Autocrine secretion of tumor necrosis factor under the influence of interferon-gamma amplifies HLA-DR gene induction in human monocytes

Neuromodulation of innate immunity by remote ischaemic conditioning in humans: Experimental cross-over study

Experimental animal studies on the mechanisms of remote ischaemic conditioning (RIC)-induced cardioprotection against ischaemia/reperfusion injury demonstrate involvement of both neuronal and humoral pathways. Autonomic parasympathetic (vagal) pathways confer organ protection through both direct innervation and/or immunomodulation, but evidence in humans is lacking. During acute inflammation, vagal release of acetylcholine suppresses CD11b expression, a critical β2-integrin regulating neutrophil adhesion to the endothelium and transmigration to sites of injury. Here, we tested the hypothesis that RIC recruits vagal activity in humans and has an anti-inflammatory effect by reducing neutrophil CD11b expression. Participants (age:50 ​± ​19 years; 53% female) underwent ultrasound-guided injection of local anaesthetic within the brachial plexus before applying 3 ​× ​8 min cycles of brachial artery occlusion using a blood pressure cuff (RIC^block). RIC was repeated 6 weeks later without brachial plexus block. Masked analysers quantified vagal activity (heart rate, heart rate variability (HRV)) before, and 10 ​min after, the last cycle of RIC. RR-interval increased after RIC (reduced heart rate) by 40 ​ms (95% confidence intervals (95%CI):13–66; n ​= ​17 subjects; P ​= ​0.003). RR-interval did not change after brachial plexus blockade (mean difference: 20 ​ms (95%CI:-11 to 50); P ​= ​0.19). The high-frequency component of HRV was reduced after RIC^block, but remained unchanged after RIC (P ​< ​0.001), indicating that RIC preserved vagal activity. LPS-induced CD16⁺CD11b⁺ expression in whole blood (measured by flow cytometry) was reduced by RIC (3615 median fluorescence units (95%CI:475-6754); P = 0.026), compared with 2331 units (95%CI:-3921 to 8582); P = 0.726) after RIC^block.

These data suggest that in humans RIC recruits vagal cardiac and anti-inflammatory mechanisms via ischaemia/reperfusion-induced activation of sensory nerve fibres that innervate the organ undergoing RIC.

Positive Feedback Cycle of TNFα Promotes Staphylococcal Enterotoxin B-Induced THP-1 Cell Apoptosis

Staphylococcal enterotoxin B (SEB) has been demonstrated to be of importance in Staphylococcus aureus related diseases, such as atopic dermatitis (AD). Dysregulated apoptosis in AD is remarkable, and SEB can induce apoptosis of various cell types. However, the mechanisms by which SEB induces apoptosis and influences disease processes remain unclear. In this study, the recombinant SEB-induced THP-1 monocyte apoptosis was demonstrated in the absence of preliminary cell activation in a time- and dose-dependent manner. SEB could up-regulate the expression of tumor necrosis factor alpha (TNFα) in THP-1 cells and induce apoptosis via an extrinsic pathway. TNFα could in turn increase the expression of HLA-DRa, the SEB receptor on the cell surface. As a result, a positive feedback cycle of TNFα was established. TNFα expression and SEB-induced apoptosis were decreased by knocking down the expression of either HLA-DRa or TNFR1. Therefore, the feedback cycle of TNFα is crucial for SEB functions. This work provides insights into the mechanisms of SEB-induced monocyte apoptosis and emphasizes the major role of TNFα in future related studies.

Profiles of epigenetic histone post-translational modifications at type 1 diabetes susceptible genes

Both genetic and environmental factors are implicated in type 1 diabetes (T1D). Because environmental factors can trigger epigenetic changes, we hypothesized that variations in histone post-translational modifications (PTMs) at the promoter/enhancer regions of T1D susceptible genes may be associated with T1D. We therefore evaluated histone PTM variations at known T1D susceptible genes in blood cells from T1D patients versus healthy nondiabetic controls, and explored their connections to T1D. We used the chromatin immunoprecipitation-linked to microarray approach to profile key histone PTMs, including H3-lysine 4 trimethylation (H3K4me3), H3K27me3, H3K9me3, H3K9 acetylation (H3K9Ac), and H4K16Ac at genes within the T1D susceptible loci in lymphocytes, and H3K4me3, H3K9me2, H3K9Ac, and H4K16Ac at the insulin-dependent diabetes mellitus 1 region in monocytes of T1D patients and healthy controls separately. We screened for potential variations in histone PTMs using computational methods to compare datasets from T1D and controls. Interestingly, we observed marked variations in H3K9Ac levels at the upstream regions of HLA-DRB1 and HLA-DQB1 within the insulin-dependent diabetes mellitus 1 locus in T1D monocytes relative to controls. Additional experiments with THP-1 monocytes demonstrated increased expression of HLA-DRB1 and HLA-DQB1 in response to interferon-γ and TNF-α treatment that were accompanied by changes in H3K9Ac at the same promoter regions as that seen in the patient monocytes. These results suggest that the H3K9Ac status of HLA-DRB1 and HLA-DQB1, two genes highly associated with T1D, may be relevant to their regulation and transcriptional response toward external stimuli. Thus, the promoter/enhancer architecture and chromatin status of key susceptible loci could be important determinants in their functional association to T1D susceptibility.

Differential activation of alveolar and peritoneal macrophages from BCG-vaccinated guinea pigs

We compared the effect of BCG vaccination on the mRNA expression of two prototypic cytokines, IL-12 (Type 1) and IL-10 (Type 2), in guinea pig resident alveolar macrophages (AM) or resident peritoneal macrophages (PM). Cells were stimulated with live or heat-killed Mycobacterium tuberculosis, and/or with recombinant guinea pig (rgp) TNF-alpha and/or rgp IFN-gamma. AM from BCG-vaccinated guinea pigs expressed significantly less IL-10 mRNA and more IL-12p40 mRNA compared to AM from naive animals following stimulation with heat-killed mycobacteria. In PM from BCG-vaccinated guinea pigs, IL-12p40 mRNA was significantly up-regulated; however, the level of IL-10 mRNA was not affected by prior vaccination. rgp TNF-alpha or rgp IFN-gamma, both alone and together, induced a significant increase of H(2)O(2) production in PM from BCG-vaccinated animals. MHC class II expression was dramatically up-regulated in PM from BCG-vaccinated animals stimulated with both rgp TNF-alpha and rgp IFN-gamma. The levels of IL-10 and IL-12p40 mRNA were significantly enhanced in PM stimulated with combinations of rgp TNF-alpha and rgp IFN-gamma, and those cells suppressed the intracellular accumulation of viable, virulent M. tuberculosis. BCG vaccination results in the differential activation of guinea pig AM and PM to promote a Type 1 cytokine milieu and control intracellular mycobacteria.

HIV p17 reverses the anti-inflammatory activity of IL-4 on IL-15 stimulated monocytes and modulates their ability to secrete MIP-1 alpha

Monocytes play a central role in the immune system by producing and reacting to different soluble factors. Cytokine dysregulation is an hallmark in HIV-infected individuals and it is one of the most significant factors leading to impaired immunity in HIV/AIDS disease. This study investigates the possibility of modulation in the secretion of some inflammatory cytokines and chemokines induced by HIV p17 in monocytes. The results show that p17, while ineffective on resting monocytes, exerts an inflammatory action on IL-4 mediated inhibition of TNF-alpha and IFN-gamma production induced by IL-15 stimulation. In addition, p17 is able to reduce MIP-1alpha secretion, but unable to influence IL-6 production. The ability of HIV p17 to contribute to an altered pattern of secreted soluble factors might imply a key role for this viral protein in the development of AIDS pathogenesis.

Integrated measurements by flow cytometry of the cytokines IL-2, IFN-gamma, IL-12, TNF-alpha and functional evaluation of their receptors in human blood

Immunodeficiencies might be caused not only by the lack of cytokine production, but also by defective expression and/or function of the cytokine receptors. We have measured by flow cytometry, within 2 days, not only the production of IL-2, IFN-gamma, IL-12 and TNF-alpha, but also the functional expression of the receptors for these cytokines in blood samples obtained from 15 healthy donors and 13 patients suffering from tuberculosis. Cytoplasmic and surface staining with monoclonal antibodies (mAbs) was used to assess the production of cytokines and their receptors, respectively, after polyclonal stimulation. To evaluate receptor activity, peripheral blood mononuclear cells (PBMC) were first incubated with the corresponding recombinant human (rh) cytokine. CD69 was detected on lymphocytes after incubation with rhIL-2; IFN-gamma was detected in lymphocytes after co-stimulation with rhIL-12 plus PHA; iNOS induction and upregulation of major histocompatibility complex (MHC) II and MHC I was detected on monocytes after recombinant human interferon-gamma (rhIFN-gamma) stimulation; finally, COX-2 expression and MHC II upregulation were detected on monocytes after rhTNF-alpha stimulation. The assay that was developed can be used clinically to assess the activities of components of the cytokine signaling pathways of patients with immunodeficiencies or those with chronic intracellular infections such as tuberculosis.

HIV-1 matrix protein p17 increases the production of proinflammatory cytokines and counteracts IL-4 activity by binding to a cellular receptor

Purified recombinant HIV-1 p17 matrix protein significantly increased HIV-1 replication in preactivated peripheral blood mononuclear cell cultures obtained from healthy donors. Because HIV-1 infection and replication is related to cell activation and differentiation status, in the present study, we investigated the role played by p17 during the process of T cell stimulation. Using freshly isolated peripheral blood mononuclear cells, we demonstrate that p17 was able to enhance levels of tumor necrosis factor alpha and IFN-gamma released from cells stimulated by IL-2. IL-4 was found to down-regulate IFN-gamma and tumor necrosis factor alpha, and p17 restored the ability of cells to produce both cytokines. The property of p17 to increase production of proinflammatory cytokines could be a mechanism exploited by the virus to create a more suitable environment for HIV-1 infection and replication. Our data show that p17 exerts its biological activity after binding to a specific cellular receptor expressed on activated T lymphocytes. The functional p17 epitope involved in receptor binding was found to be located at the NH(2)-terminal region of viral protein. Immunization of BALB/c mice with a 14-aa synthetic peptide representative of the HIV-1 p17 functional region (SGGELDRWEKIRLR) resulted in the development of p17 neutralizing antibodies capable of blocking the interaction between p17 and its cellular receptor. Our results define a role for p17 in HIV-1 pathogenesis and contribute to our understanding of the molecular mechanism of HIV-1 infection and the development of additional antiviral therapeutic strategies.

Increased HLA-DR expression after exposure of human monocytic cells to air particulates

BACKGROUND

The expression of HLA-DR on the cell membrane of antigen-presenting cells is of major importance for the induction of an allergic response in the airways. Environmental particulates are thought to play an important role in inducing or enhancing allergic sensitization, possibly by increasing the expression of HLA-DR on the cell membrane of antigen-presenting cells. In addition, these particulates may synergize with common sensitizing agents in inducing or enhancing HLA-DR and thus antigen presentation.

OBJECTIVE

In this study, we investigated the potential of three particle types, namely carbon black, diesel exhaust particles and urban air particulates (0.1-1000 ng/cm(2)), to induce the expression of HLA-DR on differentiated THP-1 cells, taken as a model for alveolar macrophages. We also assessed the "adjuvant" potential of the particles on interferon (IFN)-gamma, a known enhancer of HLA-DR.

RESULTS

By themselves, the particles (0.1-1000 ng/cm(2)) were not able to induce HLA-DR on the THP-1 cells after an incubation of 48 h. However, even at very low concentrations, carbon black (from 1 ng/cm(2) on) and diesel exhaust particles (from 0.1 ng/cm(2) on), interacted with IFN-gamma (100 U/mL) to enhance HLA-DR expression (up to 2.5-fold increase).

CONCLUSION

This finding may reflect in vitro one of the mechanisms by which pollutant particles exert an "adjuvant" activity and may partially explain how exposure to particles can be related to the enhancement of allergic sensitization.

LPS stimulation of TNF-receptor deficient macrophages: a differential role for TNF-alpha autocrine signaling in the induction of cytokine and nitric oxide production

To evaluate the role of autocrine TNF-alpha signaling in macrophage activation, immortalized macrophages from normal mice (B6/J2) and from mice containing gene targeted disruptions of the type 1 and type 2 TNF-receptor genes (TRN) were stimulated under CD14-dependent or serum-free conditions. Although the B6/J2 and TRN clones mounted similar nitric oxide responses to LPS in the presence of serum, the TRN macrophages responded poorly when stimulated with LPS under serum free conditions. LPS stimulation of TRN and B6/J2 under serum-free conditions resulted in equivalent levels of IL-1beta, TNF-alpha, and iNOS gene expression. However, Western blot analysis revealed that iNOS protein production by TRN was 2-fold lower than that produced by B6/J2. These results indicate that autocrine TNF-alpha stimulation contributes to the signaling pathways initiated by ligation of LPS receptors in the absence of LBP and is involved in iNOS post-transcriptional regulation.

TNF-α Suppresses IFN-γ-Induced MHC Class II Expression in HT1080 Cells by Destabilizing Class II trans-Activator mRNA

Precise regulation of MHC class II gene expression is crucial for development and function of the immune system. Class II trans-activator (CIITA) has been shown to be required for constitutive and IFN-γ-induced MHC class II transcription. TNF-α is commonly coexpressed with IFN-γ during immune-mediated inflammatory responses and modulates IFN-γ-stimulated MHC class II expression. The effect of TNF-α on MHC class II expression depends on cell type and cellular differentiation state. We show here that TNF-α suppresses IFN-γ-induced CIITA mRNA accumulation, resulting in decreased MHC class II expression in human fibrosarcoma HT1080 cells. TNF-α also inhibits CIITA mRNA accumulation and protein expression in a tetracycline-regulated system without affecting promoter activity. CIITA mRNA, regulated by either IFN-γ or tetracycline, was destabilized in the presence of TNF-α, suggesting that TNF-α utilizes a distinct mechanism to suppress MHC class II expression in HT1080 cells. Consistent with this interpretation, TNF-α blocked IFN-γ-induced CIITA and MHC class II expression in mutant cells that are unresponsive to TGF-β or IFN-β. This is the first instance in which MHC class II expression is inhibited by destabilizing CIITA mRNA.

Temporal kinetics and cellular phenotype of TNF p55/p75 receptors in experimental allergic encephalomyelitis

TNF-alpha and LT-alpha are thought to be involved in the immunopathology of CNS demyelinating diseases. Both cytokines induce cellular effects through 55-kDa type-1 receptors (R1) and 75-kDa type-2 receptors (R2). To date, no study has specifically identified the various cell populations that express TNF receptors (TNFR) in the inflammatory and demyelinating mouse model, EAE. Phenotyping the TNFR positive cells is important in determining when and where the ligands may be acting and playing a role in disease pathology. We observed an upregulation of TNF R1 and R2 mRNA in high endothelial venules (HEVs) in the lymph node and CNS before the onset of EAE (preclinical phase). This upregulation of TNFR expression in HEVs was followed by a rapid increase in leukocytes within the CNS after the onset of clinical disease. The temporal kinetics of these data suggest that HEVs become activated early, probably through the release of pro-inflammatory cytokines originating from circulating leukocytes. An increase in TNFR on HEVs would make these cells more susceptible to TNF-induced changes, such as increasing cellular adhesion molecules, thereby further facilitating the trafficking of leukocytes into the CNS parenchyma.

Tumor necrosis factor induces neuroendocrine differentiation in small cell lung cancer cell lines

We studied tumor necrosis factor (TNF)-alpha as a candidate cytokine to promote neuroendocrine cell differentiation in a nitrosamine-hyperoxia hamster lung injury model. Differential screening identified expression of the genes modulated by TNF-alpha preceding neuroendocrine cell differentiation. Undifferentiated small cell lung carcinoma (SCLC) cell lines NCI-H82 and NCI-H526 were treated with TNF-alpha for up to 2 wk. Both cell lines demonstrated rapid induction of gastrin-releasing peptide (GRP) mRNA; H82 cells also expressed aromatic-L-amino acid decarboxylase mRNA within 5 min after TNF-alpha was added. Nuclear translocation of nuclear factor-kappaB immunostaining occurred with TNF-alpha treatment, suggesting nuclear factor-kappaB involvement in the induction of GRP and/or aromatic-L-amino acid decarboxylase gene expression. We also demonstrated dense core neurosecretory granules and immunostaining for proGRP and neural cell adhesion molecule in H82 cells after 7-14 days of TNF-alpha treatment. We conclude that TNF-alpha can induce phenotypic features of neuroendocrine cell differentiation in SCLC cell lines. Similar effects of TNF-alpha in vivo may contribute to the neuroendocrine cell differentiation/hyperplasia associated with many chronic inflammatory pulmonary diseases.

Glatiramer acetate blocks the activation of THP-1 cells by interferon-gamma

Glatiramer acetate (previously known as copolymer 1) is a synthetic copolymer of four amino acids that has been approved for use in the treatment of multiple sclerosis. It has been shown to suppress myelin antigen specific T cell activation by competing with these antigens at the major histocompatibility complex class II binding site and by inducing antigen specific suppressor T cells. In this study we investigated the effects of glatiramer acetate on the human monocytic cell line, THP-1, activated by lipopolysaccharide and interferon-gamma as a model for macrophages. At non-toxic concentrations of glatiramer acetate there were dose dependent reductions in the percentage of cells expressing human leukocyte DR and DQ antigen as well as in mean fluorescence intensity by flow cytometry. Production of tumor necrosis factor-alpha and the lysosomal cysteine proteinase cathepsin B were markedly inhibited, but production of interleukin-1 increased. These results suggest that glatiramer acetate might alter macrophage effector function and suggest that further studies in human monocytes and macrophages are warranted.

Modulation of topoisomerase activities by tumor necrosis factor

A number of chemotherapeutic agents which inhibit the DNA topoisomerases markedly potentiate cell death mediated by tumor necrosis factor, suggesting a role for these enzymes in the TNF cytotoxic mechanism. To investigate this possibility, topoisomerase I and II activities were assayed following TNF addition to murine L929 cells. Topoisomerase I and II activities increased within 15 min of TNF addition and returned to baseline levels within 1 and 2 hr, respectively. The increases in both topoisomerase activities were blocked by H-7 (but not H-8) and similar increases were seen following PMA addition. However, concentrations of H-7 which blocked the increased topoisomerase activities had no effect on TNF cytotoxicity nor on the enhancement of TNF cytotoxicity by topoisomerase inhibitors. Thus, in these cells topoisomerase activities are directly modified by TNF during the initial phases of a cytotoxic response. However, neither TNF cytotoxicity nor the enhancement of TNF cytotoxicity by topoisomerase inhibitors appears to require the TNF-mediated increases in topoisomerase activities.

Appraisal of potential therapeutic index of antioxidants on the basis of their in vitro effects on HIV replication in monocytes and interleukin 2-induced lymphocyte proliferation

Antioxidant molecules have been suggested to be of therapeutic value in the treatment of HIV-infected patients. To evaluate this possibility, we examined in vitro the effects of two types of antioxidant molecules in terms of inhibition of HIV replication in monocytes, one of the main reservoirs of HIV, and also in terms of modulation of the immune competence as measured by PBMC proliferation. We tested the effects of BHA, a phenolic, lipid-soluble, chain-breaking antioxidant, and NAC, a known glutathione precursor with some direct free-radical scavenging properties as well, on the regulation of HIV-1 expression in latently infected U1 cells and in productively and chronically infected U937 cells. Both antioxidants inhibited TNF- or PMA-induced NF-kappa B activity in U1 cells, as well as the sustained NF-kappa B activity permanently induced by the virus itself in chronically HIV-infected U937 cells. This resulted in only a partial inhibition of TNF- or PMA-induced HIV replication in U1 cells, and no detectable effect on HIV replication in chronically infected U937 cells. This may be the first limitation to potential antiviral effects of antioxidant therapies. Another limitation is that antioxidant concentrations high enough to block NK-kappa B activation were shown to have a suppressive effect on immune functions in vitro, because NAC and BHA blocked IL-2-induced PBMC proliferation. These data warrant prudence in the design of antioxidant-based therapies aimed at suppressing HIV replication.

Generation of nitric oxide and induction of major histocompatibility complex class II antigen in macrophages from mice lacking the interferon gamma receptor

Availability of mice with a targeted disruption of the interferon gamma (IFN-gamma) receptor gene (IFN-gamma R0/0 mice) made it possible to examine parameters of macrophage activation in the absence of a functional IFN-gamma receptor. We asked to what extent other cytokines could replace IFN-gamma in the induction of nitric oxide or major histocompatibility complex class II antigen (Ia) expression in peritoneal macrophages. In thioglycollate-elicited macrophages from wild-type mice, tumor necrosis factor (TNF) alone was virtually ineffective in inducing release of NO2- (the endproduct of nitric oxide generation), but TNF enhanced NO2- release in the presence of IFN-gamma. In macrophages from IFN-gamma R0/0 mice, which were unresponsive to IFN-gamma, TNF completely failed to stimulate NO2- release. The stimulatory actions of IFN-alpha/beta on NO2- release were indistinguishable in wild-type and IFN-gamma R0/0 macrophages: IFN-alpha/beta was ineffective on its own, showed marginal stimulation of NO2- release in combination with TNF, and was moderately effective in the presence of lipopolysaccharide. The level of constitutive Ia antigen expression was not significantly different in peritoneal macrophages from wild-type and IFN-gamma R0/0 mice. An increased Ia expression was induced by IL-4 and granulocyte-macrophage colony-stimulating factor in both wild-type and IFN-gamma R0/0 macrophages, but the magnitude of this induction was less than with optimal concentrations of IFN-gamma in macrophages from wild-type mice. IFN-alpha/beta showed only a minor stimulatory effect on Ia expression in both wild-type and IFN-gamma R0/0 macrophages. Simultaneous treatment of wild-type macrophages with IFN-alpha/beta and IFN-gamma reduced the IFN-gamma-induced Ia expression in wild-type macrophages, but IFN-alpha/beta did not show an inhibitory effect on IL-4- or granulocyte-macrophage-colony-stimulating factor-induced Ia expression in either wild-type or IFN-gamma R0/0 macrophages. The important role of IFN-gamma in the regulation of the induced expression of major histocompatibility complex class II antigen was confirmed by showing that after systemic infection with the BCG strain of Mycobacterium bovis resident peritoneal macrophages from IFN-gamma R0/0 mice had a lower level of Ia expression than macrophages from wild-type mice. The inability of other cytokines to substitute fully for IFN-gamma in macrophage activation helps to explain the earlier observed decreased resistance of IFN-gamma R0/0 mice to some infections.

Modulation of a neuronal calmodulin mRNA species in the rat brain stem by reserpine

Reserpine evokes transsynaptic impulse activity by depleting catecholaminergic neurotransmitters in the rat brain. Previous studies suggest a relationship between catecholaminergic activity and calmodulin concentration. In this report we employ Northern blot analysis to examine the effect of a single subcutaneous injection of reserpine on levels of calmodulin mRNA species which are preferentially expressed in neurons of the rat brain. Regional differences in mRNA levels were also investigated by in situ hybridization and drug-induced changes were noted particularly in specific regions of the rat brain stem. The riboprobe used in the in situ hybridization study recognized a 4.0 kilobase neuronal calmodulin mRNA species (NGB1), which was derived from the rat CaM1 gene. A calmodulin radio-immunoassay was utilized to demonstrate a drug-induced increased in calmodulin protein levels in a region which included the brain stem.

Tumor necrosis factor alpha response elements in the HLA-DRA promoter: identification of a tumor necrosis factor alpha-induced DNA-protein complex in astrocytes

The cytokine tumor necrosis factor alpha (TNF-alpha) alone does not induce class II major histocompatibility complex (MHC) expression in most primary cells but can regulate ongoing class II expression in either a positive or negative fashion. The mechanism(s) by which TNF-alpha enhances interferon gamma (IFN-gamma)-induced class II expression was examined in a primary cell type, the astrocyte, by transient transfection of the HLA-DRA promoter linked to a chloramphenicol acetyltransferase reporter gene (DRA-CAT). We show that TNF-alpha, while having no effect on its own, can synergize with IFN-gamma to increase the level of promoter activity of a DRA-CAT construct. Three known sequences--W, X, and Y--are required for TNF-alpha enhancement of IFN-gamma-induced promoter activity. The corollary effect of TNF-alpha on DNA-binding proteins specific for these elements was examined. A previous report described a DNA-binding protein, IFN-gamma-enhanced factor X (IFNEX), which is upregulated by IFN-gamma in astrocytes and is specific for the X box of the DRA promoter. In this study, we found that TNF-alpha alone did not induce any nuclear proteins; however, combined treatment of astrocytes with both IFN-gamma and TNF-alpha induced a DNA-protein complex of slower electrophoretic mobility than IFNEX. The TNF-alpha-induced complex (TIC-X) has specificity for the X element of the DRA promoter. These results suggest a mechanism by which TNF-alpha enhances IFN-gamma-induced class II MHC expression via the formation of TIC-X.

Activation pathways and human immunodeficiency virus type 1 replication are not altered in CD4+ T cells expressing the nef protein

While recent studies in Rhesus monkeys have pointed out the importance of an intact nef gene for the development of acquired immunodeficiency syndrome (AIDS), no biological function has been so far unambiguously attributed to its product. Since Nef has been described to possess GTP-binding properties and to down-regulate CD4 cell surface expression, we looked for evidences of Nef interfering with the transduction of activating signals in human CD4+ T cells. We used a murine leukemia retroviral vector to express the HIV-1BRU nef gene in two permanent tumoral T-cell lines (CEM and Jurkat) and in two nonimmortalized, interleukin-2 (IL2)-dependent, T-cell clones. The single copy recombinant provirus integrated in the genome of these cells directed the synthesis of a 27-kD protein with a half-life greater than 5 h. The levels of expression of cell surface molecules involved in T-cell functions (CD4, CD3, CD28, CD29, IL-2 receptor) were not modified in cell populations expressing Nef. In immunocompetent T-cell clones, cell proliferation and lymphokine production in response to activating stimuli (IL-2, alloantigens, phorbol esters, or antibodies directed against CD2, CD3, CD4, CD28) remained unmodified. Moreover, the presence of Nef did not change the kinetics of human immunodeficiency virus (HIV) infection.

The molecular action of tumor necrosis factor-alpha

Tumor necrosis factor-alpha (TNF-alpha) is a polypeptide hormone newly synthesized by different cell types upon stimulation with endotoxin, inflammatory mediators (C5a anaphylatoxin), or cytokines such as interleukin-1 and, in an autocrine manner, TNF itself. The net biological effect of TNF-alpha may vary depending on relative concentration, duration of cell exposure and presence of other mediators which may act in synergism with this cytokine. TNF-alpha may be relevant either in pathological events occurring in cachexia and endotoxic shock and inflammation or in beneficial processes such as host defense, immunity and tissue homeostasis. The biological effects of TNF-alpha are triggered by the binding to specific cell surface receptors. The formation of TNF-alpha-receptor complex activates a variety of biochemical pathways that include the transduction of the signal at least in part controlled by guanine-nucleotide-binding regulatory proteins (G proteins), its amplification through activation of adenyl cyclase, phospholipases and protein kinases with the generation of second messenger pathways. The transduction of selected genes in different cell types determines the characteristics of the cell response to TNF-alpha. The full understanding of the molecular mechanisms of TNF-alpha will provide the basis for a pharmacological approach intended to inhibit or potentiate selected biological actions of this cytokine.

Altered production of tumour necrosis factors alpha and beta and interferon gamma by HIV-infected individuals

In vitro studies shows that recombinant tumour necrosis factor (TNF) alpha and beta, and interferon-gamma (IFN-gamma) can enhance HIV replication, and peripheral blood mononuclear cells (PBMC) infected with HIV in vitro secrete high levels of the same cytokines. As T cells secrete all three mediators, the capacity of T cell activation signals to trigger cytokine production in PBMC from HIV-infected individuals was investigated as such patients may be immunocompromised. We demonstrate that asymptomatic seropositives in CDC group II/III as well as patients who have progressed to CDC group IV of the disease proliferate efficiently to anti-CD3 antibody, recombinant interleukin-2 (rIL-2), phytohaemagglutinin (PHA), PHA plus phorbol 12,13 dibutyrate (PMA) but secrete significantly (P less than 0.05) higher amounts of TNF-alpha, TNF-beta and IFN-gamma compared with controls in response to the same stimulants. We also show a difference between group II/III and group IV patients with the latter secreting more TNF-alpha and IFN-gamma. The kinetics of TNF-alpha and -beta, and IFN-gamma production was stimulus dependent with overall levels varying in time for each stimulus. Furthermore, the kinetics of the response to all three stimulants were altered in seropositives; CDC group II/III and group IV patients secreted higher levels of cytokines over several time points compared to controls. The altered production of these mediators by HIV-infected patients may contribute to disease progression and to the pathogenesis of AIDS.

The human leukemia cell line, THP-1: a multifacetted model for the study of monocyte-macrophage differentiation

THP-1 is a human monocytic leukemia cell line. After treatment with phorbol esters, THP-1 cells differentiate into macrophage-like cells which mimic native monocyte-derived macrophages in several respects. Compared to other human myeloid cell lines, such as HL-60, U937, KG-1, or HEL cell lines, differentiated THP-1 cells behave more like native monocyte-derived macrophages. Because of these characteristics, the THP-1 cell line provides a valuable model for studying the mechanisms involved in macrophage differentiation, and for exploring the regulation of macrophage-specific genes as they relate to physiological functions displayed by these cells.

Cytokines in chronic inflammatory arthritis. V. Mutual antagonism between interferon-gamma and tumor necrosis factor-alpha on HLA-DR expression, proliferation, collagenase production, and granulocyte macrophage colony-stimulating factor production by rheumatoid arthritis synoviocytes

The effects of a broad array of cytokines, individually and in combination, were determined on separate functions (proliferation, collagenase production, and granulocyte macrophage colony-stimulating factor [GM-CSF] production) and phenotype (expression of class II MHC antigens) of cultured fibroblast-like RA synoviocytes. The following recombinant cytokines were used: IL-1 beta, IL-2, IL-3, IL-4, IFN-gamma, tumor necrosis factor (TNF)-alpha, GM-CSF, and macrophage colony-stimulating factor (M-CSF). Only IFN-gamma induced HLA-DR (but not HLA-DQ) expression. TNF-alpha inhibited IFN-gamma-mediated HLA-DR expression (46.7 +/- 4.1% inhibition) and HLA-DR mRNA accumulation. This inhibitory effect was also observed in osteoarthritis synoviocytes. Only TNF-alpha and IL-1 increased synoviocyte proliferation (stimulation index 3.60 +/- 1.03 and 2.31 +/- 0.46, respectively). IFN-gamma (but none of the other cytokines) inhibited TNF-alpha-induced proliferation (70 +/- 14% inhibition) without affecting the activity of IL-1. Only IL-1 beta and TNF-alpha induced collagenase production (from less than 0.10 U/ml to 1.10 +/- 0.15 and 0.72 +/- 0.24, respectively). IFN-gamma decreased TNF-alpha-mediated collagenase production (69 +/- 19% inhibition) and GM-CSF production but had no effect on the action of IL-1. These data demonstrate mutual antagonism between IFN-gamma and TNF-alpha on fibroblast-like synoviocytes and suggest a novel homeostatic control mechanism that might be defective in RA where very little IFN-gamma is produced.

Regulation of the human interferon-inducible 6-16 promoter in tumor necrosis factor-sensitive and resistant mouse cells: role of cAMP as a mediator of signal transduction

The human intgerferon (IFN)-inducible 6-16 gene is also induced by tumor necrosis factor (TNF) in human and mouse cells. A reporter gene carrying the IFN regulatory sequences of the human IFN-inducible 6-16 promoter linked to the bacterial chloramphenicol acetyl-transferase gene was transfected into the adipocyte-differentiating fibroblast cell line TA1 and a TNF-resistant derivative (TA1 R-6). Both IFN and TNF induced the 6-16 reporter gene in TA1 cells. However, the induction of 6-16 by TNF was abolished by antibodies to IFNs-alpha/beta. In the TNF-resistant derivative (TA1 R6) TNF failed to induce the 6-16 plasmid construct. IFN, on the other hand, effectively induced the 6-16 promoter in TA1-R6. The block in activation of the 6-16 promoter in TNF-resistant cells can be reversed by the addition of compounds that increased the intracellular concentration of cAMP. These cAMP analogs induced IFN secretion in parental cells but not in the TA1-R6 cells.

Stimulation of a human T-cell clone with anti-CD3 or tumor necrosis factor induces NF-kappa B translocation but not human immunodeficiency virus 1 enhancer-dependent transcription

The expression of transiently transfected expression vectors under the control of the long terminal repeat (LTR) of the human immunodeficiency virus (HIV) or its enhancer sequence and the translocation of the HIV enhancer-binding protein NF-kappa B were analyzed in two human T-cell clones stimulated through their T-cell receptor complex or by tumor necrosis factor or phorbol 12-myristate 13-acetate. We found a dissociation of NF-kappa B translocation from transactivation of either the HIV LTR or the HIV enhancer. Interleukin 2 induced proliferation but not NF-kappa B translocation or LTR transactivation. Phorbol ester or specific antigen recognition induced HIV LTR transactivation, whereas stimulation with tumor necrosis factor or antibody to CD3 did not. The two latter signals were nevertheless able to induce NF-kappa B translocation with a pattern in the band-shift assay indistinguishable from that observed using phorbol ester. Our finding that induction of NF-kappa B by tumor necrosis factor or antibody to CD3 is not sufficient to induce HIV enhancer-dependent transcription in cloned T cells contrasts with results obtained in most lymphoblastoid T-cell lines and indicates that normal T lymphocytes differ from tumoral T cells in terms of requirements for HIV LTR activation. Furthermore, our results suggest that events linked to T-cell activation, in addition to NF-kappa B translocation per se, induce functional interactions of the NF-kappa B complex with the HIV enhancer.

Effects of antineoplastic phospholipids on parameters of cell differentiation in U937 cells

The proliferation of the human promonocytic leukemia cell line U937 is inhibited by several ether lipids, ether lipid analogues and by phorbol esters. An early effect of this retardation of cell growth is the induction of a basic chromosomal protein, histone H1(0). Northern blot analysis of H1(0) mRNA levels reveals an increase of the mRNA concentration within a few hours after addition of hexadecylphosphocholine and 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine. This early effect on the synthesis of a subtype of H1 proteins precedes the expression of several parameters of the monocytic differentiation of U937 cells.

Constitutive expression of human immunodeficiency virus (HIV) nef protein in human astrocytes does not influence basal or induced HIV long terminal repeat activity

Since human immunodeficiency virus (HIV) nef has been suggested to exert regulatory effects on HIV long terminal repeat (LTR) activity, we transiently transfected HIV LTR chloramphenicol acetyltransferase or luciferase expression vectors into a human astrocytoma clone (U-373nef) that constitutively expresses the HIV nef gene. In these cells, basal HIV LTR activity, as well as tumor necrosis factor-induced or tat-driven activity, was similar to that in control cells. Lack of any detectable effect of HIV nef on LTR activity was not the result of mutations in integrated nef DNA, as was shown by polymerase chain reaction. These data suggest that the role of nef in HIV genome transcription does not necessarily involve a direct influence on HIV LTR activity.

Treatment of cancer patients with recombinant interferon-gamma induces release of endogenous tumor necrosis factor-alpha

STUDY OBJECTIVE

1) to investigate serum levels of tumor necrosis factor-alpha in patients treated with recombinant interferon-gamma and 2) to relate changes in TNF serum levels to other biological responses observed during treatment with interferon gamma (IFN-gamma).

PATIENTS

Five patients suffering from metastasizing renal cell carcinoma.

INTERVENTION

Each patient received three treatment cycles of 10 micrograms, 100 micrograms and 500 micrograms IFN-gamma applied three times at weekly intervals. The treatment cycles were separated by a therapy free interval of two weeks. The order of dose levels was randomly assigned to each patient.

MEASUREMENTS AND MAIN RESULTS

Tumor necrosis factor alpha (TNF-alpha), IFN-gamma and neopterin serum levels, monocyte counts in the peripheral blood and body temperature were measured immediately before and 4, 24, 48, 72, and 168 h after each application of IFN-gamma. Results indicated that elevated serum levels of TNF-alpha are induced by 100 micrograms and 500 micrograms IFN-gamma. Repeated application of the same dose led to downregulation of TNF release into the serum. Changes in TNF serum levels did not correlate with the magnitude of febrile reactions, neopterin production or IFN-gamma serum levels.

Tumour necrosis factor (TNF alpha) in leishmaniasis. I. TNF alpha mediates host protection against cutaneous leishmaniasis

Genetically resistant CBA mice developed significantly larger lesions to Leishmania major infection when they were injected with rabbit anti-tumour necrosis factor (TNF)-specific antibodies compared to control mice injected with normal rabbit immunoglobulin. BALB/c mice recovered from a previous infection following prophylactic sublethal irradiation also developed exacerbated lesions when treated with the anti-TNF antibody. Injection of TNF into the lesion of infected CBA mice significantly reduced the lesion development. Furthermore, TNF activates macrophages to kill Leishmania in vitro. These data demonstrate that TNF plays an important role in mediating host-protection against cutaneous leishmaniasis.

Cytokine-mediated modulation of HLA-class II, ICAM-1, LFA-3 and tumor-associated antigen profile of melanoma cells. Comparison with anti-proliferative activity by rIL1-beta, rTNF-alpha, rIFN-gamma, rIL4 and their combinations

Nine different human melanomas and 16 clones, isolated from 2 of them, were characterized for susceptibility to rIL1-beta-, rIL4-, rTNF-alpha- and rIFN-gamma-mediated effects on proliferation and surface expression of class-II HLA (DR and DP), ICAM-1 and LFA-3 molecules and of 3 tumor-associated antigens (recognized by MAb 763.74T, 149.53 and R24). In spite of marked inter- and intra-tumor heterogeneity for susceptibility to the effects of each cytokine, the most frequent upregulation was induced on the HLA class-II antigens by rIFN-gamma and on adhesion molecules by rIFN-gamma, rTNF-alpha and rIL1-beta, while tumor-associated antigens were often down-modulated by rIFN-gamma. Tumor heterogeneity was also evident on tumor-cell proliferation with an apparent hierarchy in the frequency and extent of inhibitory effects: rIFN-gamma greater than rTNF-alpha greater than rIL1-beta = rIL4. Combinations of 2 cytokines resulted in rare and limited changes in the antigenic profile in comparison to the effects seen with single factors, while the combination of rTNF-alpha and rIFN-gamma resulted in significant synergistic antiproliferative effects on most tumor cells and clones. Taken together, these results indicate that single cytokines can profoundly affect the antigenic profile of melanoma cells, while strong tumor-growth inhibition is often achieved by combinations of 2 cytokines acting in synergism.

Tumor necrosis factor alpha functions in an autocrine manner in the induction of human immunodeficiency virus expression

Tumor necrosis factor alpha (TNF-alpha) is an immunoregulatory cytokine capable of inducing viral expression in cells chronically infected with the human immunodeficiency virus (HIV), such as the promonocytic line U1 and the T-lymphocytic line ACH-2. In the present study, we demonstrate an autocrine mechanism of TNF-alpha-mediated HIV induction. Stimulation of U1 and ACH-2 cells with phorbol 12-myristate 13-acetate (PMA) resulted in the induction of TNF-alpha mRNA and the secretion of TNF-alpha. Of note is the fact that anti-TNF-alpha antibodies significantly suppressed the expression of HIV in PMA-stimulated U1 and ACH-2 cells. Furthermore, anti-TNF-alpha antibodies also suppressed both the constitutive and inducible levels of viral expression in the chronically infected promonocytic clone U33.3. This study illustrates the interrelationship between the regulation of HIV expression and normal immunoregulatory mechanisms in that virus expression, both constitutive and induced, can be modulated by an autocrine pathway involving TNF-alpha, a cytokine involved in the complex network of regulation of the normal human immune response.

Tumor necrosis factor-alpha enhances interferon-gamma-mediated class II antigen expression on astrocytes

Astrocytes can function as antigen-presenting cells (APC) upon expression of class II antigens, which are induced by interferon-gamma (IFN-gamma). Tumor necrosis factor-alpha (TNF-alpha) can act synergistically with IFN-gamma with respect to class II expression on a variety of cells. As brain cells themselves can secrete TNF-like factors upon stimulation, we examined the effect of TNF-alpha on IFN-gamma-mediated class II induction on astrocytes. TNF-alpha alone had no effect on class II expression, but did synergize with IFN-gamma for enhanced expression of class II antigens. The specificity of TNF-alpha activity was demonstrated by blocking the amplifying effect of TNF-alpha with a polyclonal anti-TNF-alpha antibody. Kinetic analysis of the synergistic effect indicated that optimal TNF-alpha enhancement of class II expression was observed when astrocytes were pretreated with IFN-gamma 12-24 h prior to TNF-alpha addition. A possible mechanism for the synergistic action between IFN-gamma and TNF-alpha may be increased TNF-alpha receptor expression by IFN-gamma. Astrocytes treated with IFN-gamma for 24 h express more TNF-alpha receptors (3900/cell) than do untreated astrocytes (2483/cell), with no significant change in the binding affinity (Kd). These results suggest that the synergistic activity of TNF-alpha requires an inductive signal from IFN-gamma, which in part may be increased TNF-alpha receptor expression. Altogether, our observations indicate that TNF-alpha enhances ongoing class II major histocompatibility complex gene expression in rat astrocytes, which in this system is initially induced by IFN-gamma. TNF-alpha exerts its effect by binding to high affinity TNF-alpha receptors on astrocytes, whose expression is also enhanced by IFN-gamma. These two cytokines work in concert to elevate class II expression on astrocytes, an event which can contribute to initiation and/or perpetuation of intracerebral immune responses.