Defective inflammatory response in interleukin 6-deficient mice

Endogenous interleukin-6 contributes to hypersensitivity to cutaneous stimuli and changes in neuropeptides associated with chronic nerve constriction in mice

Partial nerve injury is a potential cause of distressing chronic pain for which conventional analgesic treatment with opiates or anti-inflammatory agents is not very effective. Constriction nerve injury, widely used to study neuropathic pain, was shown here to induce interleukin-6 (IL-6) mRNA in a subset of rat primary sensory neurons. When we inflicted chronic nerve constriction on mice with null mutation of the IL-6 gene, the hypersensitivity to cutaneous heat and pressure that is induced in wild-type mice was not evident, the loss of substance P in sensory neurons was excessive and the induction of galanin in central sensory projections was reduced. In additional experiments, intrathecal infusion of IL-6 in rats was shown to stimulate synthesis of galanin in approximately one-third of lumbar dorsal root ganglion neurons. The results of these experiments indicate that endogenous IL-6 mediates some of the hypersensitive responses that characterize peripheral neuropathic pain, and influences two neuropeptides that have been implicated in pain transmission.

New insights into the biology of the acute phase response

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

CpG-DNA upregulates the major acute-phase proteins SAA and SAP

The acute-phase response is an immediate reaction of the host against invading microorganisms. We show here that oligodeoxynucleotides (ODNs) containing a CpG motif rapidly induce the major murine acute-phase proteins in vivo, i.e. serum amyloid A (SAA) and serum amyloid P (SAP). Serum levels of these proteins are elevated within 12 h and peak at 24 h after the injection of CpG-ODN or endotoxin. Liver cells produce the proteins with the same kinetics. Injection of interleukin 6 (IL-6), IL-1beta and tumour necrosis factor alpha (TNF-alpha) induces SAA and SAP in vivo, but the CpG-ODN-mediated induction does not depend on the presence of the TNF receptor p55, as the acute-phase response in TNF receptor p55-deficient mice does not differ from that of wild-type mice. Aside from CpG-ODN, bacterial genomic DNA also induces the acute-phase response in LPS-resistant C3H/Hej mice. The induction of the major acute-phase proteins SAA and SAP is blocked by the simultaneous injection of CpG-ODN together with D-galactosamine (D-GalN). As D-GalN sensitizes the host for the toxic effects of TNF-alpha, a possible mechanism could be the prevention of synthesis of the major acute-phase proteins SAA and SAP.

Nature of the retrograde signal from injured nerves that induces interleukin-6 mRNA in neurons

In previous studies, interleukin-6 was shown to be synthesized in approximately one-third of lumbar dorsal root ganglion neurons during the first week after nerve transection. In present studies, interleukin-6 mRNA was found to be induced also in axotomized facial motor neurons and sympathetic neurons. The nature of the signal that induces interleukin-6 mRNA in neurons after nerve injury was analyzed. Blocking of retrograde axonal transport by injection of colchicine into an otherwise normal nerve did not induce interleukin-6 mRNA in primary sensory neurons, but injection of colchicine into the nerve stump prevented induction of interleukin-6 mRNA by nerve transection. Therefore, it was concluded that interleukin-6 is induced by an injury factor arising from the nerve stump rather than by interruption of normal retrograde trophic support from target tissues or distal nerve segments. Next, injection into the nerve of a mast cell degranulating agent was shown to stimulate interleukin-6 mRNA in sensory neurons and systemic administration of mast cell stabilizing agents to mitigate the induction of interleukin-6 mRNA in sensory neurons after nerve injury. These data implicate mast cells as one possible source of the factors that lead to induction of interleukin-6 mRNA after nerve injury. In search of a possible function of inducible interelukin-6, neuronal death after nerve transection was assessed in mice with null deletion of the interleukin-6 gene. Retrograde death of neurons in the fifth lumbar dorsal root ganglion was 45% greater in knockout than in wild-type mice. Thus, endogenous interleukin-6 contributes to the survival of axotomized neurons.

Endogenous cytokines during a lethal infection with Listeria monocytogenes in mice

It has been demonstrated that endogenous cytokines including gamma interferon (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) play protective roles but that IL-4 and IL-10 play detrimental roles in nonlethal Listeria monocytogenes infection in mice. In this paper, we studied the roles of endogenous cytokines in a lethal infection with L. monocytogenes in mice. TNF-alpha and IL-6 titres in the bloodstreams, spleens and livers paralleled bacterial numbers in the organs, and both these cytokines and the bacterial numbers peaked just before the mice died. The high titres of TNF-alpha notably detected in the circulation in lethal infection were different from those in nonlethal infection. The maximum production of IFN-gamma was observed before the peaks of TNF-alpha and IL-6, and IFN-gamma almost disappeared from the bloodstreams and organs just before the mice died. No notable difference of IFN-gamma titres between lethal infection and nonlethal infection in the specimens obtained from mice was observed. IL-10 was also detected in the bloodstreams earlier than the peaks of TNF-alpha and IL-6 during lethal infection, while IL-4 was never detected in the sera. The administration of monoclonal antibodies (mAbs) against TNF-alpha, IFN-gamma, IL-6, IL-4 or IL-10 failed to rescue mice from lethal L. monocytogenes infection, whereas anti-TNF-alpha mAb and anti-IFN-gamma mAb prevented mice from lethality by high-dose endotoxin shock. These results suggest that lethality in L. monocytogenes infection might not be determined solely by these cytokines.

Regulation of Spi 2.1 and 2.2 gene expression after turpentine inflammation: discordant responses to IL-6

The rat serine protease inhibitor (Spi) 2 gene family includes both positive (Spi 2.2) and negative (Spi 2.1) acute phase reactants, facilitating modeling of regulation of hepatic acute phase response (APR). To examine the role of signal transducer and activation of transcription (STAT) proteins in the divergent regulation of these model genes after induction of APR, we evaluated the proximal promoters of the genes, focusing on STAT binding sites contained in these promoter elements. Induction of APR by turpentine injection includes activation of a STAT3 complex that can bind to a gamma-activated sequence (GAS) in the Spi 2.2 gene promoter, although the Spi 2.2 GAS site can bind STAT1 or STAT5 as well. To create an in vitro model of APR, primary hepatocytes were treated with combinations of cytokines and hormones to mimic the hormonal milieu of the whole animal after APR induction. Incubation of primary rat hepatocytes with interleukin (IL)-6, a critical APR cytokine, leads to activation of STAT3 and a 28-fold induction of a chloramphenicol acetyltransferase reporter construct containing the -319 to +85 region of the Spi 2.2 promoter. This suggests the turpentine-induced increase of Spi 2.2 is mediated primarily by IL-6. In contrast, although turpentine treatment reduces Spi 2.1 mRNA in vivo and IL-6 does not increase Spi 2.1 mRNA in primary rat hepatocytes, treatment of hepatocytes with IL-6 results in a 5. 4-fold induction of Spi 2.1 promoter activity mediated through the paired GAS elements in this promoter. Differential regulation of Spi 2.1 and 2.2 genes is due in part to differences in the promoters of these genes at the GAS sites. IL-6 alone fails to reproduce the pattern of rat Spi 2 gene expression that results from turpentine-induced inflammation.

Leukemia inhibitory factor, Interleukin 6, and other cytokines using the GP130 transducing receptor: roles in inflammation and injury

Inflammation refers to a complex set of mechanisms by which tissues respond to injury and infection. Among the many soluble mediators associated with this process, cytokines are known to be crucial in regulating a variety of cellular and molecular events. Leukemia inhibitory factor (LIF), interleukin 6 (IL-6), IL-11, and possibly other members of this cytokine family are key mediators in various inflammatory processes such as the acute-phase reaction, tissue damage, and infection. These cytokines can act in both pro-inflammatory and anti-inflammatory ways, depending on a number of variables. We emphasize here recent work utilizing knockout mice, which has highlighted the roles of LIF and IL-6, particularly in interactions between the immune and nervous systems.

Nature of the retrograde signal from injured nerves that induces interleukin-6 mRNA in neurons

In previous studies, interleukin-6 was shown to be synthesized in approximately one-third of lumbar dorsal root ganglion neurons during the first week after nerve transection. In present studies, interleukin-6 mRNA was found to be induced also in axotomized facial motor neurons and sympathetic neurons. The nature of the signal that induces interleukin-6 mRNA in neurons after nerve injury was analyzed. Blocking of retrograde axonal transport by injection of colchicine into an otherwise normal nerve did not induce interleukin-6 mRNA in primary sensory neurons, but injection of colchicine into the nerve stump prevented induction of interleukin-6 mRNA by nerve transection. Therefore, it was concluded that interleukin-6 is induced by an injury factor arising from the nerve stump rather than by interruption of normal retrograde trophic support from target tissues or distal nerve segments. Next, injection into the nerve of a mast cell degranulating agent was shown to stimulate interleukin-6 mRNA in sensory neurons and systemic administration of mast cell stabilizing agents to mitigate the induction of interleukin-6 mRNA in sensory neurons after nerve injury. These data implicate mast cells as one possible source of the factors that lead to induction of interleukin-6 mRNA after nerve injury. In search of a possible function of inducible interelukin-6, neuronal death after nerve transection was assessed in mice with null deletion of the interleukin-6 gene. Retrograde death of neurons in the fifth lumbar dorsal root ganglion was 45% greater in knockout than in wild-type mice. Thus, endogenous interleukin-6 contributes to the survival of axotomized neurons.

Suppression of chronic experimental autoimmune neuritis by nasally administered recombinant rat interleukin-6

Experimental autoimmune neuritis (EAN) is a CD4+ T-cell-mediated demyelinating disease of the peripheral nervous system (PNS) and serves as experimental model for human immune-demyelinating neurophathies, especially the Guillain-Barré syndrome. In this study, we examined the effect of recombinant rat interleukin-6 (rrIL-6) on chronic EAN in Lewis rats induced by immunization with P2 peptide 57-81 and Freund's complete adjuvant (FCA). Nasal administration of rat rIL-6 (1 microg/rat/day) beginning in the initial phase of EAN as a therapeutic agent, decreased the severity and the duration of clinical EAN. Low-grade inflammation and suppression of regional demyelination within the sciatic nerves were seen in rrIL-6-treated rats. Hyporesponsiveness of lymph node T cells, down-regulation of serum tumour necrosis factor-alpha (TNF-alpha) and increased levels of P2-specific immunoglobulin G1 (IgG1) antibodies document that nasal administration of rrIL-6 was effective systemically. However, because of the non-specific nature of the treatment and multiple effects of IL-6, more experience and great caution are needed, before nasal administration of IL-6 can be considered as a treatment of human autoimmune demyelinating neurophathies.

Regulation of Inflammatory Responses by Oncostatin M

Oncostatin M (OM) is a pleiotropic cytokine produced late in the activation cycle of T cells and macrophages. In vitro it shares properties with related proteins of the IL-6 family of cytokines; however, its in vivo properties and physiological function are as yet ill defined. We show that administration of OM inhibited bacterial LPS-induced production of TNF-α and lethality in a dose-dependent manner. Consistent with these findings, OM potently suppressed inflammation and tissue destruction in murine models of rheumatoid arthritis and multiple sclerosis. T cell function and Ab production were not impaired by OM treatment. Taken together these data indicate the activities of this cytokine in vivo are antiinflammatory without concordant immunosuppression.

Presence of a reduced opioid response in interleukin-6 knock out mice

Cytokines are known to influence neuronal functions. The purpose of this study was to investigate the putative role of the cytokine interleukin-6 (IL-6) in the pathways involved in opioid-mediated responses, by using IL-6-deficient mice. We reported that with a thermal stimulus IL-6-knock-out (IL-6KO) mice presented nociceptive thresholds similar to those measured in their controls. However, they showed a reduced analgesic response both to the restraint stress and to the administration of low doses of morphine. Hypothalamic levels of the opioid peptide beta-endorphin were significantly higher in IL-6KO mice than they were in their controls. The development of tolerance to the analgesic effect of morphine was more rapid in IL-6-deficient mice than in wild-type controls. Binding experiments showed that the number of opioid receptors in the midbrain, but not in the hypothalamus, decreased in IL-6KO mice. Autoradiographic binding analysis revealed that the density of mu receptors diminished while the delta-opioid receptors did not. These results suggest that IL-6 is necessary for a correct development of neuronal mechanisms involved in the response to both endogenous and exogenous opiates.

Transgenic mouse model of AA amyloidosis

AA amyloidosis can be induced in mice experimentally through injection of certain chemical or biological compounds. However, the usefulness of this approach is limited by its dependence on exogenous inflammatory agents that stimulate cytokines to increase the synthesis of precursor serum amyloid A (SAA) protein and the transitory nature of the pathological fibrillar deposits. We now report that transgenic mice carrying the human interleukin 6 gene under the control of the metallothionein-I promoter had markedly increased concentrations of SAA and developed amyloid in the spleen, liver, and kidneys by 3 months of age. At the time of death about 6 months later, organs obtained from these animals had extensive amyloid deposits. This disease process was apparent radiographically using small-animal computer axial tomography and magnetic resonance imaging equipment. The AA nature of the amyloid was evidenced immunohistochemically and was unequivocally established by sequence analysis of protein extracted from the fibrils. The availability of this unique in vivo experimental model of AA amyloidosis provides the means to assess the therapeutic efficacy of agents designed to reduce or prevent the fibrillar deposits found in AA and other types of amyloid-associated disease.

Heme and acute inflammation role in vivo of heme in the hepatic expression of positive acute-phase reactants in rats

Acute-phase protein synthesis in the liver during inflammation is regulated via cytokines and glucocorticoids. Using quantitative reverse transcription (RT)-PCR analysis and immunoassay, we explored, in the rat, the response of the acute-phase protein, alpha-2 macroglobulin (A2M), after systemic inflammation induced by lipopolysaccharide (LPS) or localized inflammation induced by turpentine oil (TO). The results indicate that synthesis of A2M is higher following TO-induced inflammation than LPS-induced inflammation and is not correlated with interleukin (IL)-6 or glucocorticoid levels. We studied the putative role of heme in this differential A2M expression following localized vs. systemic inflammation; addition of heme during LPS-induced inflammation can boost the expression of A2M, whereas blocking heme synthesis (by succinyl acetone) or enhancing its consumption in parallel biosynthetic pathways (cytochrome P450 induction by phenobarbital) decreases A2M expression. This decrease was abolished by exogenous heme supplementation. Finally, we demonstrate that heme supplementation is also able to increase the A2M response in female rats to a level similar to that in male rats providing a new insight into the puzzling sexual dimorphism observed previously during localized inflammation. We propose that heme should be considered a new regulatory element in controlling liver A2M expression during inflammation.

TNF-binding protein ameliorates inhibition of skeletal muscle protein synthesis during sepsis

We examined the effects of TNF-binding protein (TNFBP) on regulatory mechanisms of muscle protein synthesis during sepsis in four groups of rats: Control; Control+TNFBP; Septic; and Septic+TNFBP. Saline (1. 0 ml) or TNFBP (1 mg/kg, 1.0 ml) was injected daily starting 4 h before the induction of sepsis. The effect of TNFBP on gastrocnemius weight, protein content, and the rate of protein synthesis was examined 5 days later. Sepsis reduced the rate of protein synthesis by 35% relative to controls by depressing translational efficiency. Decreases in protein synthesis were accompanied by similar reductions in protein content and muscle weight. Treatment of septic animals with TNFBP for 5 days prevented the sepsis-induced inhibition of protein synthesis and restored translational efficiency to control values. TNFBP treatment of Control rats for 5 days was without effect on muscle protein content or protein synthesis. We also assessed potential mechanisms regulating translational efficiency. The phosphorylation state of p70(S6) kinase was not altered by sepsis. Sepsis reduced the gastrocnemius content of eukaryotic initiation factor 2Bepsilon (eIF2Bepsilon), but not eIF2alpha. The decrease in eIF2Bepsilon content was prevented by treatment of septic rats with TNFBP. TNFBP ameliorates the sepsis-induced changes in protein metabolism in gastrocnemius, indicating a role for TNF in the septic process. The data suggest that TNF may impair muscle protein synthesis by reducing expression of specific initiation factors during sepsis.

Role of central melanocortins in endotoxin-induced anorexia

Inflammation and microbial infection produce symptoms, including fever, anorexia, and hypoactivity, that are thought to be mediated by endogenous proinflammatory cytokines. Melanocortins are known to act centrally to suppress effects on fever and other sequelae of proinflammatory cytokine actions in the central nervous system, but the roles of melanocortins in anorexia and hypoactivity occurring during the acute phase response are unknown. The present study was designed to determine the effects of exogenous and endogenous alpha-melanocyte stimulating hormone (alpha-MSH) on lipopolysaccharide (LPS)-induced anorexia in relation to their effects on fever. Rats were fasted overnight to promote feeding behavior, then injected intraperitoneally with LPS (100 micrograms/kg ip), followed 30 min later by intracerebroventricular injection of either alpha-MSH or the melanocortin receptor subtype 3/subtype 4 (MC3-R/MC4-R) antagonist SHU-9119. Food intake, locomotor activity, and body temperature (Tb) were monitored during the ensuing 24-h period. Each of two intracerebroventricular doses of alpha-MSH (30 and 300 ng) potentiated the suppressive effects of LPS on food intake and locomotion, despite the fact that the higher dose alleviated LPS-induced fever. In control rats that were not treated with LPS, only the higher dose of alpha-MSH significantly inhibited food intake, and Tb and locomotor activity were unaffected. To assess the roles of endogenous central melanocortins, LPS-treated rats received intracerebroventricular SHU-9119 (200 ng). Central MC3-R/MC4-R blockade did not affect Tb or food intake in the absence of LPS treatment, but it reversed the LPS-induced reduction in 24-h food intake and increased LPS-induced fever without altering the LPS-induced suppression of locomotion. Taken together, the results suggest that exogenous and endogenous melanocortins acting centrally exert divergent influences on different aspects of the acute phase response, suppressing LPS-induced fever but contributing to LPS-induced anorexia and hypoactivity.

Endotoxin and interleukin-1 decrease hepatic lipase mRNA levels

The acute phase response induces a multitude of changes in lipoprotein metabolism including hypertriglyceridemia, triglyceride enriched LDL, and decreased HDL levels accompanied by changes in HDL composition including increased free cholesterol and triglycerides and a decrease in esterified cholesterol. Here we demonstrate that endotoxin (LPS) induces a 56% decrease in hepatic lipase activity in liver and a 45% decrease in hepatic lipase activity in post heparin plasma in Syrian hamsters. LPS treatment also produces a marked decrease in hepatic lipase mRNA levels in the liver. Half maximal reduction in hepatic lipase mRNA levels occurred at approximately 0.2 microg LPS/100 g BW with a maximal decrease at 1.0 microg/100 g BW ( > 90% decrease), indicating that inhibition of hepatic lipase is a sensitive host response to LPS. Additionally, IL-1 produced a marked decrease in hepatic lipase mRNA levels while TNF had no effect. Moreover, IL-1 treatment of HepG2 cells in vitro also decreased hepatic lipase mRNA levels suggesting that IL-1 can directly regulate hepatic lipase expression in liver cells. LPS decreased hepatic lipase mRNA levels in control as well as IL-1 type 1 receptor deficient mice indicating that IL-1 action is not absolutely essential and that several cytokines and/or small molecular mediators can regulate hepatic lipase during the acute phase response. The LPS and IL-1 induced decrease in hepatic lipase could have several consequences including decreasing the clearance of triglyceride rich lipoprotein particles and producing an increase in triglyceride rich HDL. The decrease in hepatic lipase activity and mRNA levels may be part of a series of coordinated changes in lipoprotein metabolism that occur during the acute phase response. These changes may be initially beneficial to the host but if present for an extended period may be proatherogenic.

Subversion of cytokine networks by viruses

Viruses and the immune system have been competitors throughout their co-evolution. It is therefore not surprising that the viruses in circulation today possess a variety of strategies to counteract those aspects of the immune system that are involved in virus clearance. Examination of these virus encoded functions provides an important view of immune function and an appreciation of the complexity of the virus-host interaction. It is clear that viruses, seeking to subvert the immune system, have become adept in blocking the communication channels of the immune system. There are numerous examples of viral proteins that target the cytokine networks, disrupting the processes by which the delicately balanced immune system is regulated. This review focuses on the gene products of poxviruses, adenoviruses and herpesviruses that function primarily as immune-modulators.

The role of interleukin-6 in the activation of the hypothalamo-pituitary-adrenocortical axis and brain indoleamines by endotoxin and interleukin-1 beta

Interleukin-6 (IL-6) is one of several cytokines that can stimulate the hypothalamo-pituitary-adrenocortical (HPA) axis. Because IL-6 is produced in response to the administration of endotoxin (LPS) and interleukin-1 (IL-1), it is possible that IL-6 contributes to the neuroendocrine and neurochemical changes induced by them. In this study, intraperitoneal (i.p.) injection of LPS elevated plasma concentrations of IL-6 while activating the HPA axis in a dose-dependent manner. Both responses reached a peak at around 2-3 h. Mouse IL-1beta administration (100 ng, i.p.) induced large increases in plasma corticosterone and a substantial, but short-lived increase in plasma IL-6 with a peak at 2 h. Pretreatment of mice intraperitoneally with a monoclonal antibody to mouse IL-6 significantly attenuated the plasma ACTH and corticosterone responses to LPS at 3 h, but not at 1 h. Anti-IL-6 treatment also attenuated the LPS-induced increases of tryptophan and the serotonin catabolite, 5-hydroxyindoleacetic acid (5-HIAA), but not that of the norepinephrine catabolite, 3-methoxy,4-hydroxyphenylethyleneglycol (MHPG). Pretreatment of mice with anti-IL-6 significantly attenuated the IL-1-induced increases of plasma ACTH and corticosterone at 2 h, but not at 4 h. The IL-1-induced increases of MHPG, tryptophan and 5-HIAA in hypothalamus and brain stem were not significantly altered. These results suggest that IL-6 contributes to the later phases of the LPS- and IL-1-induced stimulations of the HPA axis and to the indoleaminergic responses to LPS, but not to IL-1.

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.

IL-6-Deficient Mice Are Resistant to Experimental Autoimmune Encephalomyelitis: Roles of IL-6 in the Activation and Differentiation of Autoreactive T Cells

Although autoreactive T cells recognizing self myelin Ags are present in most individuals, autoimmune disease of the central nervous system is a relatively rare medical condition. Development of autoimmune disease may require not only the presence of autoreactive T cells but also that autoreactive T cells become activated. Activation of T cells may require a minimum of two signals: an Ag-specific signal delivered by MHC-peptide complex and a second signal delivered by costimulatory molecules or cytokines. Although in vitro studies have suggested that cytokines, especially proinflammatory cytokines such as IL-1, IL-6, and TNF are involved in T cell activation, their precise roles in vivo are not clear. To determine the roles of proinflammatory cytokines in T cell activation in vivo and in the development of autoimmune disease, we have studied experimental autoimmune encephalomyelitis (EAE) in mice deficient in IL-6. We found that IL-6-deficient mice were completely resistant to EAE induced by myelin oligodendrocyte glycoprotein (MOG), whereas IL-6-competent control mice developed EAE characterized by focal inflammation and demyelination in the central nervous system and deficiency in neurologic functions. Furthermore, we established that the resistance to EAE in IL-6-deficient mice was associated with a deficiency of MOG-specific T cells to differentiate into either Th1 or Th2 type effector cells in vivo. These results strongly suggest that IL-6 plays a crucial role in the activation and differentiation of autoreactive T cells in vivo and that blocking IL-6 function can be an effective means to prevent EAE.

Behavioural characterization of interleukin-6 overexpressing or deficient mice during agonistic encounters

Interleukin-6 (IL-6) is a cytokine released by activated immune cells which has been shown to affect brain function. In this experiment aggressive and affiliative behaviour exhibited during agonistic encounters by transgenic male mice either not expressing (IL-6 -/-) or overexpressing (NSE-hIL-6) IL-6 in the central nervous system was investigated. All subjects were isolated for 24 days before the aggressive encounter and were 52 days old at the time of testing. Subjects were placed for 5 consecutive days in a neutral cage for 15 min with an opponent of the Balb/c strain that had been previously isolated for the same amount of time. The first and the last test sessions were videotaped to evaluate the first approach and the establishment of the social role, respectively. A number of behavioural categories were later scored. When compared with wild-type controls, IL-6 -/- mice showed a higher degree of aggressive behaviour as indicated by a higher frequency of Offensive Upright Posture, an effect more pronounced on the fifth encounter. On the contrary, NSE-hIL-6 subjects showed a tendency to be more involved in affiliative-type social interactions, displaying a higher frequency and duration of behaviours such as Anogenital, Nose or Body Sniff. IL-6 -/- mice showed a clear tendency to exhibit less affiliative interactions compared with their controls while dopamine levels were found to be modified in a number of brain regions in these mice. Overall, these data suggest that IL-6 affects both aggressive and affiliative-type interactions, although the behaviour of the NSE-hIL-6 subjects was less affected than that of the IL-6 -/- group. The effects of the genetic background of the animal in screening the outcome of gene manipulations on behaviour are also discussed.

Sepsis in mice stimulates muscle proteolysis in the absence of IL-6

We tested the role of interleukin-6 (IL-6) in sepsis-induced muscle proteolysis by determining ubiquitin mRNA levels and protein breakdown rates in incubated extensor digitorum longus muscles from septic and sham-operated IL-6 knockout and wild-type mice. In addition, the effect of treatment of mice with human recombinant IL-6 on muscle protein breakdown rates was determined. Finally, protein breakdown rates were measured in myotubes treated for up to 48 h with different concentrations of IL-6. Sepsis in wild-type mice resulted in an approximately ninefold increase in plasma IL-6 levels, whereas IL-6 was not detectable in plasma of sham-operated or septic IL-6 knockout mice. Total and myofibrillar muscle protein breakdown rates were increased by approximately 30% and threefold, respectively, in septic IL-6 wild-type mice with an almost identical response noted in septic IL-6 knockout mice. Ubiquitin mRNA levels determined by dot blot analysis were increased during sepsis in muscles from both IL-6 knockout and wild-type mice, although the increase was less pronounced in IL-6 knockout than in wild-type mice. Treatment of normal mice or of cultured L6 myotubes with IL-6 did not influence protein breakdown rates. The present results suggest that IL-6 does not regulate muscle proteolysis during sepsis.

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

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

The combined inactivation of tumor necrosis factor and interleukin-6 prevents induction of the major acute phase proteins by endotoxin

The constellation of changes known as the acute phase response (APR) is a cytokine-driven process initiated by tissue inflammation. The proinflammatory cytokines, TNF, IL-1 and IL-6, are considered to be the primary mediators of the APR. IL-6 and IL-1beta gene-deleted mice (Fattori et al., J. Exp. Med. 1994. 180: 1243-1250; Kopf et al., Nature 1994. 368: 339-342; Fantuzzi et al., J. Immunol. 1996. 157: 291-296, respectively), exhibit impaired APR to turpentine injection but only a slight reduction in plasma acute phase protein levels in response to lipopolysaccharide (LPS). This infers an important role for TNF in the LPS-induced APR, however, in the present study, normal APR to both turpentine and LPS were observed in TNF/LTalpha-deficient mice. A striking absence of elevated major acute phase proteins, SAP and SAA, was observed in mice deficient in TNF/LTalpha and IL-6, suggesting that TNF-alpha or LTalpha do indeed exert important nonredundant synergism in the IL-1/IL-6 primary response. The regulation of other parameters typically altered in an APR, body weight, blood glucose and haptoglobin, was normal in LPS-dosed TNF/LTalpha-deficient and wild-type mice. The observed transcriptional response for SAA and SAP in these TNF/LTalpha/IL-6-deficient mice, in lieu of elevated plasma levels, suggests that SAA and SAP expression is possibly posttranscriptionally regulated.

Postnatally induced inactivation of gp130 in mice results in neurological, cardiac, hematopoietic, immunological, hepatic, and pulmonary defects

The pleiotrophic but overlapping functions of the cytokine family that includes interleukin (IL)-6, IL-11, leukemia inhibitory factor, oncostatin M, ciliary neurotrophic factor, and cardiotrophin 1 are mediated by the cytokine receptor subunit gp130 as the common signal transducer. Although mice lacking individual members of this family display only mild phenotypes, animals lacking gp130 are not viable. To assess the collective role of this cytokine family, we inducibly inactivated gp130 via Cre-loxP-mediated recombination in vivo. Such conditional mutant mice exhibited neurological, cardiac, hematopoietic, immunological, hepatic, and pulmonary defects, demonstrating the widespread importance of gp130-dependent cytokines.

The acute phase response in apolipoprotein A-1 knockout mice: apolipoprotein serum amyloid A and lipid distribution in plasma high density lipoproteins

In plasma, the bulk of apoSAA, a positive acute phase reactant protein, is transported in high density lipoproteins (HDL), especially HDLH (apoA1-rich HDL). In this study we tested whether apoA1 deficiency would adversely affect apoSAA concentration and lipid distribution in mouse plasma lipoproteins. Acute phase response (APR) was induced in C57BL/6J (apoA1+/+) and apoA1-knockout mice (apoA1-/-) by a subcutaneous injection of silver nitrate. The APR increased cholesterol concentrations in LDL of apoA1-/- mice and apoA1+/+ mice in a like manner. In contrast to apoA1+/+ mice, concentrations of cholesterol, phospholipids and proteins in both HDLL (1.063<d<1.103 g/ml) and HDLH (1.103<d<1.21 g/ml) were significantly increased by the APR in apoA1-/- mice. Total concentration of plasma apoSAA and its distribution in lipoprotein fractions was similar in both APR groups. The bulk of plasma apoSAA was contained in HDL and not in VLDL or LDL even when the HDL concentration was low. In apoA1-/- mice, HDLL and HDLH contained more apoSAA than in apoA1+/+ mice. These results indicate that apoA1-/- mice are not deterred from mounting an apoSAA response similar to apoA1+/+ mice and that apoA1-rich HDL particles are not necessary for apoSAA transport in the plasma.

Intracerebroventricular injection of anti-Fas activates the hypothalamus-pituitary-adrenal axis and induces peripheral interleukin-6 and serum amyloid A in mice: comparison with other ligands of the tumor necrosis factor/nerve growth factor receptor superfamily

Fas is a receptor of the tumor necrosis factor (TNF)/ nerve growth factor (NGF) receptor superfamily that mediates apoptosis and some inflammatory changes. As the central administration of TNF is known to activate the hypothalamus-pituitary-adrenal axis (HPAA) and to induce peripheral responses including induction of serum interleukin (IL)-6 and serum amyloid A (SAA), we investigated the effects of intracerebroventricular (i.c.v.) administration of agonist anti-Fas monoclonal antibody Jo2. Centrally administered anti-Fas (1 microg/mouse, i.c.v.) induced elevated levels of corticosterone, IL-6, and SAA comparable to those observed after i.c.v. administration of recombinant murine TNF. On the other hand, administration of murine NGF did not elevate serum corticosterone or IL-6, but induced SAA. Thus, Fas can trigger a centrally mediated anti-inflammatory response (HPAA activation) and induce a peripheral acute-phase response comparable to that induced with TNF, whereas NGF induces only acute-phase proteins.

Tumor growth and food intake in interleukin-6 gene knock-out mice

Interleukin (IL)-6 has potential antitumor activity and at the same time is responsible for tumor-derived cachexia. Using IL-6 gene knock-out (GKO) mice, we investigated the effect of IL-6 deficiency on the survival time, tumor growth and daily food intake of mice inoculated with Ehrlich ascites carcinoma. IL-6 GKO mice gained weight due to tumor growth more rapidly than the wild-type mice. The daily food intake of wild-type mice declined on day 2 after tumor inoculation and was only 37% on day 8. In contrast, the daily food intake of IL-6 GKO mice was constant for the first 7 days after tumor inoculation. Although wild-type mice suffered from cachexia, their survival time was significantly longer than that of IL-6 GKO mice. We propose that both IL-6 secretion and cancer cachexia syndrome may be involved in the defense mechanism against tumor progression.

Nitric oxide synthase inhibition and the induction of cytochrome P-450 affect heme oxygenase-1 messenger RNA expression after partial hepatectomy and acute inflammation in rats

OBJECTIVES

a) To evaluate in vivo, in rat liver, heme oxygenase-1 (HO-1) messenger RNA (mRNA) expression level and the regulation of 3',5'-cyclic guanosine monophosphate (cGMP) production during hepatic regeneration, localized inflammation, and systemic inflammation; and b) to investigate the effect of the induction of cytochrome P-450 and nitric oxide synthase (NOS) inhibition on HO-1 mRNA level and cGMP production in the liver.

DESIGN

Experimental, comparative study.

SETTING

Biochemical and molecular biology laboratory.

SUBJECTS

Six-wk-old male Sprague-Dawley rats (n = 60).

INTERVENTIONS

We randomly divided the rats into four groups: a) saline controls; b) animals receiving lipopolysaccharide (600 microg/kg) for systemic inflammation; c) animals receiving turpentine oil (5 mL/kg) for localized inflammation obtained by sterile abscess; and d) partially hepatectomized animals (two-thirds removal of the parenchyma) for hepatic regeneration.

MEASUREMENTS AND MAIN RESULTS

Hepatic regeneration induced HO-1 mRNA expression, as shown by quantitative reverse transcription-polymerase chain reaction analysis. The time course of liver HO-1 mRNA induction after partial hepatectomy and localized and systemic inflammation showed a similar and gradual increase, with a maximum at 6 hrs and a return to a minimal level 48 hrs after treatments. Liver HO-1 mRNA was overexpressed during localized vs. systemic inflammation. This overexpression was not correlated with either serum IL-6 or corticosterone concentrations, but is related to increased cGMP production. The administration of phenobarbital, a cytochrome P-450 inducer and of nitro-L-arginine methyl ester, a NOS inhibitor, prevented cGMP production and abolished the overexpression of HO-1 mRNA.

CONCLUSIONS

The results of this study indicate that HO-1 mRNA is induced during hepatic regeneration with a similar time course to that observed during acute inflammation. In addition, we demonstrated that: a) HO-1 mRNA is overexpressed during localized vs. systemic inflammation; b) this overexpression is not correlated with IL-6 or corticosterone concentrations but is related to intrahepatic cGMP production; c) induction of cytochromes P-450 and/or inhibition of NOS both reduce liver cGMP production and HO-1 mRNA expression. These results suggest that in rat liver, a cGMP-transducing pathway may control HO-1 mRNA expression. Thus, there may be a role for HO-1 mRNA in the modulation of the hepatic stress response.

The PACAP-type I receptor agonist maxadilan from sand fly saliva protects mice against lethal endotoxemia by a mechanism partially dependent on IL-10

Sand fly saliva contains maxadilan, a peptide that causes vasodilation and modifies the secretion of pro-inflammatory cytokines by macrophages. We show that 1 to 10 microg maxadilan protected BALB/c mice against a lethal dose of LPS. Maxadilan reduced serum levels of TNF-alpha by approximately tenfold, while it caused a threefold increase in IL-6 and IL-10. The protective effect of maxadilan is partially dependent on its ability to induce IL-10 production since maxadilan did not prevent death from endotoxic shock in IL-10(-/-) mice. Finally, maxadilan is a selective agonist of the pituitary adenylate cyclase-activating peptide (PACAP) type I receptor, and we found that the natural ligand of this receptor (PACAP 38) also protected mice against lethal endotoxemia. These results indicate that activation of the PACAP type I receptor may contribute to the control of systemic inflammation by a mechanism that is partially dependent on IL-10.

The role of tumour necrosis factor, interleukin 6, interferon-gamma and inducible nitric oxide synthase in the development and pathology of the nervous system

Proinflammatory cytokines, tumour necrosis factor (TNF)-alpha, interferon (IFN)-gamma and interleukin (IL)-6, have multiple effects in the central nervous system (CNS) not strictly cytotoxic being involved in controlling neuronal and glial activation, proliferation, differentiation and survival, thus influencing neuronal and glial plasticity, degeneration as well as development and regeneration of the nervous system. Moreover, they can contribute to CNS disorders, including multiple sclerosis. Alzheimer's disease and human immunodeficiency virus-associated dementia complex. Recent results with deficient mice in the expression of those cytokines indicate that they are in general more sensible to insults resulting in neural damage. Some of the actions induced by TNF-alpha, and IFN-gamma, including both beneficial and detrimental, are mediated by inducible nitric oxide synthase (iNOS)-derived nitric oxide (NO) production. NO produced by iNOS may be beneficial by promoting the differentiation and survival of neurons. IL-6 does not induce iNOS, explaining why this cytokine is less often involved in this dual role protection pathology. Some of the proinflammatory as well as the neurotrophic effects of those cytokines also involve upregulation of cell adhesion molecules (CAM). Those apparently conflicting results may be reconciled considering that proinflammatory cytokines are involved in promoting the disease, mostly by inducing expression of CAM leading to alteration of the blood-brain barrier integrity, whereas they have a protective role once disease is established due to its immunosuppressive or neurotrophic role. Understanding the dichotomy pathogenesis/neuroprotection of those cytokines may provide a rationale for better therapeutic strategies.

IL-6 and IL-1 beta in fever. Studies using cytokine-deficient (knockout) mice

Previous data support the hypothesis that during inflammation, interleukin (IL)-1 beta and IL-6 are involved in fever, in activation of the hypothalamic-pituitary-adrenal (HPA) axis, and in the induction of eicosanoids. Most of the pathophysiologic effects of IL-1 beta and Il-6 are mediated by prostaglandins (PGs), modulated by other cytokines, and antagonized by glucocorticoids (GC), a final product of the HPA axis. To further test these relationships, we measured changes in body temperature using biotelemetry in mice deficient in genes for IL-1 beta and/or IL-6 (IL-1 beta knockout [KO] and IL-6 KO) following injection with lipopolysaccharide (LPS) to induce systemic inflammation or turpentine to induce local abscess. Circulating IL-6, tumor necrosis factor alpha (TNF-alpha), GC, and PGE2 were measured in these mice after treatment. IL-1 beta KO mice responded with reduced fever and IL-6 KO mice with normal fever to a high dose of LPS. In contrast, neither type of KO mice produced fever to turpentine. PGE2 levels (measured in the circulation) were suppressed in both types of KO mice injected with turpentine. IL-1 beta KO mice showed deficiency in IL-6 following turpentine, but not LPS, injection. LPS-induced increases in TNF-alpha did not differ between IL-1 beta KO mice and their wild-type counterparts, whereas IL-6 KO mice showed exacerbated LPS-induced circulating TNF-alpha. No differences were noted in plasma elevations of GC between KO and wild-type mice following injection of LPS or turpentine, indicating that IL-1 beta and IL-6 are not required for activation of the HPA axis during inflammation. Our data demonstrate that in the mouse, IL-1 beta and IL-6 are critical for the induction of fever during local inflammation, whereas in systemic inflammation they appear only to contribute to fever.

IL-6 knock-out mice show modified basal immune functions, but normal immune responses to stress

To better determine the role of interleukin-6 in the mechanisms that regulate stress-induced immunosuppression, we used in this study an interleukin-6-deficient mice model recently generated by gene targeting. We report here that, in basal conditions, mutant mice are characterized by altered immune functions. Natural killer activity and interleukin-2 production are lower in splenocytes of interleukin-6 deficient mice compared to those of controls, whereas Concanavalin A-induced splenocyte proliferation is comparable with that observed in wild-type mice. Moreover, splenocyte concentrations of the immunosuppressive opioid peptide beta-endorphin are higher in interleukin-6 deficient mice while serum corticosterone concentrations are unchanged. After exposure to 16 h of restraint stress, a significant suppression of the immune parameters is exhibited and a significant increase of splenocyte beta-endorphin concentrations are present in knock-out and normal animals. Finally, corticosterone is normally induced in stressed interleukin-6-deficient mice, thus demonstrating that interleukin-6 is not crucial for the activation of the hypothalamic-pituitary-adrenal axis. In conclusion, our results indicate that interleukin-6 is not a key factor in the immunosuppression observed after restraint stress.

Semantics, inflammation, cytokines and common sense

Semantic evaluation of some of the terms we regularly employ--inflammation, anti-inflammatory, pro-inflammatory, anti-inflammatory drugs, cytokines, homeostasis and stress--raises concerns about their precise meanings and about their mechanistic implications. Semantic imprecision may have undesirable conceptual consequences.

Hepatocyte growth factor induces hepatocyte proliferation in vivo and allows for efficient retroviral-mediated gene transfer in mice

Recombinant retroviral vectors are an attractive means of transferring genes into the liver because they integrate into the host cell genome and result in permanent gene expression. However, efficient in vivo gene transfer is limited by the requirement of active cell division for integration. Traditional approaches to induce liver proliferation have the disadvantage of inducing hepatocellular injury by delivery of toxins or by surgical partial hepatectomy. As a nontraumatic alternative, we show that exogenous hepatocyte growth factor (HGF) is a powerful and safe mitogen for the mature intact murine liver when delivered continuously into the portal vein. A 5-day infusion of human HGF (5 mg/kg/d) resulted in > 140% increase in relative liver mass, which returned to normal in 4 to 5 weeks. This clearly shows that an exogenous growth factor can induce robust liver proliferation in vivo. In addition, we show that the HGF-induced proliferation was independent of interleukin-6, an essential cytokine involved in liver regeneration after partial hepatectomy. When recombinant retroviral vectors were infused in combination with HGF, 30% of hepatocytes were stably transduced with no indication of hepatic injury or histopathology. These results show the ability to obtain a clinically relevant transduction efficiency with retroviral vectors in vivo without the prior induction of liver injury. The level of hepatic gene transfer achieved has the potential to be curative for a large number of genetic liver diseases.

Increased production of TNF-alpha and decreased levels of dienoic eicosanoids, IL-6 and IL-10 in mice fed menhaden oil and juniper oil diets in response to an intraperitoneal lethal dose of LPS

Eicosapentaenoic acid (EPA) and the non-methylene interrupted fatty acids (NMIFA) displace arachidonic acid (AA: 20:4omega6 -5,8,11,14) in the membrane phospholipids. Unlike EPA (20:5omega3 -5,8,11,14,17), the NMIFA (20:3omega6 -5,11,14 and 20:4omega3 -5,11,14,17) lacking the delta-8 double bond are not substrates for the formation of eicosanoids. For 20 days, the mice were fed diets containing 5wt% dietary fats from various sources. The magnitudes in the production of eicosanoids and cytokines produced in response to an intraperitoneal injection of endotoxin in mice fed menhaden fish oil (MO) diets enriched with EPA were compared with those maintained on juniper oil (JO) containing NMIFA or on safflower oil (SO), a major source of the AA precursor, linoleic acid. The levels of PGE2, 6-keto-PGF1alpha and TXB2 were markedly lower (P < 0.01) in animals fed either MO or JO diets compared to the controls. The plasma levels of tumor necrosis factor (TNF)-alpha were significantly higher (P < 0.05) with a concomitant decrease of interleukin (IL)-6 and of IL-10 in mice fed MO or JO diets (P < 0.01) compared to those fed SO diet. These data suggest that the effects of consuming NMIFA of JO despite their inability to form eicosanoids are similar to those of feeding EPA which forms biologically active alternate metabolites.

Role of IL-6 and TNF in thermoregulation and survival during sepsis in mice

Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) have been implicated as key mediators in inflammation, morbidity, and mortality associated with sepsis. We examined the role of IL-6 and TNF-alpha signaling on hypothermia, fever, cachexia, anorexia, and survival during sepsis induced by cecal ligation and puncture (CLP) in male and female gene knockout mice. Male wild-type mice developed an initial hypothermia and subsequent fever during sepsis. Male IL-6 knockout mice did not develop fever; rather, they maintained a profound hypothermia during sepsis. Male TNF p55/p75 receptor (TNFR) knockout mice had attenuated hypothermia, but developed a virtually identical fever as wild-type mice. Cachexia did not differ between male wild-type and IL-6 or TNFR knockout mice, whereas anorexia was prolonged in IL-6 knockout mice. Due to the rapid lethality of sepsis in female mice, survival was the only variable we were able to statistically compare among female genotypes. Female wild-type mice had significantly decreased survival compared with male wild-type mice. Survival was significantly enhanced in male and female TNFR knockout mice compared with their wild-type controls. Lack of IL-6 did not affect male or female lethality. These data support the hypothesis that IL-6 is a key mediator of fever and food intake, whereas TNF is responsible for the initial hypothermia and lethality of sepsis in both sexes of mice. The enhanced lethality of CLP-treated female mice supports a role for sex steroids during sepsis.

IL-6 Produced by Kupffer Cells Induces STAT Protein Activation in Hepatocytes Early During the Course of Systemic Listerial Infections

Kupffer cells were the principal source of IL-6 produced in the livers of mice following i.v. inoculation of Listeria monocytogenes. IL-6 mRNA expression and the production of IL-6 were reduced drastically within the nonparenchymal liver cell population derived from mice rendered Kupffer cell depleted by pretreatment with liposome-encapsulated dichloromethylene diphosphonate. A sharp increase in the appearance of activated STAT3 occurred in extracts of purified hepatocytes derived from normal mice infected i.v. with Listeria. Remarkably, the kinetics of this increase overlapped IL-6 mRNA expression by Kupffer cells; each peaked at approximately 30 min postinfection. No increase in STAT3 activation was observed in IL-6-deficient or Kupffer cell-depleted animals. The results of these experiments indicate that the synthesis of IL-6 and the activation of STAT3 within hepatocytes are critical functions of Kupffer cells occurring very early during the course of systemic listerial infections.

Testosterone and IL-6 Requirements for Human C-Reactive Protein Gene Expression in Transgenic Mice

In vitro, IL-6 is the main inducer of the human C-reactive protein (CRP) gene, and IL-1 and steroids can enhance this effect. However, in mice, IL-6 is necessary but not sufficient for induction of the human CRP transgene, and testosterone is required for its constitutive expression by males. To examine the relative contributions of testosterone and IL-6 in the regulation of CRP gene expression, we produced CRP-transgenic (CRPtg), IL-6-deficient (IL-6−/−) mice. Male CRPtg/IL-6−/− mice expressed CRP constitutively, but CRP levels were not increased after injection of LPS. However, acute-phase CRP levels were attained after injection of IL-6. In contrast, female CRPtg/IL-6−/− mice did not express CRP constitutively or after administration of LPS, IL-6, IL-1, or IL-6 plus IL-1. Like males, testosterone-treated CRPtg/IL-6−/− females expressed CRP constitutively, and their transgene responded to injection of IL-6. The endogenous acute-phase protein serum amyloid P (SAP) was expressed constitutively equally by male and female IL-6−/− mice, responded minimally to LPS, and did not respond to either IL-6 or IL-1 alone. Acute-phase levels of SAP were induced in IL-6−/− mice by injection of IL-6 together with IL-1 or LPS. We conclude that in vivo, both constitutive and IL-6-dependent acute-phase expression of the CRP transgene require testosterone. In contrast, testosterone is not required for expression of the SAP gene, which requires IL-1 plus IL-6 for acute-phase induction.

A protective role for IL-6 during early infection with Toxoplasma gondii

IL-6 deficient mice were found to be significantly more susceptible to peroral infection with Toxoplasma gondii than their wild-type counterparts as measured by survival, brain cyst burdens and brain pathology at 28 days post infection. The physical manifestations of disease, such as weight loss, were not observed in IL-6 deficient animals until at least seven days later than such changes occurred in wildtype mice. During this early stage of infection IL-6+/+ but not IL-6-/- mice mounted a peripheral blood neutrophilia. Furthermore, between 6-8 days post-infection there was a significant increase in plasma IFN-gamma levels in wild-type but not IL-6 deficient mice. Not until days 18-23 post-infection, concurrent with the majority of deaths in IL-6-/- mice, were plasma IFN-gamma levels substantially and significantly raised in IL-6-/- mice. At this time not only were these plasma IFN-gamma levels 20-fold higher than background but eight-fold greater than peak (6-8 days post-infection) IFN-gamma levels in IL-6+/+ mice. IFN-gamma dependent parasite specific IgG2a levels were also significantly higher in IL-6-/- mice over this period and thereafter. Overall the evidence suggests that in the absence of IL-6 mice are unable to initiate a rapid proinflammatory response against T. gondii, which allows increased parasite growth. Increased mortality in IL-6-/- mice may be directly due to this increased parasite burden and the excessive inflammatory response this induces three weeks post-infection.

Cytokine mediation of ozone-induced pulmonary adaptation

Previous studies have shown that a single exposure of animals to ozone (O3) can induce protection or adaptation to the acute injurious effects of a subsequent O3 challenge. Although a number of mechanisms have been proposed to account for this response, none appear to be fully explanatory. We examined the role interleukin (IL)-6 may play in the induction of adaptation to O3-induced pulmonary injury. A statistically significant 29-fold increase in bronchoalveolar lavage fluid IL-6 levels was observed in rats exposed to 0.5 ppm O3 during nighttime hours when compared with daytime hours even though similar kinetics of inflammation were induced by each exposure. Animals receiving an initial nighttime O3 exposure showed a lesser degree of inflammation following a subsequent O3 exposure when compared with animals which received an initial daytime exposure. Rats pretreated with IL-6 both intratracheally and intraperitoneally and subsequently exposed to O3 showed a lesser degree of cellular inflammation when compared with respective controls. Pretreatment of rats with anti-IL-6-receptor antibodies (ra) prior to the nighttime O3 exposure completely abrogated the O3-induced cellular adaptive response without effecting the inflammatory response induced by the initial nighttime O3 exposure. In fact, administration of anti-IL-6ra augmented the neutrophil influx following the second O3 exposure. Anti-IL-6ra treatment did not alter the pulmonary edema adaptive response, suggesting that the O3-induced cellular and edema adaptive responses are regulated by different mechanisms. Our data indicate that mobilization of pulmonary antioxidants does not play a role in the IL-6-mediated early cellular adaptive response and suggest that IL-6 is an essential mediator of the O3-induced cellular adaptive response.

Adrenomedullin stimulates interleukin-6 production in Swiss 3T3 cells

Adrenomedullin (AM) has very recently been demonstrated to be produced and secreted from fibroblasts. The production of AM in the fibroblasts is augmented by inflammation-related substances, and Swiss 3T3 fibroblast cells express AM specific receptors coupled with adenylate cyclase. To assess the functions of AM secreted from fibroblasts, we measured the effect of AM on production in Swiss 3T3 cells of interleukin-6 (IL-6), a typical cytokine involved in the general inflammatory reactions. AM stimulated basal secretion of IL-6 5.5-fold, while other peptides elicited much weaker stimulatory effects. The effect of AM was inhibited with an AM receptor antagonist and a cAMP-dependent protein kinase (PKA) inhibitor. Furthermore, AM remarkably potentiated stimulatory effects of tumor necrosis factor-alpha, IL-1 beta and lipopolysaccharide on IL-6 production. This stimulatory effect of AM was induced through activation of gene transcription, which reached maximum within 30 min. These findings verify that AM is a rapid and extraordinarily potent regulator of IL-6 production in Swiss 3T3 cells acting through the cAMP-PKA pathway. The data thus obtained suggest that AM is a peptidergic regulator of inflammation.

Interleukin 6 is required for the development of collagen-induced arthritis

Interleukin-6 (IL-6) is overproduced in the joints of patients with rheumatoid arthritis (RA) and, based on its multiple stimulatory effects on cells of the immune system and on vascular endothelia, osteoclasts, and synovial fibroblasts, is believed to participate in the development and clinical manifestations of this disease. In this study we have analysed the effect of ablating cytokine production in two mouse models of arthritis: collagen-induced arthritis (CIA) in DBA/1J mice and the inflammatory polyarthritis of tumor necrosis factor alpha (TNF-alpha) transgenic mice. IL-6 was ablated by intercrossing an IL-6 null mutation into both arthritis-susceptible genetic backgrounds and disease development was monitored by measuring clinical, histological, and biochemical parameters. Two opposite responses were observed; while arthritis in TNF-alpha transgenic mice was not affected by inactivation of the IL-6 gene, DBA/1J, IL-6(-/-) mice were completely protected from CIA, accompanied by a reduced antibody response to type II collagen and the absence of inflammatory cells and tissue damage in knee joints. These results are discussed in the light of the present knowledge of cytokine networks in chronic inflammatory disorders and suggest that IL-6 receptor antagonists might be beneficial for the treatment of RA.

Hepatic and extra-hepatic transcription of inter-alpha-inhibitor family genes under normal or acute inflammatory conditions in rat

The expression and level of the mRNAs for the five genes that code for a set of plasma proteins collectively referred to as the inter-alpha-inhibitor family have been studied in rat under a normal condition or in the course of a turpentine-induced, systemic inflammation. In healthy rats, all five mRNAs [H1, H2, H3, H4, and alpha1-microglobulin/bikunin precursor (AMBP)] are expressed primarily in liver and two of them (H2 and H3) are found to a lower extent in brain. By in situ hybridization onto sections of a normal brain, the H3 mRNA has been precisely localized to the hypothalamus, amygdala, pontine area, optic tectum, and cerebellum. By reverse transcriptase-polymerase chain reaction of total RNAs obtained from a panel of organs, low amounts of one or more mRNA(s) could be detected in other locations (e.g., intestine and stomach). Furthermore, the extrahepatic expressions of several of these genes are up- or downregulated at 20 h after the start of a turpentine-induced inflammation. In liver, the contents of H3 and H4 mRNA are upregulated, whereas those of AMBP and H2 are downregulated during the acute phase. This is accounted for by changes in gene transcription, the kinetics of which is gene-specific. This behavior of H1, H2, H3, H4, and AMBP mRNAs in rat liver is in keeping with more limited analyses made at mRNA and/or protein levels in other species (human, pig) suffering from an acute inflammation. Therefore, the inflammation-associated regulation of these five genes that is conserved between species indicates that the inter-alpha-inhibitor family members are likely to be important partners of the acute phase response.

Induction and modulation of acute-phase response by protein malnutrition in rats: comparative effect of systemic and localized inflammation on interleukin-6 and acute-phase protein synthesis

The acute-phase protein (APP) response is regulated by cytokines such as interleukin-6 (IL-6), interleukin-1 (IL-1) and tumor necrosis factor (TNF), but may also be influenced by malnutrition. The aims of this study were as follows: 1) to determine in rats the effect of a protein-deficient diet on IL-6 mRNA expression in intestine, liver and peripheral blood mononuclear cells (PBMC), and on alpha-1 acid glycoprotein (AGP) and alpha-2 macroglobulin (A2M) serum levels and hepatic mRNA expression; 2) to compare, in protein-deficient rats, the IL-6 and APP responses after a turpentine (TO)- or a lipopolysaccharide (LPS)-induced inflammation; and 3) to determine the effect of a protein malnutrition on IL-6 mRNA expression in rat PBMC treated ex vivo with LPS. Interleukin-6 mRNA was present in intestine and PBMC but not in the liver of malnourished rats, and was absent in any tissue or cells of controls. A2M was present in the serum from malnourished rats but not after refeeding. AGP mRNA expression was not influenced by protein malnutrition. In malnourished rats, IL-6 serum level peaked later than in controls after TO and LPS treatment. In malnourished TO-treated rats, A2M mRNA increased earlier than in controls and remained detectable later than in controls. AGP mRNA expression after TO was not influenced by protein malnutrition. In PBMC of malnourished rats, LPS-induced IL-6 mRNA expression occurred earlier and lasted longer than in controls. Our results indicate that protein malnutrition by itself induces IL-6 and A2M expression, and that it modulates the APP response to inflammation.

IL-6 is an antiinflammatory cytokine required for controlling local or systemic acute inflammatory responses

IL-6 is induced often together with the proinflammatory cytokines TNFalpha and IL-1 in many alarm conditions, and circulating IL-6 plays an important role in the induction of acute phase reactions. However, whether this endogenous IL-6 plays any additional pro- or antiinflammatory roles in local or systemic responses remains unclear. In this study, the role of IL-6 in acute inflammatory responses was investigated in animal models of endotoxic lung or endotoxemia by using IL-6+/+ and IL-6-/- mice. Aerosol exposure of endotoxin induced increased IL-6 and proinflammatory cytokines TNFalpha and MIP-2 and a neutrophilic response in the lung of IL-6+/+ mice. However, the levels of TNFalpha and MIP-2 and neutrophilia were significantly higher in the lung of IL-6-/- mice. The rate of neutrophil apoptosis in these mice was similar to that in IL-6+/+ mice. A low constitutive level of antiinflammatory cytokine IL-10 was not enhanced by endotoxin and remained similar in the lung in both IL-6+/+ and IL-6-/- mice. Systemically, intraperitoneal delivery of endotoxin resulted in much more pronounced circulating levels of TNFalpha, MIP-2, GM-CSF, and IFNgamma in IL-6-/- mice than in IL-6+/+ mice, and administration of recombinant IL-6 to IL-6-/- mice abolished these differences. In contrast, circulating IL-10 levels were induced to a similar degree in both IL-6+/+ and IL-6-/- mice. Thus, our studies reveal that endogenous IL-6 plays a crucial antiinflammatory role in both local and systemic acute inflammatory responses by controlling the level of proinflammatory, but not antiinflammatory, cytokines, and that these antiinflammatory activities by IL-6 cannot be compensated for by IL-10 or other IL-6 family members.

Interleukin-6 Induces Monocyte Chemotactic Protein-1 in Peripheral Blood Mononuclear Cells and in the U937 Cell Line

Induction of chemokine gene expression from peripheral blood mononuclear cells (PBMCs) stimulated by proinflammatory cytokines plays an important role in both wound repair and response to infectious agents. In the present study, we show that the proinflammatory cytokine interleukin-6 (IL-6) potently induced mRNA expression and secretion of the CC chemokine monocyte chemotactic protein 1 (MCP-1) in PBMCs. In addition, because human immunodeficiency virus (HIV) infection in vivo and in vitro has been shown to dysregulate the production of and/or the response to cytokines, PBMCs from both healthy uninfected and HIV-infected individuals were studied for their constitutive and IL-6–induced expression of MCP-1. No substantial differences were observed between the two groups of individuals. In addition, IL-6 upregulated MCP-1 expression in the promonocytic cell line U937 and in its chronically HIV-infected counterpart, U1. In these cell lines, IL-6 selectively induced MCP-1 and not other chemokines, including regulated upon activation normal T cells expressed and secreted (RANTES), macrophage inflammatory protein-1α (MIP-1α), MIP-1β, and IL-8. IL-6 induction of MCP-1 was partially inhibited by hydrocortisone in U1 cells. Thus, IL-6 activates PBMCs to secrete MCP-1, a CC chemokine pivotal for monocyte recruitment in tissue and organs in which important inflammatory events occur.