Tumor necrosis factor induces a selective shedding of its p75 receptor from human neutrophils

Dermatologic Manifestations of Noninflammasome-Mediated Autoinflammatory Diseases

Autoinflammatory diseases (AIDs) arise from disturbances that alter interactions of immune cells and tissues. They give rise to prominent (auto)inflammation in the absence of aberrant autoantibodies and/or autoreactive T cells. AIDs that are predominantly caused by changes in the inflammasome pathways, such as the NLRP3- or pyrin-associated inflammasome, have gained substantial attention over the last years. However, AIDs resulting primarily from other changes in the defense system of the innate immune system are less well-studied. These noninflammasome-mediated AIDs relate to, for example, disturbance in the TNF or IFN signaling pathways or aberrations in genes affecting the IL-1RA. The spectrum of clinical signs and symptoms of these conditions is vast. Thus, recognizing early cutaneous signs constitutes an important step in differential diagnoses for dermatologists and other physicians. This review provides an overview of the pathogenesis, clinical presentation, and available treatment options highlighting dermatologic aspects of noninflammasome-mediated AIDs.

Protease inhibitors, inflammatory markers, and their association with outcome in dogs with naturally occurring acute pancreatitis

Background

Acute pancreatitis (AP) presumably is associated with pancreatic protease activation, protease inhibitor (PI) depletion, and inflammatory mediator secretion.

Objectives

Examine PIs and inflammatory mediator concentrations in dogs with AP and their association with death.

Animals

Thirty‐one dogs diagnosed with AP based on clinical signs, ultrasonographic findings, and increased canine pancreatic lipase immunoreactivity (cPLI) and 51 healthy control dogs.

Methods

Antithrombin and α₂‐antiplasmin activity (ATA and α₂AP, respectively) and concentrations of α₁‐proteinase inhibitor (α₁PI), α₂‐macroglobulin (α₂MG), C‐reactive protein (CRP), interleukins (ILs)‐2,6,8 and tumor necrosis factor‐α (TNF‐α) were prospectively measured. Severity of AP was assessed by clinical severity scoring systems.

Results

Mortality rate was 19%. Antithrombin activity was lower (P = .004) and maximal CRP, IL‐6, and TNF‐α concentrations higher (P < .04) in the AP group compared to the controls, whereas IL‐2, IL‐8, α₁PI, and α₂AP concentrations did not differ between groups. Serum α₂MG concentration was not reliably detected. Serum cPLI, CRP, and IL‐6 concentrations were significantly and positively correlated. The ATA was lower (P = .04), and canine acute pancreatitis severity (CAPS) scores higher (P = .009) in nonsurvivors compared to survivors. Higher CAPS scores were associated (P < .05) with decreased ATA and increased cPLI, CRP, and IL‐6 concentrations.

Conclusions and Clinical Importance

Systemic inflammation in dogs with AP is manifested by increased inflammatory mediator concentrations, correlating with cPLI and CRP concentrations. Hypoantithrombinemia is associated with death. Serum concentrations of α₂AP and α₁PI are less useful prognostic markers. The CAPS score is a useful prognostic marker in dogs with AP.

Post-stroke inflammation-target or tool for therapy?

Inflammation is currently considered a prime target for the development of new stroke therapies. In the acute phase of ischemic stroke, microglia are activated and then circulating immune cells invade the peri-infarct and infarct core. Resident and infiltrating cells together orchestrate the post-stroke inflammatory response, communicating with each other and the ischemic neurons, through soluble and membrane-bound signaling molecules, including cytokines. Inflammation can be both detrimental and beneficial at particular stages after a stroke. While it can contribute to expansion of the infarct, it is also responsible for infarct resolution, and influences remodeling and repair. Several pre-clinical and clinical proof-of-concept studies have suggested the effectiveness of pharmacological interventions that target inflammation post-stroke. Experimental evidence shows that targeting certain inflammatory cytokines, such as tumor necrosis factor, interleukin (IL)-1, IL-6, and IL-10, holds promise. However, as these cytokines possess non-redundant protective and immunoregulatory functions, their neutralization or augmentation carries a risk of unwanted side effects, and clinical translation is, therefore, challenging. This review summarizes the cell biology of the post-stroke inflammatory response and discusses pharmacological interventions targeting inflammation in the acute phase after a stroke that may be used alone or in combination with recanalization therapies. Development of next-generation immune therapies should ideally aim at selectively neutralizing pathogenic immune signaling, enhancing tissue preservation, promoting neurological recovery and leaving normal function intact.

Association of high levels of plasma OX40 with acute adult T-cell leukemia

OX40, a member of the tumor necrosis factor receptor (TNFR) superfamily, co-stimulates activated T cells following interaction with its own ligand OX40L. Human T-cell leukemia virus type-1 (HTLV-1) is an etiological agent of adult T-cell leukemia (ATL). ATL cells are known to express cell surface OX40; however, the level of soluble OX40 (sOX40) in blood samples from ATL patients is unknown. Quantitative enzyme-linked immune-sorbent assay (ELISA) showed that sOX40 levels were significantly higher in plasma from acute ATL patients than those from asymptomatic HTLV-1 carriers and healthy donors, and correlated with sCD25 levels and HTLV-1 proviral loads in peripheral blood mononuclear cells (PBMCs). Fresh PBMCs from acute ATL patients showed a higher percentage of OX40-positive cells compared with those from carriers, and shed sOX40 into culture supernatants. Shedding of sOX40 was partially inhibited by a matrix metalloproteinase (MMP) inhibitor, GM6001. A fraction of sOX40 was capable of binding to OX40L. These results suggest that high levels of sOX40 are shed into blood from a large number of ATL cells in acute ATL patients. Thus, abnormally elevated plasma sOX40 levels may be useful as an additional diagnostic marker of acute ATL.

Differential changes in gene expression in human neutrophils following TNF-α stimulation: Up-regulation of anti-apoptotic proteins and down-regulation of proteins involved in death receptor signaling

Responses of human neutrophils to TNF‐α are complex and multifactorial. Exposure of human neutrophils to TNF‐α in vitro primes the respiratory burst, delays apoptosis and induces the expression of several genes including chemokines, and TNF‐α itself. This study aimed to determine the impact of TNF‐α exposure on the expression of neutrophil genes and proteins that regulate apoptosis. Quantitative PCR and RNA‐Seq, identified changes in expression of several apoptosis regulating genes in response to TNF‐α exposure. Up‐regulated genes included TNF‐α itself, and several anti‐apoptotic genes, including BCL2A1, CFLAR (cFLIP) and TNFAIP3, whose mRNA levels increased above control values by between 4‐20 fold (n = 3, P < 0.05). In contrast, the expression of pro‐apoptotic genes, including CASP8, FADD and TNFRSF1A and TNFRSF1B, were significantly down‐regulated following TNF‐α treatment. These changes in mRNA levels were paralleled by decreases in protein levels of caspases 8 and 10, TRADD, FADD, TNFRSF1A and TNFRSF1B, and increased cFLIP protein levels, as detected by western blotting. These data indicate that when neutrophils are triggered by TNF‐α exposure, they undergo molecular changes in transcriptional expression to up‐regulate expression of specific anti‐apoptotic proteins and concomitantly decrease expression of specific proteins involved in death receptor signaling which will alter their function in TNF‐α rich environments.

TNFR2 increases the sensitivity of ligand-induced activation of the p38 MAPK and NF-κB pathways and signals TRAF2 protein degradation in macrophages

Tumour necrosis factor (p55 or p60) receptor (TNFR) 1 is the major receptor that activates pro-inflammatory signalling and induces gene expression in response to TNF. Consensus is lacking for the function of (p75 or p80) TNFR2 but experiments in mice have suggested neuro-, cardio- and osteo-protective and anti-inflammatory roles. It has been shown in various cell types to be specifically required for the induction of TNFR-associated factor-2 (TRAF2) degradation and activation of the alternative nuclear factor (NF)-kappaB pathway, and to contribute to the activation of mitogen-activated protein kinases (MAPK) and the classical NF-kappaB pathway. We have investigated the signalling functions of TNFR2 in primary human and murine macrophages. We find that in these cells TNF induces TRAF2 degradation, and this is blocked in TNFR2(-/-) macrophages. TRAF2 has been previously reported to be required for TNF-induced activation of p38 MAPK. However, TRAF2 degradation does not inhibit TNF-induced tolerance of p38 MAPK activation. Neither TNF, nor lipopolysaccharide treatment, induced activation of the alternative NF-kappaB pathway in macrophages. Activation by TNF of the p38 MAPK and NF-kappaB pathways was blocked in TNFR1(-/-) macrophages. In contrast, although TNFR2(-/-) macrophages displayed robust p38 MAPK activation and IkappaBα degradation at high concentrations of TNF, at lower doses the concentration dependence of signalling was weakened by an order of magnitude. Our results suggest that, in addition to inducing TRAF2 protein degradation, TNFR2 also plays a crucial auxiliary role to TNFR1 in sensitising macrophages for the ligand-induced activation of the p38 MAPK and classical NF-kappaB pro-inflammatory signalling pathways.

Sublytic concentrations of Staphylococcus aureus Panton-Valentine leukocidin alter human PMN gene expression and enhance bactericidal capacity

CA-MRSA infections are often caused by strains encoding PVL, which can cause lysis of PMNs and other myeloid cells in vitro, a function considered widely as the primary means by which PVL might contribute to disease. However, at sublytic concentrations, PVL can function as a PMN agonist. To better understand this phenomenon, we investigated the ability of PVL to alter human PMN function. PMNs exposed to PVL had enhanced capacity to produce O(2)(-) in response to fMLF, but unlike priming by LPS, this response did not require TLR signal transduction. On the other hand, there was subcellular redistribution of NADPH oxidase components in PMNs following exposure of these cells to PVL--a finding consistent with priming. Importantly, PMNs primed with PVL had an enhanced ability to bind/ingest and kill Staphylococcus aureus. Priming of PMNs with other agonists, such as IL-8 or GM-CSF, altered the ability of PVL to cause formation of pores in the plasma membranes of these cells. Microarray analysis revealed significant changes in the human PMN transcriptome following exposure to PVL, including up-regulation of molecules that regulate the inflammatory response. Consistent with the microarray data, mediators of the inflammatory response were released from PMNs after stimulation with PVL. We conclude that exposure of human PMNs to sublytic concentrations of PVL elicits a proinflammatory response that is regulated in part at the level of gene expression. We propose that PVL-mediated priming of PMNs enhances the host innate immune response.

Characterization of TNF receptor subtype expression and signaling on pulmonary endothelial cells in mice

TNF plays a crucial role in the pathogenesis of acute lung injury. However, the expression profile of its two receptors, p55 and p75, on pulmonary endothelium and their influence on TNF signaling during lung microvascular inflammation remain uncertain. Using flow cytometry, we characterized the expression profile of TNF receptors on the surface of freshly harvested pulmonary endothelial cells (PECs) from mice and found expression of both receptors with dominance of p55. To investigate the impact of stimulating individual TNF receptors, we treated wild-type and TNF receptor knockout mice with intravenous TNF and determined surface expression of adhesion molecules (E-selectin, VCAM-1, ICAM-1) on PECs by flow cytometry. TNF-induced upregulation of all adhesion molecules was substantially attenuated by absence of p55, whereas lack of p75 had a similar but smaller effect that varied between adhesion molecules. Selective blockade of individual TNF receptors by specific antibodies in wild-type primary PEC culture confirmed that the in vivo findings were due to direct effects of TNF receptor inhibition on endothelium and not other cells (e.g., circulating leukocytes). Finally, we found that PEC surface expression of p55 dramatically decreased in the early stages of endotoxemia following intravenous LPS, while no change in p75 expression was detected. These data demonstrate a crucial in vivo role of p55 and an auxiliary role of p75 in TNF-mediated adhesion molecule upregulation on PECs. It is possible that the importance of the individual receptors varies at different stages of pulmonary microvascular inflammation following changes in their relative expression.

Soluble inflammatory markers as predictors of liver histological changes in patients with chronic hepatitis C virus infection

Host immune response seems to be mainly responsible for the progression of liver disease among patients with hepatitis C virus (HCV) infection. Immune activation involves the release of cytokines and their receptors that can be measured in plasma samples. The study aimed to evaluate the association between plasma levels of chemokines and soluble tumor necrosis factor receptors (sTNFR) and liver histological changes among patients with chronic HCV infection. Seventy-one treatment-naive patients were included. Plasma levels of CCL2, CCL3, CCL11, CCL24, CXCL9, CXCL10, sTNFR1, and sTNFR2 were measured and liver histological findings were reviewed. Plasma levels of CXCL9, sTNFR1, and sTNFR2 were significantly associated with liver fibrosis, with higher median levels found among patients with moderate/severe fibrosis (F >or= 2) if compared to those with no or mild fibrosis (p = 0.014; p = 0.012; p = 0.009, respectively). Plasma sTNFR2 levels were significantly associated with necroinflammatory activity, with higher median levels among patients with moderate/severe activity (A >or= 2) if compared to those with no or mild activity (2.34 ng/mL vs. 1.99 ng/mL; p = 0.019). In conclusion, plasma levels of CXCL9, sTNFR1, and sTNFR2 were independently associated with liver histological changes, suggesting a role of TNF activation and Th1-type cell-mediated immune response in the pathogenesis of HCV infection.

Role of TNF-α in human female reproduction

TNF-α is a highly versatile cytokine, playing an important role in both apoptosis and inflammation, which is central to reproduction. It belongs to the Th1 type of cytokines. Thus, TNF-α is a proinflammatory cytokine and is involved during follicle development and ovulation, corpus luteum formation and regression and cyclic endometrium function. It has been postulated to be detrimental to the survival of the conceptus due to apoptosis of human primary villous trophoblast cells, leading to miscarriage. However, TNF-α may have a dual role in early pregnancy. Hormonally regulated uterine TNF-α in the mother is probably essential for trophoblast cell invasion, while increased production of TNF-α by maternal macrophages may facilitate labor. The current knowledge on the role of TNF-α and its receptors in the female reproduction is described in this review.

MMPs/TIMPs and inflammatory signalling de-regulation in human incisional hernia tissues

Background: Incisional hernia is a common and important complication of laparotomies. Epidemiological studies allude to an underlying biological cause, at least in a subset of population. Interest has mainly focused on abnormal collagen metabolism. However, the role played by other determinants of extracellular matrix (ECM) composition is unknown. To date, there are few laboratory studies investigating the importance of biological factors contributing to incisional hernia development. We performed a descriptive tissue-based analysis to elucidate the possible relevance of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in association with local cytokine induction in human incisional hernia tissues. The expression profiles of MMPs, TIMPs and pro-inflammatory cytokine signalling were investigated in aponeurosis and skeletal muscle specimens taken intraoperatively from incisional hernia (n= 10) and control (n= 10) patients. Semiquantitative RT-PCR, zymography and immunoblotting analyses were done. Incisional hernia samples displayed alterations in the microstructure and loss of ECM, as assessed by histological analyses. Moreover, incisional hernia tissues showed increased MMP/TIMP ratios and de-regulated inflammatory signalling (tumor necrosis factor [TNFA] and interleukin [IL]-6 tended to increase, whereas aponeurosis TNFA receptors decreased). The changes were tissue-specific and were detectable at the mRNA and/or protein level. Statistical analyses showed several associations between individual MMPs, TIMPs, interstitial collagens and inflammatory markers. The increment of MMPs in the absence of a counterbalance by TIMPs, together with an ongoing de-regulated inflammatory signalling, may contribute in inducing a functional defect of the ECM network by post-translational mechanisms, which may trigger abdominal wall tissue loss and eventual rupture. The notable TIMP3 protein down-regulation in incisional hernia fascia may be of pathophysiological significance. We conclude that this study may help to pinpoint novel hypotheses of pathogenesis that can lead to a better understanding of the disease and ultimately to improvement in current therapeutic approaches.

Shedding of epidermal growth factor receptor is a regulated process that occurs with overexpression in malignant cells

Soluble isoforms of the epidermal growth factor receptor (sEGFR) previously have been identified in the conditioned culture media (CCM) of the vulvar adenocarcinoma cell line, A431 and within exosomes of the keratinocyte cell line HaCaT. Here, we report that the extracellular domain (ECD) of EGFR is shed from the cell surface of human carcinoma cell lines that express 7x10(5) receptors/cell or more. We purified this proteolytic isoform of EGFR (PI-sEGFR) from the CCM of MDA-MB-468 breast cancer cells. The amino acid sequence of PI-sEGFR was determined by reverse-phase HPLC nano-electrospray tandem mass spectrometry of peptides generated by trypsin, chymotrypsin or GluC digestion. The PI-sEGFR protein is identical in amino acid sequence to the EGFR ECD. The release of PI-sEGFR from MDA-MB-468 cells is enhanced by phorbol 12-myristate 13-acetate, heat-inactivated fetal bovine serum, pervanadate, and EGFR ligands (i.e., EGF and TGF-alpha). In addition, 4-aminophenylmercuric acetate, an activator of metalloproteases, increased PI-sEGFR levels in the CCM of MDA-MB-468 cells. Inhibitors of metalloproteases decreased the constitutive shedding of EGFR while the PMA-induced shedding was inhibited by metalloprotease inhibitors, by the two serine protease inhibitors leupeptin and 3,4-dichloroisocoumarin (DCI), and by the aspartyl inhibitor pepstatin. These results suggest that PI-sEGFR arises by proteolytic cleavage of EGFR via a mechanism that is regulated by both PKC- and phosphorylation-dependent pathways. Our results further suggest that when proteolytic shedding of EGFR does occur, it is correlated with a highly malignant phenotype.

Circulating levels of tumor necrosis factor receptors are highly predictive of mortality in patients with rheumatoid arthritis

OBJECTIVE

To investigate whether circulating levels of soluble tumor necrosis factor receptors (sTNFR) are predictive of mortality in rheumatoid arthritis (RA).

METHODS

Levels of sTNFRI and sTNFRII at study entry were quantified using enzyme-linked immunosorbent assays in sera from 401 white patients with RA followed up for 13 years. Patients were tracked via the National Health Service Central Register, and the relationship between sTNFR levels and mortality was analyzed using a Cox proportional hazards regression model. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were calculated.

RESULTS

At the end of the followup period, 132 (32.9%) of 401 patients had died. Of these, 64 (48.5%) died of cardiovascular disease (CVD). Significant associations between all-cause mortality and baseline levels of sTNFRI and sTNFRII were identified in men (HR 1.7 [95% CI 1.2-2.4] and HR 1.18 [95% CI 1.05-1.32], respectively) and women (HR 1.33 [95% CI 0.99-1.8] and HR 1.14 [95% CI 1.02-1.28], respectively). Analysis including levels of both sTNFRI and sTNFRII indicated that the sTNFRII level was the best overall predictor of mortality. Multivariate analysis also revealed that the sTNFRII level was a predictor of all-cause and CVD mortality independently of age, sex, disease duration, C-reactive protein level, erythrocyte sedimentation rate, rheumatoid factor, nodular disease, modified Health Assessment Questionnaire score, taking CVD drugs, and smoking.

CONCLUSION

Our data indicate that serum levels of sTNFR are powerful predictors of mortality in RA. Elevated levels are particularly associated with mortality due to CVD and may be useful for identifying patients at increased risk of premature death.

The role of TNF-alpha in Trichuris muris infection I: influence of TNF-alpha receptor usage, gender and IL-13

Th1 and Th2 responses to the gut-dwelling nematode Trichuris muris have been well established in mouse models of infection, with Th2 responses clearly playing an important role in resistance. TNF-alpha has previously been shown to play an undefined role in resistance, although it is not a typical Th2 cytokine. However, the relative importance of the two TNF-alpha receptors, p55 and p75, has not previously been investigated. We demonstrate that p55 is the dominant TNF-alpha receptor during T. muris infection as p55-/- mice are more susceptible to infection than p75-/- mice. Moreover, p75 clearly plays a role in negatively regulating TNF-alpha. We also demonstrate that a gender difference influences the immune response of p55-/- and p75-/- mice in response to T. muris infection, with female mice fully expelling by day 35 post-infection (p.i.) and male mice harbouring chronic infections. Further, this gender difference can be reversed with recombinant IL-13 (rIL-13) in male gene-deficient mice or IL-13R2.Fc treatment in female gene-deficient mice.

Importance of the liver in systemic complications associated with acute pancreatitis: the role of Kupffer cells

Although its exact nature is still unknown, acute pancreatitis progresses with a local production of inflammatory mediators, eventually leading to systemic inflammatory response syndrome. Knowing that almost all pancreatic mediators released from the pancreas to the bloodstream may pass through the liver before their dilution in the systemic circulation, it would be reasonable to assume a determinant role for this organ in the development of the inflammatory response associated with acute pancreatitis. Thus, recent studies have shown the involvement of the liver in the complex network of events triggering the multiorgan dysfunction associated with the disease. Once pancreatic mediators reach the liver, they strongly activate Kupffer cells, the resident macrophages, greatly amplifying the release of cytokines into the bloodstream and thus contributing to the systemic manifestations of acute pancreatitis. Altogether, these results show that the pancreas is not the only source of mediators that trigger the deleterious effects of acute pancreatitis, but that the liver may orchestrate the final outcome of the disease. The purpose of this review is to discuss progress in understanding the function of the liver in the early stages of the development of systemic organ dysfunction secondary to acute pancreatitis.

Adenovirus RID complex enhances degradation of internalized tumour necrosis factor receptor 1 without affecting its rate of endocytosis

The receptor internalization and degradation (RID) complex of adenovirus plays an important role in modulating the immune response by downregulating the surface levels of tumour necrosis factor receptor 1 (TNFR1), thereby inhibiting NF-κB activation. Total cellular content of TNFR1 is also reduced in the presence of RID, which can be inhibited by treatment with lysosomotropic agents. In this report, surface biotinylation experiments revealed that, although RID and TNFR1 were able to form a complex on the cell surface, the rate of TNFR1 endocytosis was not affected by RID. However, the degradation of internalized TNFR1 was enhanced significantly in the presence of RID. Therefore, these data suggest that RID downregulates TNFR1 levels by altering the fate of internalized TNFR1 that becomes associated with RID at the plasma membrane, probably by promoting its sorting into endosomal/lysosomal degradation compartments.

Aminopeptidase N (CD13) Regulates Tumor Necrosis Factor-α-induced Apoptosis in Human Neutrophils

Neutrophil apoptosis plays a central role in the resolution of granulocytic inflammation. We have shown previously that tumor necrosis factor-alpha (TNFalpha) enhances the rate of neutrophil apoptosis at early time points via a mechanism involving both TNF receptor (TNFR) I and TNFRII. Here we reveal a marked but consistent variation in the magnitude of the pro-apoptotic effect of TNFalpha in neutrophils isolated from healthy donors, and we show that inhibition of cell surface aminopeptidase N (APN) using actinonin, bestatin, or inhibitory peptides significantly enhanced the efficacy of TNFalpha-induced killing. Notably, an inverse correlation is shown to exist between neutrophil APN activity and the sensitivity of donor cells to TNFalpha-induced apoptosis. Inhibition of cell surface APN appears to interfere with the shedding of TNFRI, and as a consequence results in augmented TNFalpha-induced apoptosis, cell polarization, and TNFalpha-primed, formyl-methionyl-leucyl-phenylalanine-stimulated respiratory burst. Of note, actinonin and bestatin had no effect on TNFRII expression under resting or TNFalpha-stimulated conditions and did not alter CXCRI or CXCRII expression. These data suggest significant variation in the activity of APN/CD13 on the cell surface of neutrophils in normal individuals and reveal a novel mechanism whereby APN/CD13 regulates TNFalpha-induced apoptosis via inhibition of TNFRI shedding. This has therapeutic relevance for driving neutrophil apoptosis in vivo.

Circulating TNF-alpha and its soluble receptors during experimental acute pancreatitis

Clinical and experimental studies have shown increased concentrations of TNF-alpha and its soluble receptors in serum of patients with acute pancreatitis. In this work, we have investigated the time-course of TNF-alpha and its soluble receptors during taurocholate-induced acute pancreatitis. In addition, since TNF-alpha itself could mediate the shedding of its receptors, we have assessed the effect of inhibiting TNF-alpha production on the release of soluble TNF-alpha receptors in experimental acute pancreatitis. Our results indicate that soluble receptors are released in the early stages of the disease and this increase is concomitant with the release of TNF-alpha, which is mainly bound to specific proteins. The increased concentrations of its receptors strongly suggest that they could be these binding proteins. Inhibition of TNF-alpha generation with pentoxifylline abrogated the shedding of sTNF-alphaR1, but had no effect on sTNF-alphaR2. This finding suggests that the shedding of sTNF-alphaR1 is induced by TNF-alpha itself, but in the case of sTNF-alphaR2, the shedding appears to be induced by another mechanism.

In vivo expression of inflammatory cytokine receptors in the joint compartments of patients with arthritis

To test a hypothesis of compartmentalized pathogenesis of different types of arthritis, namely inflammatory arthritis (IA) and osteoarthritis (OA), synovial and cartilage biopsies were examined for the expression of TNF and IL-1 receptors. In cartilage, we found constitutive expression of all receptors in normal tissues, and decreased expression of signal-transducing receptors in pathological chondrocytes. In synovium, there was a lower expression of signal-transducing receptors in cases of OA compared to those of IA. In OA, the three signal-transducing receptors were more abundantly expressed in cartilage, while in IA they were mainly present in synovial tissue (TNFRp75 being expressed more than p55). IL-1 decoy receptor type II was low or absent in synovial tissues, but present in cartilage. The increased expression of TNFRp75 and IL-1RI in OA cartilage, compared to IA, in addition to the abundant local cytokine production, strengthens the hypothesis of autocrine/paracrine action by inflammatory cytokines in the pathogenesis of cartilage damage.

TIMP-3 deficiency leads to dilated cardiomyopathy

BACKGROUND

Despite the mounting clinical burden of heart failure, the biomolecules that control myocardial tissue remodeling are poorly understood. TIMP-3 is an endogenous inhibitor of matrix metalloproteinases (MMPs) that has been found to be deficient in failing human myocardium. We hypothesized that TIMP-3 expression prevents maladaptive tissue remodeling in the heart, and accordingly, its deficiency in mice would alone be sufficient to trigger progressive cardiac remodeling and dysfunction similar to human heart failure.

METHODS AND RESULTS

Mice with a targeted timp-3 deficiency were evaluated with aging and compared with age-matched wild-type littermates. Loss of timp-3 function triggered spontaneous LV dilatation, cardiomyocyte hypertrophy, and contractile dysfunction at 21 months of age consistent with human dilated cardiomyopathy. Its absence also resulted in interstitial matrix disruption with elevated MMP-9 activity, and activation of the proinflammatory tumor necrosis factor-alpha cytokine system, molecular hallmarks of human myocardial remodeling.

CONCLUSIONS

TIMP-3 deficiency disrupts matrix homeostasis and the balance of inflammatory mediators, eliciting the transition to cardiac dilation and dysfunction. Therapeutic restoration of myocardial TIMP-3 may provide a novel approach to limit cardiac remodeling and the progression to failure in patients with dilated cardiomyopathy.

The ectodomain shedding of CD30 is specifically regulated by peptide motifs in its cysteine-rich domains 2 and 5

Tumor necrosis factor (TNF)-alpha converting enzyme (TACE) is responsible for the ectodomain release of various membrane proteins by proteolytic cleavage in close proximity to the cell membrane. Despite the wide spectrum of possible substrates, selective cleavage can be achieved by substrate cross-linking. To explore the underlying mechanism, we studied the TACE-mediated shedding of CD30. Whereas the constitutive release of the soluble ectodomain of CD30 (sCD30) from the lymphoma cell line Karpas 299 was enhanced by most anti-CD30 antibodies, it was inhibited by antibodies Ber-H2 and Ki-4. On the basis of the recognized epitopes, shedding seemed to depend on the availability of the cysteine-rich domains (CRD) 2 and 5 of the CD30 ectodomain. CRD2 and 5 have almost identical amino acid sequences and are localized distant from the TACE-targeted cleavage site. Soluble CD30, the product of this enzyme reaction, did not inhibit, but on the contrary, it stimulated CD30 shedding in a CRD2/5-dependent manner. This process could also be induced by CRD2/5-derived peptides but not by a CRD1-derived control peptide. This example of a product-activation was CD30 selective since other TACE substrates such as TNFR1 or TNF-alpha were not affected. These data suggest that CD30 shedding is stimulated by an elevated local availability of CRD2 or 5, possibly by forming a docking station for the releasing enzyme through substrate aggregation.

Tumor necrosis factor-alpha promotes macrophage-induced vascular smooth muscle cell apoptosis by direct and autocrine mechanisms

OBJECTIVE

We have previously shown that human macrophages induce human plaque vascular smooth muscle cell (VSMC) apoptosis by cell-cell proximity, Fas-L, and nitric oxide (NO), thereby predisposing to plaque rupture. This study sought to analyze whether tumor necrosis factor-alpha (TNF-alpha) contributes additionally to macrophage-induced VSMC apoptosis.

METHODS AND RESULTS

Macrophage-induced VSMC apoptosis was examined in direct coculture. Antagonistic antibodies to TNF-receptor (R1) inhibited VSMC apoptosis, and preincubation of monocytes and VSMCs indicated that TNF-R1 on both cell types contributed to macrophage-induced VSMC apoptosis. Correspondingly, both monocytes and VSMCs expressed TNF-R1, and macrophages expressed cell surface TNF-alpha. Two NO donors upregulated VSMC surface TNF-R1, and exogenous TNF-alpha induced VSMC apoptosis synergistically with the NO donor diethylenetriamine/NO, indicating that NO sensitizes VSMCs to TNF-alpha. Neutralizing anti-TNF-R1 antibodies inhibited macrophage activation assessed by Fas-L expression and NO secretion.

CONCLUSIONS

TNF-alpha promotes macrophage-induced VSMC apoptosis by autocrine and direct pathways.

Tumor necrosis factor regulates intestinal epithelial cell migration by receptor-dependent mechanisms

Altered mucosal integrity and increased cytokine production, including tumor necrosis factor (TNF), are the hallmarks of inflammatory bowel disease (IBD). In this study, we addressed the role of TNF receptors (TNFR) on intestinal epithelial cell migration in an in vitro wound closure model. With mouse TNFR1 or TNFR2 knockout intestinal epithelial cells, gene transfection, and pharmacological inhibitors, we show a concentration-dependent receptor-mediated regulation of intestinal cell migration by TNF. A physiological TNF level (1 ng/ml) enhances migration through TNFR2, whereas a pathological level (100 ng/ml) inhibits wound closure through TNFR1. Increased rate of wound closure by TNFR2 or inhibition by TNFR1 cannot be explained by either increased proliferation or apoptosis, respectively. Furthermore, inhibiting Src tyrosine kinase decreases TNF-induced focal adhesion kinase (FAK) tyrosine phosphorylation and cellular migration. We therefore conclude that TNFR2 activates a novel Src-regulated pathway involving FAK tyrosine phosphorylation that enhances migration of intestinal epithelial cells.

Signaling to gene activation and cell death by tumor necrosis factor receptors and Fas

Tumor necrosis factor (TNF) receptors and Fas elicit a wide range of biological responses, including cell death, cell proliferation, inflammation, and differentiation. The pleiotropic character of these receptors is reflected at the level of signal transduction. The cytotoxic effects of TNF and Fas result from the activation of an apoptotic/necrotic program. On the other hand, TNF receptors, and under certain conditions also Fas, exert a proinflammatory function that results from the induction of several genes. In this context, the transcription factor nuclear factor-kappa B (NF-kappaB) plays an important role. NF-kappaB is also important for the induction of several antiapoptotic genes, which explains at least partially why several cell types can only be killed by TNF in the presence of transcription or translation inhibitors. It is the balance between proapoptotic and antiapoptotic pathways that determines whether a cell will finally die or proliferate. A third signal transduction pathway that is activated in response to TNF is the mitogen-activated protein kinase cascade, which plays an important role in the modulation of transcriptional gene activation.

Pharmacological analysis for mechanisms of GPI-80 release from tumour necrosis factor-alpha-stimulated human neutrophils

1 GPI-80, a glycosylphosphatidylinositol (GPI)-anchored protein initially identified on human neutrophils, plays a role(s) in the regulation of beta2 integrin function. Previous studies have shown that GPI-80 is sublocated in secretory vesicles. It is also found in soluble form in the synovial fluid of rheumatoid arthritis patients, and in the culture supernatant of formyl-methionyl-leucyl-phenylalanine-stimulated neutrophils. To understand the behaviour of GPI-80 under conditions of stimulation, we investigated the effects of tumour necrosis factor (TNF)-alpha on its expression and release. We also probed the mechanism of its release with various pharmacologic tools. 2 TNF-alpha induced the release of GPI-80 from human neutrophils in a concentration- and time-dependent manner (in the range of 1-100 u ml(-1) and 30-120 min, respectively), but did not affect surface GPI-80 levels. 3 Cytochalasin B, genistein, and SB203580 but not PD98059 inhibited TNF-alpha-stimulated GPI-80 release and neutrophil adherence at the same concentration. In addition, TNF-alpha-induced GPI-80 release was inhibited by blocking monoclonal antibodies specific to components of Mac-1 (CD11b and CD18). 4 Antioxidants (pyrrolidine dithiocarbamate and N-acetyl-L-cysteine) inhibited GPI-80 release by TNF-alpha stimulation, but superoxide dismutase did not. Antioxidants but not superoxide dismutase reduced an intracellular oxidation state. 5 These findings indicate that TNF-alpha-stimulated GPI-80 release from human neutrophils depends upon adherence via beta2 integrins. They also suggest that cytochalasin B, genistein, and SB203580 inhibit GPI-80 release by suppressing signals for cell adherence, rather than by a direct effect on its secretion. Finally, we suggest that GPI-80 release involves an intracellular change in a redox state.

Exercise training increases membrane bound form of tumor necrosis factor-alpha receptors with decreases in the secretion of soluble forms of receptors in rat adipocytes

We examined the effects of exercise training (treadmill running over 9 weeks) on the ability of isolated adipocytes to secrete tumor necrosis factor-alpha (TNF-alpha) and type 1 soluble TNF receptor (sTNFR1) in vitro in Wistar rats. We also examined the effects of exercise training on the expression of membrane bound forms of type 1 TNF receptor (mTNFR1) in adipocyte crude membranes of the same rat subjects. Exercise training significantly increased the secretions of TNF-alpha from isolated adipocytes. Treatment with a cyclooxygenase inhibitor, either indomethacin (100 microM) or eicosatetraynoic acid (100 microM), significantly blocked the release of TNF-alpha from adipocytes in both exercise-trained rat group and sedentary control rat group, suggesting that some cyclooxygenase metabolite(s) acts as a ligand in TNF-alpha synthesis. Decreased amounts of TNF-alpha were found to be significantly greater in both exercise-trained rat group than in sedentary control rat group after incubation with inhibitors. Thus, the inhibitory effect of both indomethacin and eicosatetraynoic acid was significantly greater in adipocytes from exercise-trained rats. Both plasma sTNFR1 levels and adipocytes-derived sTNFR1 were found to be significantly less in the exercise-trained rat group. Western blot analysis revealed that exercise training remarkably increased the expressions of mTNFR1 in adipocyte crude membrane. Thus, exercise training enhanced the ability of isolated adipocytes to secrete TNF-alpha with reduced secretion of sTNFR1, and provoked the greater expressions of mTNFR1 in adipocyte crude membrane. These alterations may induce enhanced the autocrine effects of TNF-alpha within adipocytes in exercise-trained rats.

TNF receptor subtype signalling: differences and cellular consequences

Tumour necrosis factor-alpha (TNF alpha) is a multifunctional cytokine belonging to a family of ligands with an associated family of receptor proteins. The pleiotropic actions of TNF range from proliferative responses such as cell growth and differentiation, to inflammatory effects and the mediation of immune responses, to destructive cellular outcomes such as apoptotic and necrotic cell death mechanisms. Activated TNF receptors mediate the association of distinct adaptor proteins that regulate a variety of signalling processes including kinase or phosphatase activation, lipase stimulation, and protease induction. Moreover, the cytokine regulates the activities of transcription factors, heterotrimeric or monomeric G-proteins and calcium ion homeostasis in order to orchestrate its cellular functions. This review addresses the structural basis of TNF signalling, the pathways employed with their cellular consequences, and focuses on the specific role played by each of the two TNF receptor isotypes, TNFR1 and TNFR2.

Soluble tumor necrosis factor receptor levels identify a subgroup of heart failure patients with increased cardiomyocyte apoptosis

BACKGROUND

We studied whether the presence of cardiomyocyte apoptosis (CA) in explanted failing hearts is related to previous exposure to the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha).

METHODS

Serum levels of TNF-alpha and its soluble type two receptors (sTNFRII) were measured with ELISAs in 15 cardiac transplant recipients. CA was quantified with TUNEL assay in the explanted failing hearts and autopsy samples from six normal hearts.

RESULTS

The number of CA was significantly higher in explanted failing hearts than in normal hearts (0.041% vs. 0.007%, p<0.01). In heart failure patients, serum TNF-alpha was highly variable and did not correlate with CA. In contrast, serum sTNFRII showed a significant correlation (Pearson's r=0.74, p=0.002) with the amount of CA in explanted hearts. sTNFRII level >4500 pg/ml identified seven patients with 2.7 times higher percentage of CA than the other heart failure patients.

CONCLUSION

Increased levels of sTNFRII identify a heart failure patient subgroup with high CA activity.

Role of tumor necrosis factor receptor 2 (TNFR2) in colonic epithelial hyperplasia and chronic intestinal inflammation in mice

BACKGROUND & AIMS

Tumor necrosis factor (TNF) induces multiple effects including cell proliferation and death by ligation with TNF receptor type II (TNFR2). We studied the role of TNFR2 in chronic inflammation-induced colonic epithelial alteration.

METHODS

TNFR2 expression in colonic epithelial cells (CECs) was assessed by ribonuclease protection assay (RPA) and immunohistochemistry (IHC) in patients with inflammatory bowel disease (IBD) and murine colitis models. TNFR2 expression was also analyzed using COLO205 cells. The role of TNFR2 in colonic epithelial homeostasis was examined by generating interleukin 6-deficient TCR alpha KO (alpha IL-6DKO) or TNFR2-deficient TCR alpha (alpha TNFR2DKO) mice.

RESULTS

TNFR2 expression was up-regulated in CEC in both human ulcerative colitis and Crohn's disease. In vitro studies showed that TNFR2 expression was up-regulated by a cooperative effect of key proinflammatory cytokines. By RPA, the increased expression of TNFR2 was detectable in TCR alpha KO mice with colitis compared with TCR alpha KO mice without colitis or wild-type mice. In alpha IL-6DKO mice, TNFR2 expression, proliferation, and nuclear factor kappa B activation of CECs were markedly reduced compared with TCR alpha KO mice. alpha TNFR2 mice also showed significantly less colonic epithelial proliferation compared with TCR alpha KO mice.

CONCLUSIONS

Expression of TNFR2 is consistently increased on CECs in both murine colitis models as well as patients with IBD. TNFR2 may play an important role in colonic inflammation-associated alteration in the intestinal epithelium.

Potent inhibition of neutrophil migration by cryptococcal mannoprotein-4-induced desensitization

Cryptococcal capsular Ags induce the production of proinflammatory cytokines in patients with cryptococcal meningitis. Despite this, their cerebrospinal fluid typically contains few neutrophils. Capsular glucuronoxylomannan is generally considered to mediate the inhibition of neutrophil extravasation. In the current study, culture supernatant harvested from the nonglucuronoxylomannan-producing strain CAP67 was found to be as potent as supernatant from wild-type strains in preventing migration. We identified capsular mannoprotein (MP)-4 as the causative agent. Purified MP-4 inhibited migration of neutrophils toward platelet-activating factor, IL-8, and fMLP, probably via a mechanism involving chemoattractant receptor cross-desensitization, as suggested by its direct chemotactic activity. Supporting this hypothesis, MP-4 elicited Ca(2+) transients that were inhibited by preincubation with either fMLP, IL-8, or C5a, but not platelet-activating factor, and vice versa. Moreover, MP-4 strongly decreased the neutrophil surface expression of L-selectin and induced shedding of TNF receptors p55/p75, whereas CD11b/18 increased. Finally, MP-4 was clearly detectable in both serum and cerebrospinal fluid of patients suffering from cryptococcal meningitis. These findings identify MP-4 as a novel capsular Ag prematurely activating neutrophils and desensitizing them toward a chemoattractant challenge.

Tumor necrosis factor-alpha (TNF-alpha)-induced and interleukin-1 beta (IL-1 beta)-induced shedding of TNF receptors from gingival fibroblasts

Tumor necrosis factor-alpha (TNF-alpha) exerts its functions by binding two different receptors (TNFR55 and TNFR75). Both TNFR55 and TNFR75 exist in cell-associated and soluble forms. Soluble TNF receptors (sTNFR), sTNFR55 and sTNFR75, are proteolytically shed upon inflammatory stimuli and then modulate various TNF-alpha bioactivities. As human gingival fibroblasts (HGF) can be potential targets for TNF-alpha in inflamed gingiva, we hypothesized that HGF partially modulate the cellular responses to TNF-alpha by regulating their own TNFR. In this study, the kinetics of expression of cell-associated and soluble forms of both receptors from cultured HGF in response to proinflammatory cytokines TNF-alpha and interleukin-1 beta (IL-1 beta) were investigated in vitro. Both TNF-alpha and IL-1 beta upregulated the gene expression of TNFR75 and did not affect that of TNFR55. TNF-alpha and IL-1 beta decreased binding of [(125)I]TNF-alpha to HGF. Moreover, TNF-alpha and IL-1 beta upregulated the release of sTNFR75 from HGF but not that of sTNFR55. These results suggest that HGF under inflammatory conditions may contribute to the inactivation of circulating TNF-alpha through the preferential induction and shedding of TNFR75.

Serum level of soluble tumor necrosis factor receptor II (sTNF-R75) is apparently an index of overall monocyte-related infectious and inflammatory activity

BACKGROUND

The serum level of soluble tumor necrosis factor receptor II (sTNF-R75) has been recently found to correlate with the activity and/or severity of several different infectious and inflammatory diseases. These results have led us to presume that the serum sTNF-R75 level reflects the active immune activity of all causes and may correlate well with nonspecific infectious and inflammatory markers such as peripheral leukocyte counts and serum C-reactive protein level.

METHODS

In total, 110 apparently healthy adults, 55 men and 55 women, were enrolled in the study. Serum levels of sTNF-R75, C-reactive protein, globulin, alkaline phosphatase, lactate dehydrogenase, creatinine, urea nitrogen, and counts of neutrophils, lymphocytes, monocytes, eosinophils, and basophils were checked. The relationships between the serum sTNF-R75 level and other parameters were analyzed using the SAS statistical program.

RESULTS

By various statistical methods, the serum sTNF-R75 level showed consistently significant positive links with peripheral monocyte count, serum C-reactive protein level, and two parameters of renal clearance function (serum urea nitrogen and creatinine levels). Serum levels of alkaline phosphatase and lactate dehydrogenase had significant positive links with the serum sTNF-R75 level by multivariate regression analysis. There was no significant link between the serum sTNF-R75 level and counts of neutrophils, lymphocytes, eosinophils, or basophils.

CONCLUSIONS

Our results, together with those of recent reports showing positive correlations between the serum sTNF-R75 level and activities/severities of different infectious and inflammatory diseases, and also that TNF-alpha is principally produced by monocytes and macrophages, suggest that the serum sTNF-R75 level is very probably an index of overall monocyte-related infectious and inflammatory activities.

TNF-Induced shedding of TNF receptors in human polymorphonuclear leukocytes: role of the 55-kDa TNF receptor and involvement of a membrane-bound and non-matrix metalloproteinase

A down-modulation of both the 55-kDa (TNF-R55) and the 75-kDa (TNF-R75) TNF receptors is observed in neutrophils exposed to a variety of stimuli. Proteolytic cleavage of the extracellular region of both receptors (shedding) and, with TNF, internalization of TNF-R55 and shedding of TNF-R75 are the proposed mechanisms. We have characterized the TNF-induced shedding of TNF receptors in neutrophils and determined the nature of the involved proteinase. Neutrophils exposed to TNF release both TNF receptors. A release of TNF receptors comparable to that observed with TNF was induced with TNF-R55-specific reagents (mAbs and a mutant of TNF) but not with the corresponding TNF-R75-specific reagents. A hydroxamic acid compound (KB8301) almost completely inhibited shedding of TNF-R55 and to a lesser degree shedding of TNF-R75. KB8301 also inhibited FMLP-induced shedding to a similar extent. Shedding was also inhibited by 1,10-phenanthroline, but this effect was considered nonspecific as the compound, at variance with KB8301, almost completely inhibited TNF and FMLP-induced PMN activation. Diisopropylfluorophosphate partially inhibited shedding of TNF-R75, suggesting the contribution of a serine proteinase to the release of this receptor. Shedding activity was not affected by matrix metalloproteinases inhibitors nor was it released in the supernatants of FMLP-stimulated neutrophils. These results suggest that TNF induces release of its receptors, that such a release is mediated via TNF-R55, and that a membrane-bound and non-matrix metalloproteinase is involved in the process. The possibility that ADAM-17, which we show to be expressed in neutrophils, might be the involved proteinase is discussed.

The two tumor necrosis factor receptors mediate opposite effects on differentiation and glucose metabolism in human adipocytes in primary culture

Tumor necrosis factor-alpha (TNF) inhibits fat cell differentiation and may also mediate insulin resistance in adipocytes. Both TNF receptors are expressed in adipose tissue, but it is unknown how both receptors are involved in these biological functions. We therefore studied the effect of receptor-specific TNF muteins on adipose differentiation and insulin-stimulated glucose transport of in vitro differentiated human adipocytes in primary culture. Adipocyte precursor cells exposed to the 60-kDa TNF receptor (p60-TNFR)-specific TNF(R32W-S86T) showed a marked decrease in the percentage of differentiating cells in response to adipogenic factors as well as a reduction in peroxisome proliferator-activated receptor-gamma2 (PPARgamma2) messenger RNA (mRNA) and glycerophosphate dehydrogenase (GPDH) activity, but increased endogenous TNF mRNA expression. When cells were incubated with the p80-TNFR-specific TNF(D143N-A145R), adipogenesis and PPARgamma2 mRNA expression were stimulated, GPDH activity was unchanged, and TNF mRNA was completely suppressed. Insulin-stimulated 2-deoxy-D-glucose transport was inhibited by both muteins. The p60-TNFR-mediated inhibition increased continuously during 6 h of treatment and was associated with a down-regulation of glucose transporter-4 (GLUT4) mRNA and GLUT4 protein, whereas the p80-TNFR-specific mutein caused a transient increase in GLUT4 mRNA, but did not alter GLUT4 protein expression after a 24-h incubation. We conclude that p60-TNFR mediates the antiadipogenic effect as well as the down-regulation of GLUT4 by TNF, thereby leading to long-term inhibition of insulin-stimulated glucose transport. In contrast, activation of the p80-TNFR induces an adipogenic effect and transiently up-regulates GLUT4 expression. Here, the acute inhibition of insulin-stimulated glucose transport may be induced by interference with the insulin signaling pathway.

IgA1 protease from Neisseria gonorrhoeae inhibits TNFalpha-mediated apoptosis of human monocytic cells

The modulation of programmed cell death is a common theme in the patho-physiology of inflammation and infectious disease. The synthesis and secretion of an IgA1 protease is strictly associated with virulence of the Neisseria species. Here, we report on the inhibition of tumor necrosis factor alpha (TNFalpha)-mediated apoptosis of the human myelo-monocytic cell line U937 by highly purified IgA1 protease. Apoptosis was verified by the cell surface exposure of phosphatidyl serine and by terminal transferase mediated end-labeling of fragmented DNA. Interestingly, IgA1 protease specifically cleaved the TNF receptor II (TNF-RII) on the surface of intact cells whereas TNF-RI was not affected by the enzyme. Therefore, inhibition of TNFalpha-mediated apoptosis might be correlated to specific cleavage of the TNF-RII by neisserial IgA1 protease.

Tumor necrosis factor (TNF)-alpha induces leptin production through the p55 TNF receptor

Tumor necrosis factor (TNF)-alpha acts directly on adipocytes to increase production of the lipostatic factor, leptin. However, which TNF receptor (TNFR) mediates this response is not known. To answer this question, leptin was measured in plasma of wild-type (WT), p55, and p75 TNFR knockout (KO) mice injected intraperitoneally with murine TNF-alpha and in supernatants from cultured WT, p55, and p75 TNFR KO adipocytes incubated with TNF-alpha. Leptin also was measured in supernatants from C3H/HeOuJ mouse adipocytes cultured with blocking antibodies to each TNFR and TNF-alpha as well as in supernatants from adipocytes incubated with either human or murine TNF-alpha, which activate either one or both TNFR, respectively. The results using all four strategies show that the induction of leptin production by TNF-alpha requires activation of the p55 TNFR and that although activation of the p75 TNFR alone cannot cause leptin production, its presence affects the capability of TNF-alpha to induce leptin production through the p55 TNFR. These results provide new information on the interplay between cells of the immune system and adipocytes.

Effect of nutrition on tumor necrosis factor receptors in weight-gaining and -losing rats

Previous studies showed that weight-gaining rats had greater retention and reduced turnover of 125I-labeled tumor necrosis factor (TNF)-alpha in the circulation compared with weight-losing animals. We therefore tested the hypothesis that protein-energy restriction with weight loss reduces the levels of soluble TNF-alpha receptor (sTNFR) and membrane TNFR (mTNFR) and the cellular expression of TNF-alpha mRNA. Twenty-six male rats weighing 200-220 g were fed a liquid formula diet for 10 days and divided equally into weight-gaining rats meeting all nutritional requirements (WG rats) and weight-losing rats with protein-energy restriction (WL rats). 125I-TNF-alpha binding was demonstrated in plasma and plasma membrane to proteins of molecular masses of 92 and 243 kDa, a finding identical to that seen with purified human p55. Excess unlabeled TNF-alpha displaced the binding showing its specificity. The degree of binding to plasma protein and liver plasma membrane was markedly reduced in WL rats. Northern analysis showed that the expression of p55 mRNA was increased in the lungs and reduced in kidneys of WL compared with WG rats. The expression of p75 mRNA was not influenced by the nutritional status. We conclude that levels of sTNFR and mTNFR were reduced in WL rats. Reduced sTNFR and liver mTNFR are not due to a reduction in the expression of either p55 or p75 mRNA in WL rats. Reduced mTNFR, together with reduced shedding of soluble receptors, may have a protective role in WL rats.

Immunolocalization of tumor necrosis factor-alpha and its receptors in inflammatory myopathies

Adhesion molecule upregulation occurs in inflammatory myopathies, and is one of the myriad functions of tumor necrosis factor-alpha (TNF-alpha). TNF-alpha acts via two different receptors of 55 (TNF-R55) and 75 kD (TNF-R75). We immunolocalized TNF-alpha and its receptors in polymyositis, inclusion body myositis and dermatomyositis. In each myopathy, TNF-alpha was detected in macrophages, in myonuclei in regenerating muscle fibers, and freely dispersed in endomysial or perimysial connective tissue. Many endothelial cells in dermatomyositis expressed TNF-alpha. TNF-R55 was strongly expressed on myonuclei of regenerating muscle fibers. TNF-R75 was increased on endothelial cells in the midst of inflammatory infiltrates in each myopathy, and on perifascicular and perimysial endothelia, remote from inflammatory foci in dermatomyositis. Possible TNF-alpha-mediated effects include: increased transendothelial cell trafficking, activation of T/B cells and macrophages, induction of MHC-I gene products, and focal muscle fiber atrophy. In dermatomyositis, the upregulated TNF-R75, via its consensus elements for transcription factors, may be involved in endothelial cell degeneration. Strong TNF-R55 expression on regenerating myonuclei is consistent with a role of TNF-alpha and TNF-R55 in muscle regeneration.

Inhibition of receptor internalization by monodansylcadaverine selectively blocks p55 tumor necrosis factor receptor death domain signaling

The 55-kDa receptor for tumor necrosis factor (TR55) triggers multiple signaling cascades initiated by adapter proteins like TRADD and FAN. By use of the primary amine monodansylcadaverine (MDC), we addressed the functional role of tumor necrosis factor (TNF) receptor internalization for intracellular signal distribution. We show that MDC does not prevent the interaction of the p55 TNF receptor (TR55) with FAN and TRADD. Furthermore, the activation of plasmamembrane-associated neutral sphingomyelinase activation as well as the stimulation of proline-directed protein kinases were not affected in MDC-treated cells. In contrast, activation of signaling enzymes that are linked to the "death domain" of TR55, like acid sphingomyelinase and c-Jun-N-terminal protein kinase as well as TNF signaling of apoptosis in U937 and L929 cells, are blocked in the presence of MDC. The results of our study suggest a role of TR55 internalization for the activation of select TR55 death domain signaling pathways including those leading to apoptosis.

Germline mutations in the extracellular domains of the 55 kDa TNF receptor, TNFR1, define a family of dominantly inherited autoinflammatory syndromes

Autosomal dominant periodic fever syndromes are characterized by unexplained episodes of fever and severe localized inflammation. In seven affected families, we found six different missense mutations of the 55 kDa tumor necrosis factor receptor (TNFR1), five of which disrupt conserved extracellular disulfide bonds. Soluble plasma TNFR1 levels in patients were approximately half normal. Leukocytes bearing a C52F mutation showed increased membrane TNFR1 and reduced receptor cleavage following stimulation. We propose that the autoinflammatory phenotype results from impaired downregulation of membrane TNFR1 and diminished shedding of potentially antagonistic soluble receptor. TNFR1-associated periodic syndromes (TRAPS) establish an important class of mutations in TNF receptors. Detailed analysis of one such mutation suggests impaired cytokine receptor clearance as a novel mechanism of disease.

Differential expression of tumor necrosis factor receptor subtypes on leukocytes in systemic inflammatory response syndrome

OBJECTIVE

To determine the expression of tumor necrosis factor (TNF) receptor in patients with systemic inflammatory response syndrome (SIRS).

DESIGN

Prospective study.

SETTING

Intensive care unit and central laboratory.

PATIENTS

Blood specimens from 18 healthy volunteers (controls) and 16 patients with SIRS.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Using monoclonal antibodies, fluorescence labeling, and high sensitivity flow cytometry, we measured the expression of membrane TNF receptor subtypes TNF-R55 and TNF-R75 on peripheral blood leukocytes. Receptor expression is expressed as mean fluorescence intensity +/- SD (units: detection channel number). In controls, TNF-R55 was only weakly expressed (monocytes: 2.5+/-1.8; neutrophils: 0.7+/-0.8), whereas expression of TNF-R75 was higher (monocytes: 28.6+/-9.0; neutrophils: 4.8+/-1.0) and was also found on lymphocytes (on CD8+ lymphocytes: 5.7+/-1.8; CD16+: 5.5+/-1.2; CD4+: 9.7+/-3.7). In SIRS, we observed increased expression of TNF-R55 on monocytes (6.9+/-3.4, p<.001) and neutrophils (2.2+/-1.9, p<.01), as well as decreased expression of TNF-R75 on monocytes (17.3+/-13.2; p<.001). The extent of TNF-R55 up-regulation did not correlate with that of TNF-R75 down-regulation. TNF-R55 on monocytes and neutrophils strongly correlated with body temperature but not with survival, whereas monocyte TNF-R75 was considerably lower in nonsurvivors, albeit not significantly (12.3+/-7.1 vs. 23.9+/-16.7; p = .07).

CONCLUSIONS

These data indicate that leukocyte TNF-R55 and TNF-R75 react differentially and probably serve different functions in SIRS, which prompts the investigation of receptor subtype-specific therapeutic approaches.

Soluble tumor necrosis factor receptors in chronic hepatitis C: a correlation with histological fibrosis and activity

BACKGROUND/AIMS

Tumor necrosis factor-alpha (TNF) is a mediator of inflammation and cellular immune response. Soluble TNF receptors (sTNFR) sTNF-R55 and sTNF-R75, which compete with cellular receptors for the binding of TNF, have been detected at high levels in infectious diseases including human immunodeficiency virus and HBV infection. In order to investigate the activation of the TNF system in HCV infection, we have analyzed the balance between TNF and sTNF-R in 60 HCV-infected subjects according to their clinical, biological, virological and histological characteristics.

METHODS

Serum TNF, sTNF-R55 and sTNF-R75 levels were determined by ELISA before any therapy and were compared to a control group of 60 healthy subjects and a group of 34 HBV-infected patients.

RESULTS

Mean TNF levels were 50.5+/-4.5 pg/ml in HCV patients, and undetectable (<5 pg/ml) in the control subjects. sTNF-R55 and sTNF-R75 levels were significantly higher in HCV-infected patients than in the controls: 2.88+/-0.14 ng/ml vs. 1.30+/-0.05, (p = 0.0001), and 9.54+/-0.58 ng/ml vs. 4.19+/-016, (p = 0.0001), respectively. sTNF-R55 and TNF-alpha levels in HCV patients were not significantly different from levels in HBV patients. sTNF-R75 levels were slightly lower than in HBV patients (9.54+/-0.58 vs. 11.4+/-0.79 ng/ml, p = 0.03). In contrast to other infectious diseases, there was no correlation between levels of sTNF-R and TNF. sTNF-R75 but not TNF levels were correlated with aminotransferases levels (p = 0.0001 and p = 0.0015 for aspartate and alanine aminotransferase, respectively), while sTNF-R55 levels were significantly correlated only with aspartate aminotransferase levels (p = 0.003). sTNF-R75 levels were significantly correlated with the Metavir activity index (p = 0.01), and sTNF-R55 and sTNF-R75 levels were significantly higher in patients with vs. without cirrhosis (3.22+/-0.21 vs. 2.54+/-0.17 ng/ml (p<0.02) and 11.6+/-0.86 vs. 7.5+/-0.53 ng/ml (p<0.001), respectively). sTNF-R55, sTNF-R75 and TNF levels were not correlated with viral load, genotype or response to interferon therapy.

CONCLUSIONS

Levels of soluble TNF receptors, and particularly sTNF-R75, are significantly correlated with the severity of the disease but not with virological parameters such as quantitative viremia and genotype. High TNF-R production could thus suggest that HCV-related liver disease involves immunological mechanisms, including activation of the TNF system.

Role of the 75-kDa TNF Receptor in TNF-Induced Activation of Neutrophil Respiratory Burst

The exclusive role of the 55-kDa TNF receptor (TNF-R55) as the signaling receptor in TNF-induced activation of respiratory burst by human polymorphonuclear leukocytes residing on biologic surfaces has been inferred from results obtained with receptor-specific monoclonal and polyclonal Abs. In this work, we confirm this assumption by a more direct approach, i.e., by using receptor-specific TNF mutants (p55TNF and p75TNF) and, as a novel contribution, we show that cooperation of the 75-kDa TNF receptor (TNF-R75) is required for a full blown response to the cytokine. This conclusion stems from three sets of data: 1) none of the TNF-R55-specific agonists used, i.e., mAbs or p55TNF, induced a respiratory burst comparable with that induced by TNF; 2) selective down-modulation of TNF-R75 resulted in a diminished response to TNF but not to TNF-R55-specific agonists or to the chemotactic peptide FMLP; and 3) mAbs that either block or stabilize binding of TNF to TNF-R75 inhibited the response to the cytokine, suggesting that cooperation requires not only TNF binding to the receptor but also an appropriate dissociability from it. The inhibitory effect of the Abs increased as the cytokine concentrations decreased, indicating that cooperation by TNF-R75 becomes more relevant at low TNF doses. Such a cooperation does not seem to rely on the activation of a TNF-R75-linked signaling pathway independent of TNF-R55, since the response to p55TNF and p75TNF given in combination was not higher than the response to p55TNF alone. The possible mechanisms of cooperation are discussed.