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.     

Effects of i.c.v. administration of interleukin-1 on sleep and body temperature of interleukin-6-deficient mice

Cytokines in brain contribute to the regulation of physiological processes and complex behavior, including sleep. The cytokines that have been most extensively studied with respect to sleep are interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, and IL-6. Administration of these cytokines into laboratory animals, or in some cases into healthy human volunteers, increases the amount of time spent in non-rapid eye movement (NREM) sleep. Although antagonizing the IL-1 or TNF systems reduces the amount of time laboratory animals spend in NREM sleep, interactions among these three cytokine systems as they pertain to the regulation of physiological NREM sleep are not well understood. To further elucidate mechanisms in brain by which IL-1beta, TNFalpha, and/or IL-6 contribute to NREM sleep regulation, we injected recombinant murine interleukin-1beta (muIL-1beta) into C57BL/6J mice and into IL-6-deficient mice (IL-6 knockout, KO). IL-6 KO (B6.129S6-Il6(tm1Kopf); n=13) and C57BL/6J mice (n=14) were implanted with telemeters to record the electroencephalogram (EEG) and core body temperature, as well as with indwelling guide cannulae targeted to one of the lateral ventricles. After recovery and habituation, mice were injected intracerebroventricularly just prior to dark onset on different days with either 0.5 microl vehicle (pyrogen-free saline; PFS) or with 0.5 microl PFS containing one of four doses of muIL-1beta (2.5 ng, 5 ng, 10 ng, 50 ng). No mouse received more than two doses of muIL-1beta, and administration of muIL-1beta doses was counter-balanced to eliminate potential order effects. Sleep-wake behavior was determined for 24 h after injections. i.c.v. administration of muIL-1beta increased in NREM sleep of both mouse strains in a dose-related fashion, but the maximal increase was of greater magnitude in C57Bl/6J mice. muIL-1beta induced fever in C57Bl/6J mice but not in IL-6 KO mice. Collectively, these data demonstrate IL-6 is necessary for IL-1 to induce fever, but IL-6 is not necessary for IL-1 to alter NREM sleep.     

Hyperammonemia increases sensitivity to LPS

Metabolic and cognitive alterations occur during hyperammonemia. Here, we report that chronic hyperammonemia also leads to increased sensitivity to LPS. Sparse-fur mice were challenged i.p. with LPS or saline control and then tested for motivation to investigate a novel juvenile over 24 h. Cytokine, ammonia, and urea concentration were quantified at the peak of sickness (2 h post injection). Chronic hyperammonemic Otc(spf-ash) mice displayed more pronounced and prolonged sickness behavior in response to LPS (P=0.02). LPS significantly (P<0.0001) increased plasma concentrations of TNFalpha, IL-1 beta, IL-6, IL-15, IL-9, IL-2, IL-1 alpha, IL-1 beta, Rantes, MIP1 alpha, MIP1 beta, MCP-1, KC, GM-CSF, G-CSF, Eotaxin, IL-13, and IL-12 in both wild type and Otc(spf-ash) mice. No significant genotype/treatment interactions (P>0.1) were detected for any cytokine. Adult Otc(spf-ash) mice (168+/-41 microM) had four times higher plasma ammonia compared to wild type mice (40 +/- 6 microM) (P=0.002). Two hours after LPS injection, plasma ammonia concentrations tended (P=0.08) to decrease in both wild type and Otc(spf-ash) mice. Learning and memory behaviors were assessed in mice under basal conditions to determine the impact of chronic hyperammonemia on cognition. Otc(spf-ash) mice performed significantly poorer in the two trial Y-maze (P=0.02) and the Morris water maze (P=0.001) than their littermate wild type controls. Taken together, these data indicate that chronic hyperammonemia results in impaired cognition and creates a state of LPS hypersensitivity.     

Hypothermic response of mice to ornithine-containing lipids and to endotoxin.

The hypothermic response of mice to ornithine-containing lipids (Orn-Ls) of the form alpha-N-(3-acyloxyacyl)-ornithine and to endotoxin (Escherichia coli 0111:B4 lipopolysaccharide [LPS]) was studied. After the administration of Orn-L or LPS to C3H/HeSlc mice, body temperature decreases were determined at 30-min intervals by inserting a thermistor into the rectum of each mouse. When Orn-L (750 microg) or LPS (70 microg) was injected into the mice, body temperature decreases of 0.8 and 2.0 degrees C, respectively, occurred 1.8 to 2.0 h later. These body temperature decreases were completely suppressed by the preadministration of indomethacin. When anti-tumor necrosis factor alpha (TNF-alpha) antibody was administered before the administration of Orn-L or LPS, only the body temperature decrease by LPS was suppressed. The body temperature decrease by Orn-L was suppressed by anti-interleukin-1beta (IL-1beta) antibody preadministration. Next, in order to study IL-1beta and TNF-alpha mRNA expression in macrophages, peritoneal macrophages were collected 40 min after the administration of Orn-L or LPS to mice. The expression of IL-1beta mRNA by stimulation with Orn-L was as strong as that by stimulation with LPS, but the expression of TNF-alpha mRNA by stimulation with Orn-L was very weak. Our previous studies of in vitro macrophage activation by Orn-L proved that strong induction of IL-1 and prostaglandin E2 generation by Orn-L occurred (Y. Kawai and K. Akagawa, Infect. Immun. 57:2086-2091, 1989). From these experiments, the weak body temperature decrease in mice caused by Orn-L was found to be mediated by cytokines different from those which mediate the strong body temperature decrease caused by LPS. Namely, it was caused by prostaglandin E2 being mediated by IL-1 but not by TNF-alpha.     

Lipopolysaccharide-induced elevation and secretion of interleukin-1beta in the submandibular gland of male mice

The intraperitoneal injection of lipopolysaccharide (LPS) (400 microg/kg body weight) induced the expression of mRNAs of inflammatory cytokines such as interleukin (IL)-1beta, IL-6 and tumour necrosis factor (TNF)-alpha in the submandibular gland (SMG) of C3H/HeN mice but not that of C3H/HeJ mice, a mutant strain for Toll-like receptor-4 (TLR-4(-) mutant). The mRNA levels of these cytokines in the SMG of the wild-type mice increased as early as 3 hr after injection, peaked at 3-6 hr, and had decreased again by 24 hr. In this study, we particularly focused on IL-1beta, and induction by this endotoxin was investigated in detail. Denervation of the superior cervical trunk and chorda tympani nerve did not diminish the LPS-induced elevation of IL-1beta mRNA in the SMG, indicating the irrelevance of the central nervous system in this induction. TLR-4 mRNA and protein were shown to be strongly expressed in the SMG, suggesting the direct action of LPS on this gland. IL-1beta proteins were localized in the secretory granules of granular convoluted tubular (GCT) cells, and their molecular weights in the gland were 17.5 and 20 kDa. IL-1beta of the same size appeared in the saliva 6 hr after LPS injection in C3H/HeN but not in C3H/HeJ mice. The present study thus suggests that IL-1beta, an inflammation cytokine, is induced and secreted into the saliva in response to endotoxin injected intraperitoneally.     

Cholecystokinin receptors do not mediate the suppression of food-motivated behavior by lipopolysaccharide and interleukin-1 beta in mice

During the course of an infection, profound metabolic and behavioral changes are observed. The resulting decrease in food intake can be reproduced by administration of lipopolysaccharide (LPS) or the proinflammatory cytokines (e.g., interleukin-1 [IL-1] and tumor necrosis factor it induces. To test the possibility that cholecystokinin (CCK) mediates anorexia induced by IL-1 beta and LPS, mice trained to poke their noses in a hole to obtain a food reward according to a fixed ratio (1 reward per 20 actions) were pretreated with the CCK-A receptor antagonist L364,718 (at 1 mg/kg) or with the CCK-B receptor antagonist L365,260 (50 microg/kg) before being injected with LPS (100 microg/kg) or IL-1 beta (20 microg/kg). All injections were given via the intraperitoneal (i.p.) route. In spite of its ability to block the effects of exogenous CCK-8 on food-motivated behavior in mice, the CCK-A receptor antagonist did not block the depressive actions of LPS and IL-1 beta on food-motivated behavior. The CCK-B receptor antagonist was not more effective at blocking. These results do not support a role for CCK in the anorexic effect of LPS and IL-1 beta.     

Role of TNF and IL-1 in infections with Toxoplasma gondii.

Mice lethally infected with the C56 strain of Toxoplasma gondii and treated with purified recombinant murine tumour necrosis factor (TNF, 1 microgram/day/mouse for 8 days), recombinant human interleukin-1 (IL-1 alpha or IL-1 beta, 100 ng/day/mouse for 5 days) or a single dose of a combination of TNF (1 microgram/mouse) and IL-1 alpha or IL-1 beta (100 ng/mouse) were significantly protected against death (P less than 0.05-0.001, as compared with untreated infected controls). Mice infected with 100,000 tachyzoites of the highly virulent RH strain of T. gondii released serum TNF in relation to the time after infection and were primed to secrete an enhanced level of serum TNF upon stimulation with bacterial lipopolysaccharide (LPS). In vitro studies showed that interferon-gamma (IFN-gamma) increased the antimicrobial activity of murine peritoneal macrophages whereas TNF, IL-1 alpha and IL-1 beta did not. TNF, however, synergized with the anti-toxoplasmic effect provided by IFN-gamma and this activity was blocked by anti-TNF antibodies. IFN-gamma induced the production of TNF and the anti-toxoplasmic effect provided by IFN-gamma seemed to be dependent partly on the production of TNF. We conclude that TNF and IL-1 may play a significant role in modulating the host's immune defence against T. gondii infection.     

The role of IL-1beta in stress-induced sensitization of proinflammatory cytokine and corticosterone responses

Proinflammatory cytokines often sensitize neuronal, hormonal, and behavioral responses to subsequent challenge. Recently, it was observed that exposure to inescapable tailshock enhances peripheral and central proinflammatory cytokine and corticosterone (CORT) responses to subsequent immune challenge up to 4 days later. Thus, we examined the role of central interleukin-1beta (IL-1beta) in stress-induced sensitization of proinflammatory cytokine and CORT responses to a subsequent immune challenge. Rats were administered IL-1 receptor antagonist (IL-1ra) or vehicle into the intra-cisterna magna 1 h prior to tailshock (100, 1.6 mA 5 s shocks) exposure. Twenty-four hours later, rats were challenged i.p. with 10 microg/kg lipopolysaccharide (LPS) and killed 1 h later. IL-1ra had no effect on basal proinflammatory cytokines, but completely blocked the stress-induced enhancement in central and pituitary IL-1beta and plasma IL-6 release following LPS challenge. IL-1ra had no effect on stress-induced enhancement in CORT responses following LPS challenge. Additional rats were administered i.c.v. hrIL-1beta or vehicle and returned to their home cage. Twenty-four hours later, rats were challenged i.p. with either saline or 10 microg/kg LPS and killed 1 h later. Central hrIL-1beta administration significantly elevated central IL-1beta levels and plasma CORT following LPS challenge compared with vehicle-injected controls. These data demonstrate that elevations in central IL-1beta, whether stress-induced or exogenously administered, are sufficient for sensitizing central IL-1beta and CORT responses to subsequent immune challenge. However, during times of stress, exogenous central IL-1ra administration only blocked sensitization of subsequent central IL-1beta responses, not CORT responses, suggesting other factors during the stress response can sensitize CORT responses.     

Thymulin, a thymic peptide, prevents the overproduction of pro-inflammatory cytokines and heat shock protein Hsp70 in inflammation-bearing mice

The effects of synthetic analogue of peptide hormone thymulin, which is normally produced by thymic epithelial cells, on immune cells activity and blood cytokine profile had been studied in male NMRI mice with acute inflammation induced by injection of lipopolysaccharide from gram-negative bacteria (LPS, 250 microg/100 g of body weight). Inflammation induced by LPS resulted in accumulation of several plasma pro-inflammatory cytokines, IL-1 beta, IL-2, IL-6, TNF-alpha, interferon-gamma, and also IL-10, anti-inflammatory cytokine. Thymulin previously injected in dose of 15 microg/100 g body weight, prevented the accumulation of proinflammatory cytokines in plasma. Thymulin also prevented LPS-induced up-regulation of production of several cytokines by spleen lymphocytes and peritoneal macrophages. Added in vitro, thymulin decreased the peak of TNF-alpha production in macrophages cultivated with LPS. In addition, thymulin lowered the peak of Hsp70 production induced by LPS treatment. The results indicate that thymulin having significant anti-inflammatory effect may be promising in clinical application.     

Endotoxin-induced lethality in neonatal mice is counteracted by interleukin-10 (IL-10) and exacerbated by anti-IL-10.

The lethal effects occurring in neonatal (<24-h-old) BALB/c mice after challenge with 25 mg of lipopolysaccharide (LPS) per kg of body weight were significantly counteracted by pretreatment with recombinant interleukin-10 (rIL-10; 25 or 50 ng/mouse). Concordantly, blockage of endogenous IL-10 with the SXC1 monoclonal antibody increased LPS-induced mortality. Both IL-10 and SXC1 modulated the release of tumor necrosis factor alpha (TNF-alpha) so that, relative to controls, peak TNF-alpha values after LPS challenge were decreased by rIL-10 and increased by anti-IL-10.     

Immunohistochemical staining of IL-1 alpha and IL-1 receptor antagonist but not IL-1 beta in cultures of sertoli cells

The interleukin-1 (IL-1) system has been suggested to be involved in the cell cell cross talk within the testis. To identify a testicular cell source of IL-1 alpha, IL-1 beta and IL-1 receptor antagonist (IL-1ra), immature mouse Sertoli cells were isolated, purified, cultured and examined for the cellular compartment localization of these cytokines by immunohistochemical staining. Our results show that both Germ cells and Sertoli cells in unpurified Sertoli cell cultures (before hypotonic shock) and purified culture of Sertoli cells (after hypotonic shock) were stained for IL-1 alpha. The levels of this cytokine were increased in Sertoli cells when the purified cultures were stimulated with lipopolysaccharide (LPS) (5 microg/mL). However, we could not identify a positive staining for IL-1 beta when Sertoli cell cultures were stained for this cytokine, even after stimulation with various concentrations of LPS (0.1-10 microg/mL). On the other hand, immunohistochemical staining of isolated Sertoli cells without treatment with hypotonic shock (cultures containing Sertoli cells and Germ cells) for IL-1ra showed constitutive positive staining of both cell types (Sertoli cells and Germ cells). Our results, using immunohistochemical staining, may indicate the different expression of IL-1 alpha, IL-1 beta and IL-1ra in Sertoli cells. These results may suggest the involvement of IL-1 system in the autocrine and paracrine regulation of testicular cell functions.     

Increased susceptibility to systemic candidiasis in interleukin-6 deficient mice.

Interleukin-6 (IL-6) is a multifunctional cytokine that regulates multiple aspects of the innate immune response. It has been recently shown that endogenous IL-6 is crucial for an efficient defence against severe infections with Gram-negative and Gram-positive bacteria. The aim of the present study was to investigate the role of endogenous IL-6 in the defence against infection with the yeast Candida albicans. During experimental candidemia, IL-6 deficient mice (IL-6-/-) had a decreased survival and an increased fungal load in their organs when compared with IL-6+/+ controls, despite increased plasma concentrations of tumour necrosis factor-alpha (TNF), interleukin-1 alpha (IL-1 alpha) and IL-1 beta, IL-6-/- mice were not able to mount an efficient neutrophil response during the infection. When mice were rendered neutropenic by cyclophosphamide, neutropenic IL-6-/- mice were equally susceptible to C. albicans when compared to neutropenic IL-6+/+ mice, implying that neutrophils mediate the beneficial effect of endogenous IL-6. In conclusion, IL-6-/- mice are more susceptible to disseminated candidiasis, and the effect of IL-6 is most likely mediated by neutrophils.     

Inverse regulation of interleukin-6 (IL-6) and IL-6 receptor in histamine deficient histidine decarboxylase-knock-out mice

Interleukin-6, a multifunctional cytokine upon binding to its receptor on hepatocytes regulates production of acute phase proteins involved in local and systemic inflammation. Gene expression and biosynthesis of IL-6 and its receptor (IL-6 R/gp130) is under complex regulation. Histamine, in addition to its principal role in immediate type hypersensitivity has been described to modulate IL-6 production and expression of IL-6 receptor. In this study, the IL-6 and IL-6 receptor expression was examined in histamine deficient histidine decarboxylase (HDC) knock-out mouse model. Our data suggest that in histamine deficient mice the inducibility of IL-6 is significantly reduced, whilst more IL-6 receptor/gp130 mRNA expresses in the liver than in wild type (HDC^+/+) mice. These in vivo findings confirm earlier in vitro results and emphasize the efficacy of antihistamines in local IL-6 related processes.     

Differential effects of lipopolysaccharide in the social behavior of dominant and submissive mice

Acutely infected animals show a set of non-specific behavioral changes known as sickness behavior. Recent studies have shown that occurrence of sickness behavior is regulated according to a motivational perspective. Thus, the display of sickness behavior may compete with display of other behaviors. In this work, we sought to determine the effects of lipopolysaccharide (LPS) administration (15 microg/mouse i.p.) in the social behavior of dominant and submissive mice. Results showed that social hierarchy influences the expression of sickness behavior. While dominant mice treated with LPS showed an expected reduction in total frequency of behaviors displayed, such decrease did not happen following the same treatment to submissive mice. Similar results occurred regarding social and aggressive behavior. The use of a motivational perspective provides the assumption that, due to their high social ranking, dominant mice were able to prioritize recuperative behavior. Submissive mice, on the other hand, even though treated with LPS, seemed to essentially focus on social defensive behaviors since they remained in the presence of the dominant individuals. Effects of sickness on the hierarchical organization of mice remain to be further investigated.     

HSF1对LPS诱导的急性肺损伤小鼠的保护作用及其相关差异表达基因的筛选

目的:探讨热休克因子1(heat shock factor 1,HSF1)减轻脂多糖(lipopolysaccharide,LPS)诱导的小鼠急性肺损伤的作用及其分子机制。方法:采用气管滴注LPS的方法制备小鼠急性肺损伤模型,观察HSF1野生型小鼠(HSF1~(+/+))和HSF1敲除小鼠(HSF1~(-/-))肺大体改变和肺组织病理改变,检测支气管肺泡灌洗液(bronchoalveolar lavage fluid,BALF)中总蛋白、血管内皮生长因子(vascular endothelial growth factor,VEGF)、肿瘤坏死因子α(tumor necrosis factor-α,TNF-α)、白细胞介素(interleukin,IL)-1β和IL-6的蛋白表达。采用基因芯片技术筛选经LPS处理后的HSF1~(+/+)和HSF1~(-/-)小鼠肺组织中的差异表达基因,并进一步采用real-time PCR对CXC趋化因子受体2(CXC chemokine receptor 2,CXCR2)的表达进行验证。结果:与经LPS刺激后的HSF1~(+/+)小鼠相比,经LPS刺激的HSF1~(-/-)小鼠肺大体和病理损伤加重,BALF中总蛋白、VEGF、TNF-α、IL-1β和IL-6的含量升高,差异具有统计学意义(P0.05)。基因芯片分析发现,与经LPS处理的HSF1~(+/+)小鼠相比,HSF1~(-/-)小鼠共筛选出918个差异基因,有65个基因表达差异明显,其中Atg7、ccr1、cxcr2、Tbl1xr1、Mmp9、Pparg、Plcb2、Arrb2、Cntn1、Col4a6等共28个基因在HSF1~(-/-)小鼠的肺组织中表达明显上调;Fgfr1、Fgfr2、Map4k4、Ddx58、Tfg、Stat3、Smad4、Lamc1、Sdc3等共37个基因表达明显下调。Real-time PCR结果显示,CXCR2的mRNA水平在LPS刺激的HSF1~(-/-)小鼠肺组织较HSF1~(+/+)小鼠表达明显上调,表达趋势与基因芯片结果一致。结论:HSF1能减轻LPS诱导的小鼠急性肺损伤,CX-CR2可能参与了对肺组织的保护作用。     

Modulation of IL-1 alpha, IL-1 beta, and 25K Mr non-IL-1 activity released by human mononuclear cells

To determine if the release of IL-1 alpha and IL-1 beta by cultured PBMC could be independently modulated by different exogenous stimuli, we examined the effect of LPS, IFN gamma, latex beads, and indomethacin on the release of IL-1 alpha and IL-1 beta. PBMC culture supernatants were fractionated by Sephacryl-S-200 column chromatography or HPLC (TSK G3000SW), and each fraction was tested for thymocyte mitogenic activity in the presence or absence of preincubation with anti-IL-1 alpha or anti IL-1 beta monoclonal antibody (mAb) and for the presence of IL-1 alpha or IL-1 beta protein by ELISA. In all experiments, thymocyte mitogenic activity not neutralizable by anti-IL-1 alpha or anti-IL-1 beta mAb was detected in the 25K Mr range, which ranged from 12 to 50% of the total thymocyte mitogenic activity released, depending on the stimuli. Cultured PBMC from 95% of individuals release thymocyte mitogenic activity in the absence of exogenous stimuli, which was increased 1.3-to 7-fold by lopopolysaccharide (LPS) (25-50 micrograms/ml). All of this increased activity was due to increased release of IL-1 beta and non-IL-1 thymocyte mitogenic activity, with no change in the total amount of IL-1 alpha released. Indomethacin (0.1 microgram/ml) induced release of increased thymocyte mitogenic activity of 1.3- to 1.4-fold over unstimulated cultures. All of this increased activity was due to increased release of IL-1 alpha and non-IL-1 activity with a concomitant decrease in IL-1 beta release. Interferon gamma (40-100 U/ml) increased the amount of IL-1 alpha and decreased IL-1 beta and non-IL-1 activity released, resulting in no overall change in the total amount of thymocyte mitogenic activity. Molecular weight fractionation of the PBMC culture supernatants revealed that thymocyte mitogenic activity eluting in the 25K Mr range was not due to IL-1 alpha or IL-1 beta. With certain culture conditions, thymocyte mitogenic activity was detected in the 30-40K Mr range. PBMC cultured with LPS and latex beads in the absence of serum released 30-40K Mr IL-1 alpha, as well as 17K Mr IL-1 alpha and 17K Mr IL-1 beta. PBMC cultured in 2% fetal calf serum (FCS) alone from some donors released only 30-40K Mr thymocyte mitogenic activity. Both IL-1 alpha and IL-1 beta protein was detected by ELISA in this Mr range but only the IL-1 alpha was bioactive.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lipopolysaccharide-induced lethality and cytokine production in aged mice.

This study was designed to define the lipopolysaccharide (LPS) sensitivity of aged mice in terms of lethality and cytokine production and to determine down-regulating responses of corticosterone and interleukin 10 (IL-10). The 50% lethal doses of LPS in young (6- to 7-week-old) and aged (98- to 102-week-old) mice were 601 and 93 microg per mouse (25.6 and 1.6 mg per kg of body weight), respectively. Aged mice were approximately 6.5-fold more sensitive to the lethal toxicity of LPS in micrograms per mouse (16-fold more sensitive in milligrams per kilogram) than young mice. Levels in sera of tumor necrosis factor-alpha (TNF-alpha) IL-1alpha, and IL-6 after intraperitoneal injection of 100 microg of LPS peaked at 1.5, 3, and 3 h, respectively, and declined thereafter in both groups of mice. However, the peak values of these cytokines were significantly higher in aged than in young mice (P < 0.05). Gamma interferon (IFN-gamma) was detectable at 3 h, and sustained high levels were still detected after 12 h in both age groups. Although there were no significant differences in levels of IFN-gamma in sera from both groups, aged mice showed higher IFN-gamma levels throughout the 3- to 12-h study period. Administration of increasing doses of LPS revealed that aged mice had a lower threshold to IL-1alpha production than young mice. In addition, aged mice were approximately 4-fold more sensitive to the lethal toxicity of exogenous TNF in units per mouse (10-fold more sensitive in units per kilogram) than young mice. With regard to down-regulating factors, corticosterone amounts were similar at basal levels and no differences in kinetics after the LPS challenge were observed, whereas IL-10 levels in sera were significantly higher in aged mice at 1.5 and 3 h than in young mice (P < 0.01). These results indicate that aged mice are more sensitive to the lethal toxicities of LPS and TNF than young mice. We conclude that a relatively activated, or primed, state for LPS-induced cytokine production, in spite of full down-regulating responses by corticosterone and IL- 10, may explain at least in part LPS sensitivity in aged mice.     

Exaggerated sickness behavior and brain proinflammatory cytokine expression in aged mice in response to intracerebroventricular lipopolysaccharide

Age-associated changes in glial reactivity may predispose individuals to exacerbated neuroinflammatory cytokine responses that are permissive to cognitive and behavioral complications. The purpose of this study was to determine if aging is associated with an exaggerated sickness response to central innate immune activation. Our results show that intracerebroventricular (i.c.v.) administration of lipopolysaccharide (LPS) caused a heightened proinflammatory cytokine response (IL-1beta, IL-6, and TNFalpha) in the cerebellum 2h post i.c.v. injection in aged mice compared to adults. This amplified inflammatory profile was consistent with a brain region-dependent increase in reactive glial markers (MHC class II, TLR2 and TLR4). Moreover, LPS caused a prolonged sickness behavior response in aged mice that was paralleled by a protracted expression of brain cytokines in the cerebellum and hippocampus. Finally, central LPS injection caused amplified and prolonged IL-6 levels at the periphery of aged mice. Collectively, these data establish that activation of the central innate immune system leads to exacerbated neuroinflammation and prolonged sickness behavior in aged as compared to adult mice.     

Contribution of interleukin-11 and prostaglandin(s) in lipopolysaccharide-induced bone resorption in vivo

We previously demonstrated that interleukin-1 (IL-1) and tumor necrosis factor (TNF) activities only partially account for calvarial bone resorption induced by local application of lipopolysaccharide (LPS) in mice. The present study was undertaken to determine the role and relative contribution of IL-11 and prostaglandin(s) (PG[s]) in LPS-induced bone resorption in vivo. A one-time dose of LPS was injected into the subcutaneous tissue overlying calvaria of mice lacking IL-1 receptor type I (IL-1RI(-/-)), mice lacking TNF receptor p55 and IL-1RI (TNFRp55(-/-)-IL-1RI(-/-)), and wild-type mice. Mice were then treated with injections of anti-IL-11 monoclonal antibody (MAb), indomethacin, or phosphate-buffered saline (PBS) and sacrificed 5 days later. Histological sections stained for tartrate-resistant acid phosphatase (TRAP) were quantified by histomorphometric analysis. At low doses of LPS (100 microg/mouse), the percentages of bone surface covered by osteoclasts were found to be similar in three strains of mice. The increase was reduced by 37% with anti-IL-11 MAb and by 46% with indomethacin. At higher doses of LPS (500 microg/mouse), we found an eightfold increase in these percentages in wild-type mice and a fivefold increase in these percentages in IL-1RI(-/-) and TNFRp55(-/-)-IL-1RI(-/-) mice after normalizing with the value from the saline-PBS control group in the same strain of mice. The increase was reduced by 55 and 69% in wild-type mice and by 50 and 57% in IL-1RI(-/-) and TNFRp55(-/-)-IL-1RI(-/-) mice treated with anti-IL-11 MAb or indomethacin, respectively. Our findings suggest that in vivo, at low doses of LPS (100 microg/mouse), LPS-induced bone resorption is mediated by IL-11 and PGs, while at high doses of LPS (500 microg/mouse), it is mediated by IL-11, PGs, IL-1, and TNF signaling. IL-11 and PGs mediate LPS-induced bone resorption by enhancing osteoclastogenesis independently of the IL-1 or TNF signaling.     

Regulation of primary Strongyloides ratti infections in mice: a role for interleukin-5.

C57BL/6 mice genetically deficient in interleukin-5 (IL-5-/-) and normal C57BL/6 (IL-5+/+) mice were infected with larvae of a homogonic strain of the nematode Strongyloides ratti. In primary infections both male and female IL-5-/- mice released two to four times more eggs and larvae than IL-5+/+ mice. IL-5-/- mice harboured about 60% more intestinal worms, which were more fecund, than IL-5+/+ mice. The duration of the infection was similar in normal and IL-5-deficient mice. Both IL-5-/- and IL-5+/+ mice resisted a secondary infection. IL5-/- mice lost more weight during the infection than normal mice and took longer to regain their initial weight after expelling the worms. The number of eosinophils increased in the bone marrow, peritoneal cavity and small intestine of IL-5+/+ mice, but not IL-5-/- mice, following infection. No significant differences between infected IL-5+/+ and IL-5-/- mice in mast cells or other leucocytes were observed in the peritoneal cavity. Thus, IL-5 functions to protect the host in a primary infection of S. ratti by limiting the number and fecundity of worms establishing in the small intestine. This protection is correlated with elevated blood and tissue eosinophilia which occurs in normal mice but not in IL-5-/- mice.