DRG2 in macrophages is crucial for initial inflammatory response and protection against Listeria monocytogenes infection.

Innate immune response is critical for the control of Listeria monocytogenes infection. Here, we identified developmentally regulated GTP-binding protein 2 (DRG2) in macrophages as a major regulator of the innate immune response against L. monocytogenes infection. Both whole-body DRG2 knockout (KO) mice and macrophage-specific DRG2 KO mice had low levels of IL-6 during early infection and increased susceptibility to L. monocytogenes infection. Following an initial impaired inflammatory response of macrophages upon i.p. L. monocytogenes infection, DRG2-/- mice showed delayed recruitment of neutrophils and monocytes into the peritoneal cavity, which led to elevated bacterial burden, inflammatory cytokine production at a late infection time point, and liver micro-abscesses. DRG2 deficiency decreased the transcriptional activity of NF-κB and impaired the inflammatory response of both bone marrow-derived and peritoneal macrophages upon L. monocytogenes stimulation. Our findings reveal that DRG2 in macrophages is critical for the initial inflammatory response and protection against L. monocytogenes infection.

Activation of ROS-PERK-TFEB by filbertone ameliorates neurodegenerative diseases via enhancing the autophagy-lysosomal pathway.

The molecular mechanisms underlying the pathogenesis of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease (PD), and Huntington's disease remain enigmatic, resulting in an unmet need for therapeutics development. Here, we suggest that filbertone, a key flavor compound found in the fruits of hazel trees of the genus Corylus, can ameliorate PD via lowering the abundance of aggregated α-synuclein. We previously reported that inhibition of hypothalamic inflammation by filbertone is mediated by suppression of nuclear factor kappa-B. Here, we report that filbertone activates PERK through mitochondrial reactive oxygen species production, resulting in the increased nuclear translocation of transcription factor-EB in SH-SY5Y human neuroblastoma cells. TFEB activation by filbertone promotes the autophagy-lysosomal pathway, which in turn alleviates the accumulation of α-synuclein. We also demonstrate that filbertone prevented the loss of dopaminergic neurons in the substantia nigra and striatum of mice on high-fat diet. Filbertone treatment also reduced high-fat diet-induced α-synuclein accumulation through upregulation of the autophagy-lysosomal pathway. In addition, filbertone improved behavioral abnormalities (i.e., latency time to fall and decrease of running distance) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced PD murine model. In conclusion, filbertone may show promise as a potential therapeutic for neurodegenerative disease.

PERK activation by SB202190 ameliorates amyloidogenesis via the TFEB-induced autophagy-lysosomal pathway.

The protein kinase R (PKR)-like endoplasmic reticulum (ER) kinase (PERK), a key ER stress sensor of the unfolded protein response (UPR), can confer beneficial effects by facilitating the removal of cytosolic aggregates through the autophagy-lysosome pathway (ALP). In neurodegenerative diseases, the ALP ameliorates the accumulation of intracellular protein aggregates in the brain. Transcription factor-EB (TFEB), a master regulator of the ALP, positively regulates key genes involved in the cellular degradative pathway. However, in neurons, the role of PERK activation in mitigating amyloidogenesis by ALP remains unclear. In this study, we found that SB202190 selectively activates PERK independently of its inhibition of p38 mitogen-activated protein kinase, but not inositol-requiring transmembrane kinase/endoribonuclease-1α (IRE1α) or activating transcription factor 6 (ATF6), in human neuroblastoma cells. PERK activation by SB202190 was dependent on mitochondrial ROS production and promoted Ca2+-calcineurin activation. The activation of the PERK-Ca2+-calcineurin axis by SB202190 positively affects TFEB activity to increase ALP in neuroblastoma cells. Collectively, our study reveals a novel physiological mechanism underlying ALP activation, dependent on PERK activation, for ameliorating amyloidogenesis in neurodegenerative diseases.

Anti-4-1BB antibody-based combination therapy augments antitumor immunity by enhancing CD11c+CD8+ T cells in renal cell carcinoma.

To improve the potential treatment strategies of incurable renal cell carcinoma (RCC), which is highly resistant to chemotherapy and radiotherapy, the present study established a combination therapy with immunostimulatory factor (ISTF) and anti-4-1BB monoclonal antibodies (mAbs) to augment the antitumor response in a murine RCC model. ISTF isolated from Actinobacillus actinomycetemcomitans stimulates macrophages, dendritic cells and B cells to produce IL-6, TNF-α, nitric oxide and major histocompatibility complex class II expression. 4-1BB (CD137) is expressed in activated immune cells, including activated T cells, and is a promising target for cancer immunotherapy. The administration of anti-4-1BB mAbs promoted antitumor immunity via enhancing CD11c+CD8+ T cells. The CD11c+CD8+ T cells were characterized by high killing activity and IFN-γ-producing ability, representing a phenotype of active effector cytotoxic T lymphocytes. The present study showed that combination therapy with ISTF and anti-4-1BB mAbs promoted partial tumor regression with established RCC, but monotherapy with ISTF or anti-4-1BB mAbs did not. These effects were speculated to be caused by the increase in CD11c+CD8+ T cells in the spleen and tumor, and IFN-γ production. These insights into the effector mechanisms of the combination of ISTF and anti-4-1BB mAbs may be useful for targeting incurable RCC.

Pretreatment with 6-Gingerol Ameliorates Sepsis-Induced Immune Dysfunction by Regulating the Cytokine Balance and Reducing Lymphocyte Apoptosis.

Sepsis is characterized by an initial net hyperinflammatory response, followed by a period of immunosuppression, termed immunoparalysis. During this immunosuppressive phase, patients may have difficulty eradicating invading pathogens and are susceptible to life-threatening secondary hospital-acquired infections. Due to progress in antimicrobial treatment and supportive care, most patients survive early sepsis. Mortality is more frequently attributed to subsequent secondary nosocomial infections and multiorgan system failure. 6-Gingerol is the major pharmacologically active component of ginger. Although it is known to exhibit a variety of biological activities, including anti-inflammation and antioxidation, the role of 6-gingerol in sepsis-induced immune dysfunction remains elusive. Thus, we investigated whether 6-gingerol improves septic host response to infections during sepsis. 6-Gingerol-treated mice showed significantly lower mortality in polymicrobial sepsis induced by cecal ligation and puncture LPS via enhanced bacterial clearance in the peritoneum, blood, and organs (liver, spleen, and kidney) and inhibited the production of TNF-α and IL-6 in TLR2 and/or TLR4-stimulated macrophages. In addition, we demonstrated that survival improvement of secondary infection following septic insult was associated with an initial response of enhanced neutrophil numbers and function at the infection site, reduced apoptosis of immune cells, and a shift from a T helper cell type 2 (Th2) to a T helper cell type 1 (Th1) cytokine balance in the hypoinflammation phase. Our overall findings suggest that 6-gingerol potentially restores sepsis-induced immune dysfunction by shifting the balance of Th1/Th2 and by regulating apoptosis of immune cells.

The involvement of 4-1BB/4-1BBL signaling in glial cell-mediated hypothalamic inflammation in obesity.

Obesity-induced inflammation occurs not only in peripheral tissues but also in areas of the central nervous system. Glial cells such as astrocytes and microglia play crucial roles in obesity-related hypothalamic inflammation, leading to the derangement of energy metabolism and neurodegenerative pathologies. Here, we show that the interaction of 4-1BB/4-1BBL between lipid-laden astrocytes/microglia promotes hypothalamic inflammation in obesity. Stimulation of 4-1BB, a member of the TNF receptor superfamily, and/or its ligand 4-1BBL on astrocytes and/or microglia with a specific agonist resulted in activation of the inflammatory signaling pathway and enhanced production of inflammatory mediators. Contact coculture of lipid-laden astrocytes and microglia increased the production of inflammatory mediators, and blockade of the 4-1BB/4-1BBL interaction reduced the inflammatory response. Moreover, deficiency of 4-1BB reduced hypothalamic inflammation in obese mice fed an high-fat diet. These findings suggest that 4-1BBL/4-1BB signaling enhances the glial cell-mediated inflammatory cross talk and participates in obesity-induced hypothalamic inflammation.

The novel resveratrol derivative 3,5-diethoxy-3',4'-dihydroxy-trans-stilbene induces mitochondrial ROS-mediated ER stress and cell death in human hepatoma cells in vitro.

Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a well-known polyphenol that is present in grapes, peanuts, pine seeds, and several other plants. Resveratrol exerts deleterious effects on various types of human cancer cells. Here, we analyzed the cell death-inducing mechanisms of resveratrol-006 (Res-006), a novel resveratrol derivative in human liver cancer cells in vitro. Res-006 was more effectively suppressed the viability of HepG2 human hepatoma cells than resveratrol (the IC50 values were 67.2 and 354.8 µmol/L, respectively). Co-treatment with the ER stress regulator 4-phenylbutyrate (0.5 mmol/L) or the ROS inhibitor N-acetyl-L-cysteine (NAC, 1 mmol/L) significantly attenuated Res-006-induced HepG2 cell death, suggesting that pro-apoptotic ER stress and/or ROS may govern the Res-006-induced HepG2 cell death. We further revealed that treatment of HepG2 cells with Res-006 (65 µmol/L) immediately elicited the dysregulation of mitochondrial dynamics and the accumulation of mitochondrial ROS. It also collapsed the mitochondrial membrane potential and further induced ER stress and cell death. These events, except for the change in mitochondrial morphology, were prevented by the exposure of the HepG2 cells to the mitochondrial ROS scavenger, Mito-TEMPO (300-1000 µmol/L). The results suggest that Res-006 may kill HepG2 cells through cell death pathways, including the ER stress initiated by mitochondrial ROS accumulation. The cell death induced by this novel resveratrol derivative involves crosstalk between the mitochondria and ER stress mechanisms.

Absence of 4-1BB reduces obesity-induced atrophic response in skeletal muscle.

Obesity-induced inflammation causes skeletal muscle atrophy accompanied by disruption of oxidative metabolism and is implicated in metabolic complications such as insulin resistance and type 2 diabetes. We previously reported that 4-1BB, a member of the tumor necrosis factor receptor superfamily, participated in obesity-induced skeletal muscle inflammation. Here, we show that the absence of 4-1BB in obese mice fed a high-fat diet led to a decrease in expression of atrophic factors (MuRF1 and Atrogin-1) with suppression of NF-κB activity, and that this was accompanied by increases in mitochondrial oxidative metabolic genes/proteins (e.g., PGC-1α, CPT1ß, etc.) expression and oxidative muscle fibers marker genes/proteins in the skeletal muscle. These findings suggest that 4-1BB-mediated inflammatory signaling could be a potential target for combating obesity-related muscle atrophy and metabolic derangement in skeletal muscle.

IL-33-induced hematopoietic stem and progenitor cell mobilization depends upon CCR2.

IL-33 has been implicated in the pathogenesis of asthma, atopic allergy, anaphylaxis, and other inflammatory diseases by promoting the production of proinflammatory cytokines and chemokines or Th2 immune responses. In this study, we analyzed the in vivo effect of IL-33 administration. IL-33 markedly promoted myelopoiesis in the bone marrow and myeloid cell emigration. Concomitantly, IL-33 induced hematopoietic stem and progenitor cell (HSPC) mobilization and extramedullary hematopoiesis. HSPC mobilization was mediated mainly through increased levels of CCL7 produced by vascular endothelial cells in response to IL-33. In vivo treatment of IL-33 rapidly induced phosphorylation of ERK, JNK, and p38, and inhibition of these signaling molecules completely blocked the production of CCL7 induced by IL-33. Consistently, inhibitor of CCR2 markedly reduced IL-33-mediated HSPC mobilization in vivo and migration of HSPCs in response to CCL7 in vitro. IL-33-mobilized HSPCs were capable of homing to, and of long-term reconstitution in, the bone marrow of irradiated recipients. Immune cells derived from these recipients had normal antifungal activity. The ability of IL-33 to promote migration of HSPCs and myeloid cells into the periphery and to regulate their antifungal activity represents a previously unrecognized role of IL-33 in innate immunity. These properties of IL-33 have clinical implications in hematopoietic stem cell transplantation.

Neural epidermal growth factor-like like protein 2 (NELL2) promotes aggregation of embryonic carcinoma P19 cells by inducing N-cadherin expression.

NELL2 was first identified as a mammalian homolog of chick NEL (Neural EGF-like) protein. It is almost exclusively expressed in neurons of the rat brain and has been suggested to play a role in neural differentiation. However, there is still no clear evidence for the detailed function of NELL2 in the differentiation of neurons. In this study, we identified NELL2 function during neural differentiation of mouse embryonic carcinoma P19 cells. Endogenous expression of NELL2 in the P19 cells increased in parallel with the neuronal differentiation induced by retinoic acid (RA). We found that the mouse NELL2 promoter contains RA response elements (RAREs) and that treatment with RA increased NELL2 promoter activity. Transfection of P19 cells with NELL2 expression vectors induced a dramatic increase in cell aggregation, resulting in the facilitation of neural differentiation. Moreover, NELL2 significantly increased N-cadherin expression in the P19 cell. These data suggest that NELL2 plays an important role in the regulation of neuronal differentiation via control of N-cadherin expression and cell aggregation.

Involvement of CD137 ligand signaling in neural stem cell death.

CD137 is a member of the tumor necrosis factor/nerve growth factor receptor superfamily. Interaction of CD137 with its ligand (CD137L) affects the apoptosis, proliferation and differentiation of immune cells. Interestingly, the CD137 receptor/ligand system involves the bi-directional transduction of signals. The expression of CD137 and its ligand is not restricted to immune organs, but can also be detected in a wide variety of tissues such as the brain, kidney, lung and heart. However, its role in brain is largely unknown. This study was performed to determine the role of CD137L reverse signaling in the apoptosis of neural stem cells. We identified the expression of CD137 and its ligand in C17.2 neural stem cells derived from mouse embryonic cerebellum. We found that the activation of CD137L reverse signaling by CD137 resulted in a decrease in cell adhesion to the fibronectin-coated culture basement, thus causing detachment-induced cell death. Furthermore, we showed that the cell death induced by CD137 was completely ameliorated by integrin activators and caspase inhibitors. Therefore we suggest that CD137L reverse signaling exerts a pro-apoptotic effect by suppressing integrin-mediated survival signals in neural stem cells.

CD137 expressed on neutrophils plays dual roles in antibacterial responses against Gram-positive and Gram-negative bacterial infections.

Severe sepsis and septic shock caused mainly by bacterial infections are life-threatening conditions that urge the development of novel therapies. However, host responses to and pathophysiology of sepsis have not been clearly understood, which remains a major obstacle for the development of effective therapeutics. Recently, we have shown that stimulation of a costimulatory molecule, CD137, enhanced survival of mice infected with the Gram-positive (G(+)) intracellular bacterium Listeria monocytogenes but decreased survival in a polymicrobial sepsis model. Herein, we report that CD137 deficiency or blocking of CD137 signaling decreased antibacterial responses of mice infected with G(+) bacteria (Staphylococcus aureus, Streptococcus pneumoniae, and Enterococcus faecalis) but increased these responses in mice infected with Gram-negative (G(-)) bacteria (Escherichia coli, Pseudomonas aeruginosa, and Salmonella enterica serovar Typhimurium). Consistent with these findings, stimulation of CD137 by administration of agonistic antibody enhanced responses against G(+) bacteria, whereas it decreased these responses against G(-) bacteria. Neutrophils were responsible for CD137-mediated opposite roles in control of G(+) and G(-) bacterial infections. Stimulation of CD137 enhanced activities of neutrophils against S. aureus but decreased these activities against E. coli, while CD137 blocking produced opposite results with the stimulation of CD137 in vivo and in vitro. Furthermore, we found that combined signaling of CD137 and Toll-like receptor 2 (TLR2) induced synergistic production of tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) by neutrophils, but combined signaling of CD137 and TLR4 did not. Our data strongly suggest that CD137 may play a dual role in sepsis in association with TLRs.

Blockade of 4-1BB and 4-1BBL interaction reduces obesity-induced skeletal muscle inflammation.

Obesity-induced skeletal muscle inflammation is characterized by increased macrophage infiltration and inflammatory cytokine production. In this study, we investigated whether 4-1BB, a member of the TNF receptor superfamily (TNFRSF9) that provides inflammatory signals, participates in obesity-induced skeletal muscle inflammation. Expression of the 4-1BB gene, accompanied by increased levels of inflammatory cytokines, was markedly upregulated in the skeletal muscle of obese mice fed a high-fat diet, in muscle cells treated with obesity factors, and in cocultured muscle cells/macrophages. In vitro stimulation of 4-1BB with agonistic antibody increased inflammatory cytokine levels in TNFα-pretreated muscle cells, and this effect was absent in cells derived from 4-1BB-deficient mice. Conversely, disruption of the interaction between 4-1BB and its ligand (4-1BBL) with blocking antibody decreased the release of inflammatory cytokines from cocultured muscle cells/macrophages. Moreover, deficiency of 4-1BB markedly reduced macrophage infiltration and inflammatory cytokine production in the skeletal muscle of mice fed a high-fat diet. These findings indicate that 4-1BB mediates the inflammatory responses in obese skeletal muscle by interacting with its ligand 4-1BBL on macrophages. Therefore, 4-1BB and 4-1BBL may be useful targets for prevention of obesity-induced inflammation in skeletal muscle.

4-1BB/4-1BBL interaction promotes obesity-induced adipose inflammation by triggering bidirectional inflammatory signaling in adipocytes/macrophages.

Obesity-induced adipose inflammation is characterized by recruitment of macrophages to adipose tissue and release of inflammatory cytokines. 4-1BB, a costimulatory receptor, modulates inflammatory processes through interaction with its ligand 4-1BBL on immune cell surfaces. In this study, we examined whether a 4-1BB/4-1BBL interaction between adipocytes and macrophages participates in obesity-induced adipose inflammation. We found that 4-1BB was expressed on adipocytes and was upregulated by obesity-related factors, which also enhanced 4-1BBL expression on macrophages. 4-1BB and/or 4-1BBL agonists, respectively, activated inflammatory signaling molecules (MAPK/IκBα and MAPK/Akt) in adipocytes and macrophages and enhanced the release of inflammatory cytokines (MCP-1, TNF-α, and IL-6). Moreover, disruption of the 4-1BB/4-1BBL interaction decreased the release of inflammatory cytokines from contact cocultured adipocytes/macrophages. These findings indicate that 4-1BB/4-1BBL-mediated bidirectional signaling in adipocytes/macrophages promotes adipose inflammation. 4-1BB and 4-1BBL may be useful targets for protection against obesity-induced adipose inflammation.

Administration of 6-gingerol greatly enhances the number of tumor-infiltrating lymphocytes in murine tumors.

Tumor-infiltrating lymphocytes (TILs) play critical roles in host antitumor immune responses. It is known that cancer patients with tumor-reactive lymphocyte infiltration in their tumors have better prognoses, while patients with tumors infiltrated by immunosuppressive cells have worse prognoses. We found that administration of 6-gingerol, which is a component of ginger, inhibited tumor growth in several types of murine tumors, such as B16F1 melanomas, Renca renal cell carcinomas and CT26 colon carcinomas, which were established by inoculating tumor cells on the flanks of mice. However, administration of 6-gingerol did not lead to complete eradication of the tumors. 6-Gingerol treatment of tumor-bearing mice caused massive infiltration of CD4 and CD8 T-cells and B220(+) B-cells, but reduced the number of CD4(+) Foxp3(+) regulatory T-cells. The CD8 tumor-infiltrating T lymphocytes in 6-gingerol-treated mice strongly expressed IFN-γ, a marker of activation of cytotoxic T lymphocytes (CTL) CD107a and chemokine receptors that are expressed on T(H) 1 cells, such as CXCR3 and CCR5. To test whether 6-gingerol could promote infiltration of tumor antigen-specific CD8 T-cells into tumors, we adoptively transferred CFSE-labeled OT-1 CD8 T-cells into EG7 tumor-bearing mice. We found that CD8 T cells isolated from 6-gingerol pretreated OT-1 mice, but not from control OT-1 mice, massively infiltrated tumors and tumor draining lymph nodes and divided several times. Our results strongly suggest that 6-gingerol can be used in tumor immunotherapy to increase the number of TILs.

The presence of high level soluble herpes virus entry mediator in sera of gastric cancer patients.

The development of gastric cancer (GC) is closely related to chronic inflammation caused by Helicobacter pylori infection, and herpes virus entry mediator (HVEM) is a receptor expressed on the surface of leukocytes that mediates potent inflammatory responses in animal models. However, the role of HVEM in human GC has not been studied. Previously, we showed that the interaction of HVEM on human leukocytes with its ligand LIGHT induces intracellular calcium mobilization, which results in inflammatory responses including induction of proinflammatory cytokine production and anti-bacterial activities. In this study, we report that leukocytes from GC patients express lower levels of membrane HVEM (mHVEM) and have lower LIGHT-induced bactericidal activities than those from healthy controls (HC). In contrast, levels of soluble HVEM (sHVEM) in the sera of GC patients were significantly higher than in those of HC. We found that monocyte membrane-bound HVEM is released into the medium when cells are activated by proinflammatory cytokines such as TNF-α and IL-8, which are elevated in the sera of GC patients. mHVEM level dropped in parallel with the release of sHVEM, and release was completely blocked by the metalloprotease inhibitor, GM6001. We also found that the low level of mHVEM on GC patient leukocytes was correlated with low LIGHT-induced bactericidal activities against H. pylori and S. aureus and production of reactive oxygen species. Our results indicate that mHVEM on leukocytes and sHVEM in sera may contribute to the development and/or progression of GC.

HVEM-deficient mice fed a high-fat diet are protected from adipose tissue inflammation and glucose intolerance.

HVEM is a member of the TNF receptor superfamily that plays a role in the development of various inflammatory diseases. In this study, we show that HVEM deficiency attenuates adipose tissue inflammatory responses and glucose intolerance in diet-induced obesity. Feeding a high-fat diet (HFD) to HVEM-deficient mice elicited a reduction in the number of macrophages and T cells infiltrated into adipose tissue. Proinflammatory cytokine levels in the adipose tissue decreased in HFD-fed HVEM-deficient mice, while levels of the anti-inflammatory cytokine IL-10 increased. Moreover, glucose intolerance and insulin sensitivity were markedly improved in the HFD-fed HVEM-deficient mice. These findings indicate that HVEM may be a useful target for combating obesity-induced inflammatory responses and insulin resistance.

Characterization of Kunitz-type protease inhibitor purified from hemolymph of Galleria mellonella larvae.

We characterized a Kunitz-type protease inhibitor (Gm KTPI) obtained from the hemolymph of Galleria mellonella larvae immunized with Escherichia coli. The structural analysis of the cloned cDNA showed that it consists of 56 residues derived from the precursor of 75 amino acids. The peptide was constitutively produced in the fat bodies, but not in the midgut nor the integument of larvae. In our analysis of stage-dependent expression, its transcript was detected within the midgut, the fat bodies and the integument of the prepupae, which undergo tissue remodeling. The inhibition assays showed that Gm KTPI was capable of inhibiting only the trypsin-like activity of the larval midgut extracts. Furthermore, it was determined that Gm KTPI induced the activation of extracellular signal-regulated kinase (ERK) in the fat bodies and integument cells, and this kinase is known to perform a central role in cell proliferation signaling. Its effect on ERK activation was also verified in a control experiment using a human endothelial cell culture. Collectively, it was suggested that Gm KTPI might be responsible for the protection of other tissues against proteolytic attack by trypsin-like protease(s) from larval midgut during metamorphosis, and might play a role in the proliferation of cells in the fat body and integument.

The immune signaling molecule 4-1BB stimulation reduces adiposity, insulin resistance, and hepatosteatosis in obese mice.

Immune cells (e.g. macrophages and T cells) in adipose tissue play a crucial role in the development of obesity-induced inflammation and metabolic disorders. Here we report findings suggesting that the immune signaling molecule 4-1BB/CD137 is a novel target for treatment of obesity and metabolic disorders. 4-1BB stimulation with agonistic antibody reduced body weight and adiposity and markedly improved glucose intolerance and hepatosteatosis in diet-induced obese mice and genetically obese/diabetic mice. Increases in lymphoid T cell expansion/activation and adipose/hepatic CD8+ T cell recruitment were evident in the anti-4-1BB antibody-treated obese mice. Glycolysis, ß-oxidation, and oxygen consumption rates also increased in the treated mice. These findings suggest that 4-1BB-stimulation accompanied by CD8+ T cell expansion/activation enhances glucose/lipid metabolism, leading to increased energy expenditure. Manipulation of 4-1BB may provide a unique immunological strategy against obesity and metabolic disorders.

Blockade of CD137 signaling counteracts polymicrobial sepsis induced by cecal ligation and puncture.

Sepsis, a leading cause of death worldwide, involves proinflammatory responses and inefficient bacterial clearance. Previously, we have shown that CD137 (4-1BB), a member of the tumor necrosis factor receptor superfamily, plays critical roles in eradicating infective Listeria monocytogenes, a gram-positive bacterium, and that stimulation of CD137 protects mice from sepsis-induced death. In this study, we unexpectedly found that CD137 activation aggravated polymicrobial sepsis due to mixed gram-positive and gram-negative bacterial infection induced by cecal ligation and puncture (CLP). CD137-deficient (CD137(-/-)) mice showed significantly lower mortality than CD137-sufficient (CD137(+/+)) mice in the CLP model. Administration of an agonistic anti-CD137 monoclonal antibody (MAb) to CD137(+/+) mice decreased their survival in this infection model, while administration of a blocking anti-CD137 ligand MAb (TKS-1) to such mice increased their survival. CD137(-/-) mice and TKS-1-treated CD137(+/+) mice had lower levels of chemokines/proinflammatory cytokines (monocyte chemoattractant protein 1, interleukin-6 [IL-6], tumor necrosis factor alpha, IL-12) and an anti-inflammatory cytokine (IL-10), exhibited improved bacterial clearance in the peritoneum, liver, and blood, and had greater numbers of infiltrated peritoneal neutrophils and macrophages in the CLP model than control mice. Our data suggest that CD137 activation aggravates polymicrobial sepsis induced by CLP.