IL-1 type I receptor mediates acute phase response to turpentine, but not lipopolysaccharide, in mice

The role of interleukin-1 in perinatal inflammation and its impact on transitional circulation

Preterm birth is defined as delivery at <37 weeks of gestational age (GA) and exposes 15 million infants worldwide to serious early life diseases. Lowering the age of viability to 22 weeks GA entailed provision of intensive care to a greater number of extremely premature infants. Moreover, improved survival, especially at extremes of prematurity, comes with a rising incidence of early life diseases with short- and long-term sequelae. The transition from fetal to neonatal circulation is a substantial and complex physiologic adaptation, which normally happens rapidly and in an orderly sequence. Maternal chorioamnionitis or fetal growth restriction (FGR) are two common causes of preterm birth that are associated with impaired circulatory transition. Among many cytokines contributing to the pathogenesis of chorioamnionitis-related perinatal inflammatory diseases, the potent pro-inflammatory interleukin (IL)-1 has been shown to play a central role. The effects of utero-placental insufficiency-related FGR and in-utero hypoxia may also be mediated, in part, via the inflammatory cascade. In preclinical studies, blocking such inflammation, early and effectively, holds great promise for improving the transition of circulation. In this mini-review, we outline the mechanistic pathways leading to abnormalities in transitional circulation in chorioamnionitis and FGR. In addition, we explore the therapeutic potential of targeting IL-1 and its influence on perinatal transition in the context of chorioamnionitis and FGR.

Neural Mechanisms of Inflammation-Induced Fever

Fever is a common symptom of infectious and inflammatory disease. It is well-established that prostaglandin E2 is the final mediator of fever, which by binding to its EP3 receptor subtype in the preoptic hypothalamus initiates thermogenesis. Here, we review the different hypotheses on how the presence of peripherally released pyrogenic substances can be signaled to the brain to elicit fever. We conclude that there is unequivocal evidence for a humoral signaling pathway by which proinflammatory cytokines, through their binding to receptors on brain endothelial cells, evoke fever by eliciting prostaglandin E2 synthesis in these cells. The evidence for a role for other signaling routes for fever, such as signaling via circumventricular organs and peripheral nerves, as well as transfer into the brain of peripherally synthesized prostaglandin E2 are yet far from conclusive. We also review the efferent limb of the pyrogenic pathways. We conclude that it is well established that prostaglandin E2 binding in the preoptic hypothalamus produces fever by disinhibition of presympathetic neurons in the brain stem, but there is yet little understanding of the mechanisms by which factors such as nutritional status and ambient temperature shape the response to the peripheral immune challenge.

IL-1 signaling mediates intrauterine inflammation and chorio-decidua neutrophil recruitment and activation

Neutrophil infiltration of the chorioamnion-decidua tissue at the maternal-fetal interface (chorioamnionitis) is a leading cause of prematurity, fetal inflammation, and perinatal mortality. We induced chorioamnionitis in preterm rhesus macaques by intraamniotic injection of LPS. Here, we show that, during chorioamnionitis, the amnion upregulated phospho-IRAK1-expressed neutrophil chemoattractants CXCL8 and CSF3 in an IL-1-dependent manner. IL-1R blockade decreased chorio-decidua neutrophil accumulation, neutrophil activation, and IL-6 and prostaglandin E2 concentrations in the amniotic fluid. Neutrophils accumulating in the chorio-decidua had increased survival mediated by BCL2A1, and IL-1R blockade also decreased BCL2A1+ chorio-decidua neutrophils. Readouts for inflammation in a cohort of women with preterm delivery and chorioamnionitis were similar to findings in the rhesus macaques. IL-1 is a potential therapeutic target for chorioamnionitis and associated morbidities.

Sex Differences in Severity of Inflammation-Induced Anorexia and Weight Loss

Food intake and body weight changes in response to induction of acute inflammation were examined in intact cycling females, ovariectomized females, and sham-operated male rats. In intact females, body weight and feeding responses were compared between rats in which inflammation was induced on day of estrus with rats in which inflammation was induced on day of diestrus. Anorexia and weight loss were more severe in the female rats with inflammation induced on estrus day, which coincides with peak serum estrogen levels. In ovariectomized females, inflammation was induced the day after rats received injections of estrogen, progesterone, or sesame oil (vehicle). Males received vehicle injections. Among female rats, the group that received estradiol injections the previous day displayed the most severe anorexia. The least severe anorexia was observed in female rats that received progesterone the previous day. Food intake of female rats that received vehicle injections prior to induction of inflammation was greater than the rats receiving estrogen but less than the rats receiving progesterone. Male rats displayed the most severe anorexia and greatest weight loss. These data suggest that, although females exposed to estradiol prior to induction of acute inflammation display more severe anorexia than those exposed to progesterone, it may be that progesterone attenuates severity of anorexia rather than estrogen solely potentiating severity. Male rats, however, appear to experience the most severe anorexia in response to this form of inflammation.

ORMDL proteins regulate ceramide levels during sterile inflammation

The bioactive sphingolipid metabolite, ceramide, regulates physiological processes important for inflammation and elevated levels of ceramide have been implicated in IL-1-mediated events. Although much has been learned about ceramide generation by activation of sphingomyelinases in response to IL-1, the contribution of the de novo pathway is not completely understood. Because yeast ORM1 and ORM2 proteins negatively regulate ceramide levels through inhibition of serine palmitoyltransferase, the first committed step in ceramide biosynthesis, we examined the functions of individual mammalian ORM orthologs, ORM (yeast)-like (ORMDL)1-3, in regulation of ceramide levels. In HepG2 liver cells, downregulation of ORMDL3 markedly increased the ceramide precursors, dihydrosphingosine and dihydroceramide, primarily from de novo biosynthesis based on [U-(13)C]palmitate incorporation into base-labeled and dual-labeled dihydroceramides, whereas downregulation of each isoform increased dihydroceramides [(13)C]labeled in only the amide-linked fatty acid. IL-1 and the IL-6 family cytokine, oncostatin M, increased dihydroceramide and ceramide levels in HepG2 cells and concomitantly decreased ORMDL proteins. Moreover, during irritant-induced sterile inflammation in mice leading to induction of the acute-phase response, which is dependent on IL-1, expression of ORMDL proteins in the liver was strongly downregulated and accompanied by increased ceramide levels in the liver and accumulation in the blood. Together, our results suggest that ORMDLs may be involved in regulation of ceramides during IL-1-mediated sterile inflammation.

Sleep and immunomodulatory responses to systemic lipopolysaccharide in mice selectively expressing interleukin-1 receptor 1 on neurons or astrocytes

Sleep-wake behavior is altered in response to immune challenge. Although the precise mechanisms that govern sickness-induced changes in sleep are not fully understood, interleukin-1β (IL-1) is one mediator of these responses. To better understand mechanisms underlying sleep and inflammatory responses to immune challenge, we used two transgenic mouse strains that express IL-1 receptor 1 (IL1R1) only in the central nervous system and selectively on neurons or astrocytes. Electroencephalographic recordings from transgenic and wild-type mice reveal that systemic challenge with lipopolysaccharide (LPS) fragments sleep, suppresses rapid eye movement sleep (REMS), increases non-REMS (NREMS), diminishes NREM delta power, and induces fever in all genotypes. However, the magnitude of REMS suppression is greater in mice expressing IL1R1 on astrocytes compared with mice in which IL1R1 is selectively expressed on neurons. Furthermore, there is a delayed increase in NREM delta power when IL1R1 is expressed on astrocytes. LPS-induced sleep fragmentation is reduced in mice expressing IL1R1 on neurons. Although LPS increases IL-1 and IL-6 in brain of all genotypes, this response is attenuated when IL1R1 is expressed selectively on neurons or on astrocytes. Collectively, these data suggest that in these transgenic mice under the conditions of this study it is neuronal IL1R1 that plays a greater role in LPS-induced suppression of REMS and NREM delta power, whereas astroglial IL1R1 is more important for sleep fragmentation after this immune challenge. Thus, aspects of central responses to LPS are modulated by IL1R1 in a cell type-specific manner.

Sphingosine-1-phosphate inhibits IL-1-induced expression of C-C motif ligand 5 via c-Fos-dependent suppression of IFN-β amplification loop

The neuroinflammation associated with multiple sclerosis involves activation of astrocytes that secrete and respond to inflammatory mediators such as IL-1. IL-1 stimulates expression of many chemokines, including C-C motif ligand (CCL) 5, that recruit immune cells, but it also stimulates sphingosine kinase-1, an enzyme that generates sphingosine-1-phosphate (S1P), a bioactive lipid mediator essential for inflammation. We found that whereas S1P promotes IL-1-induced expression of IL-6, it inhibits IL-1-induced CCL5 expression in astrocytes. This inhibition is mediated by the S1P receptor (S1PR)-2 via an inhibitory G-dependent mechanism. Consistent with this surprising finding, infiltration of macrophages into sites of inflammation increased significantly in S1PR2(-/-) animals. However, activation of NF-κB, IFN regulatory factor-1, and MAPKs, all of which regulate CCL5 expression in response to IL-1, was not diminished by the S1P in astrocytes. Instead, S1PR2 stimulated inositol 1,4,5-trisphosphate-dependent Ca(++) release and Elk-1 phosphorylation and enhanced c-Fos expression. In our study, IL-1 induced the IFNβ production that supports CCL5 expression. An intriguing finding was that S1P induced c-Fos-inhibited CCL5 directly and also indirectly through inhibition of the IFN-β amplification loop. We propose that in addition to S1PR1, which promotes inflammation, S1PR2 mediates opposing inhibitory functions that limit CCL5 expression and diminish the recruitment of immune cells.

RelB/p50 complexes regulate cytokine-induced YKL-40 expression

The secreted protein, YKL-40, has been proposed as a biomarker of a variety of human diseases characterized by ongoing inflammation, including chronic neurologic pathologies such as multiple sclerosis and Alzheimer's disease. However, inflammatory mediators and the molecular mechanism responsible for enhanced expression of YKL-40 remained elusive. Using several mouse models of inflammation, we now show that YKL-40 expression correlated with increased expression of both IL-1 and IL-6. Furthermore, IL-1 together with IL-6 or the IL-6 family cytokine, oncostatin M, synergistically upregulated YKL-40 expression in both primary human and mouse astrocytes in vitro. The robust cytokine-driven expression of YKL-40 in astrocytes required both STAT3 and NF-κB binding elements of the YKL-40 promoter. In addition, YKL-40 expression was enhanced by constitutively active STAT3 and inhibited by dominant-negative IκBα. Surprisingly, cytokine-driven expression of YKL-40 in astrocytes was independent of the p65 subunit of NF-κB and instead required subunits RelB and p50. Mechanistically, we show that IL-1-induced RelB/p50 complex formation was further promoted by oncostatin M and that these complexes directly bound to the YKL-40 promoter. Moreover, we found that expression of RelB was strongly upregulated during inflammation in vivo and by IL-1 in astrocytes in vitro. We propose that IL-1 and the IL-6 family of cytokines regulate YKL-40 expression during sterile inflammation via both STAT3 and RelB/p50 complexes. These results suggest that IL-1 may regulate the expression of specific anti-inflammatory genes in nonlymphoid tissues via the canonical activation of the RelB/p50 complexes.

K63-linked polyubiquitination of transcription factor IRF1 is essential for IL-1-induced production of chemokines CXCL10 and CCL5

Although interleukin 1 (IL-1) induces expression of the transcription factor IRF1 (interferon-regulatory factor 1), the roles of IRF1 in immune and inflammatory responses and mechanisms of its activation remain elusive. Here we found that IRF1 was essential for IL-1-induced expression of the chemokines CXCL10 and CCL5, which recruit mononuclear cells into sites of sterile inflammation. Newly synthesized IRF1 acquired Lys63 (K63)-linked polyubiquitination mediated by the apoptosis inhibitor cIAP2 that was enhanced by the bioactive lipid S1P. In response to IL-1, cIAP2 and the sphingosine kinase SphK1 (the enzyme that generates S1P) formed a complex with IRF1, which led to its activation. Thus, IL-1 triggered a hitherto unknown signaling cascade that controlled the induction of IRF1-dependent genes that encode molecules important for sterile inflammation.

Comparison of anorexia, lethargy, and fever induced by bacterial and viral mimetics in rats

Although it has been established that some acute phase responses present differently depending on whether a virus or bacteria activates the innate immune system, it has not yet been established whether fever and sickness behaviors, such as anorexia and lethargy, present differently. We therefore investigated the effects of administering lipopolysaccharide (LPS) and polyinosinic : polycytidylic acid (poly I:C) on body temperature, food intake, body mass, and activity (cage activity and wheel running). Male Sprague-Dawley rats were randomly assigned to receive an intraperitoneal injection of one of LPS (75 microg/kg or 250 microg/kg), poly I:C (3000 microg/kg or 4000 microg/kg), or saline. Administration of LPS or poly I:C induced fever, anorexia, and lethargy. Although voluntary wheel running and cage activity were both significantly reduced after administration of LPS or poly I:C, they were not affected equally. Indeed voluntary wheel running was decreased on average by approximately 30% more than cage activity regardless of the dose or type of mimetic administered. Our results indicate that poly I:C is less effective at inducing anorexia, lethargy, and fever in rats than is LPS, and that avoidance of exercise in animals and humans during infection is likely to be a more prominent feature of illness than is avoidance of routine daily activity.

IL-1 mediates pulmonary and systemic inflammatory responses to chorioamnionitis induced by lipopolysaccharide

RATIONALE

Chorioamnionitis frequently associates with preterm delivery and increased amniotic fluid IL-1, and causes fetal lung and systemic inflammation. However, chorioamnionitis is also associated with a paradoxical reduction in the incidence of surfactant deficiency-related respiratory distress syndrome in preterm infants.

OBJECTIVES

To identify the role of IL-1 signaling in the mediation of pulmonary and systemic inflammation and lung maturation in a fetal sheep model of lipopolysaccharide (LPS) induced chorioamnionitis.

METHODS

After confirming the efficacy of recombinant human IL-1 receptor antagonist (rhIL-1ra), fetal sheep were exposed to intraamniotic (IA) injections of Escherichia coli LPS with or without prior IA injections of rhIL-1ra. Preterm lambs were delivered at 82% of term gestation.

MEASUREMENTS AND MAIN RESULTS

rhIL-1ra decreased IA LPS-induced lung inflammation assessed by decreased lung neutrophil and monocyte influx, inducible nitric oxide synthase expression, lung IL-6 and IL-1beta mRNA expression, and airway myeloperoxidase concentrations. rhIL-1ra inhibited IA LPS-induced fetal systemic inflammation assessed by decreased plasma IL-8, protein carbonyls, blood neutrophilia, and the expression of serum amyloid A3 mRNA in the liver. rhIL-1ra also partially blocked the lung maturational effects of IA LPS. Therefore blockade of IL-1 signaling in the amniotic compartment inhibited fetal lung and systemic inflammation and lung maturation in response to LPS-induced chorioamnionitis.

CONCLUSIONS

IL-1 plays a central role in the pathogenesis of chorioamnionitis-induced fetal inflammatory responses.

A study on the differential protein profiles in liver cells of heat stress rats with and without turpentine treatment

BACKGROUND

Heat stress (HS) and related illnesses are a major concern in military, sports, and fire brigadiers. HS results in physiologic responses of increased temperature, heart rate and sweating. In heat stroke, inflammatory response plays an important role and it is evidenced that turpentine (T) induced circulating inflammatory cytokines reduced survival rate and duration at 42 degrees C. Here we report the alteration in the protein expression in liver cells upon HS with and without T treatment using two dimensional gel electrophoresis (2-DE), tryptic in-gel digestion and MALDI-TOF-MS/MS approaches.

RESULTS

The effects of HS and T treatments alone and a combined treatments (T+HS) was performed in Wistar rat models. Proteomic analysis of liver in the HS and T+HS groups were analyzed compared to liver profiles of resting control and T treated groups. The study revealed a total of 25 and 29 differentially expressed proteins in the HS and T+HS groups respectively compared to resting control group. Fourteen proteins showed altered expression upon T treatment compared to resting control group. Proteins that are involved in metabolic and signal transduction pathways, defense, redox regulation, and cytoskeletal restructuring functions were identified. The altered expression of proteins reflected in 2D gels were corroborated by quantitative real time RT-PCR analysis of 8 protein coding genes representing metabolic and regulatory pathways for their expression and normalized with the house keeping gene beta-actin.

CONCLUSION

The present study has identified a number of differentially expressed proteins in the liver cells of rats subjected to T, HS and T+HS treatments. Most of these proteins are implicated in cell metabolism, as well as adaptive response to incurred oxidative stress and tissue damage due to T+HS and HS effects.

Localized inflammation in peripheral tissue signals the CNS for sickness response in the absence of interleukin-1 and cyclooxygenase-2 in the blood and brain

The CNS can be activated by both local and systemic inflammation, resulting in the manifestation of sickness symptoms. The pathways by which the CNS is activated under these two conditions, however, may differ. In this study, we injected casein into the peritoneal cavity (i.p.) or into an s.c. air pouch of mice to induce restricted local inflammation. Both routes of casein injection caused fever and reduced locomotor activity. These responses were not accompanied by the statistically significant induction of the inflammatory cytokine interleukin-1 (IL-1) in the blood and brain. Further, these responses were produced without the induction of brain cyclooxygenase-2 (COX-2), which has been implicated as an obligatory step in systemic inflammation-induced activation of the CNS. Induction of IL-1, interleukin-6 (IL-6), and COX-2, however, was found consistently at the sites of casein injection. The local inflammation-induced febrile and locomotor activity responses were blunted in animals deficient in functional Toll-like receptor 4 (TLR4), type I interleukin-1 receptor (IL-1R1), IL-6, or COX-2. Therefore, the observed febrile and locomotor activity effects appear to require local, but not central, IL-1, IL-6, and COX-2. These findings suggest that local inflammation can activate the CNS via pathways distinguishable from those mediating systemic inflammation-induced CNS activation.

Pre-existing inflammatory state compromises heat tolerance in rats exposed to heat stress

This study investigated the roles of endotoxemia and heat-induced tissue damage in the pathology of heat stroke. In groups of eight, male Wistar rats were treated with heat exposure only (HE), or heat exposure with turpentine (T+HE), dexamethasone (D+HE), and turpentine and dexamethasone combined (TD+HE). The rats remained sedated for 2 h after receiving the respective treatments, followed by heat exposure until the core temperature (Tc) was 42°C for 15 min; control rats received turpentine (T), dexamethasone (D), and turpentine and dexamethasone (TD) without heat stress. Blood samples were collected before treatment ( baseline I), after 2 h of passive rest ( baseline II), at Tc 40°C (T40), and 15 min after achieving Tc 42°C (T42). No rats died in the nonheat-stressed groups. Survival rate was lowest in the TD+HE rats (37.5%), followed by the HE (62.5%), T+HE (75%), and D+HE (100%) rats ( P < 0.05). The duration of survival at T42°C was shortest in the TD+HE rats (9.9 ± 6.2 min) ( P < 0.01), followed by the T+HE (11.3 ± 6.1 min) and the HE (12.2 ± 4 min) ( P < 0.05) rats. The increase in plasma IL-6 concentrations was highest in the T+HE (352%) and HE (178%) rats ( P < 0.05). D+HE treatment suppressed the increases in plasma aspartate transaminase, alanine aminotransferase, and IL-6 and LPS concentrations during severe heat stress. Heat stroke can be triggered by endotoxemia or heat-induced tissue damage, and preexisting inflammation compromises heat tolerance, whereas blocking endotoxemia increases heat tolerance.

Inhibition of caspase-1/interleukin-1beta signaling prevents degeneration of retinal capillaries in diabetes and galactosemia

The proinflammatory cytokine, interleukin (IL)-1beta, is known to induce vascular dysfunction and cell death. We investigated the role of IL-1beta and caspase-1 (the enzyme that produces it) in diabetes-induced degeneration of retinal capillaries. Caspase-1 activity is increased in retinas of diabetic and galactosemic mice and diabetic patients. First, we investigated the effect of agents known to inhibit caspase-1 (minocycline and tetracycline) on IL-1beta production and retinal capillary degeneration in diabetic and galactose-fed mice. Second, we examined the effect of genetic deletion of the IL-1beta receptor on diabetes-induced caspase activities and retinal capillary degeneration. Diabetic and galactose-fed mice were injected intraperitoneally with minocycline or tetracycline (5 mg/kg). At 2 months of diabetes, minocycline inhibited hyperglycemia-induced caspase-1 activity and IL-1beta production in the retina. Long-term administration of minocycline prevented retinal capillary degeneration in diabetic (6 months) and galactose-fed (13 months) mice. Tetracycline inhibited hyperglycemia-induced caspase-1 activity in vitro but not in vivo. Mice deficient in the IL-1beta receptor were protected from diabetes-induced caspase activation and retinal pathology at 7 months of diabetes. These results indicate that the caspase-1/IL-1beta signaling pathway plays an important role in diabetes-induced retinal pathology, and its inhibition might represent a new strategy to inhibit capillary degeneration in diabetic retinopathy.

Interleukin-6 and leptin mediate lipopolysaccharide-induced fever and sickness behavior

Pro-inflammatory cytokines, interleukin (IL)-1beta, IL-6 and tumor necrosis factor-alpha (TNF-alpha) synthesized by activated macrophages and monocytes in response to administration of lipopolysaccharide (LPS), are considered important mediators of fever and sickness behavior. We administered rat-specific antisera for TNF-alpha, IL-1beta, IL-6 and leptin, to determine the involvement of peripherally released cytokines in LPS-induced fever and sickness behavior, measured as suppression of voluntary wheel-running and food intake. Male Sprague-Dawley rats (approximately 200 g) selected for their predisposition to spontaneously run on running wheels were anaesthetized with a combination of ketamine hydrochloride (80 mg/kg i.m.) and xylazine (4 mg/kg i.m.) and implanted intra-abdominally with temperature-sensitive radiotelemeters. Rats were injected intraperitoneally with anti-rat sera to one of the following, TNF-alpha, IL-1beta, IL-6 or leptin or with pre-immune sheep serum, followed by a subcutaneous injection of either LPS (250 microg/kg) or sterile saline. Lipopolysaccharide administration induced a approximately 1.3 (0.2) degrees C fever lasting approximately 10 h and reduced voluntary running by 93 (8.6)% and food intake by 51 (21.3)% compared to the saline response (ANOVA, P<0.05). Injection of anti-IL-6 serum or anti-leptin serum abolished the LPS-induced fever, anti-TNF-alpha serum affected only the early phase of fever and anti-IL-1beta serum had no effect on fever (ANOVA, P<0.05). LPS-induced suppression of voluntary running and food intake were attenuated in rats receiving anti-IL-6 serum, while the decrease in food intake was totally abolished in rats receiving anti-leptin serum (ANOVA, P<0.05). Injection of anti-TNF-alpha or anti-IL-1beta serum had no effect on LPS-induced sickness behavior. Peripherally released IL-6 and leptin therefore appear to be important in regulating LPS-induced fever and sickness behavior.

Thermoregulatory responses to lipopolysaccharide in the mouse: dependence on the dose and ambient temperature

Most published studies of thermoregulatory responses of mice to LPS involved a stressful injection of LPS, were run at a poorly controlled and often subneutral ambient temperature (Ta), and paid little attention to the dependence of the response on the LPS dose. These pitfalls have been overcome in the present study. Male C57BL/6 mice implanted with jugular vein catheters were kept in an environmental chamber at a tightly controlled Ta. The relationship between the Tas used and the thermoneutral zone of the mice was verified by measuring tail skin temperature, either by infrared thermography or thermocouple thermometry. Escherichia coli LPS in a wide dose range (100-104μg/kg) was administered through an extension of the jugular catheter from outside the chamber. The responses observed were dose dependent. At a neutral Ta, low (just suprathreshold) doses of LPS (100-101μg/kg) caused a monophasic fever. To a slightly higher dose (101.5μg/kg), the mice responded with a biphasic fever. To even higher doses (101.75-104μg/kg), they responded with a polyphasic fever, of which three distinct phases were identified. The dose dependence and dynamics of LPS fever in the mouse appeared to be remarkably similar to those seen in the rat. However, the thermoregulatory response of mice to LPS in a subthermoneutral environment is remarkably different from that of rats. Although very high doses of LPS (104μg/kg) did cause a late (latency, ∼3 h) hypothermic response in mice, the typical early (latency, 10–30 min) hypothermic response seen in rats did not occur. The present investigation identifies experimental conditions to study LPS-induced mono-, bi-, and polyphasic fevers and late hypothermia in mice and provides detailed characteristics of these responses.

Impaired febrile responses to immune challenge in mice deficient in microsomal prostaglandin E synthase-1

Fever is a common, centrally elicited sign of inflammatory and infectious processes and is known to be induced by the action of PGE2 on its specific receptors in the thermogenic region of the hypothalamus. In the present work, using genetically modified mice, we examined the role of the inducible terminal PGE2-synthesizing enzyme microsomal prostaglandin E synthase-1 (mPGES-1) for the generation of immune-elicited fever. Animals with a deletion of the Ptges gene, which encodes mPGES-1, or their wild-type littermates were given either a subcutaneous injection of turpentine--a model for aseptic cytokine-induced pyresis--or an intraperitoneal injection of interleukin-1beta. While both procedures resulted in typical febrile responses in wild-type animals, these responses were strongly impaired in the mPGES-1 mutant mice. In contrast, both genotypes showed psychogenic stress-induced hyperthermia and displayed normal diurnal temperature variations. Both wild-type and mPGES-1 mutant mice also showed strongly reduced motor activity following turpentine injection. Taken together with previous observations on mPGES-1 induction in the brain vasculature during various inflammatory conditions and its role in endotoxin-induced pyresis, the present findings indicate that central PGE2 synthesis by mPGES-1 is a general and critical mechanism for fever during infectious and inflammatory conditions that is distinct from the mechanism(s) underlying the circadian temperature regulation and stress-induced hyperthermia, as well as the inflammation-induced activity depression.

Characteristics of thermoregulatory and febrile responses in mice deficient in prostaglandin EP1 and EP3 receptors

Previous studies have disagreed about whether prostaglandin EP1 or EP3 receptors are critical for producing febrile responses. We therefore injected lipopolysaccharide (LPS) at a variety doses (1 microg kg(-1)-1 mg kg(-1)) intraperitoneally (i.p.) into wild-type (WT) mice and mice lacking the EP1 or the EP3 receptors and measured changes in core temperature (Tc) by using telemetry. In WT mice, i.p. injection of LPS at 10 microg kg(-1) increased Tc about 1 degrees C, peaking 2 h after injection. At 100 microg kg(-1), LPS increased Tc, peaking 5-8 h after injection. LPS at 1 mg kg(-1) decreased Tc, reaching a nadir at 5-8 h after injection. In EP1 receptor knockout (KO) mice injected with 10 microg kg(-1) LPS, only the initial (< 40 min) increase in Tc was lacking; with 100 microg kg(-1) LPS the mice showed no febrile response. In EP3 receptor KO mice, LPS decreased Tc in a dose- and time-dependent manner. Furthermore, in EP3 receptor KO mice subcutaneous injection of turpentine did not induce fever. Both EP1 and EP3 receptor KO mice showed a normal circadian cycle of Tc and brief hyperthermia following psychological stress (cage-exchange stress and buddy-removal stress). The present study suggests that both the EP1 and the EP3 receptors play a role in fever induced by systemic inflammation but neither EP receptor is involved in the circadian rise in Tc or psychological stress-induced hyperthermia in mice.

Primary role of interleukin-1 alpha and interleukin-1 beta in lipopolysaccharide-induced hypoglycemia in mice

Within a few hours of its injection into mice, lipopolysaccharide (LPS) induces hypoglycemia and the production of various cytokines. We previously found that interleukin-1 alpha (IL-1 alpha), IL-1 beta, and tumor necrosis factor alpha (TNF-alpha) induce hypoglycemia and that the minimum effective dose of IL-1 alpha or IL-1 beta is about 1/1000 that of TNF-alpha. In the present study, we examined the contribution made by IL-1 to the hypoglycemic action of LPS. Nine other cytokines tested were all inactive at inducing hypoglycemia. LPS produced hypoglycemia in mice deficient in either IL-1 alpha or IL-1 beta but not in mice deficient in both cytokines (IL-1 alpha and -1 beta knockout [IL-1 alpha/beta KO] mice). IL-1 alpha, IL-1 beta, and TNF-alpha induced hypoglycemia in IL-1 alpha/beta KO mice, as they did in normal control mice. The LPS-induced elevation of serum cortisol was weaker in IL-1 alpha/beta KO mice than in control mice, and, in the latter, serum cortisol was markedly raised while blood glucose was declining. IL-1 alpha decreased blood glucose both in NOD mice (which have impaired insulin production) and in KK-Ay mice (insulin resistant). These results suggest that (i). cortisol may not be involved in mediating the resistance of IL-1 alpha/beta KO mice to the hypoglycemic action of LPS, (ii). as a mediator, IL-1 is a prerequisite for the hypoglycemic action of LPS, (iii). IL-1 alpha and IL-1 beta perform mutual compensation, and (iv). IL-1 plays a role as the primary stimulator of the many anabolic reactions required for the elaboration of immune responses against infection.

Role of alpha(2)-macroglobulin in fever and cytokine responses induced by lipopolysaccharide in mice

Alpha(2)-macroglobulin (alpha(2)M) is not only a proteinase inhibitor in mammals, but it is also a specific cytokine carrier that binds pro- and anti-inflammatory cytokines implicated in fever, including interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha). To define the role of alpha(2)M in regulation of febrile and cytokine responses, wild-type mice and mice deficient in alpha(2)M (alpha(2)M -/-) were injected with lipopolysaccharide (LPS). Changes in body temperature as well as plasma levels of IL-1beta, IL-6, and TNF-alpha and hepatic TNF-alpha mRNA level during fever in alpha(2)M -/- mice were compared with those in wild-type control mice. The alpha(2)M -/- mice developed a short-term markedly attenuated (ANOVA, P < 0.05) fever in response to LPS (2.5 mg/kg ip) compared with the wild-type mice. At 1.5 h after injection of LPS, the plasma concentration of TNF-alpha, but not IL-1beta or IL-6, was significantly lower (by 58%) in the alpha(2)M -/- mice compared with their wild-type controls (ANOVA, P < 0.05). There was no difference in hepatic TNF-alpha mRNA levels between alpha(2)M -/- and wild-type mice 1.5 h after injection of LPS. These data support the hypotheses that 1) alpha(2)M is important for the normal development of LPS-induced fever and 2) a putative mechanism of alpha(2)M involvement in fever is through the inhibition of TNF-alpha clearance. These findings indicate a novel physiological role for alpha(2)M.

Invited review: cytokine regulation of fever: studies using gene knockout mice

Fever is defined as a regulated rise in body temperature. The regulation of this phenomenon is accomplished by the actions of two types of endogenous cytokines, some functioning as pyrogens and others as antipyretics. Previous data obtained with the use of traditional pharmacological techniques, such as the injection of neutralizing antibodies, implicate interleukin (IL)-1 and IL-6 as endogenous pyrogens or inducers of fever. In almost all instances in which the endogenous actions of IL-1 or IL-6 are antagonized, fevers are attenuated. Other cytokines, such as tumor necrosis factor-alpha (TNF-alpha) and IL-10, are thought to act as endogenous antipyretics or inhibitors of fever. In several studies, the inhibition of TNF action has enhanced fever. Recently, mice genetically engineered to lack cytokines or their receptors in all tissues of the body have been used to examine the regulation of IL-1, IL-6, TNF, and IL-10 on fever. Data obtained with these mice shed new light on our understanding of cytokine interactions in fever and, in some instances, contradict data obtained with pharmacological methods. This review summarizes the responses of cytokine and cytokine receptor knockout mice to fevers induced by lipopolysaccharide, turpentine, and sepsis.

TNF-alpha and IL-1 beta are not essential to the inflammatory response in LPS-induced airway disease

To determine the role of tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 beta in the lower respiratory tract inflammatory response after inhalation of lipopolysaccharide (LPS), we conducted inhalation exposure studies in mice lacking expression of TNF-alpha and/or IL-1 receptor type 1 and in mice with functional blockade of these cytokines using adenoviral vector delivery of soluble receptors to one or both cytokines. Alterations in airway physiology were assessed by pulmonary function testing before and immediately after 4 h of LPS exposure, and the cellular inflammatory response was measured by whole lung lavage and assessment of inflammatory cytokine protein and mRNA expression. Airway resistance after LPS exposure was similarly increased in all groups of mice without evidence that blockade of either or both cytokines was protective from this response. Additionally, all groups of mice demonstrated significant increases in lung lavage fluid cellularity with a complete shift in the population of cells to a predominantly neutrophilic infiltrate as well as elevation in inflammatory cytokine protein and mRNA levels. There were no significant differences between the groups in measures of lung inflammation. These results indicate that TNF-alpha and IL-1 beta do not appear to have an essential role in mediating the physiological or inflammatory response to inhaled LPS.

Impaired Cytokine Signaling in Mice Lacking the IL-1 Receptor-Associated Kinase

Stimulation of the type 1 IL-1R (IL-1R1) and the IL-18R by their cognate ligands induces recruitment of the IL-1R-associated kinase (IRAK). Activation of IRAK leads in turn to nuclear translocation of NF-κB, which directs expression of innate and adaptive immune response genes. To study IRAK function in cytokine signaling, we generated cells and mice lacking the IRAK protein. IRAK-deficient fibroblasts show diminished activation of NF-κB when stimulated with IL-1. Immune effector cells without IRAK exhibit a defective IFN-γ response to costimulation with IL-18. Furthermore, mice lacking the Irak gene demonstrate an attenuated response to injected IL-1. Deletion of Irak, however, does not affect the ability of mice to develop delayed-type hypersensitivity or clear infection with the intracellular parasite, Listeria monocytogenes. These results demonstrate that although IRAK participates in IL-1 and IL-18 signal transduction, residual cytokine responsiveness operates through an IRAK-independent pathway.

New insights into the biology of the acute phase response

Innate or natural immunity is a highly conserved defense mechanism against infection found in all multicellular organisms. The acute phase response is the set of immediate inflammatory responses initiated by pattern recognition molecules. These germ cell-encoded proteins recognize microbial pathogens based on shared molecular structures and induce host responses that localize the spread of infection and enhance systemic resistance to infection. Innate immunity also influences the initiation and type of adaptive immune response by regulating T cell costimulatory activity and antigen presentation by antigen presenting cells and by influencing mediator production, which affects lymphocyte function and trafficking. Acute phase protein concentrations rapidly increase after infection, and their production is controlled primarily by IL-6- and IL-1-type cytokines. The acute phase proteins provide enhanced protection against microorganisms and modify inflammatory responses by effects on cell trafficking and mediator release. For example, serum amyloid A has potent leukocyte activating functions including induction of chemotaxis, enhancement of leukocyte adhesion to endothelial cells, and increased phagocytosis. The constellation of inflammatory responses seen after endotoxin administration to humans represents an in vivo model of the acute phase response. Studies with inflammatory modifying agents, such as soluble dimeric TNF receptor and IL-10, show that these responses are not dependent on a single mediator but result from multiple overlapping inflammatory pathways. Understanding the factors that initiate and alter the magnitude and duration of the acute phase response represents an important step in the development of new therapies for infectious and inflammatory diseases.

TRAF6 deficiency results in osteopetrosis and defective interleukin-1, CD40, and LPS signaling

Bone resorption and remodeling is an intricately controlled, physiological process that requires the function of osteoclasts. The processes governing both the differentiation and activation of osteoclasts involve signals induced by osteoprotegerin ligand (OPGL), a member of tumor necrosis factor (TNF) superfamily, and its cognate receptor RANK. The molecular mechanisms of the intracellular signal transduction remain to be elucidated. Here we report that mice deficient in TNF receptor-associated factor 6 (TRAF6) are osteopetrotic with defects in bone remodeling and tooth eruption due to impaired osteoclast function. Using in vitro assays, we demonstrate that TRAF6 is crucial not only in IL-1 and CD40 signaling but also, surprisingly, in LPS signaling. Furthermore, like TRAF2 and TRAF3, TRAF6 is essential for perinatal and postnatal survival. These findings establish unexpectedly diverse and critical roles for TRAF6 in perinatal and postnatal survival, bone metabolism, LPS, and cytokine signaling.

C/EBPalpha is critical for the neonatal acute-phase response to inflammation

Members of the C/EBP (CCAAT/enhancer binding protein) family of transcription factors play important roles in mediating the acute-phase response (APR), an inflammatory process resulting from infection and/or tissue damage. Among the C/EBP family of proteins, C/EBPbeta and -delta were thought to be the primary mediators of the APR. The function of C/EBPalpha in the APR has not been fully characterized to date. Here, we investigate the role of C/EBPalpha in the APR by using neonatal mice that lack C/EBPalpha expression. Northern blot analysis of acute-phase protein gene expression in neonatal mice treated with purified bacterial lipopolysaccharide or recombinant interleukin 1beta as an inflammation stimulus showed a strong APR in wild-type mice, but a response in C/EBPalpha null animals was completely lacking. The C/EBPalpha knockout and wild-type mice demonstrated elevations in C/EBPbeta and -delta mRNA expression and DNA binding as well as increased DNA binding of NF-kappaB, all of which are known to be important in the APR. Null mice, however, failed to activate STAT3 binding in response to lipopolysaccharide. Our results provide the first evidence that C/EBPalpha is absolutely required for the APR in neonatal mice, is involved in STAT3 regulation, and cannot be compensated for by other C/EBP family members.

Interleukin (IL)-1 receptor-associated kinase (IRAK) requirement for optimal induction of multiple IL-1 signaling pathways and IL-6 production

Interleukin (IL)-1 is a proinflammatory cytokine with pleiotropic effects in inflammation. IL-1 binding to its receptor triggers a cascade of signaling events, including activation of the stress-activated mitogen-activated protein (MAP) kinases, c-Jun NH2-terminal kinase (JNK) and p38 MAP kinase, as well as transcription factor nuclear factor kappaB (NF-kappaB). IL-1 signaling results in cellular responses through induction of inflammatory gene products such as IL-6. One of the earliest events in IL-1 signaling is the rapid interaction of IL-1 receptor-associated kinases, IRAK and IRAK-2, with the receptor complex. The relative roles of IRAK and IRAK-2 in IL-1 signaling pathways and subsequent cellular responses have not been previously determined. To evaluate the importance of IRAK in IL-1 signaling, IRAK-deficient mouse fibroblast cells were prepared and studied. Here we report that IL-1-mediated activation of JNK, p38, and NF-kappaB were all reduced in embryonic fibroblasts deficient in IRAK expression. In addition, IL-6 production in response to IL-1 was also dramatically reduced in IRAK-deficient embryonic fibroblasts and in skin fibroblasts prepared from IRAK-deficient mice. Our results demonstrate that IRAK plays an essential proximal role in coordinating multiple IL-1 signaling pathways for optimal induction of cellular responses.

Production of mice deficient in genes for interleukin (IL)-1alpha, IL-1beta, IL-1alpha/beta, and IL-1 receptor antagonist shows that IL-1beta is crucial in turpentine-induced fever development and glucocorticoid secretion

Interleukin (IL)-1 is a major mediator of inflammation and exerts pleiotropic effects on the neuro-immuno-endocrine system. To elucidate pathophysiological roles of IL-1, we have first produced IL-1alpha/beta doubly deficient (KO) mice together with mice deficient in either the IL-1alpha, IL-1beta, or IL-1 receptor antagonist (IL-1ra) genes. These mice were born healthy, and their growth was normal except for IL-1ra KO mice, which showed growth retardation after weaning. Fever development upon injection with turpentine was suppressed in IL-1beta as well as IL-1alpha/beta KO mice, but not in IL-1alpha KO mice, whereas IL-1ra KO mice showed an elevated response. At this time, expression of IL-1beta mRNA in the diencephalon decreased 1.5-fold in IL-1alpha KO mice, whereas expression of IL-1alpha mRNA decreased >30-fold in IL-1beta KO mice, suggesting mutual induction between IL-1alpha and IL-1beta. This mutual induction was also suggested in peritoneal macrophages stimulated with lipopolysaccharide in vitro. In IL-1beta KO mice treated with turpentine, the induction of cyclooxygenase-2 (EC 1.14.99.1) in the diencephalon was suppressed, whereas it was enhanced in IL-1ra KO mice. We also found that glucocorticoid induction 8 h after turpentine treatment was suppressed in IL-1beta but not IL-1alpha KO mice. These observations suggest that IL-1beta but not IL-1alpha is crucial in febrile and neuro-immuno-endocrine responses, and that this is because IL-1alpha expression in the brain is dependent on IL-1beta. The importance of IL-1ra both in normal physiology and under stress is also suggested.

Blockade of brain type II interleukin-1 receptors potentiates IL1beta-induced anorexia in mice

Interleukin-1beta (IL1beta) peripheral activities are mediated by type I IL1 receptors (IL1RI), whereas type II IL1 receptors (IL1RII) act as 'decoy' targets. To study the functionality of IL1RII in the brain, mice were treated with an intracerebroventricular injection of a neutralising MoAb directed against IL1RII (4E2, 1 microg) followed by recombinant rat IL1beta at a dose (2 ng) that produced a moderate but significant decrease of food intake 1 h 30 min after injection. The administration of 4E2 to IL-1beta treated mice significantly potentiated IL1beta-induced decrease in food intake without altering hypothermia. The effects of IL1beta were abrogated in the positive control group treated with IL1ra (2 microg, i.c.v). These results suggest that brain IL1RII down-regulate the effects of IL1beta on its cell targets in the brain.