Transmembrane Tumor Necrosis Factor Research Articles

Opposing Functions of Microglial and Macrophagic TNFR2 in the Pathogenesis of Experimental Autoimmune Encephalomyelitis

In multiple sclerosis (MS), soluble tumor necrosis factor (TNF) is detrimental via activation of TNF receptor 1 (TNFR1), whereas transmembrane TNF is beneficial primarily by activating TNF receptor 2 (TNFR2). Here, we investigate the role of TNFR2 in microglia and monocytes/macrophages in experimental autoimmune encephalomyelitis (EAE), a model of MS, by cell-specific gene targeting. We show that TNFR2 ablation in microglia leads to early onset of EAE with increased leukocyte infiltration, Tcell activation, and demyelination in the central nervous system (CNS). Conversely, TNFR2 ablation in monocytes/macrophages results in EAE suppression with impaired peripheral Tcell activation and reduced CNS Tcell infiltration and demyelination. Our work uncovers a dichotomy of function for TNFR2 in myeloid cells, with microglial TNFR2 providing protective signals to contain disease and monocyte/macrophagic TNFR2 driving immune activation and EAE initiation. This must be taken into account when targeting TNFR2 for therapeutic purposes in neuroinflammatory diseases.

Oligodendroglial TNFR2 Mediates Membrane TNF-Dependent Repair in Experimental Autoimmune Encephalomyelitis by Promoting Oligodendrocyte Differentiation and Remyelination.

Tumor necrosis factor (TNF) is associated with the pathophysiology of various neurological disorders, including multiple sclerosis. It exists as a transmembrane form tmTNF, signaling via TNF receptor 2 (TNFR2) and TNFR1, and a soluble form, solTNF, signaling via TNFR1. Multiple sclerosis is associated with the detrimental effects of solTNF acting through TNFR1, while tmTNF promotes repair and remyelination. Here we demonstrate that oligodendroglial TNFR2 is a key mediator of tmTNF-dependent protection in experimental autoimmune encephalomyelitis (EAE). CNP-cre:TNFR2(fl/fl) mice with TNFR2 ablation in oligodendrocytes show exacerbation of the disease with increased axon and myelin pathology, reduced remyelination, and increased loss of oligodendrocyte precursor cells and mature oligodendrocytes. The clinical course of EAE is not improved by the solTNF inhibitor XPro1595 in CNP-cre:TNFR2(fl/fl) mice, indicating that for tmTNF to promote recovery TNFR2 in oligodendrocytes is required. We show that TNFR2 drives differentiation of oligodendrocyte precursor cells, but not proliferation or survival. TNFR2 ablation leads to dysregulated expression of microRNAs, among which are regulators of oligodendrocyte differentiation and inflammation, including miR-7a. Our data provide the first direct in vivo evidence that TNFR2 in oligodendrocytes is important for oligodendrocyte differentiation, thereby sustaining tmTNF-dependent repair in neuroimmune disease. Our studies identify TNFR2 in the CNS as a molecular target for the development of remyelinating agents, addressing the most pressing need in multiple sclerosis therapy nowadays. Our study, using novel TNF receptor 2 (TNFR2) conditional KO mice with selective TNFR2 ablation in oligodendrocytes, provides the first direct evidence that TNFR2 is an important signal for oligodendrocyte differentiation. Following activation by transmembrane TNF, TNFR2 initiates pathways that drive oligodendrocytes into a reparative mode contributing to remyelination following disease. This identifies TNFR2 as a new molecular target for the development of therapeutic agents in multiple sclerosis.

Inflammatory Cytokines Are Involved in Focal Demyelination in Leprosy Neuritis.

Mycobacterium leprae (ML) infection causes nerve damage that often leads to permanent loss of cutaneous sensitivity and limb deformities, but understanding of the pathogenesis of leprous neuropathy that would lead to more effective treatments is incomplete. We studied reactional leprosy patients with (n = 9) and without (n = 8) acute neuritis. Nerve conduction studies over the course of the reactional episode showed the findings of demyelination in all patients with neuritis. Evaluation of patient sera revealed no correlation of the presence of antibodies against gangliosides and the clinical demyelination. In nerve biopsies of 3 patients with neuritis, we identified tumor necrosis factor (TNF), TNF receptors, and TNF-converting enzyme in Schwann cells (SCs) using immunofluorescence. To elucidate immunopathogenetic mechanisms, we performed experiments using a human SC line. ML induced transmembrane TNF and TNF receptor 1 expression in the SCs; TNF also induced interleukin (IL)- 6 and IL-8 production by the SCs; and ML induced IL-23 secretion, indicating involvement of this previously unrecognized factor in leprosy nerve damage. These data suggest that ML may contribute to TNF-mediated inflammation and focal demyelination by rendering SCs more sensitive to TNF within the nerves of patients with leprous neuropathy.

Mechanisms behind efficacy of tumor necrosis factor inhibitors in inflammatory bowel diseases.

Biological treatment with tumor necrosis factor (TNF) inhibitors is successful in the management of inflammatory bowel disease (IBD). All TNF inhibitors antagonize the pro-inflammatory cytokine TNF-α but with varying efficacies in IBD. The variations in efficacy probably are caused by structural differences between the agents that affect their mechanisms of action and pharmacokinetic properties. Several mechanisms have been proposed, such as modulation of the expression of pro-inflammatory mediators and a reduction in the number of activated immune cells. However, it seems that clinical efficacy is the result of a number of different mechanisms and that binding of transmembrane TNF by TNF inhibitors. Knowledge of the mechanisms of action has been obtained mainly through the use of in vitro assays that may differ significantly from the situation in vivo. This review discusses the available data on TNF inhibitors in order to identify mechanisms of importance for their efficacy in IBD. Thus, a better understanding of the mechanistic basis for clinical efficacy can lead to a more rational use of TNF inhibitors in the management of IBD.

Editorial: secretion of cytokines and chemokines by innate immune cells.

Editorial: secretion of cytokines and chemokines by innate immune cells.

Inhibition of soluble TNF protects mice against brain inflammation and demyelination in a cuprizone model for multiple sclerosis

Tumor necrosis factor (TNF) mediates chronic inflammatory pathologies including those affecting the central nervous system (CNS), but non-selective TNF inhibitors exacerbate multiple sclerosis (MS) and TNF receptor SF1A is associated with MS, indicating beneficial effects of TNF in CNS pathology. In this study, we compared the effects of soluble (solTNF) and transmembrane TNF (tmTNF) in a mouse model of chronic MS induced by oral administration of the neurotoxin cuprizone (CPZ). In this model disease is compartmentalized behind an intact blood brain barrier (BBB) and monitored by widespread activation and proliferation of microglia, astrocytes and oligodendrocyte precursor cells (OPC) after 2weeks of CPZ and progressive demyelination and neurodegeneration, most obvious in the corpus callosum, with maximum lesions being observed at 5weeks of administration.

Dendritic-cell exosomes cross-present Toll-like receptor-ligands and activate bystander dendritic cells

Dendritic cells (DCs) are the major sentinel, antigen-presenting and regulatory components of the immune system. One of the central DC functions is to rapidly sense and alert host immune system of a pathogen invasion. In the present study, we investigated the role of DC exosomes (DCex) in this sentinel function. We demonstrated that DCex could bind bacterial Toll-like-receptor ligands (TLR-Ls), and acquire their ability to strongly activate bystander DCs. Consequently, bystander DCs enhance the expression of transmembrane tumor necrosis factor, secretion of proinflammatory cytokines and cross-talk with natural killer cells leading to the elevated secretion of IFNγ. These findings newly show that DCex can bind and cross-present TLR-Ls to innate-immunity effector cells, and indicate a potent mechanism to systemically alert the host immune system of pathogen invasion. They also suggest a potential novel strategy to generate effective vaccines by binding TLR-L-immune adjuvants to DCex.

Bacterial overload enhances duodenal anion secretion via PKA upregulation (1109.15)

The duodenal mucosa senses luminal bacteria via pattern recognition receptors. Rats, as coprovores, likely populate their foregut with fecal flora, which we hypothesized would enhance anion secretory responses in the duodenum.We measured short‐circuit current (Isc) in Ussing chambered muscle‐stripped mucosa‐submucosa preparations of rat duodenum. Animals were treated with a suspension of homogenized feces (Fecal, 0.1 g/kg, ig) with or without vehicle (Veh) or omeprazole treatment (OPZ, 10 mg/kg, ig) up to 7 days. Duodenal microflora were assessed by culturing duodenal mucosal scrapes on Brucella blood agar or Lactobacillus‐MRS agar plates.Basolateral application of forskolin (FK, 10 µM) increased Isc, which was further increased by the addition of carbachol (CCh, 10 µM). The Isc increase in response to FK and CCh was markedly enhanced in OPZ+Fecal group, compared to Veh group, whereas no differences were noted among Veh+Fecal, OPZ, or Veh groups. Acetazolamide‐sensitive Isc was increased in OPZ+Fecal group, consistent with enhanced HCO3‐ secretion. Expression of protein kinase A (PKA) catalytic domain a and b, and regulatory domain 1a and 2a was significantly increased in Veh+Fecal and OPZ+Fecal groups, while the expression of the cystic fibrosis transmembrane conductance regulator (CFTR), cyclooxygenase (COX)‐2 or tumor necrosis factor (TNF)‐α was not changed. OPZ treatment increased the detection frequency of lactobacillus in the duodenum, and OPZ+Fecal treatment markedly increased lactobacillus colony counts.These results suggest that increased foregut bacterial exposure enhances the anion secretory response to FK in the duodenal mucosa. Since lactobacillus is a major probiotics, upregulation of PKA by probiotics may be a novel pathway to modulate the duodenal mucosal defenses.Grant Funding Source: Supported by VA Merit Review, NIH R01 DK54221

Segmental vitiligo after infliximab use for rheumatoid arthritis - A case report

The tumor necrosis factor alpha is a cytokine related to immune and inflammatory processes by acting on different parts of the body. It is secreted by several cell types including macrophages, lymphocytes, monocytes, neutrophils, dendritic cells, among others. Infliximab is a chimeric monoclonal antibody that specifically binds to soluble and transmembrane tumor necrosis factor alpha form blocking its action. In rheumatoid arthritis it is used because the cytokines that cause inflammation in this disease are regulated by tumor necrosis factor alpha and IL-1. We report the case of a 46-year-old patient with rheumatoid arthritis who developed segmental vitiligo after two months using infliximab. The event aims to alert to the existence of this adverse effect that can be induced with the use of this medication.

Tumor Necrosis Factor–Neuropeptide Y Cross Talk Regulates Inflammation, Epithelial Barrier Functions, and Colonic Motility

Neuro-immune interactions play a significant role in regulating the severity of inflammation. Our previous work demonstrated that neuropeptide Y (NPY) is upregulated in the enteric nervous system during murine colitis and that NPY knockout mice exhibit reduced inflammation. Here, we investigated if NPY expression during inflammation is induced by tumor necrosis factor (TNF), the main proinflammatory cytokine. Using primary enteric neurons and colon explant cultures from wild type and NPY knockout (NPY(-/-)) mice, we determined if NPY knockdown modulates TNF release and epithelial permeability. Further, we assessed if NPY expression is inducible by TNF in enteric neuronal cells and mouse model of experimental colitis, using the TNF inhibitors-etanercept (blocks transmembrane and soluble TNF) and XPro1595 (blocks soluble TNF only). We found that enteric neurons express TNF receptors (TNFR1 and R2). Primary enteric neurons from NPY(-/-) mice produced less TNF compared with wild type. Further, TNF activated NPY promoter in enteric neurons through phospho-c-Jun. NPY(-/-) mice had decreased intestinal permeability. In vitro, NPY increased epithelial permeability through phosphatidyl inositol-3-kinase (PI3-K)-induced pore-forming claudin-2. TNF inhibitors attenuated NPY expression in vitro and in vivo. TNF inhibitor-treated colitic mice exhibited reduced NPY expression and inflammation, reduced oxidative stress, enhanced neuronal survival, and improved colonic motility. XPro1595 had more protective effects on neuronal survival and motility compared with etanercept. We demonstrate a novel TNF-NPY cross talk that modulates inflammation, barrier functions, and colonic motility during inflammation. It is also suggested that selective blocking of soluble TNF may be a better therapeutic option than using anti-TNF antibodies.

Anti-TNF Antibodies in Inflammatory Bowel Disease: Do We Finally Know How it Works?

Tumor necrosis factor (TNF) is a central pro-inflammatory cytokine that regulates the expression of numerous signaling pathways implicated in the progression of the immunological reaction. Unraveling the importance of TNF on the pathogenesis of inflammatory bowel disease (IBD) promoted anti-TNF antibodies as novel therapeutic agents. Initially, the main hypothesis behind the clinical application of anti-TNF antagonists in the clinic was that they exert their effects solely through neutralization of TNF. Anti-TNF antibodies induce and maintain clinical remission in patients with minimal side-effects. However, the cellular and molecular mechanisms of actions of the anti-TNF antibodies remain unknown. Various mechanisms of action have been proposed such as activation of transmembrane TNF mediated reverse signaling, induction of apoptosis, pro-inflammatory cytokine down-regulation, complement dependent cytotoxicity, antibodydependent cell-mediated cytotoxicity, and finally activation of regulatory immune cells via interactions with the Fc receptors. The observed discrepancies in the clinical efficacies as well as the differences in the structure of the various TNF antagonists nourish the investigation for additional modes of function.

AB0482 The cytotoxic effects of certolizumab pegol and golimumab mediated by transmembrane tumor necrosis factor α

BackgroundAnti-tumor necrosis factor α (anti-TNFα) agents have been successfully applied for the treatment of rheumatoid arthritis (RA), Crohn’s disease (CD) and other chronic inflammatory diseases. Not only the neutralization of...

The Cytotoxic Effects of Certolizumab Pegol and Golimumab Mediated by Transmembrane Tumor Necrosis Factor α

Anti-tumor necrosis factor α (anti-TNF-α) agents have been successfully applied for the treatment of rheumatoid arthritis, Crohn's disease, and other chronic inflammatory diseases. Not only the neutralization of soluble TNF-α but also the effect on transmembrane TNF-α is important mechanisms of action of anti-TNF-α agents. This study investigated the cytotoxic effects of new anti-TNF-α agents, certolizumab pegol and golimumab, which are mediated by transmembrane TNF-α. Transmembrane TNF-α-expressing Jurkat T cells that did not express TNF receptors were used. The binding ability of each anti-TNF-α agent to transmembrane TNF-α, antibody-dependent cell-mediated cytotoxicity, complement-dependent cytotoxicity, and the apoptotic effect were examined. Certolizumab pegol and golimumab bound to transmembrane TNF-α. Golimumab induced antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity, which was comparable to infliximab and adalimumab. However, certolizumab pegol did not induce antibody-dependent cell-mediated cytotoxicity or complement-dependent cytotoxicity. Certolizumab pegol directly induced nonapoptotic cell death in transmembrane TNF-α-expressing cells. Golimumab induced a weaker apoptotic effect than infliximab and adalimumab. The cytotoxic effects of anti-TNF-α agents on TNF-α-expressing cells are considered to be associated with the clinical effect of these agents on granulomatous diseases. The direct cytotoxic effect of certolizumab pegol on TNF-α-producing cells may contribute to its clinical efficacy in Crohn's disease. Golimumab may be less effective for granulomatous diseases.

Reactivation of M. tuberculosis Infection in Trans-Membrane Tumour Necrosis Factor Mice

Of those individuals who are infected with M. tuberculosis, 90% do not develop active disease and represents a large reservoir of M. tuberculosis with the potential for reactivation of infection. Sustained TNF expression is required for containment of persistent infection and TNF neutralization leads to tuberculosis reactivation. In this study, we investigated the contribution of soluble TNF (solTNF) and transmembrane TNF (Tm-TNF) in immune responses generated against reactivating tuberculosis. In a chemotherapy induced tuberculosis reactivation model, mice were challenged by aerosol inhalation infection with low dose M. tuberculosis for three weeks to establish infection followed chemotherapeutic treatment for six weeks, after which therapy was terminated and tuberculosis reactivation investigated. We demonstrate that complete absence of TNF results in host susceptibility to M. tuberculosis reactivation in the presence of established mycobacteria-specific adaptive immunity with mice displaying unrestricted bacilli growth and diffused granuloma structures compared to WT control mice. Interestingly, bacterial re-emergence is contained in Tm-TNF mice during the initial phases of tuberculosis reactivation, indicating that Tm-TNF sustains immune pressure as in WT mice. However, Tm-TNF mice show susceptibility to long term M. tuberculosis reactivation associated with uncontrolled influx of leukocytes in the lungs and reduced IL-12p70, IFNγ and IL-10, enlarged granuloma structures, and failure to contain mycobacterial replication relative to WT mice. In conclusion, we demonstrate that both solTNF and Tm-TNF are required for maintaining immune pressure to contain reactivating M. tuberculosis bacilli even after mycobacteria-specific immunity has been established.

Transmembrane tumour necrosis factor is neuroprotective and regulates experimental autoimmune encephalomyelitis via neuronal nuclear factor-κB

Tumour necrosis factor mediates chronic inflammatory pathologies including those affecting the central nervous system, but non-selective tumour necrosis factor inhibitors exacerbate multiple sclerosis. In addition, TNF receptor SF1A, which encodes one of the tumour necrosis factor receptors, has recently been identified as a multiple sclerosis susceptibility locus in genome-wide association studies in large patient cohorts. These clinical data have emphasized the need for a better understanding of the beneficial effects of tumour necrosis factor during central nervous system inflammation. In this study, we present evidence that the soluble and transmembrane forms of tumour necrosis factor exert opposing deleterious and beneficial effects, respectively, in a multiple sclerosis model. We compared the effects, in experimental autoimmune encephalomyelitis, of selectively inhibiting soluble tumour necrosis factor, and of both soluble and transmembrane tumour necrosis factor. Blocking the action of soluble tumour necrosis factor, but not of soluble tumour necrosis factor and transmembrane tumour necrosis factor, protected mice against the clinical symptoms of experimental autoimmune encephalomyelitis. Therapeutic benefit was independent of changes in antigen-specific immune responses and focal inflammatory spinal cord lesions, but was associated with reduced overall central nervous system immunoreactivity, increased expression of neuroprotective molecules, and was dependent upon the activity of neuronal nuclear factor-κB, a downstream mediator of neuroprotective tumour necrosis factor/tumour necrosis factor receptor signalling, because mice lacking IκB kinase β in glutamatergic neurons were not protected by soluble tumour necrosis factor blockade. Furthermore, blocking the action of soluble tumour necrosis factor, but not of soluble tumour necrosis factor and transmembrane tumour necrosis factor, protected neurons in astrocyte-neuron co-cultures against glucose deprivation, an in vitro neurodegeneration model relevant for multiple sclerosis, and this was dependent upon contact between the two cell types. Our results show that soluble tumour necrosis factor promotes central nervous system inflammation, while transmembrane tumour necrosis factor is neuroprotective, and suggest that selective inhibition of soluble tumour necrosis factor may provide a new way forward for the treatment of multiple sclerosis and possibly other inflammatory central nervous system disorders.

Inhibition of soluble tumour necrosis factor is therapeutic in experimental autoimmune encephalomyelitis and promotes axon preservation and remyelination

Tumour necrosis factor is linked to the pathophysiology of various neurodegenerative disorders including multiple sclerosis. Tumour necrosis factor exists in two biologically active forms, soluble and transmembrane. Here we show that selective inhibition of soluble tumour necrosis factor is therapeutic in experimental autoimmune encephalomyelitis. Treatment with XPro1595, a selective soluble tumour necrosis factor blocker, improves the clinical outcome, whereas non-selective inhibition of both forms of tumour necrosis factor with etanercept does not result in protection. The therapeutic effect of XPro1595 is associated with axon preservation and improved myelin compaction, paralleled by increased expression of axon-specific molecules (e.g. neurofilament-H) and reduced expression of non-phosphorylated neurofilament-H which is associated with axon damage. XPro1595-treated mice show significant remyelination accompanied by elevated expression of myelin-specific genes and increased numbers of oligodendrocyte precursors. Immunohistochemical characterization of tumour necrosis factor receptors in the spinal cord following experimental autoimmune encephalomyelitis shows tumour necrosis factor receptor 1 expression in neurons, oligodendrocytes and astrocytes, while tumour necrosis factor receptor 2 is localized in oligodendrocytes, oligodendrocyte precursors, astrocytes and macrophages/microglia. Importantly, a similar pattern of expression is found in post-mortem spinal cord of patients affected by progressive multiple sclerosis, suggesting that pharmacological modulation of tumour necrosis factor receptor signalling may represent an important target in affecting not only the course of mouse experimental autoimmune encephalomyelitis but human multiple sclerosis as well. Collectively, our data demonstrate that selective inhibition of soluble tumour necrosis factor improves recovery following experimental autoimmune encephalomyelitis, and that signalling mediated by transmembrane tumour necrosis factor is essential for axon and myelin preservation as well as remyelination, opening the possibility of a new avenue of treatment for multiple sclerosis.

Role of TNF superfamily ligands in innate immunity

Natural killer (NK) cells and dendritic cells (DCs) are essential effector cells of the innate immune system that rapidly recognize and eliminate microbial pathogens and abnormal cells, and induce and regulate adaptive immune functions. While NK cells express perforin and granzymes in the lysosomal granules and transmembrane tumor necrosis factor superfamily ligands (tmTNFSFL) on the plasma membrane, DCs express only tmTNFSFL on the plasma membrane. Perforin and granzymes are cytolytic molecules, which NK cells use to mediate a secretory/necrotic killing mechanism against rare leukemia cell targets. TNFSFL are pleiotropic transmembrane molecules, which can mediate a variety of important functions such as apoptosis, development of peripheral lymphoid tissues, inflammation and regulation of immune functions. Using tmTNFSFL, NK cells and DCs mediate a cell contact-dependent non-secretory apoptotic cytotoxic mechanism against virtually all types of cancer cells, and cross talk that leads to polarization and reciprocal stimulation and amplification of Th1 type cytokines secreted by NK cells and DCs. In this paper, we review and discuss the supporting evidence of the non-secretory, tmTNFSFL-mediated innate mechanisms of NK cells and DCs, their roles in anticancer immune defense and potential of their modulation and use in prevention and treatment of cancer.

Allergic Lung Inflammation Is Mediated by Soluble Tumor Necrosis Factor (TNF) and Attenuated by Dominant-Negative TNF Biologics

Tumor Necrosis Factor (TNF) is a pleiotropic cytokine consisting of soluble and transmembrane forms, with distinct roles in inflammation and immunity. TNF is an important factor in allergic airway inflammation. However, the disparate functions of soluble (sol) and transmembrane (tm) TNF in lung pathology are not well understood. Our aim was to assess the activities of solTNF and tmTNF in murine models of allergic airway disease, and to evaluate the efficacy of solTNF-selective inhibition. We used ovalbumin sensitization and challenge of TNF knockout, tmTNF knockin, and wild-type C57BL/6 mice to distinguish differences in airway inflammation and hyperreactivity mediated by solTNF and tmTNF. Functions of solTNF and tmTNF in hyperresponsive, wild-type Balb/c mice were assessed by comparing dominant-negative anti-TNF biologics, which antagonize solTNF yet spare tmTNF, to etanercept, a nonselective inhibitor of both TNF forms. Responses in transgenic C57BL/6 mice demonstrated that solTNF, and not tmTNF, is necessary to drive airway inflammation. In Balb/c mice, dominant-negative TNF biologics administered during immunization decreased the recruitment of eosinophils and lymphocytes into the bronchoalveolar space and lung parenchyma, reduced specific serum IgE, goblet-cell hyperplasia, and eosinophilic inflammation, and suppressed methacholine-induced airway hyperreactivity. Concentrations of IL-5, CCL5/RANTES, CCL11/eotaxin, and CCL17/TARC were also reduced in bronchoalveolar lavage. Dominant-negative TNFs reduced lung eosinophilia, even when given only during antigen challenge. The selective inhibition of soluble TNF suppresses inflammation, hyperreactivity, and remodeling in transgenic and wild-type murine models of allergic airway disease, and may offer safety advantages in therapies that preserve the immunoprotective functions of transmembrane TNF.

Virally infected and matured human dendritic cells activate natural killer cells via cooperative activity of plasma membrane-bound TNF and IL-15

AbstractRecombinant adenovirus-engineered dendritic cells (Ad.DCs) are potent immunologic adjuvants of antiviral and anticancer vaccines. The effectiveness of Ad.DC-based vaccines may depend on the ability of Ad.DCs to crosstalk with natural killer (NK) cells and to activate, polarize, and bridge innate and adaptive immunity. We investigated, for the first time, whether and how human Ad.DCs activate NK cells, and compared the Ad.DC function with that of immature DCs and matured DCs (mDCs). We found that adenovirus transduction and lipopolysaccharide/interferon-γ-induced maturation increased expression of transmembrane tumor necrosis factor (TNF) and trans-presented (trans) interleukin-15 (IL-15) on DCs, leading to enhanced NK cell activation without enhancing DC susceptibility to NK cell-mediated killing. This crosstalk enhanced NK cell CD69 expression, interferon-γ secretion, proliferation, and antitumor activities, with Ad.DCs being significantly more effective than immature DCs, but less effective than mDCs. The Ad.DC and mDC crosstalk with NK cells was largely prevented by physical separation of DCs and NK cells, and neutralization of total TNF and IL-15, but not by selective sequestration of soluble TNF. These findings demonstrate that both Ad.DCs and mDCs can efficiently promote innate immune functions by activation of NK cells through the cooperative activities of tmTNF and trans-IL-15 mediated by cell-to-cell contact.

A novel cell–cell signaling by microglial transmembrane TNFα with implications for neuropathic pain

Neuropathic pain is accompanied by neuroimmune activation in dorsal horn of spinal cord. We have observed that in animal models this activation is characterized by an increased expression of transmembrane tumor necrosis factor α (mTNFα) without the release of soluble tumor necrosis factor α (sTNFα). Herein we report that the pain-related neurotransmitter peptide substance P (SP) increases the expression of mTNFα without the release of sTNFα from primary microglial cells. We modeled this interaction using an immortalized microglial cell line; exposure of these cells to SP also resulted in the increased expression of mTNFα but without any increase in the expression of the TNF-cleaving enzyme (TACE) and no release of sTNFα. In order to evaluate the biological function of uncleaved mTNFα, we transfected COS-7 cells with a mutant full-length TNFα construct resistant to cleavage by TACE. Coculture of COS-7 cells expressing the mutant TNFα with microglial cells led to microglial cell activation indicated by increased OX42 immunoreactivity and release of macrophage chemoattractant peptide 1 (CCL2) by direct cell–cell contact. These results suggest a novel pathway through which the release of SP by primary afferents activates microglial expression of mTNFα, establishing a feed-forward loop that may contribute to the establishment of chronic pain.