Response of brain-derived neurotrophic factor to combining cognitive and physical exercise.

PURPOSE: Brain-derived neurotrophic factor (BDNF) is well known for its potential to promote brain plasticity. It has been proposed that combining cognitive and physical exercise (CCPE) may have the potential to generate more synergistic benefits in cognitive function than either cognitive exercise (CE) or physical exercise (PE) alone. The purpose of this study was to examine acute responses of peripheral BDNF levels and cognitive performance to CE, PE, and CCPE. METHODS: Thirteen healthy adult men participated in four experimental sessions; a 30-min CE, a 30-min cycling PE at an intensity of 60% peak oxygen uptake, a 30-min CCPE at the same intensity as PE, and a 30-min session of complete rest. Plasma BDNF levels and cognitive performance were measured before and after each session. RESULTS: Both PE and CCPE significantly increased plasma BDNF levels (p < .05). CE led to no significant increase (p ≥ .05), and there was no significant difference in peripheral BDNF levels between PE and CCPE (p ≥ .05). No session induced a significant change in cognitive performance (p ≥ .05). CONCLUSIONS: Our study suggests that CE and PE have different responses of peripheral BDNF levels and that CCPE had no additional or synergistic effect on peripheral BDNF levels compared with PE alone. This study offers further insights into the potential mechanisms underlying the respective roles of CE, PE, and CCPE for peripheral BDNF levels and cognitive performance.

Effect of Neuromuscular Electrical Stimulation on Brain-derived Neurotrophic Factor.

Brain-derived neurotrophic factor (BDNF) has been considered an essential mediator responsible for the beneficial effects of physical activity in preventing cognitive impairment. This study aimed at examining the effects of a single bout of neuromuscular electrical stimulation (NMES) on levels of BDNF in the plasma and on cognitive performance in healthy adult men. Thirteen healthy adult men participated in three experimental sessions. The first session was 30 min of NMES to both legs, the second was 30 min of cycling exercise at the intensity of 60% peak oxygen uptake, and the third was 30 min of complete rest. Blood was examined for plasma BDNF levels and glucose concentrations, and cognitive performance tests were performed before and after each session. A single bout of NMES significantly increased plasma BDNF levels (p<0.05), which were equivalent to the amount of plasma BDNF released during the exercise session (p>0.05). However, there were no significant changes in cognitive performance between the sessions (p>0.05). The present study found that a single bout of NMES significantly increased plasma BDNF to levels normally present during moderate voluntary exercise. Therefore, NMES could serve as an alternative method of exercise, and might shed light on individuals for whom voluntary physical exercise is contraindicated.

Cisplatin-induced acute renal failure in mice is mediated by chymase-activated angiotensin-aldosterone system and interleukin-18.

Mechanism(s) of cisplatin-induced acute renal failure, as manifested by increases in blood urea nitrogen and creatinine, was evaluated in relation to production and activation of endogenous mediator(s) in mice. In interleukin (IL)-18-deficient (IL-18KO) mice, cisplatin failed to induce acute renal failure. Administration of recombinant IL-18 prior to cisplatin restored acute renal failure in IL-18KO mice. Accumulation of cisplatin in the kidney was not different in IL-18KO and wild-type (WT) mice, but, clearance of cisplatin was more rapid in IL-18KO mice than in WT mice. Cisplatin increased serum levels of aldosterone and angiotensin II in WT mice, but only angiotensin II levels in IL-18 KO mice. Administration of IL-18 augmented plasma levels of aldosterone and angiotensin II in WT mice. Eplerenone, an aldosterone receptor blocker, TY-51469, a chymase inhibitor and PD123319, a selective angiotensin II type 2 (AT2) receptor antagonist, but not benazepril, an angiotensin-converting enzyme inhibitor, and candesartan, a selective angiotensin II type 1 (AT1) receptor antagonist improved acute renal failure caused by cisplatin, confirming involvement of IL-18, aldosterone and angiotensin II in cisplatin-induced, chymase-dependent acute renal failure in mice. These results show that IL-18, aldosterone and angiotensin II synergistically act to prolong the accumulation of cisplatin in the kidney, leading to acute renal failure. Combined therapy with inhibitors for chymase and aldosterone receptors or AT2 receptors might reduce acute renal failure induced by cisplatin.

Abrogation of Treg function deteriorates rheumatoid arthritis.

An early prognostic indicator which warns of progressive joint destruction of rheumatoid arthritis (RA) was explored using a novel suspension-array technique in moderate (Steinbrocker stage I and II) and severe (Steinbrocker stage IV) RA patients. DNA microarray analysis of peripheral blood lymphocytes showed significant increase of interleukin (IL)-2 receptor α-chain (CD25) gene expression, a regulatory T cell (Treg) surface marker in severe RA patients. In contrast, suspension array, a comprehensive bead-based enzyme-linked immunosorbent assay (ELISA), revealed decreased production of IL-10 and increased production of interferon (IFN)-γ in sera in the incipient stage of the aggressive disease process. Both in moderate and in severe RA patients, the IFN-γ/IL-10 ratio indicated deterioration of the disease with universal validity. Fluorescence-activated cell sorting (FACS) and reverse-transcription polymerase chain reaction (RT-PCR) analysis showed extant CD4+CD25+ regulatory T cells in severe RA patients, however Foxp3, a regulatory T cell-specific transcription factor, gene expression was absent, while glucocorticoid-induced tumor necrosis factor (TNF) receptor family-related protein (GITR), which transmits a signal that abrogates regulatory T cell functions, was elevated. In the current study, we showed the validity of suspension-array analysis for enabling more complete understanding of RA, and showed that IFN-γ/IL-10 ratio can be a prognostic tool for early lesion and more aggressive RA.

Immunodeficiency reduces neural stem/progenitor cell apoptosis and enhances neurogenesis in the cerebral cortex after stroke.

Acute inflammation in the poststroke period exacerbates neuronal damage and stimulates reparative mechanisms, including neurogenesis. However, only a small fraction of neural stem/progenitor cells survives. In this report, by using a highly reproducible model of cortical infarction in SCID mice, we examined the effects of immunodeficiency on reduction of brain injury, survival of neural stem/progenitor cells, and functional recovery. Subsequently, the contribution of T lymphocytes to neurogenesis was evaluated in mice depleted for each subset of T lymphocyte. SCID mice revealed the reduced apoptosis and enhanced proliferation of neural stem/progenitor cells induced by cerebral cortex after stroke compared with the immunocompetent wild-type mice. Removal of T lymphocytes, especially the CD4(+) T-cell population, enhanced generation of neural stem/progenitor cells, followed by accelerated functional recovery. In contrast, removal of CD25(+) T cells, a cell population including regulatory T lymphocytes, impaired functional recovery through, at least in part, suppression of neurogenesis. Our findings demonstrate a key role of T lymphocytes in regulation of poststroke neurogenesis and indicate a potential novel strategy for cell therapy in repair of the central nervous system.

Interleukin-18 prevents apoptosis via PI3K/Akt pathway in normal human keratinocytes.

Interleukin-18 (IL-18) is a pleiotropic cytokine expressed in both immune and non-immune cells. In the present study, we demonstrate an anti-apoptotic role of IL-18 in normal human neonatal foreskin epidermal keratinocytes (NHEK-F). Cultured NHEK-F spontaneously produced the active form of IL-18. Treatment of NHEK-F cells with anti-IL-18 receptor alpha-chain neutralizing antibody increased apoptosis and caspase-3 activity. Exogenous IL-18 augmented phosphorylation of Akt and activation of NF-kappaB. The promotion of Akt phosphorylation by IL-18 was abolished by LY294002, a PI3K inhibitor, but not SN50, an NF-kappaB inhibitor, indicating that IL-18 functions via the PI3K/Akt pathway and independently of NF-kappaB. In addition, IL-18 was found to augment expression of anti-apoptotic proteins, Bcl-2, XIAP and glucose regulated protein78/BiP, while anti-IL-18 receptor alpha-chain neutralizing antibody suppressed expression of Bcl-2, XIAP, glucose regulated protein94 and protein disulfide isomerase. Taken together, these results indicate that IL-18 plays an important role in keratinocyte survival.

A role for IL-18 in human neutrophil apoptosis.

Decreased neutrophil apoptosis is associated with persistent inflammation, the severity of which correlates with serum IL-18 levels. IL-18 receptors as well as Toll-like receptors, including Toll-like receptor 4, a receptor for LPS, possess a highly conserved intracellular domain called "Toll-IL-1R domain" and activate overlapping signaling pathways. Here, we show that IL-18 modulates neutrophil apoptosis and compare its mechanism of action with LPS. We found that both IL-18 and LPS decreased neutrophil apoptosis in a similar dose- and time-dependent fashion. However, pretreatment with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 increased apoptosis more effectively in IL-18- than in LPS-stimulated cells, whereas the ERK inhibitor PD98059 had the same effect in both. In contrast, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 had no influence on apoptosis at all. Neutrophils constitutively expressed mRNA for IL-18 receptor beta, but little or no receptor alpha, both of which increased during coculture with either IL-18 or LPS in a time- and dose-dependent manner. Of the Bcl-2 family, antiapoptotic A1/Bfl-1 tended to increase on IL-18 and LPS stimulation, but was further increased despite increased apoptosis in the presence of MAPK inhibitors. Thus, human neutrophils can express mRNA for IL-18 receptors alpha and beta, and IL-18, like LPS, inhibits neutrophil apoptosis by activating PI3K and ERK pathways but not p38MAPK. However, PI3K may play more important role(s) in IL-18- than in LPS-induced inhibition of apoptosis. Mitogen-activated protein kinases seem to mediate antiapoptotic signals through factors other than Bcl-2 gene family expression.

Protection of CD8+ T cells from activation-induced cell death by IL-18.

Role of IL-18 on proliferation and survival of CD8+ T cells, activated by immobilized anti-CD3 antibody (anti-CD3), was examined. Proliferation and survival of activated T cells, especially that of CD8+ T cells, were impaired by IL-18 deficiency [IL-18 knockout (KO)]. After 3 days of culture with anti-CD3, the number of living CD8+ T cells from IL-18KO mice was approximately 25% of that from wild-type (WT) mice but was increased to the same level as WT cells by the addition of IL-18. The expression of IL-18 receptors (IL-18Rs), particularly IL-18Rbeta chain, in naïve CD8+ T cells was very low but elevated after stimulation with anti-CD3. Blockade of IL-18R by anti-IL-18R antibody on activated WT CD8+ T cells resulted in reduction of living cells, suggesting that IL-18 promotes survival of proliferating CD8+ T cells. Levels of Bcl-2 in activated IL-18KO CD8+ T cells were lower than those in WT cells but were raised by exogenous IL-18. Blockade of IL-18R on WT CD8+ T cells decreased the expression of surface markers CD122 and CD94, which are related to cell viability, and the expression of these markers was increased by exogenous IL-18 in IL-18KO cells. These results suggest that IL-18 acts directly on activated CD8+ T cells through IL-18Rs and promotes their survival to expand the population.

Neutrophil activation and arteritis induced by C. albicans water-soluble mannoprotein-beta-glucan complex (CAWS).

We have established a mouse model which shows the symptoms of coronary arteritis after consecutive injections of CAWS, which is released from Candida albicans. In this study, we examined neutrophil activation in the initial period after CAWS injection intraperitoneally. During 10 min to 16 h after the injection, blood profiles and neutrophil functions were determined. At the same time, levels of inflammatory cytokines and chemokines in plasma were measured. Furthermore, level of ICAM-1 as a marker of lesion in arterial endothelial cells was measured. Counts of the peripheral leukocytes increased immediately after CAWS injection, especially involving neutrophil. In vitro sensitivity of neutrophils to stimuli was enhanced. Moreover, proinflammatory cytokines (IL-1beta, IL-12 and IL-6) increased in plasma initially followed by an increase in IL-10, G-CSF, MIP-2 and soluble ICAM-1. Locally, ICAM-1 message in arterial walls was significantly increased 16 h after CAWS injection. A decrease in C3 levels was observed in plasma, suggesting complement activation and consumption. In summary, neutrophil activation occurred after CAWS injection, followed by complement activation, and production of proinflammatory cytokines chemokines and G-CSF which may be involved in development of coronary arteritis.

Production of IL-13 in spleen cells by IL-18 and IL-12 through generation of NK-like cells.

Treatment of Nylon wool-passed cells (NWC) prepared from the spleen of C57BL/6 mice with IL-18 and IL-12, but not with IL-18 alone, resulted in induction of IFN-gamma, a Th1 cytokine, and GM-CSF at 24 h, and IL-13, a Th2 cytokine at 72 h. The induction of IL-13 was suppressed by anti-GM-CSF antibody, indicating involvement of GM-CSF in IL-13 production. When NWC incubated with IL-18 and IL-12 for 72 h ("primary treatment") were treated again with the same cytokines ("secondary treatment"), IL-13 was induced much more quickly than observed in the primary treatment. Flow cytometric analysis of NWC after the primary treatment showed marked increases in the CD4(-)CD8(-) non-T cell population bearing CD25(+), CD45RB(super high) and CD122(+). These cells were positive for CD49b but negative for NK1.1, indicating that they were not typical but NK-like cells. The NK-like cells produced IL-13 in response to the treatment with IL-18 alone, indicating that the generation of these cells in the primary treatment likely accounts for the quick production of IL-13 in the secondary treatment. These results show that IL-18 and IL-12 generates the NK-like cells in NWC by a process mediated by GM-CSF that are ready for producing IL-13.

Chylomicron remnants stimulate release of interleukin-1beta by THP-1 cells.

Recent findings suggest that the oxidative modification of low-density lipoproteins (LDL) and an increase in triglyceride-rich lipoprotein particles including chylomicron remnants contribute to the progression of atherosclerosis, as does the inflammatory response. We therefore examined whether and how these lipoproteins affected interleukin (IL)-1beta release and mRNA expression for IL-1beta and IL-18 in THP-1 cells, a human monocyte cell line. Chylomicron remnants increased IL-1beta release into the conditioned medium by THP-1 in a dose- and time-dependent manner. At concentrations up to 1 microg/ml, chylomicron remnants increased IL-1beta release by 4-fold compared with the control. Neither native LDL nor oxidized LDL (OxLDL) significantly increased IL-1beta release. Chylomicron remnants increased IL-1beta mRNA expression by 3 times. Native LDL or OxLDL did not increase IL-1beta mRNA, while neither these lipoproteins nor chylomicron remnants increased IL-18 mRNA. Chylomicron remnants also increased the activities of caspase-1 and nuclear factor (NF)-kappaB significantly, while native LDL or OxLDL did not. In conclusion, chylomicron remnants stimulated IL-1beta mRNA expression and IL-1beta protein production probably via caspase-1 and NF-kappaB activation in THP-1 cells.

A role of the adrenal gland in stress-induced up-regulation of cytokines in plasma.

To reveal a pathway by which psychological/physical stresses influence host defense capability, responses to immobilization stress in mice were investigated, focusing on a multifunctional cytokine, interleukin-18 (IL-18). Immobilization stress induced interleukin-18 accumulation in plasma and in the adrenal gland. Inhibition on ACTH resulted in suppressed levels of IL-18 both in plasma and the adrenal gland. In hemi-adrenalectomized mice, plasma IL-18 levels after stress were lower than in sham-operated mice. This, together with the observation in stressed hemi-adrenalectomized mice that IL-6 levels in plasma were suppressed but up-regulated by recombinant IL-18, showed that the adrenal gland plays a crucial role in stress-related elevation of IL-6 in plasma via IL-18. Adrenal gland is highlighted as an organ connecting the psychological, endocrine, and immune systems. Controlling the secretion of IL-18 from the adrenal gland may serve as a possible preventative means against a stress-related disruption of host defenses.

Role of interleukin 18 in nitric oxide production and pancreatic damage during acute pancreatitis.

The release of the immunomodulator, interleukin 18 (IL-18) into sera early in acute pancreatitis (AP) corresponds to disease severity. IL-18 induces nitric oxide (NO), which is involved in the pathophysiology of pancreatitis. The objective of this study was to clarify the role of IL-18 in pathogenesis and NO production during early AP using recombinant mouse (rm) IL-18 protein and IL-18 gene knockout (KO) mice. After pretreatment with phosphate-buffered saline or rmIL-18, wild-type (WT) or KO mice were injected intraperitoneally with phosphate-buffered saline (sham) or cerulein (AP) hourly for 3 h. Blood, pancreas, spleen, and liver were collected until 24 h after the first dose. Main outcome measures were serum IL-18, amylase and lipase levels, histological evaluation of the pancreas with parenchyma vacuolization of acinar cells, mRNA expression of inducible NO synthase (iNOS) in the pancreas, and spleen, liver, and plasma NO metabolite level. Serum IL-18 was significantly increased immediately after induction of AP in WT mice. Serum amylase, lipase, and the numbers of acinar cells with parenchyma vacuolization were significantly higher in the group AP/KO than in the group AP/WT, but these parameters were improved by dose-dependent pretreatment with rmIL-18 administration in both groups. Pancreatic iNOS gene expression and plasma NO metabolites were significantly increased by 6 h after the initiation of AP, but were significantly lower in the group AP/KO than in the AP/WT mice. Pretreatment with rmIL-18 also significantly increased these levels in both groups. Splenic and hepatic iNOS expression was not changed after the initiation of AP in WT mice, whereas pretreatment with rmIL-18 also increased these levels. Administration of aminoguanidine, a selective iNOS inhibitor, before AP induction abolished the protective effect of pretreatment with rmIL-18 on pancreatic injury. IL-18 appears to protect the pancreas during early induced-induced AP in mice, probably through induction of NO release from an iNOS source. IL-18 may be a target for new AP therapeutics.

IL-18; a cytokine translates a stress into medical science.

Psychological/physical stresses have been reported to exacerbate auto-immune and inflammatory diseases. To clarify a mechanism by which non-inflammatory stresses disrupt host defenses, responses to immobilization stress in mice were investigated, focusing on the role of a multifunctional cytokine, interleukin-18 (IL-18). In the adrenal cortex, the stress induced IL-18 precursor proteins (pro-IL-18) via ACTH and a superoxide-mediated caspase-1 activation pathway, resulting in conversion of pro-IL-18 to the mature form which was released into plasma. Inhibitors of caspase-1, reactive oxygen species and P38 MAPK prevented stress-induced accumulation of plasma IL-18. These inhibitors also blocked stress-induced IL-6 expression. This, together with the observation that IL-6 was not induced in stressed-IL-18 deficient mice, showed that IL-6 induction by stress is dependent on IL-18. In stressed organisms, IL-18 may influence pathological and physiological processes. Controlling the caspase-1 activating pathway to suppress IL-18 levels may provide preventative means against stress-related disruption of host defenses.

Plasma interleukin-18 concentration: a novel marker of myocardial ischemia rather than necrosis in humans.

OBJECTIVE: Myocardial ischemia contributes to cytokine expression in the myocardium in animals; therefore, plasma interleukin-18 concentration may be a good marker of myocardial ischemia/injury in patients with possible acute coronary syndrome. We sought to determine whether increases in plasma interleukin-18 concentrations might be indicative of myocardial ischemia in patients with acute coronary syndrome. METHODS: Plasma interleukin-18 concentrations were assessed in 27 acute coronary syndrome patients in whom creatine kinase activity was within normal range on admission, in addition to 10 controls. Myocardial infarction was retrospectively evidenced in 15 of the 27 patients. All patients with acute coronary syndrome were treated by emergent coronary interventions just after admission. Blood sampling was done immediately after admission to determine plasma IL-18 concentration and biochemical markers of myocardial infarction. RESULTS: An increase in plasma interleukin-18 concentration was observed in acute coronary syndrome patients on admission, regardless of the retrospective evidence of myocardial necrosis. Plasma interleukin-18 elevation preceded creatine kinase-MB elevation in myocardial infarction patients. Plasma interleukin-18 concentrations on admission did not correlate with peak creatine kinase-MB (r=0.38, P=n.s.) or with left ventricular ejection fraction (r=-0.14, P=n.s.). CONCLUSIONS: Plasma interleukin-18 concentration elevates quickly after severe myocardial ischemic event regardless of evolving myocardial necrosis. Thus, plasma interleukin-18 concentration may be a good and early marker to identify whether the symptom is due to myocardial ischemia, and therefore, may be used in deciding the therapeutic strategy in individual patients with possible acute coronary syndrome.

A stress-induced, superoxide-mediated caspase-1 activation pathway causes plasma IL-18 upregulation.

Psychological/physical stresses are known to cause relapses of autoimmune and inflammatory diseases. To reveal a mechanism by which noninflammatory stresses affect host defenses, responses to immobilization stress in mice were investigated, focusing on the role of a multifunctional cytokine, interleukin-18 (IL-18). In the adrenal cortex, the stress induced IL-18 precursor proteins (pro-IL-18) via adrenocorticotropic hormone (ACTH) and a superoxide-mediated caspase-1 activation pathway, resulting in conversion of pro-IL-18 to the mature form, which was released into plasma. Inhibitors of caspase-1, reactive oxygen species, and P38 mitogen-activated protein kinase (MAPK) suppressed stress-induced accumulation of plasma IL-18. These inhibitors also blocked stress-induced IL-6 expression. This, together with the observation that IL-6 was not induced in IL-18-deficient mice, showed that IL-6 induction by stress is dependent on IL-18. In stressed organisms, IL-18 may influence pathological and physiological processes. Controlling the caspase-1 activating pathway to suppress IL-18 levels may provide preventative means against stress-related disruption of host defenses.

Protection against bleomycin-induced lung injury by IL-18 in mice.

The role of interleukin (IL)-18 in the protection from interstitial pneumonia and pulmonary fibrosis induced by bleomycin (BLM) was investigated by comparing the severity of BLM-induced lung injuries between wild-type and C57BL/6 mice with a targeted knockout mutation of the IL-18 gene (IL-18-/- mice). IL-18-/- mice showed much worse lung injuries than wild-type mice, as assessed by the survival rate, histological images, and leukocyte infiltration in the bronchoalveolar lavage fluid and myeloperoxidase activity. In wild-type mice, administration of IL-18 before BLM instillation resulted in suppression of lung injuries, increases in the hydroxyproline content, and decreases in the granulocyte-macrophage colony-stimulating factor content in the lung. Preadministration of IL-18 also resulted in prevention of the reduction of the lung IL-10 content caused by BLM-induced damage of alveolar epithelial. BLM instillation suppressed superoxide dismutase (SOD) activity in IL-18-/- mice to a greater extent than in wild-type mice. Pretreatment of IL-18 augmented Mn-containing superoxide dismutase (Mn-SOD) messenger RNA expression and SOD activity in the lung and prevented the reduction of SOD activity caused by BLM in both wild-type and IL-18-/- mice. These results suggest that IL-18 plays a protective role against BLM-induced lung injuries by upregulating a defensive molecule, Mn-SOD.

Nonredundant roles of Sema4A in the immune system: defective T cell priming and Th1/Th2 regulation in Sema4A-deficient mice.

The class IV semaphorin Sema4A provides a costimulatory signal to T cells. To investigate the possible developmental and regulatory roles of Sema4A in vivo, we generated Sema4A-deficient mice. Although Sema4A-deficient mice develop normally, DCs and T cells from knockout mice display poor allostimulatory activities and T helper cell (Th) differentiation, respectively. Interestingly, in addition to its expression on DCs, Sema4A is upregulated on Th1-differentiating cells, and it is necessary for in vitro Th1 differentiation and T-bet expression. Consequently, in vivo antigen-specific T cell priming and antibody responses against T cell-dependent antigens are impaired in the mutant mice. Additionally, Sema4A-deficient mice exhibit defective Th1 responses. Furthermore, reconstitution studies with antigen-pulsed DCs reveal that DC-derived Sema4A is important for T cell priming, while T cell-derived Sema4A is involved in developing Th1 responses. Collectively, these results indicate a nonredundant role of Sema4A not only in T cell priming, but also in the regulation of Th1/Th2 responses.

Inhibition by interleukin-18 of the growth of Dunn osteosarcoma cells.

To examine the usefulness of interleukin-18 (IL-18) in the treatment of osteosarcomas, the effect of IL-18 on the growth of Dunn osteosarcoma cells was investigated. Daily intraperitoneal (i.p.) injection of mouse recombinant IL-18 (2 microg/mouse) suppressed the growth of Dunn osteosarcoma cells transplanted subcutaneously (s.c.) into syngeneic C3H mice. This IL-18-induced suppression was not affected by simultaneous treatment with anti-asialo GM1 serum, which inactivates natural killer (NK) cells. However, IL-18 failed to suppress the growth of Dunn osteosarcoma cells transplanted into BALB/c-nude mice devoid of T lymphocytes or C3H-gld/gld mice deficient in functional Fas ligand (FasL). IL-18 also failed to suppress the growth of Dunn osteosarcoma cells in vitro, although expression of IL-18 receptor mRNA and MyD88 mRNA as well as Fas mRNA was detected by reverse transcriptase-polymerase chain reaction (RT-PCR). On the other hand, antimouse Fas antibody showed cytotoxicity against Dunn osteosarcoma cells in a dose-dependent manner in vitro. In addition, treatment of C3H mice with IL-18 enhanced the cytotoxic activity of CD8(+) T lymphocytes against Dunn osteosarcoma cells. These results indicate that IL-18 inhibits the growth of Dunn osteosarcoma cells in vivo by enhancing the cytotoxic activity of CD8(+) T lymphocytes through the FasL-Fas system.