Interleukin-1 beta and tumour necrosis factor-alpha stimulate the mRNA expression of interleukin-1 receptors in mouse anterior pituitary AtT-20 cells

Genome-wide DNA methylation mediates the resistance to vibriosis in Cynoglossus semilaevis

Chinese tongue sole (Cynoglossus semilaevis) is an economically important marine fish in China. However, vibriosis has caused huge mortality and economic losses in its culturing industry. To reveal the effect of DNA methylation on the resistance to vibriosis in tongue sole, we conducted RNA sequencing and whole genome bisulfite sequencing (WGBS), and compared the gene expressions and DNA methylation patterns between the resistant and susceptible families. We identified a total of 741 significantly differentially expressed genes (DEGs) in kidney and 17460 differentially methylated genes (DMGs), which were both enriched in immune-related pathways, such as "cAMP signaling pathway" and "NOD-like receptor signaling pathway". Through the correlation analysis of DEGs and DMGs, we identified two important immune pathways, including "complement and coagulation cascades", and "cytokine-cytokine receptor interaction", which played important roles in regulating the inflammation level and immune homeostasis. For example, the expression of proinflammatory cytokine il17c was down-regulated under the regulation of DNA methylation; in addition, the expression of protease-activated receptor 3 (par3) was up-regulated, which could induce the up-expressionof il8. These results demonstrated that the regulation of DNA methylation on the genes involved in immune responses might contribute to the resistance to vibriosis in tongue sole, and provided a basis for the control of diseases in fish aquaculture.

Characterization of IL-1β and two types of IL-1 receptors in miiuy croaker and evolution analysis of IL-1 family

Interleukin (IL)-1β is a prototypical proinflammatory cytokine that belongs to the IL-1 family. This cytokine possesses two receptor types, namely, IL-1 receptor type I (IL-1RI) and IL-1 receptor type II (IL-1RII). IL-1RI, is an IL-1 receptor that plays a crucial role in immune responses and IL-1RII is a decoy receptor for IL-1β signaling inhibitors in mammals. IL-1β, together with its two types of receptors, has been characterized in mammals and implicated in immunity. However, IL-1β and IL-1 receptors in teleost species have been rarely investigated. In this study three genes, namely, IL-1β, IL-1RI, and IL-1RII, were identified and characterized from miiuy croaker. Structural and comparative analysis revealed that miiuy croaker IL-1β, IL-1RI and IL-1RII, particularly their functional domains, were conservative in most of the species. Simultaneously, synteny phylogenetic analysis indicated that IL-1β and IL-18 were widely distributed in vertebrates and hence might be the ancestors of the IL-1 family. Challenge experiment demonstrated that IL-1β, IL-1RI and IL-1RII expression in miiuy croaker was induced by LPS and poly (I:C). IL-1RI expression was also induced by the overexpressed miiuy croaker IL-1β protein which in cell supernatant, whereas IL-1RII was not induced.

Molecular and functional characterization of IL-1 receptor type 2 in grass carp: a potent inhibitor of IL-1β signaling in head kidney leukocytes

IL-1 receptor type 2 (IL-1R2) is known as one of natural IL-1β singling inhibitors in mammals. However, the functional role of IL-1R2 in fish remains largely unknown. In this study, grass carp (Ctenopharyngodon idellus) IL-1R2 (gcIL-1R2) was identified and functionally characterized. Similar to its fish homologs, the deduced protein of gcIL-1R2 possessed two Ig-like domains in its extracellular region but lacked an intracellular signaling domain. The involvement of gcIL-1R2 in immune response was demonstrated by investigating its expression profiles in head kidney and head kidney leukocytes (HKLs) following in vivo bacterial infection and in vitro LPS treatment, respectively. Moreover, recombinant grass carp IL-1β (rgcIL-1β) was able to stimulate gcIL-1R2 mRNA expression with a rapid kinetics. This stimulation was possibly dependent on p38, JNK, p42/44 and NF-κB pathways in grass carp HKLs, revealing a new regulatory point of IL-1β signaling at receptor level in fish. Furthermore, recombinant protein of the gcIL-1R2 extracellular region (rgcIL-1R2) was demonstrated to interact with rgcIL-1β by using ELISA, elucidating the binding specificity of gcIL-1R2. Importantly, the stimulatory effect of rgcIL-1β on its own mRNA expression was blocked by rgcIL-1R2 in a dose-dependent manner in grass carp HKLs, providing the evidence for a functional role of IL-1R2 in IL-1β signaling in teleost. These findings suggested that teleost IL-1R2 may serve as a local naturally occurring inhibitor involving in IL-1β signaling as seen in mammals.

IL-1 receptor 2 (IL-1R2) and its role in immune regulation

The cytokine IL-1 is critical to the pathogenesis of a variety of human conditions and diseases. Unlike most other cytokines, IL-1 is counterbalanced by two endogenous inhibitors. The functional significance of IL-1 receptor antagonist (IL-1RA) is well documented due to the clinical utilization of the recombinant human IL-1RA analog, anakinra. In contrast, much less is known about the type 2 IL-1 receptor (IL-1R2), which acts as a decoy receptor for IL-1. While IL-1R2 is structurally similar to the type 1 IL-1 receptor (IL-1R1) responsible for IL-1 signal transduction, its truncated cytoplasmic domain and lack of Toll-IL-1 receptor (TIR) region renders IL-1R2 incapable of transmembrane signaling. IL-1R2 competes with IL-1R1 for ligands and for the IL-1R1 co-receptor, IL-1 receptor accessory protein (IL-1RAP). Additionally, IL-1R2 exists in both a membrane bound and soluble form (sIL-1R2) that has biological properties similar to both a decoy receptor and a binding protein. Thus far, IL-1R2 has been implicated in arthritis, endometriosis, organ transplantation, sepsis/sickness behavior, diabetes, atherosclerosis, autoimmune inner ear disease (AIED), Alzheimer's disease and ulcerative colitis. In this review, we will detail the functional properties of IL-1R2 and examine its role in human disease.

A central role for neuronal adenosine 5'-monophosphate-activated protein kinase in cancer-induced anorexia

The pathogenesis of cancer anorexia is multifactorial and associated with disturbances of the central physiological mechanisms controlling food intake. However, the neurochemical mechanisms responsible for cancer-induced anorexia are unclear. Here we show that chronic infusion of 5-amino-4imidazolecarboxamide-riboside into the third cerebral ventricle and a chronic peripheral injection of 2 deoxy-d-glucose promotes hypothalamic AMP-activated protein kinase (AMPK) activation, increases food intake, and prolongs the survival of anorexic tumor-bearing (TB) rats. In parallel, the pharmacological activation of hypothalamic AMPK in TB animals markedly reduced the hypothalamic production of inducible nitric oxide synthase, IL-1beta, and TNF-alpha and modulated the expression of proopiomelanocortin, a hypothalamic neuropeptide that is involved in the control of energy homeostasis. Furthermore, the daily oral and intracerebroventricular treatment with biguanide antidiabetic drug metformin also induced AMPK phosphorylation in the central nervous system and increased food intake and life span in anorexic TB rats. Collectively, the findings of this study suggest that hypothalamic AMPK activation reverses cancer anorexia by inhibiting the production of proinflammatory molecules and controlling the neuropeptide expression in the hypothalamus, reflecting in a prolonged life span in TB rats. Thus, our data indicate that hypothalamic AMPK activation presents an attractive opportunity for the treatment of cancer-induced anorexia.

TNF-alpha acts in the hypothalamus inhibiting food intake and increasing the respiratory quotient--effects on leptin and insulin signaling pathways

Acting in the hypothalamus, tumor necrosis factor-alpha (TNF-alpha) produces a potent anorexigenic effect. However, the molecular mechanisms involved in this phenomenon are poorly characterized. In this study, we investigate the capacity of TNF-alpha to activate signal transduction in the hypothalamus through elements of the pathways employed by the anorexigenic hormones insulin and leptin. High dose TNF-alpha promotes a reduction of 25% in 12h food intake, which is an inhibitory effect that is marginally inferior to that produced by insulin and leptin. In addition, high dose TNF-alpha increases body temperature and respiratory quotient, effects not reproduced by insulin or leptin. TNF-alpha, predominantly at the high dose, is also capable of activating canonical pro-inflammatory signal transduction in the hypothalamus, inducing JNK, p38, and NFkappaB, which results in the transcription of early responsive genes and expression of proteins of the SOCS family. Also, TNF-alpha activates signal transduction through JAK-2 and STAT-3, but does not activate signal transduction through early and intermediary elements of the insulin/leptin signaling pathways such as IRS-2, Akt, ERK and FOXO1. When co-injected with insulin or leptin, TNF-alpha, at both high and low doses, partially impairs signal transduction through IRS-2, Akt, ERK and FOXO1 but not through JAK-2 and STAT-3. This effect is accompanied by the partial inhibition of the anorexigenic effects of insulin and leptin, when the low, but not the high dose of TNF-alpha is employed. In conclusion, TNF-alpha, on a dose-dependent way, modulates insulin and leptin signaling and action in the hypothalamus.

Inducible-NOS but not neuronal-NOS participate in the acute effect of TNF-α on hypothalamic insulin-dependent inhibition of food intake

TNF-alpha acts on the hypothalamus modulating food intake and energy expenditure through mechanisms incompletely elucidated. Here, we explore the hypothesis that, to modulate insulin-induced anorexigenic signaling in hypothalamus, TNF-alpha requires the synthesis of NO. TNF-alpha activates signal transduction through JNK and p38 in hypothalamus, peaking at 10(-8) M. This is accompanied by the induction of expression of the inducible and neuronal forms of NOS, in both cases peaking at 10(-12) M. In addition, TNF-alpha stimulates NOS catalytic activity. Pre-treatment with TNF-alpha at a low dose (10(-12) M) inhibits insulin-dependent anorexigenic signaling, and this effect is abolished in iNOS but not in nNOS knockout mice.

Tumor necrosis factor-alpha activates signal transduction in hypothalamus and modulates the expression of pro-inflammatory proteins and orexigenic/anorexigenic neurotransmitters

Tumor necrosis factor-alpha (TNF-alpha) is known to participate in the wastage syndrome that accompanies cancer and severe infectious diseases. More recently, a role for TNF-alpha in the pathogenesis of type 2 diabetes mellitus and obesity has been shown. Much of the regulatory action exerted by TNF-alpha upon the control of energy stores depends on its action on the hypothalamus. In this study, we show that TNF-alpha activates canonical pro-inflammatory signal transduction pathways in the hypothalamus of rats. These signaling events lead to the transcriptional activation of an early responsive gene and to the induction of expression of cytokines and a cytokine responsive protein such as interleukin-1beta, interleukin-6, interleukin-10 and suppressor of cytokine signalling-3, respectively. In addition, TNF-alpha induces the expression of neurotransmitters involved in the control of feeding and thermogenesis. Thus, TNF-alpha may act directly in the hypothalamus inducing a pro-inflammatory response and the modulation of expression of neurotransmitters involved in energy homeostasis.

Elevated IL-1beta contributes to antibody suppression produced by stress

Acute stressor exposure can facilitate innate immunity and suppress acquired immunity. The present study further characterized the potentiating effect of stress on innate immunity, interleukin-1beta (IL-1beta), and demonstrated that stress-induced potentiation of innate immunity may contribute to the stress-induced suppression of acquired immunity. The long-term effect of stress on IL-1beta was measured by using an ex vivo approach. Sprague-Dawley rats were challenged with lipopolysaccharide (LPS) in vivo, and the IL-1beta response was measured in vitro. Splenocytes, mesenteric lymphocytes, and peritoneal cavity cells had a dose- and time-dependent ex vivo IL-1beta response to LPS. Rats that were exposed to inescapable shock (IS, 100 1.6 mA, 5-s tail shocks, 60-s intertrial interval) and challenged with a submaximal dose of LPS 4 days later had elevated IL-1beta measured ex vivo. To test whether the acute stress-induced elevation in IL-1beta contributes to the long-term suppression in acquired immunity, IL-1beta receptors were blocked for 24 h after stress. Serum anti-keyhole limpet hemocyanin (KLH) immunoglobulin (Ig) was measured. In addition, the acute elevation (2 h post-IS) of splenic IL-1beta in the absence of antigen was verified. Interleukin-1 receptor antagonist prevented IS-induced suppression in anti-KLH Ig. These data support the hypothesis that stress-induced increases in innate immunity (i.e., IL-1beta) may contribute to stress-induced suppression in acquired immunity (i.e., anti-KLH Ig).

IL-10 and IL-4 regulate type-I and type-II IL-1 receptors expression on IL-1 beta-activated mouse primary astrocytes

When activated by its ligand, the interleukin receptor type I (IL-1RI) transduces signals in cooperation with the IL-1 receptor accessory protein (IL-1RacP). In contrast, IL-1RII functions as a decoy receptor without participating in IL-1 signalling. Brain astrocytes are cellular targets of IL-1 and play a pivotal role in brain responses to inflammation. The regulation of IL-1 receptors on astrocytes by anti-inflammatory cytokines such as IL-4 and IL-10 has not been studied, despite its importance for understanding the way these cells respond to IL-1. Using RT-PCR, we first showed that the expression of IL-1RI and IL-1RII, but not IL-1RacP, mRNAs are up-regulated by IL-1 beta in a time-dependent manner. Using a radioligand binding technique, we then showed that astrocytes display an equivalent number of IL-1RI and IL-1RII. IL-1 beta decreases the number of IL-1RI binding sites, whereas it increases those of IL-1RII. IL-4 and IL-10 both up-regulate IL-1RII IL-1 beta-induced, but only IL-4 does so for IL-1RI. At the protein level, IL-4 and IL-10 dramatically reverse the ability of IL-1 beta to inhibit expression of IL-1RI but neither affects the ability of IL-1 beta to enhance the number of IL-1RII. Collectively, these results establish the existence of receptor cross-talk between pro- and anti-inflammatory cytokines on a critical type of cell that regulates inflammatory events in the brain.

Biochemical mechanisms that interact with membrane-associated IL-1 RII (60-kDa decoy) receptors in populations of adherent macrophages and vascular endothelium

The aim of this investigation was to identify the potential biochemical mechanisms that alter the integrity of membrane-associated IL-1 RII (decoy) receptor complexes expressed by populations of adherent macrophages and vascular endothelium. The initial research strategy utilized to achieve this objective involved delineating the ability of macrophage activation or exposure of macrophages and vascular endothelium to a spectrum of enzyme proteases to influence the expression of membrane-associated IL-1 RII (decoy) or generate soluble fragments of this receptor complex. Results from these investigations revealed that stimulated macrophages displayed proportional increases in both the expression of membrane-associated IL-1 RII (decoy) and release of soluble receptor fragments. Exposure of macrophages and vascular endothelium to the reference proteases discovered the ability of cathepsin-D to biochemically deplete membrane-associated IL-1 RII (decoy) in addition to generating soluble fragments of this receptor complex. Complementary investigations isolated a carboxyl/aspartate protease from activated macrophages utilizing pepstatin-A affinity chromatography. Exposure of vascular endothelium to pepstatin-A binding proteins resulted in a detectable depletion of membrane-associated IL-1 RII (decoy) and generation of soluble receptor fragments. Evaluation of pepstatin-A binding proteins by SDS-PAGE identified a primary protein fraction with a molecular mass of 47-52 kDa that closely correlates with the known molecular size of leukocyte cathepsin-D fractions. Macrophage pepstatin-A binding protein fractions evaluated by nondenaturing haemoglobin-substrate PAGE (Hb-PAGE) analysis detected a lucent proteolytic band at 47-52 kDa. Macrophage pepstatin-A binding proteins also hydrolyzed a synthetic enzyme-specific substrate that selectively recognizes cathepsin-D biochemical activity. In conclusion, the leukocyte carboxyl/aspartate protease cathepsin-D can biochemically alter the integrity and generate soluble fragments of membrane-associated IL-1 RII (60-kDa decoy) receptor complexes expressed by macrophages and vascular endothelium.

Mechanisms by which blood levels of interleukin-6 (IL-6) are elevated after intracerebroventricular injection of IL-1beta in the rat: neural versus humoral control

Intracerebroventricular (icv) injection of interleukin-1beta (IL-1beta) in rats induces elevated IL-6 levels in peripheral blood, exceeding those induced by iv or ip injection. Two hypotheses postulated to explain this phenomenon were tested. Mediation by peripheral sympathetic activation was excluded by showing that agents that blocked preganglionic cholinergic synapses (chlorisondamine), beta-adrenergic receptors (propanalol, butoxamine), and alpha-adrenergic receptors (phentolamine) did not prevent the IL-6 response. That the peripheral response was due to passage of the injected IL-1beta into blood from the brain was supported by several observations. Immunoreactive IL-1beta appeared in peripheral blood by 10 min after icv injection and remained constant between 10-100 min after injection; values after icv injection were virtually identical to those after iv injection at 60 and 80 min. Radioiodine-labeled IL-1beta appeared in blood as early as 5 min, and by phamacokinetic analysis was found to be transferred from the brain at a rate greater than 2% of brain content per min(-1). IL-1beta infused iv in a pattern mimicking brain to blood transfer induced IL-6 levels that were more than double the values induced by a single bolus injection and were not significantly different from the values observed after icv injection. Sustained levels of IL-1beta in blood over time contribute to the high peripheral IL-6 response. This was shown by administering the same total dose iv as a single bolus of 100 ng or in two doses of 50 ng 1 h apart. Rats given a divided dose had 6-10 times higher blood IL-6 levels at 2 h than those given a single injection. The high levels of IL-6 in blood after icv injection of IL-1beta are best explained by the reservoir function of the brain IL-1beta pool and the self-priming effect of IL-1beta in peripheral tissues.

Dynamic regulation of the proinflammatory cytokine, interleukin-1beta: molecular biology for non-molecular biologists

Interleukin-1beta (IL-1beta) is a key mediator and modulator of a wide array of physiological responses important for survival. It is created by a variety of cell types, including immune cells, glia, and neurons. It is a very potent biological molecule, acting both at the periphery as well as within the central nervous system. The production and release of IL-1beta is tightly regulated by far more complex processes than previously thought. An appreciation of this complexity is necessary for proper interpretation of apparent contradictions in the literature where different aspects of IL-1beta expression are measured. Given that many researchers are not molecular biologists by training, yet need an appreciation of the controls that regulate the function of key proteins such as IL-1beta, this review is aimed at both: (a) clarifying the multiple levels at which IL-1beta production is modulated and (b) using IL-1beta regulation to explain the dynamics of gene regulation to non-molecular biologists. Three major topics will be discussed. First, regulation of IL-1beta production will be examined at every level from extracellular signals that trigger gene activation through release of active protein into the extracellular fluid. Second, regulation of IL-1beta bioavailability and bioactivity will be discussed. This section examines the fact that even after IL-1beta is released, it may or may not be able to exert a biological action due to multiple modulatory factors. Last is the introduction of the idea that IL-1beta regulation is, at times, beyond the direct control of host; that is, when IL-1beta production becomes dysregulated by pathogens.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.

The interleukin-1 system: receptors, ligands, and ICE in the brain and their involvement in the fever response

The ligands and the receptors of the interleukin 1 (IL-1) system constitute a highly inducible set of proteins whose expression in infection and inflammation is of key importance in the host defense. The IL-1 system participates in the stimulation of the immune system, the neuroendocrine system, and the neuroimmune system. The major soluble and secreted agonist of the system, IL-1 beta, has been studied by mutational and transgenic approaches. Furthermore, involvement of the signal-transducing type I IL-1 receptor (IL-1RI), in fever and other responses, has been studied by null mutation technique. We describe the inducible expression of the two agonists, IL-1 alpha (31 kDa and 17 kDa) and IL-1 beta (17 kDa) and of the IL-1 receptor subtypes IL-1RI and IL-1RII in the brain and in the adrenals (as well as in the pituitary cell line AtT20). We also describe an additional member of the IL-1 family: the IL-1 receptor antagonist (IL-1ra), an endogenous antagonist to IL-1 alpha and IL-1 beta. Furthermore, the IL-1 beta-converting enzyme (ICE) and its differential regulation and expression in brain and adrenals is also discussed. Fever is a systemic response to intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) injection of IL-1 alpha or IL-1 beta. IL-1 beta-induced fever can be blocked by IL-1ra pretreatment. The fever response seems to be mediated via the IL-1RI as inferred from studies with receptor subtype-specific mutants of IL-1 beta and from studies in IL-1RI knock-out (IL-1RI KO) mice. IL-1 beta knock-out mice showed a hyperresponsive fever to both IL-1 agonists, IL-1 alpha and IL-1 beta, as well as to LPS.

Type 2 interleukin-1 receptor mRNA is induced by kainic acid in the rat brain

The in situ hybridization technique was used to examine the expression of type 2 interleukin-1 receptor (IL-1R2) mRNA in the rat brain following the systemic injection of kainic acid at a convulsive dose. The expression of IL-1R2 mRNA was not detected in any brain regions of the saline-injected control rats. 8 h after the systemic injection of kainic acid, weak expression of IL-1R2 mRNA was observed in the dentate gyrus and basolateral amygdaloid nucleus. At 12 and 24 h after the injection of kainic acid, IL-1R2 mRNA was markedly induced in various brain regions including the CA1 and CA3 fields of the hippocampus, dentate gyrus, basolateral amygdaloid nucleus, piniform cortex, claustrum, tenia tecta, arcuate hypothalamic nucleus, dorsomedial hypothalamic nucleus, suprachiasmatic nucleus, tuberal magnocellular nucleus and supramammillary nucleus. In these regions, the signals of IL-1R2 mRNA were observed on likely neuronal cells. Around the mediodorsal thalamic nucleus and the paraventricular thalamic nucleus, dispersed intense signals were observed on the non-neuronal cells. In addition, the expression of the mRNA on the venules was observed at 12 h. The strength of signals significantly decreased by 48 h after the injection. These findings revealed the spatiotemporal induction of IL-1R2 mRNA in the rat brain following the systemic administration of kainic acid, which has shown to cause neuronal degeneration, suggesting the pathological roles of IL-1R2 in the brain.

Hyperresponsive febrile reactions to interleukin (IL) 1alpha and IL-1beta, and altered brain cytokine mRNA and serum cytokine levels, in IL-1beta-deficient mice

IL-1beta is an endogenous pyrogen that is induced during systemic lipopolysaccharide (LPS)- or IL-1-induced fever. We have examined the fever and cytokine responses following i.p. injection of IL-1 agonists, IL-1alpha and IL-1beta, and compared these with response to LPS (i.p.) in wild-type and IL-1beta-deficient mice. The IL-1beta deficient mice appear to have elevated body temperature but exhibit a normal circadian temperature cycle. Exogenously injected IL-1beta, IL-1alpha, or LPS induced hyperresponsive fevers in the IL-1beta-deficient mice. We also observed phenotypic differences between wild-type and IL-1beta-deficient mice in hypothalamic basal mRNA levels for IL-1alpha and IL-6, but not for IL-1beta-converting enzyme or IL-1 receptor type I or type II. The IL-1alpha mRNA levels were down-regulated, whereas the IL-6 mRNA levels were up-regulated in the hypothalamus of IL-1beta-deficient mice as compared with wild-type mice. The IL-1beta-deficient mice also responded to LPS challenge with significantly higher serum corticosterone and with lower serum tumor necrosis factor type alpha levels than the wild-type mice. The data suggest that, in the redundant cascade of proinflammatory cytokines, IL-1beta plays an important but not obligatory role in fever induction by LPS or IL-1alpha, as well as in the induction of serum tumor necrosis factor type alpha and corticosterone responses either by LPS or by IL-1alpha or IL-1beta.

Administration of neutralizing antibody against rabbit IL-1 receptor antagonist exacerbates lipopolysaccharide-induced arthritis in rabbits

Endogenous IL-1 receptor antagonist (IL-1ra) may down-regulate part of IL-1 actions. We examined the participation of endogenous IL-1ra in the production of IL-1 beta in vitro. Macrophages cultured on adherent IgG produced a 100-fold molar excess of IL-1ra, compared with IL-1 beta. In the presence of a neutralizing monoclonal antibody (mAb) against rabbit IL-1ra, the production of antigenic IL-1 beta increased by 20-60%. Since the molar ratio of IL-1ra over IL-1 was 160- to 400-fold in synovial fluid (SF) of lipopolysaccharide (LPS)-induced arthritis, we examined the functional role of endogenous IL-1ra in the regulation of inflammatory responses. When measured in the presence of anti-IL-1ra mAb, masked IL-1 activity in SF became evident, with a 3- to 4-fold increment. The administration of anti-IL-1ra mAb with LPS into rabbit knee joints increased the IL-1 activity 4-fold and the production of antigenic IL-1 beta by 30-50%. The treatment also enhanced by 20-40% LPS-induced leukocyte infiltration and protein leakage. Therefore, endogenous IL-1ra apparently acts as a down-regulating factor for limiting deleterious effects of IL-1 by masking the biological activity and by inhibiting the production.