Bacterial lipopolysaccharide fever is initiated via Toll-like receptor 4 on hematopoietic cells

Fever induction by systemic stimulation with macrophage-activating lipopeptide-2 depends upon TLR2 but not CD36

This study was designed to test the responses of TLR2-knockout mice (TLR2-KO) and wild- type mice (C57/BL-6), and of CD36 deficient spontaneously hypertensive rats (SHR) and their genetic controls [Wistar Kyoto (WKY) rats] to systemic stimulations with the TLR2/6 agonist MALP-2 and the TLR4 agonist LPS. Fever and formation of TNF-α and IL-6 induced by intraperitoneal injections of MALP-2 (1000 µg/kg) were completely blunted in TLR2-KO, while LPS (100 µg/kg)-induced responses were not abolished in these animals. In SHR lacking CD36, a reduction of fever was observed in response to MALP-2 (100 µg/kg), but LPS-fever was even more attenuated in SHR when compared with WKY controls. Concentrations of circulating IL-6 tended to be lower in SHR after stimulation with both pyrogens. However, the IL-6-mediated activation of the transcription factor STAT3 in the brain was identical in both strains, indicating that the brain-controlled inflammatory response to MALP-2 (and LPS) is not impaired in the absence of CD36. In addition, stimulation of peritoneal macrophages with LPS and MALP-2 (10 µg/ml) caused the appearance of similar concentrations of bioactive cytokines in the supernatants from cells of both rat strains. These results demonstrate that TLR2 is essential for the manifestation of MALP-2, but not LPS-induced inflammatory responses. A moderate participation of CD36 in MALP-2-induced sickness- and cytokine-responses can not be ruled out but is unlikely as LPS-induced inflammatory responses were also attenuated in SHR.

Fever, fever patterns and diseases called 'fever'--a review

Fever is a prominent feature of disease since antiquity. The febrile response is orchestrated by the central nervous system through endocrine, neurological, immunological and behavioural mechanisms. Other than a regulated rise in body temperature, fever is often accompanied by various sickness behaviours, changes in metabolic and physiological characteristics of body systems and alterations in immune responses. Fever and the febrile response, therefore, remain significant contributors to the pathogenesis, clinical presentation and outcome of many illnesses and diseases. This review highlights the pathophysiology of the febrile response and describes the fever types and patterns, including their clinical significance. The various medical illnesses called "fever" are also listed and the origins of their appellations discussed.

Neonatal bacterial infection alters fever to live and simulated infections in adulthood

Fever is a critical component of the host immune response to infection. An emerging literature demonstrates that experience with infectious organisms early in life, during the perinatal period, may permanently program immune responses later in life, including fever. We explored the influence of neonatal infection with Escherichia coli on fever responses to lipopolysaccharide (LPS) and E. coli in adulthood. Fever to a low dose of LPS in adulthood did not significantly differ as a consequence of early-life infection. Eight days after the LPS injection, the same group of rats received a high dose of live E. coli. This time, neonatally infected rats exhibited a markedly longer fever than controls. In a subsequent experiment, fever to a single high dose of E. coli without prior LPS in adulthood did not differ by group, suggesting that the previous difference was a lack of tolerance to the dual challenges in early-infected rats. Finally, both groups exhibited decreased tumor necrosis factor (TNF)-alpha and toll-like-receptor (TLR) 4 production to dual LPS challenges in isolated splenocytes, whereas only rats infected as neonates exhibited increased cyclooxygenase-2 within the hypothalamus in response to adult infection, suggesting that early infection-induced changes in fever regulation may involve a change in central mechanisms. Taken together, these data indicate that early-life infection is associated with marked changes in host temperature regulation in adulthood.

LPS-induced cytokine levels are repressed by elevated expression of HSP70 in rats: possible role of NF-kappaB

Heat shock protein (HSP)70 provides a spectrum of protection against any of a variety of stresses, preventing damage measured at the level of molecules, cells, as well as whole organism. We have previously reported that lipopolysaccharide (LPS)-induced lethality in rats is prevented by a previous exposure to a mild thermal stress and that a thermal stress sufficient to induce HSP70 expression in the liver is accompanied by an inhibition of endotoxin-mediated cytokines and modulation of febrile response. However, the effect of HSP70 upregulation on cytokine expression in animals is unknown. The aim of the present study was to demonstrate the effect of HSP70 overexpression with adenovirus administration on LPS-induced increase in cytokines levels in animals. In the present study, Sprague-Dawley rats were infected with either the control AdTrack or Ad70 virus that directs the expression of human HSP70. After a 5-day incubation, animals were injected with either saline alone or LPS (50 microg/kg). Four hours later, blood samples were drawn and plasma levels of interleukin (IL)-6 or tumor necrosis factor (TNF)-alpha were measured by enzyme-linked immunosorbent assay. Our data demonstrate for the first time that HSP70 overexpression with adenovirus injection prevented the LPS-induced increase in TNF-alpha and IL-6 levels in rats. Repression of LPS-induced cytokines expressions by HSP70 upregulation was associated with inhibited IkappaBalpha degradation and nuclear factor kappa-B (NF-kappaB) p65 nuclear translocation in liver, suggesting that HSP70 overexpression may regulate LPS-induced cytokines expression through NF-kappaB pathway. We conclude that the effects of heat stress-induced increase in HSP70 protein expression on LPS-induced cytokine elaboration in whole animals can be reproduced by the actions of a single gene product.

Systemic administration of lipopolysaccharide induces cyclooxygenase-2 immunoreactivity in endothelium and increases microglia in the mouse hippocampus

In this study, we observed the effects of lipopolysaccharide (LPS) on neurodegeneration and immune response in the hippocampus. LPS is a gram-negative bacterial cell surface proteoglycan and known as a bacterial endotoxin. For this, we investigated the optimal concentration of LPS influencing the ICR mouse hippocampus to measure the LPS receptor, e.g., toll-like receptor 4 (TLR4), expression in mouse hippocampal homogenates. TLR4 expression was significantly and prominently increased in the hippocampal homogenates of the LPS (1 mg/kg)-treated group. Next, we examined pro-inflammatory response in the hippocampus using cyclooxygenase-2 (COX-2, a marker for inflammatory response) immunohistochemistry after LPS treatment. COX-2 immunoreactivity was significantly increased in the endothelium of blood vessels in the hippocampus 6 h after LPS treatment, judging from double immunofluorescence study with platelet-derived endothelial cell adhesion molecule-1 (PECAM-1, a marker for endothelial cells): it decreased 12 h and disappeared 24 h after LPS treatment. In addition, the ionized calcium-binding adapter molecule 1 (Iba-1)-immunoreactive ((+)) microglia were morphologically activated in the mouse hippocampus after LPS treatment. At 24 h after LPS treatment, Iba-1(+) microglia of activated forms were abundant in the hippocampus. However, NeuN (a neuron-specific soluble nuclear antigen)(+) neurons were not significantly changed in the hippocampus after LPS treatment. Fluoro-jade B (a marker for neuronal degeneration)(+) cells were not detected in the hippocampus at any time after LPS treatment. In addition, there were no significant differences in permeability of blood-brain barriers at any time points after LPS treatment. In brief, our results indicate that intraperitoneal administration of 1 mg/kg LPS effectively induces LPS receptor (TLR4) expression in the hippocampus, and the treatment increases corticosterone levels, inflammation in the blood vessels, and microglial activation in the hippocampus without any neuronal damage.

Effects of repeated injections of fibroblast-stimulating lipopeptide-1 on fever, formation of cytokines, and on the responsiveness to endotoxin in guinea-pigs

AIMS

We investigated, whether the Toll-like receptors (TLRs)-2/6-agonist fibroblast-stimulating lipopeptide-1 (FSL-1), like the TLR-4 agonist lipopolysaccharide (LPS), induces a state of tolerance. We further tested the influence of repeated pre-treatment with FSL-1 on the animals' responsiveness to LPS.

METHODS

Abdominal temperature was recorded in unrestrained guinea-pigs with intra-abdominally implanted radiotransmitters. Circulating concentrations of tumour necrosis factor (TNF) and interleukin-6 (IL-6) were measured with specific bioassays. We tested the effects of intra-arterial (i.a.) or intraperitoneal (i.p.) injections of 100 microg kg(-1) FSL-1, repeated five times at intervals of 3 days. The animals' responses to i.a. or i.p. injections of 10 microg kg(-1) LPS were determined another 3 days later and compared to those of naïve guinea-pigs.

RESULTS

The FSL-1-induced TNF peak was significantly attenuated starting with the third i.a. administration, while fever was unimpaired and the IL-6-peak just tended to decrease. Fever and IL-6 in response to i.a. injections of LPS were identical in both groups, while circulating TNF was higher in naïve compared to FSL-1 pre-treated animals. The effects of repeated i.p. injections of FSL-1 were more pronounced resulting in attenuation of fever as well as circulating TNF and IL-6, the strongest reduction observed after the third stimulation with FSL-1. Repeated i.p. pre-treatment with FSL-1 induced hyporesponsiveness to i.p. administration of LPS compared to naïve animals with regard to fever and especially with regard to LPS-induced formation of cytokines.

CONCLUSIONS

There is a development of tolerance to FSL-1 and cross-tolerance between FSL-1 and LPS depending on the route of administration of the respective TLR-2/6 and TLR-4 agonists.

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.

Immune-to-brain signaling: how important are the blood-brain barrier-independent pathways?

A conceptual obstacle for understanding immune-to-brain signaling is the issue of the blood-brain barrier (BBB). In the last 30 years, several pathways have been investigated to address the question of how peripheral immune signals are transmitted into the brain. These pathways can be categorized into two types: BBB-dependent pathways and BBB-independent pathways. BBB-dependent pathways involve the BBB as a relay station or porous barrier, whereas BBB-independent pathways use neuronal routes that bypass the BBB. Recently, a complete BBB-dependent ascending pathway for immune-to-brain signaling has been described. Details of BBB-independent pathways are still under construction. In this review, I will summarize the current progress in unraveling immune-to-brain signaling pathways. In addition, I will provide a critical analysis of the literature to point to areas where our knowledge of the immunological afferent signaling to the central nervous system is still sorely lacking.

Fever response to intravenous prostaglandin E2 is mediated by the brain but does not require afferent vagal signaling

PGE2 produced in the periphery triggers the early phase of the febrile response to infection and may contribute to later phases. It can be hypothesized that peripherally synthesized PGE2 transmits febrigenic signals to the brain via vagal afferent nerves. Before testing this hypothesis, we investigated whether the febrigenic effect of intravenously administered PGE2 is mediated by the brain and is not the result of a direct action of PGE2 on thermoeffectors. In anesthetized rats, intravenously injected PGE2 (100 μg/kg) caused an increase in sympathetic discharge to interscapular brown adipose tissue (iBAT), as well as increases in iBAT thermogenesis, end-expired CO2, and colonic temperature (Tc). All these effects were prevented by inhibition of neuronal function in the raphe region of the medulla oblongata using an intra-raphe microinjection of muscimol. We then asked whether the brain-mediated PGE2 fever requires vagal signaling and answered this question by conducting two independent studies in rats. In a study in anesthetized rats, acute bilateral cervical vagotomy did not affect the effects of intravenously injected PGE2 (100 μg/kg) on iBAT sympathetic discharge and Tc. In a study in conscious rats, administration of PGE2 (280 μg/kg) via an indwelling jugular catheter caused tail skin vasoconstriction, tended to increase oxygen consumption, and increased Tc; none of these responses was affected by total truncal subdiaphragmatic vagotomy performed 2 wk before the experiment. We conclude that the febrile response to circulating PGE2 is mediated by the brain, but that it does not require vagal afferent signaling.

Regulation of MyD88-dependent signaling events by S nitrosylation retards toll-like receptor signal transduction and initiation of acute-phase immune responses

Nitric oxide (NO) has been thought to regulate the immune system through S nitrosylation of the transcriptional factor NF-kappaB. However, regulatory effects of NO on innate immune responses are unclear. Here, we report that NO has a capability to control Toll-like receptor-mediated signaling through S nitrosylation. We found that the adaptor protein MyD88 was primarily S nitrosylated, depending on the presence of endothelial NO synthase (eNOS). S nitrosylation at a particular cysteine residue within the TIR domain of MyD88 resulted in slight reduction of the NF-kappaB-activating property. This modification could be restored by the antioxidant glutathione. Through S nitrosylation, NO could negatively regulate the multiple steps of MyD88 functioning, including translocation to the cell membrane after LPS stimulation, interaction with TIRAP, binding to TRAF6, and induction of IkappaBalpha phosphorylation. Interestingly, glutathione could reversely neutralize such NO-derived effects. We also found that an acute febrile response to LPS was precipitated in eNOS-deficient mice, indicating that eNOS-derived NO exerts an initial suppressive effect on inflammatory processes. Thus, NO has a potential to retard induction of MyD88-dependent signaling events through the reversible and oxidative modification by NO, by which precipitous signaling reactions are relieved. Such an effect may reflect appropriate regulation of the acute-phase inflammatory responses in living organisms.

Involvement of a capsaicin-sensitive TRPV1-independent mechanism in lipopolysaccharide-induced fever in chickens

It has been demonstrated that capsaicin blocks lipopolysaccharide (LPS)-induced fever in mammals. In this study, we investigated TRPV1 (transient receptor potential ion channel of vanilloid subtype-1)-independent action of capsaicin on LPS-induced fever in chickens. The chicken is a valuable model for this purpose because chicken TRPV1 has been shown to be insensitive to capsaicin and thus the effects of capsaicin can be attributed to TRPV1-independent mechanisms. Administration of capsaicin (10 mg/kg, iv) to conscious unrestrained chicks at 5 days of age caused a transient decrease in body temperature. This effect of capsaicin was not observed in chicks that had been pretreated twice with capsaicin, indicating that the capsaicin-sensitive pathway can be desensitized. LPS (2 mg/kg, ip) induced fever that lasted for about 2.5 h, but fever was not induced in chicks that had been pretreated with capsaicin for 2 days. The preventive effect of capsaicin on LPS-induced fever was not blocked by capsazepine, an antagonist for TRPV1, but the antagonist per se blocked the febrile response to LPS. These findings suggest that a capsaicin-sensitive TRPV1-independent mechanism may be involved in LPS-induced fever.

Evidence that lipopolysaccharide-induced anorexia depends upon central, rather than peripheral, inflammatory signals

Systemic inflammatory stimuli cause anorexia and weight loss by disrupting the physiological regulation of energy balance. Mice lacking MyD88, an intracellular mediator of signal transduction activated by Toll-like receptor 4 or IL-1beta receptors, are resistant to anorexia induced by the bacterial endotoxin lipopolysaccharide (LPS), despite a significant circulating cytokine response. Thus, we hypothesized that induction of a peripheral inflammatory response is insufficient to cause LPS-induced anorexia when MyD88 signaling in the central nervous system and other tissues is absent. To test this hypothesis, we used bone marrow transplantation (BMT) to determine if LPS-induced anorexia can be restored to MyD88-deficient mice by reconstituting their bone marrow with wild-type (WT) immune cells. We found that restoring WT circulating immune cells to mice lacking MyD88 conferred only a mild, short-lived anorexia in response to LPS, such that food intake was fully normalized by 20 h post injection (LPS 4.1 +/- 0.5 g vs. vehicle 4.3 +/- 0.3 g), whereas LPS-induced anorexia was profound and sustained in WT controls after either autologous BMT or sham BMT. Similarly, LPS-mediated induction of hypothalamic mRNA encoding IL-1beta and TNFalpha was robust in both WT control groups but was absent in chimeric MyD88 mice, despite comparable peripheral inflammatory responses across the three groups. We conclude that LPS reduces food intake via a mechanism dependent on MyD88 signaling within brain and/or other tissues and that in the absence of this effect, robust stimulation of circulating immune cells cannot induce sustained anorexia.

Rectal temperature, calving-related factors, and the incidence of puerperal metritis in postpartum dairy cows

The objectives of this study were as follows: 1) to evaluate the association among abnormal calving, parity, and season on the incidence of puerperal metritis (PM) and clinical endometritis (CE) during d 3 to 13 and 20 to 30 postpartum, respectively; 2) to describe the rectal temperature (RT) of cows with PM before diagnosis; and 3) to document associations among PM, CE, and reproductive performance in lactating dairy cows. This study followed a prospective observational study design. Cows were classified as having an abnormal calving status (AC), i.e., cows calving with dystocia, twins, retained fetal membranes, or some combination of these conditions, and having a normal calving status (NC). Daily RT was recorded from d 3 to 13 postpartum for all cows, and health examinations were performed on cows that appeared not well. A total of 450 calvings were evaluated. Cows with an AC had greater odds of PM than cows with NC [adjusted odds ratio (AOR) = 4.8; 95% confidence interval (CI) = 2.9 to 8.0). A season by parity interaction showed that primiparous cows that calved during the warm season had lower AOR of PM than during the cool season (0.24; 95% CI = 0.09 to 0.62), whereas multiparous cows did not have seasonal effects on PM (1.43; 95% CI = 0.65 to 3.18). Cows with AC have greater AOR for CE than cows with NC (2.8; 95% CI = 1.7 to 4.9), and greater AOR of CE were detected in cows diagnosed with PM than in cows without PM (2.2; 95% CI = 1.1 to 3.9). Rectal temperature in cows with PM increased significantly 24 h before diagnosis of PM, reaching 39.2 +/- 0.05 degrees C on the day of diagnosis. In cows with PM and fever at diagnosis, the RT began to increase from 72 to 48 h before the diagnosis of PM and continued to increase to 39.7 +/- 0.09 degrees C on d 0 (day of diagnosis). Nonetheless, cows with PM without fever at diagnosis had no daily increases in RT before diagnosis of PM. Still, the RT on d 0 was different from cows without PM. Cows without PM had a stable RT (38.6 +/- 0.01 degrees C). There were no detected differences in first-service conception risk or cumulative pregnancy risk by 150 d postpartum between cows with or without PM. Still, a season effect on first-service conception AOR (warm vs. cool = 0.98; 95% CI = 0.18 to 0.72) and accumulated pregnancy AOR by 150 d postpartum was detected (warm vs. cool = 0.18; 95% CI = 0.10 to 0.33).

Characterization of the febrile response induced by fibroblast-stimulating lipopeptide-1 in guinea pigs

Recently, it has been shown that the Toll-like receptors-2 and -6 agonist fibroblast-stimulating lipopeptide-1 (FSL-1) have the capacity to induce fever and sickness behavior in rats. Since the mechanisms of the fever-inducing effects of FSL-1 are still unknown, we tested the pyrogenic properties of FSL-1 in guinea pigs and assessed a role for TNF-alpha and prostaglandins in the manifestation of the febrile response to this substance. Intra-arterial and intraperitoneal injections of FSL-1 caused dose-dependent fevers that coincided with elevated plasma levels of TNF and IL-6, the intraperitoneal route of administration being more effective than the intra-arterial route. Intra-arterial or intraperitoneal injection of a soluble form of the TNF type 1 receptor, referred to as TNF binding protein (TNFbp), together with FSL-1, completely neutralized FSL-1-induced circulating TNF and reduced fever and circulating IL-6. Intra-arterial or intraperitoneal injection of the nonselective cyclooxygenase (COX)-inhibitor diclofenac depressed fever and FSL-1-induced elevations of circulating PGE2. Circulating TNF and IL-6, however, remained unimpaired by treatment with diclofenac. In conclusion, FSL-1-induced fever in guinea pigs depends, in shape and duration, on the route of administration and is, to a high degree, mediated by pyrogenic cytokines and COX products.

5-HT2A serotoninergic receptor in the locus coeruleus participates in the first phase of lipopolysaccharide-induced fever

This study was aimed at testing the hypothesis that serotoninergic receptors in the locus coeruleus (LC) play a role in bacterial lipopolysaccharide-induced fever. To this end, 5-HT1A (WAY-100635; 3 μg/100 nL) and 5-HT2A (ketanserin; 2 μg/100 nL) antagonists were microinjected into the LC and body temperature was monitored by biotelemetry. Intra-LC microinjections of ketanserin or WAY-100635 caused no change in body temperature of euthermic animals. 5-HT2A antagonism abolished the first phase of the lipopolysaccharide-induced fever. Taken together, these results indicate that serotonin acting on 5-HT2A receptors in the LC mediates the first phase of the febrile response, whereas 5-HT1A receptors are not involved in the lipopolysaccharide-induced fever.

STAT3 and COX-2 activation in the guinea-pig brain during fever induced by the Toll-like receptor-3 agonist polyinosinic:polycytidylic acid

Intra-arterial injections of synthetic double-stranded RNA (polyinosinic:polycytidylic acid, PIPC) at a dose of 500 microg/kg evoked pronounced fever in guinea-pigs. PIPC-induced fever could be antagonized by treatment with the non-selective cyclooxygenase (COX) inhibitor diclofenac and was, in part, attenuated by the administration of the selective COX-2-inhibitor nimesulide (dose: 5 mg/kg for both COX inhibitors). We further investigated whether direct activation of brain cells during PIPC-induced fever could be demonstrated. Using radioactive in situ hybridization, we demonstrated that treatment with PIPC resulted in an upregulation of COX-2 and interleukin-1 beta mRNA in the guinea-pig brain. Thus, COX-2-specific hybridization signals seemed to be mainly associated with brain blood vessels. Intra-arterial injections of PIPC further induced the pronounced nuclear translocation of the transcription factor STAT3 in the endothelium of various fore- and hindbrain areas and in the meninges. In brain structures that lacked a tight blood-brain barrier, i.e. the sensory circumventricular organs (area postrema, vascular organ of laminae terminalis, subfornical organ), the astrocytes and a population of still undetermined cellular phenotype also showed marked STAT3 activation in response to PIPC. The Toll-like receptor-3 agonist PIPC therefore caused a similar activation of brain cells as that reported for other experimental models of systemic inflammation.

Cytokines and the immune–neuroendocrine network: What did we learn from infection and autoimmunity?

The initial view of the neuroendocrine-immune communication as the brake of immune activation is changing. Recent evidence suggests that the optimization of the body's overall response to infection could be actually the role of the immune-endocrine network. In gradually more complex organisms, the multiplicity of host-pathogen interfaces forced the development of efficient and protective responses. Molecules such as cytokines and Toll-like receptors (TLRs) are distributed both in the periphery and in the brain to participate in a coordinated adaptive function. When sustained release of inflammatory mediators occurs, as in autoimmune diseases, undesirable pathological consequences become evident with different manifestations and outcomes. Clearly, organisms are not well adapted to that disregulated condition yet, suggesting that additional partners within neuroendocrine-immune interactions might emerge from the evolutionary road.

Leptin: at the crossroads of energy balance and systemic inflammation

In addition to playing a central role in energy homeostasis, leptin is also an important player in the inflammatory response. Systemic inflammation is accompanied by fever (less severe cases) or hypothermia (more severe cases). In leptin-irresponsive mutants, the hypothermia of systemic inflammation is exaggerated, presumably due to the enhanced production and cryogenic action of tumor necrosis factor (TNF)-alpha. Mechanisms that exaggerate hypothermia can also attenuate fever, particularly in a cool environment. Another common manifestation of systemic inflammation is behavioral depression. Along with the production of interleukin (IL)-1beta, this manifestation is exaggerated in leptin-irresponsive mutants. The enhanced production of TNF-alpha and IL-1beta may be due, at least in part, to insufficient activation of the anti-inflammatory hypothalamo-pituitary-adrenal axis by immune stimuli in the absence of leptin signaling. In experimental animals and humans that are responsive to leptin, suppression of leptin production under conditions of negative energy balance (e.g., fasting) can exaggerate both hypothermia and behavioral depression. Since these manifestations aid energy conservation, exaggeration of these manifestations under conditions of negative energy balance is likely to be beneficial.

Cellular and molecular bases of the initiation of fever

All phases of lipopolysaccharide (LPS)-induced fever are mediated by prostaglandin (PG) E₂. It is known that the second febrile phase (which starts at ~1.5 h post-LPS) and subsequent phases are mediated by PGE₂ that originated in endotheliocytes and perivascular cells of the brain. However, the location and phenotypes of the cells that produce PGE₂ triggering the first febrile phase (which starts at ~0.5 h) remain unknown. By studying PGE₂ synthesis at the enzymatic level, we found that it was activated in the lung and liver, but not in the brain, at the onset of the first phase of LPS fever in rats. This activation involved phosphorylation of cytosolic phospholipase A₂ (cPLA₂) and transcriptional up-regulation of cyclooxygenase (COX)-2. The number of cells displaying COX-2 immunoreactivity surged in the lung and liver (but not in the brain) at the onset of fever, and the majority of these cells were identified as macrophages. When PGE₂ synthesis in the periphery was activated, the concentration of PGE₂ increased both in the venous blood (which collects PGE₂ from tissues) and arterial blood (which delivers PGE₂ to the brain). Most importantly, neutralization of circulating PGE₂ with an anti-PGE₂ antibody both delayed and attenuated LPS fever. It is concluded that fever is initiated by circulating PGE₂ synthesized by macrophages of the LPS-processing organs (lung and liver) via phosphorylation of cPLA₂ and transcriptional up-regulation of COX-2. Whether PGE₂ produced at the level of the blood–brain barrier also contributes to the development of the first phase remains to be clarified.

The authors show that peripherally-produced COX2 plays an important role in the earliest stages of fever.

Bovine beta-casein (1-28), a casein phosphopeptide, enhances proliferation and IL-6 expression of mouse CD19+ cells via Toll-like receptor 4

This study was conducted to elucidate the target cells and receptors which participate in the mitogenic and interleukin (IL)-6-enhancing effect of bovine beta-casein (1-28), a casein phosphopeptide. When the spleen lymphocyte subset (CD4+, CD8+, and CD19+ cells) from C3H/HeN mice was cultured with the beta-casein (1-28), it exerted a dose-dependent mitogenic effect on CD19+ cells. The effect of beta-casein (1-28) was not apparent in the case of CD19+ cells from C3H/HeJ mouse. In addition, the effect was significantly inhibited by treating the C3H/HeN mouse-derived CD19+ cells with neutralizing antibody for toll-like receptor 4 (TLR4). Reverse transcription-polymerase chain reaction analysis showed that the beta-casein (1-28) exerted an IL-6-enhancing effect on the CD19+ cells. The effect was also abrogated in either C3H/HeJ mouse-derived CD19+ cell culture or the anti-TLR4 antibody-added culture. These results suggest that the beta-casein (1-28) stimulates both proliferation and IL-6 expression of CD19+ cells via TLR4.

Endotoxin fever in granulocytopenic rats: evidence that brain cyclooxygenase-2 is more important than circulating prostaglandin E2

PGE(2) is a recognized mediator of many fevers, and cyclooxygenase (COX) is the major therapeutic target for antipyretic therapy. The source, as well as the site of action of PGE(2), as an endogenous pyrogen, is widely accepted as being central, but PGE(2) in the circulation, possibly from leukocytes, may also contribute to the development of fever. However, bacterial infections are important causes of high fever in patients receiving myelosuppressive chemotherapy, and such fevers persist despite the use of COX inhibitors. In the study reported here, the febrile response to bacterial LPS was measured in rats made leukopenic by cyclophosphamide. A striking increase in LPS fever occurred in these granulocytopenic rats when compared with febrile responses in normal animals. Unlike LPS fever in normal rats, fever in granulocytopenic rats was neither accompanied by an increase in blood PGE(2) nor inhibited by ibuprofen. Both leukopenic and normal rats showed LPS-induced COX-2-immunoreactivity in cells associated with brain blood vessels. Furthermore, LPS induced an increase of PGE(2) in cerebrospinal fluid. Induction of COX-2-expression and PGE(2) production was inhibited by ibuprofen in normal but not in leukopenic rats. Although the results presented are, in part, confirmatory, they add new information to this field and open a number of important questions as yet unresolved. Overall, the present results indicate that, in contrast to immunocompetent rats, leukocytes and/or other mechanisms other than PGE(2) are implicated in the mechanisms restricting and reducing the enhanced febrile response to endotoxin in immunosuppressed hosts.

Pathogenesis of familial periodic fever syndromes or hereditary autoinflammatory syndromes

Familial periodic fever syndromes, otherwise known as hereditary autoinflammatory syndromes, are inherited disorders characterized by recurrent episodes of fever and inflammation. The general hypothesis is that the innate immune response in these patients is wrongly tuned, being either too sensitive to very minor stimuli or turned off too late. The genetic background of the major familial periodic fever syndromes has been unraveled, and through research into the pathophysiology, a clearer picture of the innate immune system is emerging. After an introduction on fever, interleukin-1beta and inflammasomes, which are involved in the majority of these diseases, this manuscript offers a detailed review of the pathophysiology of the cryopyrin-associated periodic syndromes, familial Mediterranean fever, the syndrome of pyogenic arthritis, pyoderma gangrenosum and acne, Blau syndrome, TNF-receptor-associated periodic syndrome and hyper-IgD and periodic fever syndrome. Despite recent major advances, there are still many questions to be answered regarding the pathogenesis of these disorders.

Interleukin-1 mediates endothelin-1-induced fever and prostaglandin production in the preoptic area of rats

The intracerebroventricular injection of endothelin-1 (ET-1) induces fever and increases PG levels in the cerebrospinal fluid of rats. Likewise, the injection of IL-1 into the preoptic area (POA) of the rat hypothalamus causes both fever and increased PG production. In this study, we conducted in vivo and in vitro experiments in the rat to investigate 1) the hypothalamic region involved in ET-1-induced fever and PG biosynthesis and 2) whether hypothalamic IL-1 plays a role as a mediator of the above ET-1 activities. One hundred femtomoles of ET-1 increased body temperature when injected in the POA of conscious Wistar rats; this effect was significantly counteracted by the coinjection of 600 pmol IL-1 receptor antagonist (IL-1ra). In experiments on rat hypothalamic explants, 100 nM ET-1 caused a significant increase in PGE2 production and release from the whole hypothalamus and from the isolated POA, but not from the retrochiasmatic region, in 1-h incubations. Six nanomoles of IL-1ra or 10 nM of a cell-permeable interleukin-1 converting enzyme inhibitor completely counteracted the effect of ET-1 on PGE2 release from the POA. One hundred nanomoles ET-1 also caused a significant increase in IL-1beta immunoreactivity released into the bath solution of hypothalamic explants after 1 h of incubation, although during such time ET-1 failed to modify the gene expression of IL-1beta and other pyrogenic cytokines within the hypothalamus. In conclusion, our results show that ET-1 increases IL-1 production in the POA, and this effect appears to be correlated to ET-1-induced fever in vivo, as well as to PG production in vitro.