Endocytosis of uncleaved tumor necrosis factor-alpha in macrophages

The Contributions of the Endolysosomal Compartment and Autophagy to APOEɛ4 Allele-Mediated Increase in Alzheimer's Disease Risk

Apolipoprotein E4 (APOE4), although yet-to-be fully understood, increases the risk and lowers the age of onset of Alzheimer's disease (AD), which is the major cause of dementia among elderly individuals. The endosome-lysosome and autophagy pathways, which are necessary for homeostasis in both neurons and glia, are dysregulated even in early AD. Nonetheless, the contributory roles of these pathways to developing AD-related pathologies in APOE4 individuals and models are unclear. Therefore, this review summarizes the dysregulations in the endosome-lysosome and autophagy pathways in APOE4 individuals and non-human models, and how these anomalies contribute to developing AD-relevant pathologies. The available literature suggests that APOE4 causes endosomal enlargement, increases endosomal acidification, impairs endosomal recycling, and downregulates exosome production. APOE4 impairs autophagy initiation and inhibits basal autophagy and autophagy flux. APOE4 promotes lysosome formation and trafficking and causes ApoE to accumulate in lysosomes. APOE4-mediated changes in the endosome, autophagosome and lysosome could promote AD-related features including Aβ accumulation, tau hyperphosphorylation, glial dysfunction, lipid dyshomeostasis, and synaptic defects. ApoE4 protein could mediate APOE4-mediated endosome-lysosome-autophagy changes. ApoE4 impairs vesicle recycling and endosome trafficking, impairs the synthesis of autophagy genes, resists being dissociated from its receptors and degradation, and forms a stable folding intermediate that could disrupt lysosome structure. Drugs such as molecular correctors that target ApoE4 molecular structure and enhance autophagy may ameliorate the endosome-lysosome-autophagy-mediated increase in AD risk in APOE4 individuals.

Endosomal trafficking inhibitor EGA can control TLR7-mediated IFNα expression by human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDC) are the major producer of type 1 IFN in response to TLR7 agonists. Aberrant TLR7 activation and type 1 IFN expression by pDCs are linked to the pathogenesis of certain types of autoimmune diseases, including systemic lupus erythematosus (SLE). This study investigated the underlying mechanisms for TLR7-mediated cytokine expression by pDCs using a late endosome trafficking inhibitor, EGA (4-bromobenzaldehyde N-(2,6-dimethylphenyl) semicarbazone). We found that EGA treatment decreased IFNα expression by pDCs stimulated with imiquimod (R837), single-stranded RNA40, and influenza virus. EGA also decreased TNFα expression and secretion by R837-stimulated pDCs. Mechanistically, EGA treatment decreased phosphorylation of IKKα/β, STAT1, and p38, and prolonged degradation of IκBα. Furthermore, EGA treatment decreased the colocalization of 3F, a substituted adenine TLR7 agonist, with LAMP1+ compartments in pDCs. EGA was also capable of diminishing IFNα expression by SLE pDCs treated with R837 or live PR8/A/34 influenza viruses. Therefore, we concluded that trafficking of TLR7 agonists to LAMP1+ compartments is important for IFNα expression by pDCs. Data from this study support additional examinations of the potential benefits of EGA in treating type 1 IFN-associated inflammatory diseases in the future.

A potent endocytosis inhibitor Ikarugamycin up-regulates TNF production

Ikarugamycin (IK) is an antibiotic which has been reported to have a variety of functions, such as inhibition of clathrin-mediated endocytosis (CME), anti-tumor effects and regulation of the immune system. Whether IK influences cytokine production is poorly understood. We have investigated the relationship between IK and production of tumor necrosis factor-α (TNF). TNF plays a pivotal role in pathogenesis of many diseases. Although the dynamics of soluble TNF (sTNF) has been widely explored so far, the functions of the membrane form of TNF (mTNF) have not been fully elucidated. We demonstrated that IK increases the amount of mTNF and prolongs the duration of TNF expression. This effect is unrelated to the shedding activity of disintegrin and metalloproteinase domain-containing protein 17 (ADAM 17). Our results revealed that there is a mechanism to terminate inflammation at the cellular level which IK dysregulates. Furthermore, IK can be a tool to study TNF signaling due to its effect of increasing mTNF expression.

Biomimetic analyses of interactions between macrophages and palmar fascia myofibroblasts derived from Dupuytren's disease reveal distinct inflammatory cytokine responses

Dupuytren's disease (DD) is a common and heritable fibrosis of the hand. It is characterized by the shortening and thickening of the palmar fascia into myofibroblastic nodules that can progress to palmar-digital contractures and permanent loss of dexterity. Molecular analyses of DD tissues and the presence of inflammatory cell infiltrates suggest a pathogenesis initiated by a proinflammatory fascial milieu that promotes myofibroblast activation and palmar fascia contractures. However, the relative contributions of vascular and/or tissue derived immune system cells and cytokine-sensitive stromal myofibroblasts to the development of this proinflammatory microenvironment are poorly understood. To gain insights into this process, we have developed and tested a collagen-based 3D tissue biomimetic co-culture system to assess paracrine interactions between THP-1-derived pro-inflammatory macrophages and primary human palmar fascia myofibroblasts (PFMs). We observed significant and reproducible impacts of collagen-adherent macrophage and PFM co-cultures on the cytokine gene expression profiles of these cells compared to their respective monocultures, and significant changes to the resulting cytokine milieu in their shared culture media, notably TNF and IL-6. Our findings are consistent with central roles for PFMs in cytokine production and immunoregulation of the pro-inflammatory milieu hypothesized to promote DD development.

Human monocytes store and secrete preformed CCL5, independent of de novo protein synthesis

Monocytes are a subset of circulating peripheral blood mononuclear cells with diverse roles in immunity, including sentinel roles in cytokine secretion. Conventionally, cytokines require an inductive stimulus for their expression and secretion, resulting in a time lag from the time of stimulation to when the proteins are packaged and secreted. Because cytokines are the main communicators in the immune system, their temporal expression is a key factor in coordinating responses to efficiently resolve infection. Herein, we identify that circulating human monocytes contain preformed cytokines that are stored intracellularly, in both resting and activated states. Having preformed cytokines bypasses the time lag associated with de novo synthesis, allowing monocytes to secrete immune mediators immediately upon activation or sensing of microbe-associated molecular patterns. We demonstrate here that, out of several cytokines evaluated, human monocytes contain a previously undescribed reservoir of the preformed chemokine CCL5. Furthermore, we showed that CCL5 could be secreted from monocytes treated with the protein synthesis inhibitor (cycloheximide) and Golgi blocker (brefeldin A). We examined the possibility for uptake of extracellular CCL5 from platelet aggregates and observed no significant levels of platelet binding to our enriched monocyte preparations, indicating that the source of preformed CCL5 was not from platelets. Preformed CCL5 was observed to be distributed throughout the cytoplasm and partially colocalized with CD63+ and Rab11A+ membranes, implicating endosomal compartments in the intracellular storage and trafficking of CCL5.

Damage-Associated Molecular Patterns and Their Signaling Pathways in Primary Blast Lung Injury: New Research Progress and Future Directions

Primary blast lung injury (PBLI) is a common cause of casualties in wars, terrorist attacks, and explosions. It can exist in the absence of any other outward signs of trauma, and further develop into acute lung injury (ALI) or a more severe acute respiratory distress syndrome (ARDS). The pathogenesis of PBLI at the cellular and molecular level has not been clear. Damage-associated molecular pattern (DAMP) is a general term for endogenous danger signals released by the body after injury, including intracellular protein molecules (HMGB1, histones, s100s, heat shock proteins, eCIRP, etc.), secretory protein factors (IL-1β, IL-6, IL-10, TNF-α, VEGF, complements, etc.), purines and pyrimidines and their derived degradation products (nucleic acids, ATP, ADP, UDPG, uric acid, etc.), and extracellular matrix components (hyaluronic acid, fibronectin, heparin sulfate, biglycan, etc.). DAMPs can be detected by multiple receptors including pattern recognition receptors (PRRs). The study of DAMPs and their related signaling pathways, such as the mtDNA-triggered cGAS-YAP pathway, contributes to revealing the molecular mechanism of PBLI, and provides new therapeutic targets for controlling inflammatory diseases and alleviating their symptoms. In this review, we focus on the recent progress of research on DAMPs and their signaling pathways, as well as the potential therapeutic targets and future research directions in PBLI.

ATP redirects cytokine trafficking and promotes novel membrane TNF signaling via microvesicles

Cellular stress or injury induces release of endogenous danger signals such as ATP, which plays a central role in activating immune cells. ATP is essential for the release of nonclassically secreted cytokines such as IL-1β but, paradoxically, has been reported to inhibit the release of classically secreted cytokines such as TNF. Here, we reveal that ATP does switch off soluble TNF (17 kDa) release from LPS-treated macrophages, but rather than inhibiting the entire TNF secretion, ATP packages membrane TNF (26 kDa) within microvesicles (MVs). Secretion of membrane TNF within MVs bypasses the conventional endoplasmic reticulum- and Golgi transport-dependent pathway and is mediated by acid sphingomyelinase. These membrane TNF-carrying MVs are biologically more potent than soluble TNF in vivo, producing significant lung inflammation in mice. Thus, ATP critically alters TNF trafficking and secretion from macrophages, inducing novel unconventional membrane TNF signaling via MVs without direct cell-to-cell contact. These data have crucial implications for this key cytokine, particularly when therapeutically targeting TNF in acute inflammatory diseases.-Soni, S., O'Dea, K. P., Tan, Y. Y., Cho, K., Abe, E., Romano, R., Cui, J., Ma, D., Sarathchandra, P., Wilson, M. R., Takata, M. ATP redirects cytokine trafficking and promotes novel membrane TNF signaling via microvesicles.

The role of dietary fatty acid intake in inflammatory gene expression: a critical review

CONTEXT AND OBJECTIVE:

Diet is an important modifiable factor involved in obesity-induced inflammation. We reviewed clinical trials that assessed the effect of consumption of different fatty acids on the expression of inflammation-related genes, such as cytokines, adipokines, chemokines and transcription factors.

DESIGN AND SETTING:

Narrative review study conducted at a research center.

METHODS:

This was a review on the effect of fat intake on inflammatory gene expression in humans.

RESULTS:

Consumption of saturated fatty acids (SFAs) was related to postprandial upregulation of genes associated with pro-inflammatory pathways in peripheral blood mononuclear cells (PBMCs), in comparison with monounsaturated fatty acid (MUFA) or polyunsaturated fatty acid (PUFA) intake. In addition, acute intake of a high-SFA meal also induced a postprandial pro-inflammatory response for several inflammatory genes in subcutaneous adipose tissue. Both high-MUFA and high-PUFA diets showed anti-inflammatory profiles, or at least a less pronounced pro-inflammatory response than did SFA consumption. However, the results concerning the best substitute for SFAs were divergent because of the large variability in doses of MUFA (20% to 72% of energy intake) and n3 PUFA (0.4 g to 23.7% of energy intake) used in interventions.

CONCLUSIONS:

The lipid profile of the diet can modulate the genes relating to postprandial and long-term inflammation in PBMCs and adipose tissue. Identifying the optimal fat profile for inflammatory control may be a promising approach for treating chronic diseases such as obesity.

Expression of TNFα membrane-bound receptors in the peripheral blood mononuclear cells (PMBC) in rheumatoid arthritis patients

OBJECTIVE

To investigate the expression of TNFα membrane-bound receptors: the percentage of cells expressing these receptors and the number of molecules expressed on different immune cell subsets, and to evaluate serum concentrations of soluble TNFα and its receptors (sTNFRI and sTNFRII) in patients with rheumatoid arthritis in acute stage and after response to treatment compared to healthy donors.

METHODS

The objects of the study are peripheral blood mononuclear cells (PBMC) of healthy donors (n=150) and RA patients (n=40) subjected to hospital treatment with either biological agents (Rituximab) or glucocorticosteroids (methylprednisolone). To determine PBMC phenotype antibodies anti-hCD3-APC, anti-hCD19 PECy7, anti-hCD14 FITC (eBioscience), as well as anti-hTNFRI-PE and anti-hTNFRII-PE (R&D Systems) were used. To determine receptor number on the cells Quantibrite PE Beads (BD) were used.

RESULTS

Cells obtained from patients who responded to therapy and achieved disease remission exhibited either an increase in the percentage of TNFRI+ cells or elevated expression density of this receptor type.

CONCLUSION

Subsets of immunocompetent cells from RA patients show variation in the percentage of membrane-bound receptor positive cells and receptor expression density, which influences the development and progression of the pathological processes in RA. Response to therapy and achievement of disease remission are associated with an increase of TNFRI expression.

Vesicular trafficking and signaling for cytokine and chemokine secretion in mast cells

Upon activation mast cells (MCs) secrete numerous inflammatory compounds stored in their cytoplasmic secretory granules by a process called anaphylactic degranulation, which is responsible for type I hypersensitivity responses. Prestored mediators include histamine and MC proteases but also some cytokines and growth factors making them available within minutes for a maximal biological effect. Degranulation is followed by the de novo synthesis of lipid mediators such as prostaglandins and leukotrienes as well as a vast array of cytokines, chemokines, and growth factors, which are responsible for late phase inflammatory responses. While lipid mediators diffuse freely out of the cell through lipid bilayers, both anaphylactic degranulation and secretion of cytokines, chemokines, and growth factors depends on highly regulated vesicular trafficking steps that occur along the secretory pathway starting with the translocation of proteins to the endoplasmic reticulum. Vesicular trafficking in MCs also intersects with endocytic routes, notably to form specialized cytoplasmic granules called secretory lysosomes. Some of the mediators like histamine reach granules via specific vesicular monoamine transporters directly from the cytoplasm. In this review, we try to summarize the available data on granule biogenesis and signaling events that coordinate the complex steps that lead to the release of the inflammatory mediators from the various vesicular carriers in MCs.

Macrophage M1/M2 polarization dynamically adapts to changes in cytokine microenvironments in Cryptococcus neoformans infection

The outcome of cryptococcal pneumonia correlates with local macrophage polarization status, as M1 and M2 polarization marks protective and nonprotective responses, respectively. Overall, pulmonary macrophage polarization status changes over time during a cryptococcal infection. This could have been caused by repolarization of individual macrophages or by a replacement of M2-polarized cells by new M1-polarized cells. To explore the ability of macrophages to change between polarization states, we conducted a series of experiments using in vitro macrophages. Coculture of macrophages with Cryptococcus neoformans resulted in development of a weak M1-like phenotype, with modestly increased inducible nitric oxide synthase (iNOS) but lacking interleukin 6 (IL-6) induction. The C. neoformans-induced M1-like polarization state was plastic, as macrophages stimulated first with C. neoformans and then with gamma interferon (IFN-γ) or IL-4 expressed mRNA polarization patterns similar to those stimulated with cytokines alone. To further evaluate macrophage polarization plasticity, cytokine stimulatory conditions were established which fully polarized macrophages. IFN-γ and IL-4 stimulation differentially induced complete M1 and M2 polarization, defined by differential expression of marker mRNA panels, surface marker expression, and tumor necrosis factor alpha (TNF-α) protein production. Switching IFN-γ- to IL-4-stimulating conditions, and vice versa, resulted in uniform changes in profiles of polarization marker genes consistent with the most recent cytokine environment. Furthermore, the ability of sequentially stimulated macrophages to inhibit C. neoformans reflected the most recent polarizing condition, independent of previous polarization. Collectively, these data indicate that M1/M2 macrophage polarization phenotypes are highly plastic to external signals, and interventions which therapeutically repolarize macrophages could be beneficial for treatment of cryptococcosis.

CD40 activation induces NREM sleep and modulates genes associated with sleep homeostasis

The T-cell derived cytokine CD40 ligand is overexpressed in patients with autoimmune diseases. Through activation of its receptor, CD40 ligand leads to a tumor necrosis factor (TNF) receptor 1 (TNFR1) dependent impairment of locomotor activity in mice. Here we report that this effect is explained through a promotion of sleep, which was specific to non-rapid eye movement (NREM) sleep while REM sleep was suppressed. The increase in NREM sleep was accompanied by a decrease in EEG delta power during NREM sleep and by a decrease in the expression of transcripts in the cerebral cortex known to be associated with homeostatic sleep drive, such as Homer1a, Early growth response 2, Neuronal pentraxin 2, and Fos-like antigen 2. The effect of CD40 activation was mimicked by peripheral TNF injection and prevented by the TNF blocker etanercept. Our study indicates that sleep-wake dysregulation in autoimmune diseases may result from CD40 induced TNF:TNFR1 mediated alterations of molecular pathways, which regulate sleep-wake behavior.

Unlike for human monocytes after LPS activation, release of TNF-α by THP-1 cells is produced by a TACE catalytically different from constitutive TACE

BACKGROUND

Tumor necrosis factor-alpha (TNF-α) is a pro-inflammatory cytokine today identified as a key mediator of several chronic inflammatory diseases. TNF-α, initially synthesized as a membrane-anchored precursor (pro-TNF-α), is processed by proteolytic cleavage to generate the secreted mature form. TNF-α converting enzyme (TACE) is currently the first and single protease described as responsible for the inducible release of soluble TNF-α.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we demonstrated the presence on THP-1 cells as on human monocytes of a constitutive proteolytical activity able to cleave pro-TNF-α. Revelation of the cell surface TACE protein expression confirmed that the observed catalytic activity is due to TACE. However, further studies using effective and innovative TNF-α inhibitors, as well as a highly selective TACE inhibitor, support the presence of a catalytically different sheddase activity on LPS activated THP-1 cells. It appears that this catalytically different TACE protease activity might have a significant contribution to TNF-α release in LPS activated THP-1 cells, by contrast to human monocytes where the TACE activity remains catalytically unchanged even after LPS activation.

CONCLUSIONS/SIGNIFICANCE

On the surface of LPS activated THP-1 cells we identified a releasing TNF-α activity, catalytically different from the sheddase activity observed on human monocytes from healthy donors. This catalytically-modified TACE activity is different from the constitutive shedding activity and appears only upon stimulation by LPS.

Reactive oxygen species and p38 mitogen-activated protein kinase mediate tumor necrosis factor α-converting enzyme (TACE/ADAM-17) activation in primary human monocytes

Tumor necrosis factor α-converting enzyme (TACE) is responsible for the shedding of cell surface TNF. Studies suggest that reactive oxygen species (ROS) mediate up-regulation of TACE activity by direct oxidization or modification of the protein. However, these investigations have been largely based upon nonphysiological stimulation of promonocytic cell lines which may respond and process TACE differently from primary cells. Furthermore, investigators have relied upon TACE substrate shedding as a surrogate for activity quantification. We addressed these concerns, employing a direct, cell-based fluorometric assay to investigate the regulation of TACE catalytic activity on freshly isolated primary human monocytes during LPS stimulation. We hypothesized that ROS mediate up-regulation of TACE activity indirectly, by activation of intracellular signaling pathways. LPS up-regulated TACE activity rapidly (within 30 min) without changing cell surface TACE expression. Scavenging of ROS or inhibiting their production by flavoprotein oxidoreductases significantly attenuated LPS-induced TACE activity up-regulation. Exogenous ROS (H(2)O(2)) also up-regulated TACE activity with similar kinetics and magnitude as LPS. H(2)O(2)- and LPS-induced TACE activity up-regulation were effectively abolished by a variety of selective p38 MAPK inhibitors. Activation of p38 was redox-sensitive as H(2)O(2) caused p38 phosphorylation, and ROS scavenging significantly reduced LPS-induced phospho-p38 expression. Inhibition of the p38 substrate, MAPK-activated protein kinase 2, completely attenuated TACE activity up-regulation, whereas inhibition of ERK had little effect. Lastly, inhibition of cell surface oxidoreductases prevented TACE activity up-regulation distal to p38 activation. In conclusion, our data indicate that in primary human monocytes, ROS mediate LPS-induced up-regulation of TACE activity indirectly through activation of the p38 signaling pathway.

Hypertonicity-enhanced TNF-α release from activated human monocytic THP-1 cells requires ERK activation

BACKGROUND

Hypertonic stress enhances tumor necrosis factor (TNF)-α expression in activated monocytes. However, the underlying mechanism is unknown. The produced TNF-α is primarily cleaved and released by TNF-α-converting enzyme (TACE), and the surface expression of TACE is down-regulated by endocytosis. As hypertonicity inhibits endocytosis, we evaluated the mechanism of hypertonicity-induced TNF-α release from activated human monocytic THP-1 cells.

METHODS

THP-1 cells were stimulated with lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA) in the presence or absence of hypertonic agents (150 mM sucrose or 150-300 mM NaCl). The amount of TNF-α mRNA and protein, surface expression of TACE and activation of signaling pathways (mitogen-activated protein kinase, Akt and NF-κB) were assayed.

RESULTS

Hypertonic sucrose and NaCl significantly enhanced TNF-α release from THP-1 cells upon LPS or PMA stimulation. Hypertonic sucrose and other endocytosis inhibitors increased surface expression of TACE, but their effects on TNF-α release were inconsistent. This enhancement effect by hypertonicity was not attenuated by inhibition of TACE or IκB kinase, but it was blocked by cycloheximide and a MAP/ERK kinase inhibitor. The LPS- or PMA-induced TNF-α mRNA expression was not increased; rather, it was inhibited by hypertonicity. ERK1/2 was re-activated after sucrose treatment in LPS-stimulated THP-1 cells.

CONCLUSIONS

Hypertonicity-enhanced TNF-α protein synthesis from LPS- or PMA-activated THP-1 cells requires ERK activation and may proceed without TACE.

GENERAL SIGNIFICANCE

A vast amount of TNF-α production was regulated by a crucial post-transcriptional manner in activated human monocytic leukemia cells, and it may possibly be contributed to the cachexia condition.

Cytokine secretion is distinct from secretion of cytotoxic granules in NK cells

NK cells are renowned for their ability to kill virally infected or transformed host cells by release of cytotoxic granules containing granzymes and perforin. NK cells also have important regulatory capabilities chiefly mediated by secretion of cytokines, such as IFN-gamma and TNF. The secretory pathway for the release of cytokines in NK cells is unknown. In this study, we show localization and trafficking of IFN-gamma and TNF in human NK cells in compartments and vesicles that do not overlap with perforin or other late endosome granule markers. Cytokines in post-Golgi compartments colocalized with markers of the recycling endosome (RE). REs are functionally required for cytokine release because inactivation of REs or mutation of RE-associated proteins Rab11 and vesicle-associated membrane protein-3 blocked cytokine surface delivery and release. In contrast, REs are not needed for release of perforin from preformed granules but may be involved at earlier stages of granule maturation. These findings suggest a new role for REs in orchestrating secretion in NK cells. We show that the cytokines IFN-gamma and TNF are trafficked and secreted via a different pathway than perforin. Although perforin granules are released in a polarized fashion at lytic synapses, distinct carriers transport both IFN-gamma and TNF to points all over the cell surface, including within the synapse, for nonpolarized release.

Studies on the role of acid sphingomyelinase and ceramide in the regulation of tumor necrosis factor alpha (TNFalpha)-converting enzyme activity and TNFalpha secretion in macrophages

Acid sphingomyelinase (ASMase) has been proposed to mediate lipopolysaccharide (LPS) signaling in various cell types. This study shows that ASMase is a negative regulator of LPS-induced tumor necrosis factor alpha (TNFalpha) secretion in macrophages. ASMase-deficient (asm(-/-)) mice and isolated peritoneal macrophages produce severalfold more TNFalpha than their wild-type (asm(+/+)) counterparts when stimulated with LPS, whereas the addition of exogenous ceramides or sphingomyelinase reduces the differences. The underlying mechanism for these effects is not transcriptional but post-translational. The TNFalpha-converting enzyme (TACE) catalyzes the maturation of the 26-kDa precursor (pro-TNFalpha) to an active 17-kDa form (soluble (s)TNFalpha). In mouse peritoneal macrophages, the activity of TACE was the rate-limiting factor regulating TNFalpha production. A substantial portion of the translated pro-TNFalpha was not processed to sTNFalpha; instead, it was rapidly internalized and degraded in the lysosomes. TACE activity was 2-3-fold higher in asm(-/-) macrophages as compared with asm(+/+) macrophages and was suppressed when cells were treated with exogenous ceramide and sphingomyelinase. Indirect immunofluorescence analyses revealed distinct TNFalpha-positive structures in the close vicinity of the plasma membrane in asm(-/-) but not in asm(+/+) macrophages. asm(-/-) cells also had a higher number of early endosomal antigen 1-positive early endosomes. Experiments that involved inhibitors of TACE, endocytosis, and lysosomal proteolysis suggest that in the asm(-/-) cells a significant portion of pro-TNFalpha was sequestered within the early endosomes, and instead of undergoing lysosomal proteolysis, it was recycled to the plasma membrane and processed to sTNFalpha.

Effects of TNF-alpha-converting enzyme inhibition on acute lung injury induced by endotoxin in the rat

We studied the effects of TNF-converting enzyme inhibition with Y-41654, which down-regulates the production of soluble TNF-alpha (sTNF-alpha), on acute lung injury induced by intratracheal administration of LPS. We first verified in vitro that pretreatment of isolated alveolar macrophages from Sprague-Dawley male rats with 20 microL of 0.1-mM Y-41654, decreased significantly (P < 0.05) the concentration of sTNF-alpha in cell supernatants induced by 10 microg/mL of LPS. We then studied four groups of rats (each n = 10) including 1) a control group, 2) an LPS group (300 microg /kg, instilled intratracheally), 3) a Y-41654 group, and 4) a treatment group treated with Y-41654 after LPS instillation. Y-41654, 10 mg/kg in 0.7 mL of phosphate-buffered saline, was administered (i.v.), 15 min before and 0.5, 1.5, 2.5, and 3.5 h after saline or LPS instillation. The animals were observed for 4 h. In the animals treated with Y-41654, the concentrations of sTNF-alpha and protein in bronchoalveolar lavage fluid, and the number of neutrophils in lung tissue and bronchoalveolar lavage fluid were significantly lower at 4 h than in the LPS group (P < 0.05). In conclusion, sTNF-alpha plays an important role in the development of acute lung injury induced by intratracheal administration of LPS, in part modulating neutrophil kinetics.

Cathepsin B is involved in the trafficking of TNF-alpha-containing vesicles to the plasma membrane in macrophages

TNF-alpha is a potent proinflammatory cytokine, essential for initiating innate immune responses against invading microbes and a key mediator involved in the pathogenesis of acute and chronic inflammatory diseases. To identify molecules involved in the production of TNF-alpha, we used a functional gene identification method using retroviral integration-mediated mutagenesis, followed by LPS-stimulated TNF-alpha production analysis in macrophages. We found that cathepsin B, a lysosomal cysteine proteinase, was required for optimal posttranslational processing of TNF-alpha in response to the bacterial cell wall component LPS. Mouse bone marrow-derived macrophages from cathepsin B-deficient mice and macrophages treated with the cathepsin B-specific chemical inhibitor CA074 methyl ester or small interfering RNA against cathepsin B secreted significantly less TNF-alpha than wild-type or nontreated macrophages. We further showed that the inhibition of cathepsin B caused accumulation of 26-kDa pro-TNF-containing vesicles. Ectopic expression of GFP-conjugated pro-TNF further suggests that pro-TNF failed to reach the plasma membrane without intracellular cathepsin B activity. Altogether, these data suggest that intracellular cathepsin B activity is involved in the TNF-alpha-containing vesicle trafficking to the plasma membrane.

Hypoxia enhances lysosomal TNF-alpha degradation in mouse peritoneal macrophages

Infection, simulated by lipopolysaccharide (LPS), is a potent stimulator of tumor necrosis factor-alpha (TNF-alpha) production, and hypoxia often synergizes with LPS to induce higher levels of the secreted cytokine. However, we show that in primary mouse peritoneal macrophages and in three mouse peritoneal macrophage cell lines (RAW 264.7, J774A.1, and PMJ-2R), hypoxia (O(2) < 0.3%) reduces the secretion of LPS-induced TNF-alpha (P < 0.01). In RAW 264.7 cells this reduction was not regulated transcriptionally as TNF-alpha mRNA levels remained unchanged. Rather, hypoxia and LPS reduced the intracellular levels of TNF-alpha by twofold (P < 0.01) by enhancing its degradation in the lysosomes and inhibiting its secretion via secretory lysosomes, as shown by confocal microscopy and verified by the use of the lysosome inhibitor Bafilomycin A1. In addition, although hypoxia did not change the accumulation of the soluble receptor TNF-RII, it increased its binding to the secreted TNF-alpha by twofold (P < 0.05). We suggest that these two posttranslational regulatory checkpoints coexist in hypoxia and may partially explain the reduced secretion and diminished biological activity of TNF-alpha in hypoxic peritoneal macrophages.

Tumor necrosis factor and stroke: role of the blood-brain barrier

The progression and outcome of stroke is affected by the intricate relationship between the blood-brain barrier (BBB) and tumor necrosis factor alpha (TNFalpha). TNFalpha crosses the intact BBB by a receptor-mediated transport system that is upregulated by CNS trauma and inflammation. In this review, we discuss intracellular trafficking and transcytosis of TNFalpha, regulation of TNFalpha transport after stroke, and the effects of TNFalpha on stroke preconditioning. TNFalpha can activate cytoprotective pathways by pretreatment or persistent exposure to low doses. This explains the paradoxical observation that transport of this proinflammatory cytokine improves the survival and function of hypoxic cells and of mice with stroke. The dual effects of TNFalpha may be related to differential regulation of TNFalpha trafficking downstream to TNFR1 and TNFR2 receptors. As we better understand how peripheral TNFalpha affects its own transport and modulates neuroregeneration, we may be in a better position to pharmacologically manipulate its regulatory transport system to treat stroke.

TNF trafficking to human mast cell granules: mature chain-dependent endocytosis

Mast cells play a crucial role at the early stages of immune response against bacteria and parasites where their functionality is based on their capability of releasing highly bioactive compounds, among them TNF. Mast cells are considered the only cells storing preformed TNF, which allows for the immediate release of this cytokine upon contact with pathogens. We approached the question of mechanisms and amino acid motifs directing newly synthesized TNF for storage in cytoplasmic granules by analyzing the trafficking of a series of TNF-enhanced GFP fusion proteins in human mast cell lines HMC-1 and LAD2. Protein covering the full TNF sequence was successfully sorted into secretory granules in a process involving transient exposure on the outer membrane and re-endocytosis. In human cells, contrary to results previously obtained in a rodent model, TNF seems not to be glycosylated and, thus, trafficking is carbohydrate independent. In an effort to localize the amino acid motif responsible for granule targeting, we constructed additional fusion proteins and analyzed their trafficking, concluding that granule-targeting sequences are localized in the mature chain of TNF and that the cytoplasmic tail is expendable for endocytotic sorting of this cytokine, thus excluding direct interactions with intracellular adaptor proteins.

TNFalpha trafficking in cerebral vascular endothelial cells

Using small tags, we tracked the pathway of tumor necrosis factor (TNF)alpha across cerebral vascular endothelial cells. In cerebral microvessel derived RBE4 cells, (125)I-TNFalpha had rapid endocytosis within the first 20 min and showed substantial exocytosis in the intact form. Biotinylated TNFalpha was detected at different time points after endocytosis by streptavidin-Quantum dots which showed its time-dependent colocalization with intracellular organelles. In mice, electron microscopic autoradiography after intravenous injection of (125)I-TNFalpha showed its transcytosis, as signals emerged on the abluminal side of the endothelial cells and reached brain parenchyma. The vesicular trafficking of TNFalpha reflects the immunomodulatory potential of peripheral cytokines for the CNS.

Cytokine Secretion via Cholesterol-rich Lipid Raft-associated SNAREs at the Phagocytic Cup

Lipopolysaccharide-activated macrophages rapidly synthesize and secrete tumor necrosis factor alpha (TNFalpha) to prime the immune system. Surface delivery of membrane carrying newly synthesized TNFalpha is controlled and limited by the level of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins syntaxin 4 and SNAP-23. Many functions in immune cells are coordinated from lipid rafts in the plasma membrane, and we investigated a possible role for lipid rafts in TNFalpha trafficking and secretion. TNFalpha surface delivery and secretion were found to be cholesterol-dependent. Upon macrophage activation, syntaxin 4 was recruited to cholesterol-dependent lipid rafts, whereas its regulatory protein, Munc18c, was excluded from the rafts. Syntaxin 4 in activated macrophages localized to discrete cholesterol-dependent puncta on the plasma membrane, particularly on filopodia. Imaging the early stages of TNFalpha surface distribution revealed these puncta to be the initial points of TNFalpha delivery. During the early stages of phagocytosis, syntaxin 4 was recruited to the phagocytic cup in a cholesterol-dependent manner. Insertion of VAMP3-positive recycling endosome membrane is required for efficient ingestion of a pathogen. Without this recruitment of syntaxin 4, it is not incorporated into the plasma membrane, and phagocytosis is greatly reduced. Thus, relocation of syntaxin 4 into lipid rafts in macrophages is a critical and rate-limiting step in initiating an effective immune response.

E-cadherin transport from the trans-Golgi network in tubulovesicular carriers is selectively regulated by golgin-97

E-cadherin is a cell-cell adhesion protein that is trafficked and delivered to the basolateral cell surface. Membrane-bound carriers for the post-Golgi exocytosis of E-cadherin have not been characterized. Green fluorescent protein (GFP)-tagged E-cadherin (Ecad-GFP) is transported from the trans-Golgi network (TGN) to the recycling endosome on its way to the cell surface in tubulovesicular carriers that resemble TGN tubules labeled by members of the golgin family of tethering proteins. Here, we examine the association of golgins with tubular carriers containing E-cadherin as cargo. Fluorescent GRIP domains from golgin proteins replicate the membrane binding of the full-length proteins and were coexpressed with Ecad-GFP. The GRIP domains of p230/golgin-245 and golgin-97 had overlapping but nonidentical distributions on the TGN; both domains were on TGN-derived tubules but only the golgin-97 GRIP domain coincided with Ecad-GFP tubules in live cells. When the Arl1-binding endogenous golgins, p230/golgin-245 and golgin-97 were displaced from Golgi membranes by overexpression of the p230 GRIP domain, trafficking of Ecad-GFP was inhibited. siRNA knockdown of golgin-97 also inhibited trafficking of Ecad-GFP. Thus, the GRIP domains of p230/golgin-245 and golgin-97 bind discriminately to distinct membrane subdomains of the TGN. Golgin-97 is identified as a selective and essential component of the tubulovesicular carriers transporting E-cadherin out of the TGN.

Soluble human p55 and p75 tumor necrosis factor receptors reverse spontaneous arthritis in transgenic mice expressing transmembrane tumor necrosis factor α

OBJECTIVE

The roles of the transmembrane and secreted forms of tumor necrosis factor alpha (TNFalpha) in rheumatoid arthritis (RA) remain unclear. Agents used to inhibit TNFalpha have shown varying efficacy in RA patients, suggesting that anti-TNFalpha agents possess dissimilar mechanisms of action, including the ability to neutralize transmembrane (tmTNFalpha) and secreted TNFalpha. In this study, TNFalpha-knockout (TNFalpha-KO) mice that were genetically altered to express elevated levels of tmTNFalpha were constructed to further understand the roles of the 17-kd secreted, trimeric, and 26-kd transmembrane forms of TNFalpha.

METHODS

A speed-congenic mating scheme was used to generate 3 unique strains of mice: 1) transgenic tmTgA86 mice overexpressing 26-kd tmTNFalpha and also secreting 17-kd trimeric TNFalpha (tmTNFalpha-transgenic), 2) TNFalpha-/- mice (TNFalpha-KO), and 3) transgenic mice overexpressing tmTNFalpha backcrossed to TNFalpha-KO mice (tmTNFalpha-transgenic/TNFalpha-KO). Mice were treated with phosphate buffered saline (as vehicle control), dexamethasone (as positive control), or modified recombinant human soluble TNF receptor (sTNFR) p55 or p75, and were assessed clinically and histopathologically for signs of inflammation and development of arthritis.

RESULTS

The tmTNFalpha-transgenic/TNFalpha-KO mice were born with crinkled tails and spinal deformities similar to those in ankylosing spondylitis. By 2-4 weeks, these mice developed symmetric inflammatory arthritis, characterized by tissue swelling, pannus formation, and bone deformities. The tmTNFalpha-transgenic mice also developed spontaneous-onset arthritis, but at a slower rate (100% incidence by 10-12 weeks). Clinical and histologic progression of arthritis in the tmTNFalpha-transgenic/TNFalpha-KO mice was reduced by treatment with dexamethasone or with the p55 or p75 sTNFR (69% and 63% reduction in total histologic score, respectively).

CONCLUSION

These data show that arthritis is sufficiently initiated and maintained in tmTNFalpha-transgenic/TNFalpha-KO mice, and that it can be neutralized by recombinant human p55 or p75 sTNFR, resulting in amelioration of the biologic and subsequent histologic destructive effects of tmTNFalpha.

Contribution of TNF-alpha converting enzyme and proteinase-3 to TNF-alpha processing in human alveolar macrophages

Membrane-associated TNF-alpha cleavage is required to yield the 17.5-kD soluble product. This process is poorly understood in human cells, and no studies have related this process to the alveolar macrophage (AM). TNF-alpha-converting enzyme (TACE) is known to cleave TNF at the Ala-76-Val-77 site. We have evaluated the expression, regulation, and catalytic function of TACE in healthy human AMs. TACE was detected on the surface of AMs using flow cytometry. TACE protein can be upregulated by LPS (P = 0.036) and IFN-gamma. LPS-induced expression is downregulated by IL-10 (P = 0.04) and TNF-alpha. TACE regulation was observed at the mRNA level. TACE catalytic activity as assessed by cleavage of glutathione S-transferase-proTNF fusion protein correlates significantly with TACE protein expression (P = 0.04). However, cleavage and soluble TNF-alpha release by AMs was inhibited by matrix metalloproteinase and serine protease inhibitors, suggesting a role for a serine protease in this process. We confirmed the presence of proteinase-3 (PR-3) on the AM surface that was functionally capable of TNF cleavage. PR-3 mRNA expression was not found in AMs. However, we determined that PR-3 from neutrophil supernatants could bind to the AM membrane, suggesting that AM-derived PR-3 is from an exogenous source, which is important in the context of inflammation.

Regulation of peritoneal and systemic neutrophil-derived tumor necrosis factor-alpha release in patients with severe peritonitis: role of tumor necrosis factor-alpha converting enzyme cleavage

OBJECTIVE

Polymorphonuclear neutrophil (PMN) influx and peritoneal tumor necrosis factor (TNF)-alpha production are key host defense mechanisms during peritonitis. The aim of this study was to explore the potential interactions between TNF-alpha production and TNF-alpha converting enzyme (TACE) expression by PMN in the blood and peritoneum of patients with severe peritonitis.

DESIGN

A prospective study.

SETTING

A surgical adult intensive care unit in a university hospital.

PATIENTS

A total of 29 consecutive immunocompetent patients with severe sepsis within 48 hrs of onset were enrolled and underwent laparotomy for a diffuse secondary peritonitis. Thirteen volunteers served as controls.

MEASUREMENTS

Blood and peritoneal fluid recovered during laparotomy were analyzed and compared for 1) soluble TNF-alpha, soluble L-selectin, and type I and II TNF-alpha receptor levels; 2) PMN membrane TNF-alpha, membrane L-selectin, and TACE expression (flow cytometry); and 3) TNF-alpha production by cultured PMN. Correlations between these forms of PMN-derived TNF-alpha and the severity of the peritonitis and patient's outcome were investigated.

MAIN RESULTS

Elevated soluble TNF-alpha levels in both plasma and peritoneal fluid from the patients were found, together with decreased expression of membrane TNF-alpha and TACE up-regulation at the PMN surface. Soluble L-selectin and type I and II TNF receptors were highly released, suggesting also the role of TACE. In contrast, the capacity of both blood and peritoneal PMN to synthesize TNF-alpha in vitro, in optimal conditions of stimulation (lipopolysaccharide + interferon-gamma), was impaired as compared with controls' blood PMN. Regulation of PMN-derived TNF-alpha was similar in the two compartments, but responses were more pronounced in the peritoneum. TACE up-regulation at the surface of blood-derived PMN correlated with the Sequential Organ Failure Assessment score and vital outcome.

CONCLUSION

These human data demonstrate that mTACE is up-regulated at the PMN surface during severe peritonitis. This finding could be related to a paracrine regulatory loop involving some TACE substrates such as TNF-alpha, L-selectin, and TNF receptors.

Release of soluble CD40 ligand after platelet activation: studies on the solubilization phase

sCD40L is released from platelets as a soluble, proteolyzed form of CD40 ligand (CD40L; CD154) which is exposed on the surface after platelet activation. Ethylenediaminetetraacetate (EDTA), the CD40-blocking antibody G28-5, and GPIIb-IIIa antagonists are known to inhibit the solubilization when added prior to activation. It is assumed that the surface expression of CD40L is a result of a separate fast process and that the solubilization is secondary to this. The release of sCD40L in this solubilization phase has been studied; that is, inhibitory substances were added to platelet-rich plasma (PRP) 10 min after addition of the activation agonist (100 microM SFLLRN), at which time the secretion phase was over as tested with beta-thromboglobulin (beta-TG). G28-5 (10 microg/ml) and EDTA (5 mM) inhibited the solubilization phase which did not require the presence of an activation agonist. Prostaglandin E1 (PGE1; 20 microM) and cytochalasin D (C8273; 60 and 100 microM), which exert their effects intracellularly, inhibited the solubilization even in the presence of abciximab (ReoPro; 40 microg/ml). The intracellular effect was not related to CD40L-containing microparticles as demonstrated by ultracentrifugation. Intracellular alkalinization by preincubation of PRP with 20 mM NH4Cl for 60 min resulted in a small but reproducible reduction in the amount of extracellular sCD40L. SFLLRN induced solubilization of CD40L also from the platelets of a Glanzmann's thrombasthenia patient lacking GPIIb-IIIa, albeit at a lower rate than from normal platelets, and fibrinogen enhanced the solubilization from washed normal platelets. The data show that the solubilization of CD40L not only depends on reactions on the platelet surface but also that intracellular structures are engaged even during the solubilization phase.

Syntaxin 6 and Vti1b form a novel SNARE complex, which is up-regulated in activated macrophages to facilitate exocytosis of tumor necrosis Factor-alpha

A key function of activated macrophages is to secrete proinflammatory cytokines such as TNFalpha; however, the intracellular pathway and machinery responsible for cytokine trafficking and secretion is largely undefined. Here we show that individual SNARE proteins involved in vesicle docking and fusion are regulated at both gene and protein expression upon stimulation with the bacterial cell wall component lipopolysaccharide. Focusing on two intracellular SNARE proteins, Vti1b and syntaxin 6 (Stx6), we show that they are up-regulated in conjunction with increasing cytokine secretion in activated macrophages and that their levels are selectively titrated to accommodate the volume and timing of post-Golgi cytokine trafficking. In macrophages, Vti1b and syntaxin 6 are localized on intracellular membranes and are present on isolated Golgi membranes and on Golgi-derived TNFalpha vesicles budded in vitro. By immunoprecipitation, we find that Vti1b and syntaxin 6 interact to form a novel intracellular Q-SNARE complex. Functional studies using overexpression of full-length and truncated proteins show that both Vti1b and syntaxin 6 function and have rate-limiting roles in TNFalpha trafficking and secretion. This study shows how macrophages have uniquely adapted a novel Golgi-associated SNARE complex to accommodate their requirement for increased cytokine secretion.

Importance of Tumor Necrosis Factor-α Cleavage Process in Post-Transplantation Lung Injury in Rats

Tumor necrosis factor-alpha (TNF-alpha) has two forms with apparently different biological activities: a membrane-associated form and a soluble form. TNF-alpha-converting enzyme (TACE) mediates a cleavage of membrane-associated TNF-alpha to induce its bioactive soluble form. We hypothesized that inhibition of TACE might prevent TNF-alpha-induced tissue injury while preserving the benefits of TNF-alpha. In this study, we evaluated the role of TACE in acute inflammation using an inhibitor of the enzyme in a rat model of lung transplantation. Inbred Lewis rats underwent left lung isotransplantation, and the donor lungs were kept in Euro-Collins solution with or without the inhibitor. After 6 hours of ischemia, the left lung was transplanted into the recipient rat and reperfused for 4 hours. Inhibition of TACE significantly attenuated endothelial and alveolar septal damage, as assessed by radiolabeled albumin leakage after transplantation. The inhibition also attenuated neutrophil accumulation in the alveolar space and other histopathologic findings, including intercellular adhesion molecule-1 expression. In addition, significantly lower levels of monocyte chemotactic protein-1, cytokine-induced neutrophil chemoattractant-1, high mobility group box-1, and soluble epithelial cadherin and decreased neutrophil elastase activity were observed in bronchoalveolar lavage fluid from the rats treated with the inhibitor. We conclude that TACE mediates a critical step in the development of post-transplantation lung injury.

Justicidin A inhibits the transport of tumor necrosis factor-alpha to cell surface in lipopolysaccharide-stimulated RAW 264.7 macrophages

Exposure of macrophages to lipopolysaccharide (LPS) induces release of tumor necrosis factor-alpha (TNF-alpha), which is initially synthesized as a 26-kDa pro-TNF-alpha followed by proteolytic processing to a 17-kDa secreted form. In this study, justicidin A, an arylnaphthalide lignan isolated from Justicia procumbens, was found to inhibit LPS-stimulated TNF-alpha release from RAW 264.7 macrophages in a concentration- and time-dependent manner, and the underlying mechanism was investigated. In the presence of justicidin A, challenge with LPS increased the steady-state level of the 26-kDa membrane-bound form of TNF-alpha protein, whereas justicidin A had little effect on the expression of TNF-alpha mRNA and on the synthesis of pro-TNF-alpha protein. Results of the pulse-chase experiment, revealed that the conversion of pro-TNF-alpha to mature TNF-alpha was inhibited by justicidin A. Moreover, justicidin A suppressed the transport of TNF-alpha to cell surface as analyzed by flow cytometry. The immunofluorescence analysis demonstrated that large amounts of LPS-induced TNF-alpha accumulated primarily within Golgi complex. These results indicate that justicidin A inhibits TNF-alpha release at the step of transport of pro-TNF-alpha to cell surface, and this leads to the accumulation of TNF-alpha in Golgi complex in RAW 264.7 macrophages.

Effect of His-Gly-Lys motif derived from domain 5 of high molecular weight kininogen on suppression of cancer metastasis both in vitro and in vivo

We have demonstrated previously that kinin-free high molecular weight kininogen, its domain 5 (D5H, Gly402-Lys502), and peptides derived from D5H inhibited vitronectin-mediated migration and invasion of cancer cells in vitro (Kamiyama, F., Maeda, T., Yamane, T., Li, Y. H., Ogikubo, O., Otsuka, T., and Ohkubo, I. (2001) Biochem. Biophys. Res. Commun. 288, 975-980). In this study, we found that the amino acid sequence His-Gly-Lys (HGK) in D5H is the core motif for inhibition of adhesion and invasion of MDA-MB-231 cells in vitro. P-5m (484GHGKHKNK491, Gly484-Lys491), an octapeptide including the HGK motif derived from D5H, and HGK, a tripeptide, inhibited both cell adhesion and invasion in vitro. However, an octapeptide designated P-5m (K487R), in which Lys487 was changed to Arg, did not inhibit either cell adhesion or invasion, and peptides HGR and HGG also had no inhibitory effect. Recombinant GST-D5H expressed in Escherichia coli had a stronger inhibitory effect on cell adhesion and invasion in vitro than did GST-D5H (K487R) in which Lys487 was changed to Arg. Furthermore, P-5m (Gly484-Lys491) peptide clearly suppressed lung metastasis in mice experimentally induced by using B16-F10 cells, but P-5m (G487R) had no effect. These data strongly indicate that both the HGK motif and lysine residue (Lys487) play essential roles in inhibition of cell adhesion and invasion in vitro and in prevention of metastasis of cancer cells in vivo. We tried to identify the HGK motif binding protein on the surface of cancer cells. A 95-kDa surface biotin-labeled membrane protein was specifically detached from GST-D5H by P-5 (His479-Lys493) peptide but not by P-1 (Gly402-Lys420) peptide originating from the N-terminal region of D5H.

The t-SNARE syntaxin 4 is regulated during macrophage activation to function in membrane traffic and cytokine secretion

Activation of macrophages with lipopolysaccharide (LPS) induces the rapid synthesis and secretion of proinflammatory cytokines, such as tumor necrosis factor (TNFalpha), for priming the immune response. TNFalpha plays a key role in inflammatory disease; yet, little is known of the intracellular trafficking events leading to its secretion. In order to identify molecules involved in this secretory pathway, we asked whether any of the known trafficking proteins are regulated by LPS. We found that the levels of SNARE proteins were rapidly and significantly up- or downregulated during macrophage activation. A subset of t-SNAREs (Syntaxin 4/SNAP23/Munc18c) known to control regulated exocytosis in other cell types was substantially increased by LPS in a temporal pattern coinciding with peak TNFalpha secretion. Syntaxin 4 formed a complex with Munc18c at the cell surface of macrophages. Functional studies involving the introduction of Syntaxin 4 cDNA or peptides into macrophages implicate this t-SNARE in a rate-limiting step of TNFalpha secretion and in membrane ruffling during macrophage activation. We conclude that, in macrophages, SNAREs are regulated in order to accommodate the rapid onset of cytokine secretion and for membrane traffic associated with the phenotypic changes of immune activation. This represents a novel regulatory role for SNAREs in regulated secretion and in macrophage-mediated host defense.