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

Resistance/susceptibility to Echinococcus multilocularis infection and cytokine profile in humans. II. Influence of the HLA B8, DR3, DQ2 haplotype

Differences have been shown between HLA characteristics of patients with different courses of alveolar echinococcosis (AE). Notably the HLA B8, DR3, DQ2 haplotype was associated with more severe forms of this granulomatous parasitic disease. We compared IL-10, IL-5, interferon-gamma (IFN-gamma) and tumour necrosis factor (TNF) secretion by peripheral blood mononuclear cells (PBMC) isolated from eight HLA-DR3+, DQ2+, B8+ AE patients and from 10 HLA-DR3-, DQ2-, B8- patients after non-specific mitogenic and specific Echinococcus multilocularis antigenic in vitro stimulation. PBMC from seven HLA-DR3+, DQ2+, B8+ healthy subjects and nine HLA-DR3-, DQ2-, B8- subjects were also studied as controls. PBMC from AE patients with HLA DR3+, DQ2+ haplotype secreted higher levels of IL-10 without any stimulation and after specific antigenic stimulation than did patients without this haplotype. Higher levels of IL-5 and IFN-gamma were also produced by these patients' PBMC after stimulation with non-purified parasitic antigenic preparations; however, the specific alkaline phosphatase antigen extracted from E. multilocularis induced only Th2-type cytokine secretion. A spontaneous secretion of TNF by HLA DR3+, DQ2+ B8+ AE patients was also found. These results suggest that HLA characteristics of the host can influence immune-mediated mechanisms, and thus the course of AE in humans; specific antigenic components of E. multilocularis could contribute to the preferential Th2-type cytokine production favoured by the genetic background of the host.

Twenty-five-year panorama of corneal immunology: emerging concepts in the immunopathogenesis of microbial keratitis, peripheral ulcerative keratitis, and corneal transplant rejection

PURPOSE

To describe the most recent advances in our understanding of the cellular and molecular mechanisms involved in the immunopathogenesis of corneal immunoinflammatory disorders including microbial keratitis, peripheral ulcerative keratitis. and allograft rejection.

METHODS

Review of the published peer-reviewed literature that has contributed significantly to our modern understanding of corneal immunology. In addition, the authors have summarized the information in conceptual diagrams that highlight the critical cellular and molecular pathways that lead to corneal immune responses in the two most thoroughly studied corneal immune disorders, herpes simplex keratitis (HSK) and transplant rejection.

RESULTS

In spite of the wide array of molecular and cellular factors that mediate corneal immunity, critical mechanistic facets are shared by the various corneal immunoinflammatory disorders. These include activation and migration of local antigen-presenting cells (APCs), including Langerhans cells (LCs), upregulation in pleiotropic proinflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor-alfa (TNF-alpha) that can mediate a wide array of immune functions in addition to up-regulating protease expression. and chemokines that play a critical role on the one hand in attracting nonantigen-specific inflammatory cells such as neutrophils and on the other in attracting CD4+ T helper type 1 (Th1) cells that mediate most of the destruction in the cornea.

CONCLUSIONS

In the last 25 years, we have seen our field develop from a descriptive stage into a new phase where the fundamental processes that mediate and effect corneal immunity are being accurately deciphered. It is anticipated that this new knowledge will allow development of specific molecular and genetic therapeutic strategies that could target critical steps in the immunopathogenesis of disease without the untoward side-effects of nonspecific generalized immune suppression that still remains the standard of care today.

Effect of Staphylococcus enterotoxin B on the concurrent CD8(+) T cell response to influenza virus infection

Bacterial superantigens have potent in vivo effects. Respiratory viral infections are often associated with secondary bacterial infections, raising the likelihood of exposure to bacterial superantigens after the initiation of the anti-viral immune response. In this study, the general and V beta-specific effects of exposure to Staphylococcal enterotoxin B (SEB) during influenza virus infection on both the ongoing acute and the subsequent recall CD8(+) T cell responses were analyzed, using the well-characterized murine influenza model system and tetrameric MHC/peptide reagents to directly identify virus-specific T cells. The results show that although superantigen exposure during the primary viral infection caused delayed viral clearance, there was remarkably little effect of SEB on the magnitude or TCR repertoire of the ongoing cytolytic T cell response or on the recall response elicited by secondary viral infection. Thus, despite the well-characterized immunomodulatory effects of SEB, there was surprisingly little interference with concurrent anti-viral immunity.

Induction of necrotic-like cell death by tumor necrosis factor alpha and caspase inhibitors: novel mechanism for killing virus-infected cells

Induction of apoptotic cell death generally requires the participation of cysteine proteases belonging to the caspase family. However, and similar to most cell types, mouse fibroblasts are normally resistant to tumor necrosis factor alpha (TNF-alpha)-induced apoptosis. Surprisingly, TNF-alpha treatment of vaccinia virus-infected mouse fibroblasts resulted in necrotic-like cell death, which was significantly reduced in cells infected with a vaccinia virus mutant lacking the caspase inhibitor B13R. Furthermore, TNF-alpha also induced necrotic-like cell death of fibroblasts in the presence of peptidyl caspase inhibitors. In both cases, necrosis was accompanied by generation of superoxide species. Caspase inhibitors also sensitized fibroblasts to killing by double-stranded RNA and gamma interferon. In all cases, cell death was efficiently blocked by antioxidants or mitochondrial respiratory chain inhibitors. These results define a new mitochondrion-dependent mechanism which may be important in the killing of cells infected with viruses encoding caspase inhibitors.

Porcine reproductive and respiratory syndrome (PRRS) virus down-modulates TNF-alpha production in infected macrophages

The effect of porcine reproductive and respiratory syndrome (PRRS) virus infection on the synthesis and secretion of TNF-alpha and other pro-inflammatory cytokines by porcine alveolar macrophages (PAM) was investigated as well as the effect that TNF-alpha has on the replication of this virus. A clear reduction of phorbol myristate acetate (PMA)-induced expression of TNF-alpha mRNA was observed in cells incubated with PRRS virus. Moreover, the presence of PRRS virus also induced a decrease in IL-1 alpha and MIP-1 beta mRNAs expression with respect to PMA-stimulated uninfected cells. According to these results, exposure to the PRRS virus led to a reduction of the TNF-alpha protein in supernatants of PMA-stimulated PAM. On the other hand, addition of recombinant porcine TNF-alpha to cultures clearly reduced virus replication; however the addition of TNF-alpha to cultures containing IFN-alpha did not result in a further reduction of the produced by IFN-alpha alone. This indicates the lack of synergy in the effect of these cytokines on viral replication.

Functional effects of lymphotoxin on crushed peripheral nerve

The effect of lymphotoxin (LT) on the functional recovery of crushed peripheral nerves was studied. Using a specially designed compression device, a 5 mm segment of the right sciatic nerve of rats was subjected to a 100 g crush load with a 2 hr duration. The rats in the experimental and control groups received two doses of LT (20 micrograms/kg each) or the same volume of saline, respectively, administered intraperitoneously 24 hr and 1 hr before the procedure. Walking track tests and histologic examinations were performed at intervals up to 56 days after the crush. Motor functional recovery in the LT pretreated group started at day 7 while the crushed limb in the control group remained totally dysfunctional. The sciatic functional index improved faster in the LT group than in the control group during the second week after the crush and reached a significant difference (P < 0.05) at day 18. Subsequently, both groups had a similar evolution. Histologic results paralleled the functional findings. In conclusion, LT can promote motor functional recovery of crushed rat peripheral nerve in the early stage of regeneration.

CD4(+) T cell subsets during virus infection. Protective capacity depends on effector cytokine secretion and on migratory capability

To analyze the antiviral protective capacities of CD4(+) T helper (Th) cell subsets, we used transgenic T cells expressing an I-A(b)-restricted T cell receptor specific for an epitope of vesicular stomatitis virus glycoprotein (VSV-G). After polarization into Th1 or Th2 effectors and adoptive transfer into T cell-deficient recipients, protective capacities were assessed after infection with different types of viruses expressing the VSV-G. Both Th1 and Th2 CD4(+) T cells could transfer protection against systemic VSV infection, by stimulating the production of neutralizing immunoglobulin G antibodies. However, only Th1 CD4(+) T cells were able to mediate protection against infection with recombinant vaccinia virus expressing the VSV-G (Vacc-IND-G). Similarly, only Th1 CD4(+) T cells were able to rapidly eradicate Vacc-IND-G from peripheral organs, to mediate delayed-type hypersensitivity responses against VSV-G and to protect against lethal intranasal infection with VSV. Protective capacity correlated with the ability of Th1 CD4(+) T cells to rapidly migrate to peripheral inflammatory sites in vivo and to respond to inflammatory chemokines that were induced after virus infection of peripheral tissues. Therefore, the antiviral protective capacity of a given CD4(+) T cell is governed by the effector cytokines it produces and by its migratory capability.

Viral double-stranded RNA, cytokines, and the flu

The symptoms of the flu, such as fever, drowsiness, and malaise, are the sole means by which this common clinical syndrome is defined. The syndrome is usually the first clinical manifestation of both acute bacterial and viral infections. In the case of acute bacterial infections, several proinflammatory cytokines induced by bacterial products have been implicated as the causative agents of the flu syndrome. Viruses induce similar cytokines to bacteria, plus substantial amounts of interferon-alpha (IFN-alpha), although the direct association of these cytokines with the viral flu syndrome is less clear. Furthermore, the viral inducer(s) of cytokines has not been defined. The best candidate cytokine inducer associated with a majority of viral infections is virus-associated double-stranded RNA (dsRNA). This review examines the essential physical properties of toxic dsRNA, the cytokines induced by it, its viral and cellular sources, evidence for its presence in infected cells, its quantities in normal and infected cells, its cytotoxic mechanisms, and its cell-penetration properties. Toxic effects of viruses and dsRNA are compared. Energetics and extraction artifact issues are also discussed. Whereas most research on dsRNA toxicity has employed synthetic dsRNA, studies with virus-associated dsRNA are featured when available. Finally, a model for how viral dsRNA might initiate systemic disease is presented.

Stimulus-specific assembly of enhancer complexes on the tumor necrosis factor alpha gene promoter

The human tumor necrosis factor alpha (TNF-alpha) gene is rapidly activated in response to multiple signals of stress and inflammation. We have identified transcription factors present in the TNF-alpha enhancer complex in vivo following ionophore stimulation (ATF-2/Jun and NFAT) and virus infection (ATF-2/Jun, NFAT, and Sp1), demonstrating a novel role for NFAT and Sp1 in virus induction of gene expression. We show that virus infection results in calcium flux and calcineurin-dependent NFAT dephosphorylation; however, relatively lower levels of NFAT are present in the nucleus following virus infection as compared to ionophore stimulation. Strikingly, Sp1 functionally synergizes with NFAT and ATF-2/c-jun in the activation of TNF-alpha gene transcription and selectively associates with the TNF-alpha promoter upon virus infection but not upon ionophore stimulation in vivo. We conclude that the specificity of TNF-alpha transcriptional activation is achieved through the assembly of stimulus-specific enhancer complexes and through synergistic interactions among the distinct activators within these enhancer complexes.

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

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

An assessment of the acute effects of the serotonin releasers methylenedioxymethamphetamine, methylenedioxyamphetamine and fenfluramine on immunity in rats

The purpose of the present study was to examine the effect of the serotonin releasing amphetamine derivatives methylenedioxymethamphetamine (MDMA), methylenedioxyamphetamine (MDA) and fenfluramine (FEN) on immunity in rats. Similar to MDA and MDMA, FEN reduced the number of circulating lymphocytes, provoked a suppression of Con A-stimulated lymphocyte proliferation and total IFN-gamma and IL-10 production in diluted whole blood cultures. Thus the non-psychostimulant amphetamine derivative FEN, shares the ability of the psychostimulant methylenedioxy-substituted amphetamine derivatives to alter these indices of immune function in the rat. However, when Con A-stimulated cytokine production was normalised for the number of lymphocytes in culture in order to examine cytokine production at a cellular level, the effect of the amphetamine derivatives begins to diverge. FEN shares with MDMA and MDA the ability to suppress production of the Th2 type cytokine IL-10. However the effect of these drugs on Th1 type cytokine secretion was much more complex. While the methylendioxy-substituted amphetamines increases the secretion of the Th1 type cytokine IL-2 without altering the related Th1 type cytokine IFN-gamma, FEN did not alter IL-2 secretion, but suppressed IFN-gamma secretion. In addition to these effects on T-cell responses, all three drugs inhibited LPS-induced TNF-alpha secretion from diluted whole blood cultures suggesting that macrophage activity is impaired following treatment. In all, these data extend our previous findings concerning the effects of MDMA on the immune system and demonstrate that the related serotonin releasers MDA and FEN also provoke immunological changes in rats.

Decreased cytomegalovirus expression following proinflammatory cytokine treatment of primary human astrocytes

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

A cis-acting element in the 3'-untranslated region of human TNF-alpha mRNA renders splicing dependent on the activation of protein kinase PKR

We report a role for the 3'-untranslated region in control of mRNA splicing and show that human TNF-alpha 3' UTR harbors a cis-acting element that renders splicing of precursor transcripts dependent on activation of PKR, the RNA-activated protein kinase that phosphorylates eukaryotic initiation factor 2 (eIF2). When this element, designated 2-APRE, is present, splicing becomes sensitive to inhibition by the PKR inhibitor, 2-aminopurine, or by coexpression of transdominant-negative mutant PKR. Our results reveal that activation of PKR is required for splicing of mRNA when precursor transcripts contain the 2-APRE and that increased expression of wild-type PKR enhances their splicing efficiency. Thus, PKR responds as trans-acting factor to the 2-APRE. 2-APRE RNA forms a stable, 17-bp stem-loop structure and strongly activates PKR in vitro, inducing eIF2alpha phosphorylation. Despite its ability to activate PKR during splicing, the 2-APRE within the 3' UTR does not affect translation efficiency of the resulting TNF-alpha mRNA in transfected cells. PKR and the 3' UTR thus interact during mRNA splicing to confer a novel type of regulation on expression of the TNF-alpha gene.

Reversal of virus-induced systemic shock and respiratory failure by blockade of the lymphotoxin pathway

At present, little is known about the pathogenesis of acute virus-induced shock and pulmonary failure. A chief impediment in understanding the underlying disease mechanisms and developing treatment strategies has been the lack of a suitable animal model. This study describes a mouse model of virus-induced systemic shock and respiratory distress, and shows that blockade of the lymphotoxin beta receptor pathway reverses the disease.

Dual role of TNF-alpha in NK/LAK cell-mediated lysis of chronically HIV-infected U1 cells. Concomitant enhancement of HIV expression and sensitization of cell-mediated lysis

The U937-derived chronically HIV-infected U1 cell line and uninfected U937 cell clones were efficiently lysed by both unstimulated (NK) and IL-2-stimulated (lymphokine-activated killer; LAK) peripheral blood mononuclear cells (PBMC) of healthy HIV-seronegative donors. Pretreatment of target cells with IFN-gamma down-modulated killing of both U1 cells and two U937 cell clones, and up-regulated MHC class I expression. In contrast, TNF-alpha enhanced the sensitivity of infected U1 cells, but not of U937 cell clones to NK / LAK cell lysis. Co-cultivation of IL-2-stimulated PBMC with U1 cells triggered expression and replication of HIV by cell-cell contact, and this effect was inhibited by anti-TNF-alpha antibodies (Ab); virus production was partially inhibited by zidovudine. Of interest, anti-TNF-alpha Ab protected U1 cells from LAK cell activity. Thus, TNF-alpha can induce HIV expression from chronically infected U1 cells, but also plays an important role in sensitizing these cells to lysis.

Differential effect of a single high dose of the tricyclic antidepressant imipramine on interleukin-1beta and tumor necrosis factor-alpha secretion following an in vivo lipopolysaccharide challenge in rats

Tricyclic antidepressants (TCAs) of which imipramine is one, are commonly used in the treatment of depressive disorders and other forms of psychiatric illness. There have been many reports regarding the suppressive effects of TCAs on immune function. However, information is still limited regarding the effects of TCAs on the immune system, as many of the studies conducted to date have concentrated on in vitro exposure to such drugs, or ex vivo measures of immunity following drug administration. Thus in the present investigation, an in vivo challenge with bacterial lipopolysaccharide (LPS) (100 microg/kg; i.p.) was used to assess immunocompetence following administration of a single high dose of the TCA, imipramine (100 mg/kg, p.o.). The results demonstrated that imipramine pretreatment inhibits LPS-induced increases in serum concentrations of the proinflammatory cytokine, tumor necrosis factor (TNF)-alpha both 3 and 6 h, following administration. However, LPS-induced interleukin (IL)-1beta secretion was not significantly altered following imipramine treatment at either of the timepoints examined. In addition, serum concentrations of corticosterone and the antiinflammatory cytokine IL-10 were measured, and imipramine treatment failed to alter either basal, or LPS-induced increases in these immunosuppressive agents. In conclusion, although IL-1beta and TNF-alpha are both macrophage-derived proinflammatory cytokines, the present study demonstrates a differential sensitivity of these cytokines to the suppressive effects of the TCA imipramine. Furthermore, the suppressive effects of imipramine on LPS-induced TNF-alpha secretion could not be attributed to either increased glucocorticoid levels, or increased secretion of the antiinflammatory cytokine IL-10. The relevance of these findings to antidepressant-induced immunotoxicity are discussed.

The murine gammaherpesvirus-68 M11 protein inhibits Fas- and TNF-induced apoptosis

The murine gammaherpesvirus-68 (MHV-68) M11 gene encodes a protein predicted to have limited homology to the bcl-2 family of proteins. Unlike most of the other viral bcl-2 homologues, which have both BH1 and BH2 domains conserved with respect to bcl-2, the M11 protein has a BH1 domain, but apparently lacks a BH2 domain. Transfection of HeLa cells with an epitope-tagged MHV-68 M11 construct showed that the protein is predominantly located in the cytoplasm of cells. In HeLa cells, M11 inhibited apoptosis induced by anti-Fas antibody and by TNF-alpha. Thus, despite its limited conservation with respect to other bcl-2 family members, the MHV-68 M11 protein is a potent inhibitor of apoptosis.

Human papillomavirus type 16 E6-enhanced susceptibility of L929 cells to tumor necrosis factor alpha correlates with increased accumulation of reactive oxygen species

Human papillomavirus type 16 (HPV-16) E6 has been shown to prevent or enhance apoptosis depending on the stimulus and cell type. Here we present evidence that HPV-16 E6 sensitized murine fibrosarcoma L929 cells to tumor necrosis factor alpha (TNF)-induced cytolysis. The E6-enhanced cytolysis correlated with a precedent increase in reactive oxygen species (ROS) level and antioxidant treatment could completely block the E6-dependent sensitization. These findings represent the first demonstration of a link between a viral oncogene-sensitized cytolysis and ROS. Previous studies have shown conflicting results regarding whether TNF-induced cytolysis of L929 cells is through necrosis or apoptosis. Here we report that, although L929 cells underwent DNA fragmentation after exposure to TNF, they retained the morphology of intact nuclei while gaining permeability to propidium iodide, features characteristic of necrosis rather than apoptosis. We confirmed that the broad spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone markedly increased the susceptibility of L929 cells to TNF, and further demonstrated that E6 enhanced this susceptibility, which again correlated with increased ROS accumulation. We showed that the expression of E6 in L929 cells did not alter the stability of p53, and the cells retained a p53 response to actinomycin D. Furthermore, two E6 mutants defective for p53 degradation in other systems exhibited differential effects on TNF sensitization. These results suggest that the enhancement of TNF-induced L929 cytolysis by E6 is independent of p53 degradation. We also found that TNF-induced activation of NF-kappaB did not account for the enhanced TNF susceptibility by E6.

Secretion of TNF-alpha, IL-8 and nitric oxide by macrophages activated with polyanions, and involvement of interferon-gamma in the regulation of cytokine secretion

When macrophages derived from rat bone marrow were cultured in the presence of polyanions such as acetyl lignin (EP3), sulfonyl lignin (LS) or dextran sulfate (DS), the cells secreted TNF-alpha, IL-8 and nitric oxide (NO). EP3 had a dose-dependent effect on the secretion of TNF-alpha, IL-8 and NO. EP3 significantly affected secretion at concentrations greater than 5 microg/ml. The EP3 effect was at its maximum between concentrations of 50 and 100 microg/ml. LS and DS induced a slight increase in the secretion of cytokines and NO at a concentration of 100 microg/ml. The use of the reverse-transcription polymerase chain reaction (RT-PCR) showed that the increases in cytokine and NO secretion were due to an increase in cytokine mRNAs or NO synthase mRNA. Anti-TNF-alpha antibodies partially inhibited NO secretion by EP3-activated macrophages, although IL-8 secretion was independent of antibody treatment. The secretion of TNF-alpha and NO was also unaffected by the addition of anti-IL-8 antibodies. The addition of interferon-gamma (IFN-gamma) to the culture medium did not alter TNF-alpha and NO secretion by the EP3-activated macrophages, however, IL-8 secretion was increased when a low concentration of IFN-gamma (0.2 U/ml) was added, but was reduced in the presence of a high concentration of IFN-gamma (2000 U/ml). IFN-gamma produced similar effects on cytokine and NO secretion in macrophages activated with lipopolysaccharide (LPS). Therefore, it is concluded that macrophages treated with polyanions secrete cytokines and NO, and that INF-gamma is involved in the regulatory mechanism of cytokine and NO secretion.

Adenovirus-Induced Liver Pathology Is Mediated Through TNF Receptors I and II but Is Independent of TNF or Lymphotoxin

Mice infected with an adenovirus mutant in which the E3 region is deleted, including TNF-resistance genes, develop fatal liver pathology within 3–4 days after infection. At least 10-fold more wild-type virus was needed to cause comparable pathology. These results indicate that the E3 region is critically involved in modulating the pathogenesis of adenovirus infection and that TNF may play a role in liver damage. To explore the latter possibility, the course of disease was examined in infected mice lacking TNFR-I and/or TNFRII, TNF only, or both TNF and lymphotoxin-α. Only mice lacking both TNFRI and TNFRII were protected from the lethal affects of the mutant adenovirus. Mice deficient in TNF or TNF and lymphotoxin-α displayed the fatal pathology. This outcome is consistent with the existence of another related ligand that binds TNFRI/II to mediate liver damage during infection with this mutant.

IFN-γ Mediates a Novel Antiviral Activity Through Dynamic Modulation of TRAIL and TRAIL Receptor Expression

TNF-related apoptosis-inducing ligand (TRAIL) is able to kill many transformed cells of diverse tissue types. We show that TRAIL is inducible by IFN-γ, by TNF-α, and by infection with human CMV, and has potent antiviral activity in vitro. CMV infection and IFN-γ also reciprocally modulate TRAIL receptor (TRAIL-R) expression. CMV infection increased the expression of TRAIL-R1 and -R2, whereas IFN-γ down-regulated the expression of TRAIL-Rs on uninfected fibroblasts. Moreover, IFN-γ significantly decreased the basal level of NF-κB activation, a known survival factor that inhibits apoptosis. Thus, TRAIL selectively kills virus-infected cells while leaving uninfected cells intact, and IFN-γ potentiates these effects by dynamic modulation of TRAIL and TRAIL-R expression and by sensitizing cells to apoptosis. The regulation of TRAIL and TRAIL-R expression may represent a general mechanism that contributes to the control of TRAIL-mediated apoptosis.

Differential Cytokine Modulation and T Cell Activation by Two Distinct Classes of Thalidomide Analogues That Are Potent Inhibitors of TNF-α

TNF-α mediates both protective and detrimental manifestations of the host immune response. Our previous work has shown thalidomide to be a relatively selective inhibitor of TNF-α production in vivo and in vitro. Additionally, we have recently reported that thalidomide exerts a costimulatory effect on T cell responses. To develop thalidomide analogues with increased anti-TNF-α activity and reduced or absent toxicities, novel TNF-α inhibitors were designed and synthesized. When a selected group of these compounds was examined for their immunomodulatory activities, different patterns of cytokine modulation were revealed. The tested compounds segregated into two distinct classes: one class of compounds, shown to be potent phosphodiesterase 4 inhibitors, inhibited TNF-α production, increased IL-10 production by LPS-induced PBMC, and had little effect on T cell activation; the other class of compounds, similar to thalidomide, were not phosphodiesterase 4 inhibitors and markedly stimulated T cell proliferation and IL-2 and IFN-γ production. These compounds inhibited TNF-α, IL-1β, and IL-6 and greatly increased IL-10 production by LPS-induced PBMC. Similar to thalidomide, the effect of these agents on IL-12 production was dichotomous; IL-12 was inhibited when PBMC were stimulated with LPS but increased when cells were stimulated by cross-linking the TCR. The latter effect was associated with increased T cell CD40 ligand expression. The distinct immunomodulatory activities of these classes of thalidomide analogues may potentially allow them to be used in the clinic for the treatment of different immunopathological disorders.

Role of the individual interferon systems and specific immunity in mice in controlling systemic dissemination of attenuated pseudorabies virus infection

The importance of each of the two interferon (IFN) systems in impeding herpesvirus replication and in stimulating virus-specific lymphocytes to control an acute systemic infection is not completely understood. To further our knowledge, pseudorabies virus, attenuated by deletion of the glycoprotein E gene to impair its neurovirulence and by deletion of the thymidine kinase gene (gE-TK-PRV), was used to infect wild-type 129Sv/Ev and congenic mice with immune system-associated genetic deficiencies. Mice with mature B and T lymphocytes but lacking either one or both functional receptors for members of each of the two IFN families were infected with gE-TK-PRV. At 3 and 7 but not 14 days after infection, replicating gE-TK-PRV could be isolated only from livers or spleens of mice lacking the receptors for both IFN families, and these mice survived the infection. Therefore, functional IFN receptors were not required to induce a protective immune response against an acute infection with gE-TK-PRV. Furthermore, PRV-specific antibodies of all immunoglobulin G isotypes were produced in these mice. Mice without mature B and T lymphocytes and lacking either one or both functional receptors for members of each of the two IFN families were also infected with gE-TK-PRV. Three days after infection, replicating virus could be isolated only from mice lacking both mature B and T lymphocytes and functional IFN receptors, and these mice were not able to clear the virus. We present evidence that mice with an intact gamma IFN system but without mature B and T cells were able to prevent systemic dissemination of gE-TK-PRV.

Qualitative and Quantitative Requirements for CD4+ T Cell-Mediated Antiviral Protection

CD4+ Th cells deliver the cognate and cytokine signals that promote the production of protective virus-neutralizing IgG by specific B cells and are also able to mediate direct antiviral effector functions. To quantitatively and qualitatively analyze the antiviral functions of CD4+ Th cells, we generated transgenic mice (tg7) expressing an MHC class II (I-Ab)-restricted TCR specific for a peptide derived from the glycoprotein (G) of vesicular stomatitis virus (VSV). The elevated precursor frequency of naive VSV-specific Th cells in tg7 mice led to a markedly accelerated and enhanced class switching to virus-neutralizing IgG after immunization with inactivated VSV. Furthermore, in contrast to nontransgenic controls, tg7 mice rapidly cleared a recombinant vaccinia virus expressing the VSV-G (Vacc-IND-G) from peripheral organs. By adoptive transfer of naive tg7 CD4+ T cells into T cell-deficient recipients, we found that 105 transferred CD4+ T cells were sufficient to induce isotype switching after challenge with a suboptimal dose of inactivated VSV. In contrast, naive transgenic CD4+ T cells were unable to adoptively confer protection against peripheral infection with Vacc-IND-G. However, tg7 CD4+ T cells that had been primed in vitro with VSV-G peptide were able to adoptively transfer protection against Vacc-IND-G. These results demonstrate that the antiviral properties of CD4+ T cells are governed by the differentiation status of the CD4+ T cell and by the type of effector response required for virus elimination.

Lymphocytes delay kinetics of HSV-1 reactivation from in vitro explants of latent infected trigeminal ganglia

A persistent immune response to herpes simplex virus type 1 (HSV-1) is evidenced by the expression of cytokine transcripts along with infiltrating mononuclear cells in the ganglia of latently infected mice. In trigeminal ganglion (TG) explant co-cultures, the presence of nonirradiated or irradiated primed splenocytes significantly reduced HSV-1 reactivation as defined by secreted infectious HSV-1 found in the supernatants of TG explant cultures. Primed splenocytes depleted of CD4+ or CD8+ cells did not antagonize HSV-1 reactivation. Cytokines including interleukin (IL)-2, IL-6, IL-10, and IL-12 were all detected in the TG explant cultures containing splenocytes. To further study the role of cytokines in HSV-1 reactivation, dissociated TG cell cultures were treated with exogenous recombinant cytokines including IFN-alpha or -gamma, IL-4, 6, 10, 12 or tumor necrosis factor (TNF)-alpha at concentrations ranging from 2.0 pg to 2.0 ng/culture (or 0.3-300 units/culture for the IFNs). While no cytokines tested at any concentration significantly modified HSV-1 reactivation, neutralizing antibody to IL-6, but not to IFN-alpha/beta, significantly antagonized HSV-1 reactivation. Collectively, the results suggest that IL-6 is directly or indirectly involved in HSV-1 reactivation in TG explant cultures.

Subversion of cytokine networks by viruses

Viruses and the immune system have been competitors throughout their co-evolution. It is therefore not surprising that the viruses in circulation today possess a variety of strategies to counteract those aspects of the immune system that are involved in virus clearance. Examination of these virus encoded functions provides an important view of immune function and an appreciation of the complexity of the virus-host interaction. It is clear that viruses, seeking to subvert the immune system, have become adept in blocking the communication channels of the immune system. There are numerous examples of viral proteins that target the cytokine networks, disrupting the processes by which the delicately balanced immune system is regulated. This review focuses on the gene products of poxviruses, adenoviruses and herpesviruses that function primarily as immune-modulators.

Exercise effects on IFN-beta expression and viral replication in lung macrophages after HSV-1 infection

Mice exercised to fatigue and exposed to herpes simplex virus type 1 (HSV-1) exhibit greater mortality than control mice. In this study, we examined lung macrophage resistance to HSV-1 after exercise in terms of both viral replication and interferon (IFN)-beta production. We utilized the reverse transcriptase-rapid polymerase chain reaction to measure the IFN-beta mRNA content in alveolar macrophages. IFN release was measured with a bioassay, and viral replication within the macrophage was assessed by plaque titration. Exercised (Ex) mice ran on a treadmill until fatigue while control (Con) mice remained in lanes above the treadmill. After exercise, alveolar macrophages were removed and incubated with HSV-1. Alveolar macrophage IFN-beta mRNA was greater in Ex than in Con mice. Culture supernatant from infected macrophages showed a higher degree of IFN release and a higher number of infectious viral particles in Ex vs. Con mice. It is likely that the increase in IFN-beta mRNA occurs in response to a higher degree of viral replication. These results suggest that macrophages from Ex mice are less resistant to infection with HSV-1.

Production of key molecules by ocular neutrophils early after herpetic infection of the cornea

Herpes simplex virus infection of the eye can result in a blinding inflammatory lesion that is a T cell mediated immunopathological reaction. A prominent early event following HSV infection is neutrophil invasion of the corneal stroma. These cells may be involved in viral clearance and may influence the nature of the anti HSV T cell response which subsequently occurs. This article measures the expression of some key molecules which could participate in viral clearance and immune modulation. Using RT-PCR and in-situ hybridization, both corneal and peritoneal neutrophils were shown to be sources of iNOS and TNF alpha molecules which likely contribute to antiviral activity. Neutrophils also produce the cytokine IL-12, a key molecule which modulates the CD4+ T cell response to a type which mediates immunopathology. The present results indicate that neutrophils play an important role in the pathogenesis of herpetic ocular lesions.

A bioassay for serum interferon based on induction of 2'5'-oligoadenylate synthetase activity

We have developed a bioassay for interferons (IFN) based on measuring the amounts of 2',5' oligoadenylate synthetase (2-5AS) induced in cells of the THP-1 monocyte line in response to IFN. The assay can be completed in 20 h, gives reproducible results, and is at least 50 times more sensitive to IFN-alpha than conventional cytopathic effect inhibition antiviral assays. It is, respectively, less and much less sensitive to IFN-beta and IFN-gamma. The presence of preexisting 2-5AS activity in a sample does not influence the results. We have used this assay to measure very low levels (0.1-0.5 IU/ml) of endogenously formed IFN-alpha in serum samples from patients with various diseases and also to measure the residual small amounts of IFN-alpha still present in the serum as late as 48 h after an i.m. injection of 3 million IU, which is appreciably later than in previous methods. Thus, our highly sensitive assay offers considerable advantages, not least in relation to the clinical use of IFN.

Mechanisms of viral clearance in perforin-deficient mice

The roles of CD4+ T cells, IFN-gamma and TNF-alpha in viral clearance from the central nervous system (CNS) were examined in perforin gene deficient (PKO) mice. Depletion of CD4+ T cells from the PKO mice resulted in a significant 1 log10 PFU/gm increase in viral titer over control-treated PKO mice. PKO mice treated with anti-IFN-gamma mAb also had a significant 1 log10 increase in infectious virus whereas inhibition of TNF-alpha did not alter viral clearance or clinical disease in the PKO mice. These data suggest, in addition to perforin-mediated cytolysis, CD4+ T cells and IFN-gamma, but not TNF-alpha could contribute to JHMV clearance from the CNS.

Myasthenia gravis and tumor necrosis factor beta polymorphisms: linkage disequilibrium but no association beyond HLA-B8

Tumor necrosis factor (TNF) may contribute to the susceptibility for autoimmune diseases. We examined TNFbeta gene polymorphisms detected by AspHI and NcoI digestion of genomic DNA in patients with myasthenia gravis (n=105) and healthy controls (n=114). In both groups, the frequencies of TNFbeta alleles were not different. AspHI and NcoI polymorphisms of TNFbeta showed a strong association with HLA-B8 (p < 0.03 resp. p < 0.0001 for AspHI and Ncol) both in patients and controls. Our results imply linkage disequilibrium of TNFbeta alleles with HLA-B8 and in myasthenia gravis we were unable to show a stronger association beyond HLA-B8.

Increased levels of IFN-gamma in the trigeminal ganglion correlate with protection against HSV-1-induced encephalitis following subcutaneous administration with androstenediol

Androstenediol (AED) is a metabolic product of dehydroepiandrosterone (DHEA), an adrenal steroid known to possess immunomodulatory characteristics. The present study was undertaken to assess the efficacy of AED treatment in mice ocularly infected with herpes simplex virus type 1 (HSV-1). The subcutaneous administration of 320 mg/kg AED 4 h prior to viral inoculation was found to enhance the survival of HSV-1-infected mice while lower doses (32.0-100.0 mg/kg) were without effect. However, there were no apparent differences in the viral load in the eye or trigeminal ganglion (TG) 3 or 6 days post infection (p.i.) in vehicle- or AED (320 mg/kg)-treated mice. Likewise, there were no differences in the expression of cytokine or chemokine mRNAs in the eyes or TG early (i.e., 3 days p.i.) following infection. However, by 6 days p.i., there was a significant increase in the expression of the chemokines IP-10, MCP-1, and RANTES and the cytokines interleukin-6 (IL-6) and interferon-gamma (IFN-gamma) in the AED (320 mg/kg)-treated mice compared to vehicle-treated controls as determined by reverse transcription (RT)-polymerase chain reaction (PCR) and quantitative PCR (for IFN-gamma). Likewise, there was a corresponding increase in IFN-gamma and IL-2 but not IL-12 protein in the TG of AED-treated mice 6 days p.i. AED-treatment also induced a rise in splenic natural killer activity in a dose- and time-dependent fashion. Collectively, these results suggest that the protective effect following subcutaneous administration of AED is associated in a rise in selective type 1 cytokines (IL-2 and IFN-gamma) as well as natural killer activity.

Increased inducible activation of NF-kappaB and responsive genes in astrocytes deficient in the protein tyrosine phosphatase SHP-1

The protein tyrosine phosphatase SHP-1 is critical for controlling cytokine signaling through the Jak-Stat pathway and, consequently, for controlling inflammatory cellular immune responses dependent on these cytokines. However, the role of SHP-1 in regulating proinflammatory signaling may be incompletely understood, and it may control other distinct inflammatory agents. The present study analyzed the ability of tumor necrosis factor-alpha (TNF-alpha), double-stranded RNA, and interferon-gamma (IFN-gamma) to induce the transcription factor NF-kappaB in astrocytes expressing or lacking SHP-1. On exposure to the inducers, NF-kappaB was markedly increased in astrocytes obtained from motheaten mice lacking SHP-1 compared with normal littermate cells expressing SHP-1, consisted of p50 and p65 subunits, and was induced in a protein synthesis-independent manner. The increased nuclear NF-kappaB expression coincided with elevated loss of the cytoplasmic inhibitor IkappaB alpha in motheaten mouse cells. Enhanced NF-kappaB expression in motheaten mouse cells correlated with increased expression of genes with functional kappaB sites, including IFN regulatory factor-1 (IRF-1) and inducible nitric oxide synthase (iNOS) genes. MHC class I molecules were also increased in motheaten cells, consistent with the increased expression of IRF-1. Together, the data indicate an increased sensitivity of cells lacking SHP-1 to various inducers of NF-kappaB. Therefore, the regulation of not only Stats but also of NF-kappaB by SHP-1 may be important in controlling events promoted by proinflammatory agents in vivo that are especially apparent in multiple tissues of motheaten mice. This study suggests an additional role for SHP-1 in controlling specific and nonspecific immune responses where induction of NF-kappaB is involved.

Role of the Hypothalamic Pituitary Adrenal Axis and IL-6 in Stress-Induced Reactivation of Latent Herpes Simplex Virus Type 1

Hyperthermic stress induces reactivation of herpes simplex virus type 1 (HSV-1) in latently infected mice and also stimulates corticosterone release from the adrenals via activation of the hypothalamic pituitary adrenal axis. In the present study, we tested the hypothesis that stress-induced elevation of corticosterone potentiates HSV-1 reactivation in latently infected mice. Because of the putative role of IL-6 in facilitating HSV-1 reactivation in mice, the effect of hyperthermic stress and cyanoketone treatment on IL-6 expression in the trigeminal ganglion was also measured. Preadministration of cyanoketone, a glucocorticoid synthesis inhibitor, blocked the stress-induced elevation of corticosterone in a dose-dependent manner. Furthermore, inhibition of corticosterone synthesis was correlated with reduced levels of HSV-1 reactivation in latently infected mice. Hyperthermic stress elicited a transient rise in IL-6 mRNA levels in the trigeminal ganglion, but not other cytokine transcripts investigated. In addition, there was a significant reduction in MAC-3+, CD8+, and DX5+ (NK cell marker) cells in the trigeminal ganglion of latent HSV-1-infected mice 24 h after stress. Cyanoketone blocked the stress-induced rise in IL-6 mRNA and protein expression in the trigeminal ganglion latently infected with HSV-1. Collectively, the results indicate that the activation of the hypothalamic pituitary adrenal axis plays an important role in stimulating IL-6 expression and HSV-1 reactivation in the trigeminal ganglion following hyperthermic stress of mice.

Acceleration of virus-induced apoptosis by tumor necrosis factor

The multiplication of vesicular stomatitis virus in HeLa cells was inhibited by treating the cells with tumor necrosis factor (TNF). Comparison of the kinetics of virus multiplication and that of virus-induced apoptosis in the TNF-treated cells revealed that the antiviral effect of TNF is accompanied by a rapid induction of apoptosis in the cells upon infection, suggesting that TNF can inhibit virus multiplication by accelerating an apoptotic response in the infected cells.

Replication of bovine respiratory syncytial virus in bovine and ovine peripheral blood lymphocytes and monocytes and monocytic cell lines

The present study compared the replication of bovine respiratory syncytial virus (BRSV) in bovine and ovine peripheral blood mononuclear cells, ovine and bovine monocytic cell lines and ovine alveolar macrophages. Low titres of virus were detected in ovine and bovine lymphocytes and monocytes 24-96 h post-exposure to the virus but there was no apparent replication of the virus in ovine alveolar macrophages during the culture period. The virus replicated to higher but statistically insignificant titres in ovine and bovine peripheral blood monocytes than in lymphocytes, with lymphocytes yielding peak titres significantly earlier. The secondary cell lines obtained from ovine liver and bone marrow also supported the replication of BRSV to high titres. The titres of BRSV in ovine and bovine lymphocytes and monocytes were significantly lower than in secondary cell lines. The addition of human recombinant tumour necrosis factor alpha after exposure to the virus or pre-incubation of ovine or bovine monocytic cells with either human recombinant interleukin 2 or phorbol myristate acetate before exposure to BRSV, did not significantly affect virus titre. Pre-incubation of cells with indomethacin or actinomycin significantly lowered virus titre (p < 0.05).

Inhibition of hepatitis B virus replication during adenovirus and cytomegalovirus infections in transgenic mice

We have previously demonstrated that hepatitis B virus (HBV) replication and gene expression are abolished in the livers of HBV transgenic mice by cytotoxic T lymphocytes (CTLs) and during lymphocytic choriomeningitis virus (LCMV) infection, stimuli that trigger the production of alpha/beta interferon, gamma interferon, and tumor necrosis factor alpha in the liver. We now report that hepatic HBV replication and gene expression are inhibited by the local induction of these cytokines during adenovirus- and murine cytomegalovirus (MCMV)-induced hepatitis. Further, we show that MCMV also blocks HBV replication and gene expression in the proximal convoluted tubules of the kidney by causing interstitial nephritis and inducing the same cytokines in the renal parenchyma. These results suggest that inflammatory cytokines probably contribute to viral clearance during acute viral hepatitis in humans, and they imply that induction of these cytokines in the liver and other infected tissues of chronically infected patients might have therapeutic value.

Differential Susceptibility to Activation-Induced Apoptosis Among Peripheral Th1 Subsets: Correlation with Bcl-2 Expression and Consequences for AIDS Pathogenesis

It has been proposed that HIV infection is associated with an imbalance in Th1 and Th2 subsets. Recent reports indicate that Th1 and Th2 effectors differ in their susceptibility to activation-induced apoptosis. To determine whether increased T cell apoptosis in HIV-infected patients contributes to alterations in cytokine synthesis, we performed single-cell analysis of type 1 and type 2 cytokine production by CD4 and CD8 T cells, simultaneously with detection of apoptosis. We demonstrate that a differential alteration in representation of Th1 subsets, rather than commitment of T cells to secrete Th2 cytokines, occurs throughout HIV infection. A significant decrease in the number of IL-2- or TNF-α-producing T cells was observed, whereas those producing IFN-γ remained preserved. Furthermore, there is a gradient of susceptibility to activation-induced apoptosis (IL-2 &lt; IFN-γ &lt; TNF-α) among the different Th1 subsets. This gradient was detected in both CD4 and CD8 subsets, as well as in control donors and HIV-infected patients, in whom the susceptibility to apoptosis of IL-2 and IFN-γ producers was increased compared with controls. This differential intrinsic apoptosis susceptibility of Th1 effectors was found to be tightly regulated by Bcl-2 expression. In HIV-infected persons, disappearance of IL-2-producing T cells was a good indicator of disease progression and was correlated with the progressive shrinkage of the CD4+CD45RA+ T cell compartment and a gradual increased susceptibility to activation-induced apoptosis of the IL-2-producing subset. This close relationship between the CD45RA/CD45R0 ratio, the level of type 1 cytokine production, and susceptibility to apoptosis should be considered in HIV-infected patients under antiviral or immune-based therapies.

Effects of interferon-gamma and tumor necrosis factor alpha on the expression of the genes encoding aggrecan, biglycan, and decorin core proteins in cultured human chondrocytes

OBJECTIVE

To determine the effects of interferon-gamma (IFN gamma) and tumor necrosis factor alpha (TNF alpha), alone or in combination, on the expression of aggrecan, biglycan, and decorin core protein genes in human chondrocytes.

METHODS

Isolated human chondrocytes were cultured on poly(2-hydroxyethyl methacrylate)-coated plastic dishes to prevent the loss of cartilage-specific phenotype, and the effects of IFN gamma and TNF alpha, alone or in combination, on aggrecan, biglycan, and decorin core protein gene transcription and steady-state messenger RNA (mRNA) levels were examined.

RESULTS

The addition of IFN gamma (1.5 pM) or TNF alpha (0.3 pM) caused a decrease in the steady-state level of aggrecan mRNA (-25% and -15%, respectively), and the combination of these low-concentration cytokines caused a potent inhibition (-66%). These effects were the result of a decrease (-50%) in the transcription rate of the corresponding gene. At the concentrations used, IFN gamma did not alter the levels of biglycan mRNA or the transcription rates of the biglycan core protein gene. In contrast, TNF alpha decreased biglycan steady-state mRNA levels (-62%) and the biglycan core protein gene transcription rate (-18%). The combination of IFN gamma and TNF alpha resulted in a potentiation of the inhibitory effects of TNF alpha on biglycan mRNA levels (-79%) and transcription rate of the biglycan core protein gene (-46%). IFN gamma produced a modest decrease in decorin mRNA levels (-23%) and decorin core protein gene transcription rate (-17%). In contrast, TNF alpha resulted in a marked increase in decorin mRNA levels (+260%) that was not the result of transcriptional regulation. Notably, the combination of IFN gamma and TNF alpha potentiated the inhibitory effects of IFN gamma on decorin mRNA (-80%) and on the transcription of the corresponding gene (-43%). Similar results were obtained in fetal and adult articular chondrocytes.

CONCLUSION

These data demonstrate that 1) the expression of the core protein genes encoding the cartilage proteoglycans aggrecan, biglycan, and decorin is differentially regulated by IFN gamma and TNF alpha; 2) these effects are mediated by transcriptional and posttranscriptional mechanisms; and 3) the combination of the 2 cytokines causes a potent inhibitory effect on the expression of the genes for the core proteins of these 3 proteoglycans, which occurs largely at the transcriptional level. The inhibition of aggrecan, decorin, and biglycan core protein gene expression by the combination of IFN gamma and TNF alpha may contribute to the cartilage destruction that is characteristic of inflammatory joint diseases.

Herpesvirus in atherosclerosis and thrombosis: etiologic agents or ubiquitous bystanders?

The role of herpesvirus infections in the pathogenesis of vascular diseases remains an enigma. Although there is abundant circumstantial evidence of a role for herpesviruses in atherosclerosis and related processes, a cause-and-effect relationship has yet to be definitively established. This article will review the pathological, molecular, and biochemical evidence supporting the hypothesis that herpesviruses are involved in the development of atherosclerosis, restenosis after coronary angioplasty, accelerated atherosclerosis in recipients of heart transplants, and the induction of a prothrombotic phenotype in vascular endothelial cells.

Distinct pathways for tumor necrosis factor alpha and ceramides in human cytomegalovirus infection

Human cytomegalovirus (HCMV) infection can be fatal to immunocompromised individuals. We have previously reported that gamma interferon and tumor necrosis factor alpha (TNF-alpha) synergistically inhibit HCMV replication in vitro. Ceramides have been described as second messengers induced by TNF-alpha. To investigate the mechanisms involved in the inhibition of HCMV by TNF-alpha, in the present study we have analyzed ceramide production by U373 MG astrocytoma cells and the effects of TNF-alpha versus ceramides on HCMV replication. Our results show that U373 MG cells did not produce ceramides upon incubation with TNF-alpha. Moreover, long-chain ceramides induced by treatment with exogenous bacterial sphingomyelinase inhibited HCMV replication in synergy with TNF-alpha. Surprisingly, short-chain permeant C6-ceramide increased viral replication. Our results show that the anti-HCMV activity of TNF-alpha is independent of ceramides. In addition, our results suggest that TNF-alpha and endogenous long-chain ceramides use separate pathways of cell signalling to inhibit HCMV replication, while permeant C6-ceramide appears to activate a third pathway leading to an opposite effect.

A hemagglutinin-based multipeptide construct elicits enhanced protective immune response in mice against influenza A virus infection

Multipeptide constructs, comprising adjacent sequences of the 317-341 intersubunit region of immature influenza A hemagglutinin (H1N1), were designed and the functional properties of these branched peptides were compared to that of the corresponding linear peptides. In vivo studies revealed that the immunogenicity of the peptides was dependent on the presence of the hydrophobic fusion peptide (comprised in FP3), encompassing the N-terminal 1-13 sequence of the HA2 subunit. Antibody and T cell recognition, however, was directed against the 317-329 HA1 sequence, comprised in the P4 peptide. Multiple copies of P4, covalently linked by branched lysine residues, significantly enhanced the efficiency of antibody binding and the capacity of peptides to elicit B- and T-cell responses. A fraction of peptide induced antibodies reacted with immature or with proteolitically cleaved hemagglutinin (HA) molecules pretreated at low pH. Immunization with a multipeptide construct, (P4)4-FP3, not only resulted in elevated antibody and T cell responses but conferred enhanced protection against lethal A/PR/8/34 (H1N1) infection as compared to its subunit peptides. The beneficial functional properties of this artificial peptide antigen may be acquired by multiple properties including: (i) stabilized peptide conformation which promotes strong, polyvalent binding to both antibodies and MHC class II molecules; (ii) appropriate P4 conformation for antibody recognition stabilized by the covalently coupled fusion peptide, resulting in the production of virus cross reactive antibodies which inhibit the fusion activity of the virus; (iii) activation of peptide specific B cells which potentiate antigen presentation and peptide specific T cell responses; and (iv) generation of helper T cells which secrete lymphokines active in the resolution of infection.

Effects of interferon-gamma and tumor necrosis factor alpha on the expression of the genes encoding aggrecan, biglycan, and decorin core proteins in cultured human chondrocytes

OBJECTIVE

To determine the effects of interferon-gamma (IFN gamma) and tumor necrosis factor alpha (TNF alpha), alone or in combination, on the expression of aggrecan, biglycan, and decorin core protein genes in human chondrocytes.

METHODS

Isolated human chondrocytes were cultured on poly(2-hydroxyethyl methacrylate)-coated plastic dishes to prevent the loss of cartilage-specific phenotype, and the effects of IFN gamma and TNF alpha, alone or in combination, on aggrecan, biglycan, and decorin core protein gene transcription and steady-state messenger RNA (mRNA) levels were examined.

RESULTS

The addition of IFN gamma (1.5 pM) or TNF alpha (0.3 pM) caused a decrease in the steady-state level of aggrecan mRNA (-25% and -15%, respectively), and the combination of these low-concentration cytokines caused a potent inhibition (-66%). These effects were the result of a decrease (-50%) in the transcription rate of the corresponding gene. At the concentrations used, IFN gamma did not alter the levels of biglycan mRNA or the transcription rates of the biglycan core protein gene. In contrast, TNF alpha decreased biglycan steady-state mRNA levels (-62%) and the biglycan core protein gene transcription rate (-18%). The combination of IFN gamma and TNF alpha resulted in a potentiation of the inhibitory effects of TNF alpha on biglycan mRNA levels (-79%) and transcription rate of the biglycan core protein gene (-46%). IFN gamma produced a modest decrease in decorin mRNA levels (-23%) and decorin core protein gene transcription rate (-17%). In contrast, TNF alpha resulted in a marked increase in decorin mRNA levels (+260%) that was not the result of transcriptional regulation. Notably, the combination of IFN gamma and TNF alpha potentiated the inhibitory effects of IFN gamma on decorin mRNA (-80%) and on the transcription of the corresponding gene (-43%). Similar results were obtained in fetal and adult articular chondrocytes.

CONCLUSION

These data demonstrate that 1) the expression of the core protein genes encoding the cartilage proteoglycans aggrecan, biglycan, and decorin is differentially regulated by IFN gamma and TNF alpha; 2) these effects are mediated by transcriptional and posttranscriptional mechanisms; and 3) the combination of the 2 cytokines causes a potent inhibitory effect on the expression of the genes for the core proteins of these 3 proteoglycans, which occurs largely at the transcriptional level. The inhibition of aggrecan, decorin, and biglycan core protein gene expression by the combination of IFN gamma and TNF alpha may contribute to the cartilage destruction that is characteristic of inflammatory joint diseases.

Inhibition of tumor necrosis factor (TNF-alpha)-mediated apoptosis by hepatitis C virus core protein

Hepatitis C virus (HCV) putative core protein has displayed many intriguing biological properties. Since tumor necrosis factor (TNF) plays an important role in controlling viral infection, in this study the effect of the core protein was investigated on the TNF-alpha induced apoptosis of human breast carcinoma cells (MCF7). HCV core protein when expressed inhibited TNF-alpha-induced apoptotic cell death unlike the control MCF7 cells, as determined by cell viability and DNA fragmentation analysis. Additionally, HCV core protein blocked the TNF-induced proteolytic cleavage of the death substrate poly(ADP-ribose) polymerase from its native 116-kDa protein to the characteristic 85-kDa polypeptide. Results from this study suggest that the HCV core protein plays a role in the inhibition of TNF-alpha-mediated cell death. Thus, the ability of core protein to inhibit the TNF-mediated apoptotic signaling pathway may provide a selective advantage for HCV replication, allowing for evasion of host antiviral defense mechanisms.

Protective effect of passive immunization against TNF-alpha in mice infected with Sendai virus

TNF-alpha has been reported to be induced in mice infected with Sendai virus. We evaluated the role of TNF-alpha in the virus infection. TNF-alpha was induced locally in proportion to virus titers in the lung. The activity was correlated with suppression of body weight gain. Passive immunization against TNF-alpha improved body weight gain and ameliorated pneumonic lesions in infected mice, and prevented them from lethal infection, but lung virus induced emaciation, pneumonic lesions and death were mediated by TNF-alpha.