An Endovascular Perforation Model of Subarachnoid Haemorrhage in Rat Produces Heterogeneous Infarcts that Increase with Blood Load.

Subarachnoid haemorrhage (SAH) is a devastating disease and a major burden on society. Despite this, pharmacological treatment options are limited. Appropriate animal modelling of SAH is essential for the development of neuroprotective drugs, but experimental SAH often fails to produce widespread neuronal loss, as frequently seen in humans. We report that a recently described modification of the endovascular perforation model in rat produced widespread heterogeneous infarcts 72 h after SAH. Cerebral blood flow (CBF) was monitored, with or without intracranial pressure (ICP) measurement, for 1 h after induction of SAH. Blood load size was assessed, and brain injury was quantified at 72 h using histological staining, blood brain barrier breakdown assessment and immunofluorescent imaging of neuronal viability and microglial activation. Results showed that ICP measurement allowed for faster recovery of CBF, potentially reducing brain injury. Larger subarachnoid blood loads predicted more extensive neuronal damage which was easily quantified with the combination of histological and immunohistochemical techniques. Thus, for the investigation of neuroprotective strategies after SAH, the present protocol produces quantifiable, clinically relevant, heterogeneous patterns of infarct due to large blood loads, high ICP and low CBF.

Contribution of interleukin-1 receptor accessory protein B to interleukin-1 actions in neuronal cells.

Interleukin (IL)-1 is an important neuroimmunomodulator and a key mediator of inflammation during brain disorders. It acts on neuronal and glial cells via binding to the IL-1 type 1 receptor and IL-1 receptor accessory protein (IL-1RAcP). More recently, a neuronal-specific isoform of IL-1RAcP, named IL-1RAcPb, has been identified. Our aim was to determine the role of IL-1RAcPb in IL-1 actions in neuronal and glial cells, and to further explore the signaling mechanisms of IL-1 in neurons. We found that IL-1RAcPb deletion had no effect on IL-1α- and IL-1ß-induced activation of the extracellular signal-regulated kinase 1/2 or IL-6 release in glial cultures, although IL-6 release in response to high IL-1α concentration (30 IU/ml) was significantly reduced. We identified the p38 kinase as a key signaling element in IL-1α- and IL-1ß-induced IL-6 synthesis and release in neuronal cultures. IL-1RAcPb deletion had no effect on IL-1α- and IL-1ß-induced IL-6 release in neurons, but significantly reduced IL-1α- but not IL-1ß-induced p38 phosphorylation. Our data demonstrate that the p38 signaling pathway plays an important role in IL-1 actions in neurons, and that IL-1RAcP may regulate some, but not all, neuronal activities in response to IL-1α.

Inflammation and brain injury: acute cerebral ischaemia, peripheral and central inflammation.

Inflammation is a classical host defence response to infection and injury that has many beneficial effects. However, inappropriate (in time, place and magnitude) inflammation is increasingly implicated in diverse disease states, now including cancer, diabetes, obesity, atherosclerosis, heart disease and, most relevant here, CNS disease. A growing literature shows strong correlations between inflammatory status and the risk of cerebral ischaemia (CI, most commonly stroke), as well as with outcome from an ischaemic event. Intervention studies to demonstrate a causal link between inflammation and CI (or its consequences) are limited but are beginning to emerge, while experimental studies of CI have provided direct evidence that key inflammatory mediators (cytokines, chemokines and inflammatory cells) contribute directly to ischaemic brain injury. However, it remains to be determined what the relative importance of systemic (largely peripheral) versus CNS inflammation is in CI. Animal models in which CI is driven by a CNS intervention may not accurately reflect the clinical condition; stroke being typically induced by atherosclerosis or cardiac dysfunction, and hence current experimental paradigms may underestimate the contribution of peripheral inflammation. Experimental studies have already identified a number of potential anti-inflammatory therapeutic interventions that may limit ischaemic brain damage, some of which have been tested in early clinical trials with potentially promising results. However, a greater understanding of the contribution of inflammation to CI is still required, and this review highlights some of the key mechanism that may offer future therapeutic targets.

Dual functionality of interleukin-1 family cytokines: implications for anti-interleukin-1 therapy.

Dysregulated inflammation contributes to disease pathogenesis in both the periphery and the brain. Cytokines are coordinators of inflammation and were originally defined as secreted mediators, released from expressing cells to activate plasma membrane receptors on responsive cells. However, a group of cytokines is now recognized as having dual functionality. In addition to their extracellular effects, these cytokines act inside the nuclei of cytokine-expressing or cytokine-responsive cells. Interleukin-1 (IL-1) family cytokines are key pro-inflammatory mediators, and blockade of the IL-1 system in inflammatory diseases is an attractive therapeutic goal. All current therapies target IL-1 extracellular actions. Here we review evidence that suggests IL-1 family members have dual functionality. Several IL-1 family members have been detected inside the nuclei of IL-1-expressing or IL-1-responsive cells, and intranuclear IL-1 is reported to regulate gene transcription and mRNA splicing. However, further work is required to determine the impact of IL-1 intranuclear actions on disease pathogenesis. The intranuclear actions of IL-1 family members represent a new and potentially important area of IL-1 biology and may have implications for the future development of anti-IL-1 therapies.

Transport of interleukin-1 across cerebromicrovascular endothelial cells.

BACKGROUND AND PURPOSE: The inflammatory cytokine interleukin-1 (IL-1) has profound actions in the brain, causing neuronal cell death and exacerbating brain damage. While circulating levels are normally low, IL-1 can be produced on the vascular side of the brain endothelium, and within the brain. The naturally occurring IL-1 receptor antagonist has been administered peripherally in a Phase II trial in acute stroke patients; understanding how IL-1 and IL-1 receptor antagonist penetrate the brain is, therefore, of considerable importance. EXPERIMENTAL APPROACH: An in vitro blood-brain barrier model was generated by co-culture of porcine brain microvascular endothelial cells with astrocytes. The mechanisms of transcellular transport of IL-1beta and IL-1 receptor antagonist were characterized in this model, using endocytosis inhibitors and IL-1 receptor-blocking antibodies. KEY RESULTS: Transcellular IL-1beta and IL-1 receptor antagonist transport was temperature-dependent and IL-1beta was transported with higher affinity than IL-1 receptor antagonist. IL-1beta inhibited IL-1 receptor antagonist transport more potently than IL-1 receptor antagonist inhibited IL-1beta transport. Transport of IL-1beta and IL-1 receptor antagonist was not via adsorptive-mediated endocytosis, although inhibition of microtubule assembly significantly attenuated transport of both cytokines. An antibody directed to the type II IL-1 receptor significantly reduced IL-1beta transport. CONCLUSIONS AND IMPLICATIONS: These results are consistent with IL-1 and IL-1 receptor antagonist being transported across cultured cerebromicrovascular endothelial cells and suggest that IL-1beta transport may occur via a type II IL-1 receptor-dependent mechanism. Understanding IL-1 transport into the brain may have benefits, particularly in enhancing penetration of IL-1 receptor antagonist into the brain.

Systemic infection, inflammation and acute ischemic stroke.

Extensive evidence implicates inflammation in multiple phases of stroke etiology and pathology. In particular, there is growing awareness that inflammatory events outside the brain have an important impact on stroke susceptibility and outcome. Numerous conditions, including infection and chronic non-infectious diseases, that are established risk factors for stroke are associated with an elevated systemic inflammatory profile. Recent clinical and pre-clinical studies support the concept that the systemic inflammatory status prior to and at the time of stroke is a key determinant of acute outcome and long-term prognosis. Here, we provide an overview of the impact of systemic inflammation on stroke susceptibility and outcome. We discuss potential mechanisms underlying the impact on ischemic brain injury and highlight the implications for stroke prevention, therapy and modeling.

Interleukin-1-induced interleukin-6 synthesis is mediated by the neutral sphingomyelinase/Src kinase pathway in neurones.

BACKGROUND AND PURPOSE: Interleukin (IL)-1 is a key mediator of inflammatory and host defence responses and its effects in the brain are mediated primarily via effects on glia. IL-1 induces release of inflammatory mediators such as IL-6 from glia via the type-1 receptor (IL-1R1) and established signalling mechanisms including mitogen-activated protein kinases and nuclear factor kappa-B. IL-1 also modifies physiological functions via actions on neurones, through activation of the neutral sphingomyelinase (nSMase)/Src kinase signalling pathway, although the mechanism of IL-1-induced IL-6 synthesis in neurones remains unknown. EXPERIMENTAL APPROACH: Primary mouse neuronal cell cultures, ELISA, Western blot and immunocytochemistry techniques were used. KEY RESULTS: We show here that IL-1beta induces the synthesis of IL-6 in primary mouse neuronal cultures, and this is dependent on the activation of IL-1R1, nSMase and Src kinase. We demonstrate that IL-1beta-induced Src kinase activation triggers the phosphorylation of the NMDA receptor NR2B subunit, leading to activation of Ca(2+)/calmodulin-dependent protein kinase II (CamKII) and the nuclear transcription factor CREB. We also show that NR2B, CamKII and CREB are essential signalling elements involved in IL-1beta-induced IL-6 synthesis in neurones. CONCLUSIONS AND IMPLICATIONS: These results demonstrate that IL-1 interacts with the same receptors on neurones and glia to elicit IL-6 release, but does so via distinct signalling pathways. The mechanism by which IL-1beta induces IL-6 synthesis in neurones could be critical in both physiological and pathophysiological actions of IL-1beta, and may provide a new therapeutic target for the treatment of acute CNS injury.

Interleukin-1 and inflammatory neurodegeneration.

Inflammation occurs rapidly in response to acute brain insults such as stroke, haemorrhage or trauma, and can be sustained for long periods of time, for example in Alzheimer's or Parkinson's diseases and multiple sclerosis. Experimental evidence indicates that inflammation plays a major role in neurodegeneration under these conditions, and that the cytokine IL-1 (interleukin-1) is a pivotal mediator. IL-1 is expressed rapidly in response to neuronal injury, predominantly by microglia, and elevated levels of endogenous or exogenous IL-1 markedly exacerbate injury. The naturally occurring IL-1RA (IL-1 receptor antagonist) markedly inhibits ischaemic, excitotoxic and traumatic brain injury in rodents, and has shown promise in a Phase II clinical trial in stroke patients. The mechanisms of IL-1 expression, release and action in neurodegeneration are not fully elucidated and appear multiple. Systemic IL-1 markedly enhances ischaemic brain injury via release of neutrophils into circulation, neutrophil adhesion to injured cerebrovasculature and CNS (central nervous system) invasion, and cell death via activation of matrix metalloproteinase-9. IL-1 also influences the release of toxins from glial and endothelial cells. Neuronal responses to excitotoxins and physiological factors may have an impact on neuronal survival. IL-1RA, delivered peripherally, can enter the CNS in animals and humans and has no adverse effects in stroke or subarachnoid haemorrhage patients, but shows potential benefit in acute stroke patients.

Systemic inflammation and stroke: aetiology, pathology and targets for therapy.

There is growing evidence that systemic inflammation is involved in multiple aspects of stroke aetiology and pathology. In the present review, we provide an overview of these roles and, in particular, outline recent evidence that the underlying systemic inflammatory profile can critically alter the response to ischaemic brain injury. We also highlight the need for stroke models to more adequately account for the involvement of underlying systemic inflammation.

Neurodegenerative actions of interleukin-1 in the rat brain are mediated through increases in seizure activity.

The cytokine interleukin-1 (IL-1) is an established and important mediator of diverse forms of neuronal injury in experimental animals. However, its mechanisms of action remain largely unknown. We have reported previously that IL-1 markedly enhances excitotoxic injury induced in the rat by striatal administration of the excitotoxin alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), leading to widespread neuronal loss throughout the ipsilateral cortex. Here we tested the hypothesis that IL-1 causes this injury through induction and/or enhancement of seizure activity in the rat. Consistently with this hypothesis, intrastriatal injection of AMPA or AMPA with IL-1 in the rat brain increased c-Fos expression in regions similar to those in which c-Fos has been reported previously in response to seizures. A significant increase in cortical neuronal activity (number of c-Fos positive cells) was observed in response to AMPA with IL-1 compared with AMPA (8 hr after injection). Increased seizure duration [3,522 +/- 660 sec (SEM) vs. 1,415 +/- 301 sec; P < 0.001] and cell death volume (140 +/- 20 mm3 vs. 52 +/- 6 mm3; P < 0.001) were seen in response to coinfusion of AMPA with IL-1 vs. AMPA alone. In addition, the anticonvulsant diazepam (intraperitoneal) significantly reduced cell death (P < 0.001) and seizure duration (P < 0.001) induced by AMPA with IL-1, and a significant correlation was found between seizure duration and cell death volume. These findings support our hypothesis that IL-1 enhances excitotoxic injury by enhancement of seizures, which may be of relevance to IL-1 actions in other forms of neuronal injury, including cerebral ischemia.

A randomised phase II study of interleukin-1 receptor antagonist in acute stroke patients.

OBJECTIVES: The cytokine interleukin (IL)-1 mediates ischaemic brain damage in rodents. The endogenous, highly selective, IL-1 receptor antagonist (IL-1ra) protects against ischaemic cerebral injury in a range of experimental settings, and IL-1ra causes a marked reduction of cell death when administered peripherally or at a delay in transient cerebral ischaemia. We report here the first randomised, double blind, placebo controlled trial of recombinant human IL-1ra (rhIL-1ra) in patients with acute stroke. METHODS: Patients within 6 hours of the onset of symptoms of acute stroke were randomised to rhIL-1ra or matching placebo. Test treatment was administered intravenously by a 100 mg loading dose over 60 seconds, followed by a 2 mg/kg/h infusion over 72 h. Adverse events and serious adverse events were recorded for up to 3 months, serial blood samples were collected for biological markers up to 3 months, and 5-7 day brain infarct volume was measured by computed tomography. RESULTS: No adverse events were attributed to study treatment among 34 patients randomised. Markers of biological activity, including neutrophil and total white cell counts, C reactive protein, and IL-6 concentrations, were lower in rhIL-1ra treated patients. Among patients with cortical infarcts, clinical outcomes at 3 months in the rhIL-1ra treated group were better than in placebo treated. CONCLUSIONS: These data suggest that rhIL-1ra is safe and well tolerated in acute stroke. In addition, rhIL-1ra exhibited biological activity that is relevant to the pathophysiology and clinical outcome of ischaemic stroke. Our findings identify rhIL-1ra as a potential new therapeutic agent for acute stroke.

Cytokines and acute neurodegeneration.

Cytokines have been implicated as mediators and inhibitors of diverse forms of neurodegeneration. They are induced in response to brain injury and have diverse actions that can cause, exacerbate, mediate and/or inhibit cellular injury and repair. Here we review evidence for the contribution of cytokines to acute neurodegeneration, focusing primarily on interleukin 1 (IL-1), tumour necrosis factor-alpha (TNFalpha) and transforming growth factor-beta (TGFbeta). TGFbeta seems to exert primarily neuroprotective actions, whereas TNFalpha might contribute to neuronal injury and exert protective effects. IL-1 mediates ischaemic, excitotoxic and traumatic brain injury, probably through multiple actions on glia, neurons and the vasculature. Understanding cytokine action in acute neurodegeneration could lead to novel and effective therapeutic strategies, some of which are already in clinical trials.

Selective increases in cytokine expression in the rat brain in response to striatal injection of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate and interleukin-1.

A number of cytokines contribute to acute experimental neurodegeneration. The cytokine response can have detrimental or beneficial effects depending on the temporal profile and balance between pro- and anti-inflammatory molecules. Our recent data suggest that the pro-inflammatory cytokine interleukin-1beta (IL-1beta) acts at specific sites (e.g., the striatum) in the rat brain to cause distant cortical injury, when co-administered with the potent excitotoxin alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (S-AMPA). The objective of the present study was to investigate changes in the expression of several cytokines simultaneously in the rat striatum and cortex after intrastriatal administration of vehicle, S-AMPA or human recombinant (hr) IL-1beta alone or S-AMPA co-injected with hrIL-1beta using reverse transcription-polymerase chain reaction (RT-PCR; Taqman fluorogenic probes) and enzyme-linked immunosorbent assay (ELISA). Injection of S-AMPA alone increased IL-6 mRNA expression in the ipsilateral striatum after 8 h, whilst striatal injection of IL-1beta alone increased local IL-1beta and IL-1ra mRNAs. The levels of mRNA encoding IL-1alpha, IL-1beta, IL-1ra, IL-6, IL-10 and TNFalpha were markedly elevated in the ipsilateral cortex 8 h after co-injection of S-AMPA and hrIL-1beta. Cortical mRNA levels for IL-4, IL-18, TGFbeta and IFNgamma were not significantly different between treatment groups after 2 h or 8 h. A similar pattern of change in the levels of IL-1alpha and IL-6 protein was observed 8 h after treatment. These data demonstrate selective increases in the expression of cytokines in areas of remote cell death in response to administration of hrIL-1beta and S-AMPA. Such cytokines may be involved in the ensuing damage, and further clarification of their actions could aid future therapeutic strategies for several acute neurodegenerative disorders.

Oxidised adenosine 5'-triphosphate, a P2X(7) antagonist, is toxic to rat cerebellar granule neurones in vitro.

Adenosine 5'-triphosphate (ATP) acts as a neurotransmitter in the central nervous system. Extracellular ATP is also toxic to a number of cell types e.g. via its interaction with P2X membrane receptors, specifically the P2X(7) family member. These results have led to the hypothesis that elevated ATP levels may exacerbate damage during acute neurodegeneration [4]. The aim of this study was to examine the effects of ATP agonists and antagonists on cultured rat cerebellar granule neurones. Neither ATP, nor the P2X agonist benzoylbenzoyl-ATP (BzATP), were toxic when added to primary neurones. However, the P2X(7) antagonist, oxidised ATP (oATP) was highly neurotoxic. This toxicity was inhibited by co-incubation with BzATP. These results demonstrate that oATP is a potent neurotoxin.

Role of IL-1alpha and IL-1beta in ischemic brain damage.

The cytokine interleukin-1 (IL-1) has been strongly implicated in the pathogenesis of ischemic brain damage. Evidence to date suggests that the major form of IL-1 contributing to ischemic injury is IL-1beta rather than IL-1alpha, but this has not been tested directly. The objective of the present study was to compare the effects of transient cerebral ischemia [30 min middle cerebral artery occlusion (MCAO)] on neuronal injury in wild-type (WT) mice and in IL-1alpha, IL-1beta, or both IL-1alpha and IL-1beta knock-out (KO) mice. Mice lacking both forms of IL-1 exhibited dramatically reduced ischemic infarct volumes compared with wild type (total volume, 70%; cortex, 87% reduction). Ischemic damage compared with WT mice was not significantly altered in mice lacking either IL-1alpha or IL-1beta alone. IL-1beta mRNA, but not IL-1alpha or the IL-1 type 1 receptor, was strongly induced by MCAO in WT and IL-1alpha KO mice. Administration (intracerebroventricularly) of recombinant IL-1 receptor antagonist significantly reduced infarct volume in WT (-32%) and IL-1alpha KO (-48%) mice, but had no effect on injury in IL-1beta or IL-1alpha/beta KO mice. These data confirm that IL-1 plays a major role in ischemic brain injury. They also show that chronic deletion of IL-1alpha or IL-1beta fails to influence brain damage, probably because of compensatory changes in the IL-1 system in IL-1alpha KO mice and changes in IL-1-independent mediators of neuronal death in IL-1beta KO mice.

Anorexic but not pyrogenic actions of interleukin-1 are modulated by central melanocortin-3/4 receptors in the rat.

The cytokine interleukin-1 (IL-1), which mediates many responses to infection and injury, induces anorexia and fever through direct actions in the central nervous system. The melanocortin neuropeptides, such as alpha melanocyte-stimulating hormone (alpha-MSH), reportedly antagonize many actions of IL-1, including fever and anorexia. However, it is unknown whether endogenous melanocortins modulate anorexia induced by IL-1. The objective of the present study was to establish the effect of endogenous melanocortins on IL-1-induced anorexia and fever in the rat. Intracerebroventricular (i.c.v.) injection of IL-1beta caused a significant reduction in food intake and body weight gain, and a rise in core body temperature in conscious rats. Coadministration of the melanocortin-3/4 receptor (MC3/4-R) antagonist, SHU9119, reversed IL-1beta-induced reductions in food intake and body weight, but did not affect the febrile response to IL-1beta. These data suggest IL-1beta may elicit its effects on food intake through the melanocortin system, predominantly via the MC3-R or MC4-R. In contrast, IL-1beta-induced fever does not appear to be mediated or modulated by MC3-R or MC4-R activity.

Actions of exogenous and endogenous IL-10 on glial responses to bacterial LPS/cytokines.

The objective of this study was to investigate the actions of exogenous and endogenous IL-10 on inflammatory responses of glia. Studies were conducted in primary, mixed glial cultures from C57BL/6 (wild-type [WT]) and IL-10-deficient C57BL/6 (IL-10 knockout [KO]) neonatal mice. Activation of cultures from WT mice by bacterial lipopolysaccharide (LPS, 10 ng/ml-10 microg/ml, 24 h), caused dose-dependent increases in nitric oxide (NO) and prostaglandin E(2) (PGE(2)) release. In cultures from IL-10 KO mice, LPS elicited markedly attenuated release of NO (approximately 4-fold) and PGE(2) (approximately 17-fold). In WT cultures, co-incubation with IL-10 (10 or 100 ng/ml, 24 h) inhibited the effects of LPS on release of NO (30%) and PGE(2) (40-50%). In cultures from IL-10 KO mice, the addition of IL-10 (10 or 100 ng/ml, 24 h) completely abolished LPS-induced NO and PGE(2) release. LPS did, however, release of IL-1beta and TNF-alpha in cultures from all animals. Co-incubation of WT cultures with IL-10 (1, 10, or 100 ng/ml, 24 h) dose-dependently reduced the release of IL-1beta (by 0%, 15%, 75%, respectively). In cultures from IL-10 KO mice, co-incubation with IL-10 (1, 10, or 100 ng/ml, 24 h) completely abolished LPS induced release of IL-1beta. Co-incubation with IL-10 (1, 10, 100 ng/ml) reduced, LPS-induced TNF-alpha release dose-dependently in WT cultures (by 15%, 50% and 90%) and abolished LPS-induced TNF-alpha release in cells from IL-10 KO mice. These results indicate that in glia from WT mice, exogenous IL-10 attenuates LPS-induces release of NO, PGE(2), TNF-alpha and IL-1beta. In contrast, mixed glial cultures from IL-10 KO mice showed reduced responses to LPS, but increased sensitivity to exogenous IL-10.

Role of endogenous interleukin-1 receptor antagonist in regulating fever induced by localised inflammation in the rat.

1. Interleukin (IL)-1 is a mediator of host defence responses to inflammation and injury, including fever, but its sites of synthesis and action have not been fully elucidated. The actions of IL-1 are antagonised by IL-1 receptor antagonist (IL-1ra). The present study tested the hypothesis that IL-1 and IL-1ra are produced locally at sites of peripheral inflammation in rats, and that endogenous IL-1ra acts to limit the fever resulting from the inflammation. 2. Injection of lipopolysaccharide (LPS; 100 microg kg-1) into a subcutaneous air pouch (I.PO.) of rats induced a significant increase in body temperature. Virtually all (approximately 85 %) of the injected LPS was recovered from the pouch between 1 and 8 h (when the experiment was terminated) after injection of LPS, but LPS was undetectable (< 50 pg ml-1) in plasma at any time. Concentrations of immunoreactive IL-1alpha and IL-1beta were increased significantly in the pouch at 1, 2, 3, 5 and 8 h after injection of LPS, corresponding with the rise in body temperature and the fever peak. The appearance of IL-1ra was delayed until 2 h. Thereafter, the concentrations of IL-1beta and IL-1ra increased in parallel with the development of fever, while the concentrations of IL-1alpha remained constant. IL-1ra, but not IL-1alpha or IL-1bet, was detected in significant quantities in the plasma of LPS-injected animals. 3. Treatment of rats with an anti-IL-1ra serum (2 ml, I.PO.) at the time of injection of LPS (10 or 100 microg kg-1, I.PO.) abolished the appearance of IL-1ra in the circulation. Although neutralisation of endogenous IL-1ra did not affect the maximum body temperature reached after injection of submaximum (10 microg kg-1, I.PO.) or maximum (100 microg kg-1, I.PO.) doses of LPS, the duration of the fever was significantly prolonged, and was associated with a 3- to 4-fold increase in immunoreactive IL-1beta concentrations in the pouch fluid, but not in the plasma, at the 8 h time point. 4. These data show that effects of local (I.PO.) injection of LPS are not due to its action in the circulation or at distant sites (such as at the blood-brain barrier). These data also show that locally produced IL-1ra, in response to injection (I.PO.) of LPS, inhibits the production and/or action of locally produced IL-1beta. The ability of IL-1ra to limit the duration, rather than the magnitude of the fever, is consistent with its delayed production, relative to IL-IL-1ra, therefore, appears to play a key role in the resolution of fever induced by localised inflammatory responses.

Interleukin (IL)-6 release and fever induced by a pre-formed pyrogenic factor (PFPF) derived from LPS-stimulated macrophages.

A novel pre-formed pyrogenic factor (PFPF), released by LPS-stimulated macrophages, has been identified, that induces an indomethacin-resistant fever. Its activity has to date not been found to match that of any described cytokine. In this study we observed that PFPF induced the release of large amounts of IL-6 from rat peritoneal macrophages. A combination of anti-cytokine antibodies and heat treatment excluded IL-1, tumor necrosis factor (TNF)-alpha and lipopolysaccharide (LPS) as being responsible for this effect. PFPF also induced interleukin (IL)-1, IL-6 and TNF-alpha in a subcutaneous air pouch, as well as increasing plasma IL-6, and induced a fever of 0.58 +/- 0.07 degrees C (3 hours) that was not reduced by indomethacin (2 mg/kg, ip). Preparative isoelectric focusing (IEF) showed that the material responsible for inducing IL-6 release had a pI between 4.7 and 5.8 and corresponded to the IEF pool that induced fever when injected intracerebroventricularly.