs) were up to 1-2 per 10(3) PBMCs. These IPCs expressed the HLA-DR and CD4 antigens but not CD3, CD14, or CD19, thus resembling the natural IFN-alpha-producing cells (NIPC). The SAC was more efficient as IFN inducer when heat killed than when streptomycin inhibited. The SAC was inhibitory to virally induced IFN-alpha responses, in particular when streptomycin inhibited. Both pronase treatment and mechanical disruption of SAC cells abolished their capacity to induce IFN-alpha production. Staphylococcal strains lacking or expressing low levels of protein A (SpA) showed a decreased ability to induce IFN-alpha production. However, purified SpA did not itself induce IFN-alpha. Possibly, SpA together with other bacterial surface proteins is important for the capacity of SAC to induce IFN-alpha production in NIPC.

Tumor necrosis factor and lymphotoxin: protection against oxidative stress through induction of MnSOD

Tumor necrosis factor (TNF) and lymphotoxin (LT) are related cytokines produced in response to infection or oxidative insults such as radiation. These cytokines bind to the same receptors and have pleiotropic effects on a variety of cell types. TNF or LT pretreatment, which can induce the synthesis of "protective" proteins such as mitochondrial manganese superoxide dismutase (MnSOD), protects animals from lethal doses of radiation or the chemotherapeutic drug doxorubicin. In contrast, TNF or LT pretreatment of tumor cells, which do not express MnSOD, results in sensitization to these insults. Therefore, radio- or chemoprotection of normal cells may act partially through enhanced expression of MnSOD. On the other hand, tumor sensitization may result from activation of "killing" proteins such as interleukin-1 beta converting enzyme (ICE) or other ICE-like proteases, possibly through TNF/LT-induced oxygen free radicals. In addition to their originally described anti-tumor activity, these cytokines may have new therapeutic indications in protecting normal cells while sensitizing tumor cells to radiation or chemotherapeutic drugs.

Posttranscriptional clearance of hepatitis B virus RNA by cytotoxic T lymphocyte-activated hepatocytes

Using transgenic mice that replicate the hepatitis B virus (HBV) genome, we recently demonstrated that class I-restricted, hepatitis B surface antigen-specific cytotoxic T lymphocytes (CTLs) can noncytolytically eliminate HBV pregenomic and envelope RNA transcripts from the hepatocyte. We now demonstrate that the steady-state content of these viral transcripts is profoundly reduced in the nucleus and cytoplasm of CTL-activated hepatocytes, but their transcription rates are only slightly reduced. Additionally, we demonstrate that transcripts covering the HBV X coding region are resistant to downregulation by the CTL. These results imply the existence of CTL-inducible hepatocellular factors that interact with a discrete element(s) between nucleotides 3157 and 1239 within the viral pregenomic and envelope transcripts and mediate their degradation, thus converting the hepatocyte from a passive victim to an active participant in the host response to HBV infection.