Defective inflammatory response in interleukin 6-deficient mice

Neither interleukin-6 nor signalling via tumour necrosis factor receptor-1 contribute to the adjuvant activity of Alum and Freund's adjuvant

The potential contribution made by the inflammatory cytokines, interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-alpha) to the adjuvant activity of aluminium hydroxide gels (Alum) or Freund's complete adjuvant (FCA) was studied by comparing the immunological responses of IL-6- or TNF receptor 1- (p55; TNFR-1) deficient mice with immunocompetent control mice. While both TNFR-1- and IL-6-deficient mice primed with ovalbumin (OVA) prepared in either Alum or FCA produced similar IgG.1 responses in comparison to control mice, the pattern of T-helper type 1- (Th1) dependent IgG2a production was significantly altered. In TNFR-1-deficient mice, IgG2a responses were greater than in control mice when FCA, but not when Alum, was used as an adjuvant. Correspondingly, spleen cells from FCA-inoculated TNFR-1-deficient mice restimulated with antigen in vitro produced higher Th1 cytokine (interferon-gamma; IFN-gamma) levels with no alteration in Th2 cytokine (IL-4; IL-5, IL-6 and IL-10) production in comparison with wild-type mice. Higher levels of IgG2a were also detected in IL-6-deficient mice compared with wild-type mice following inoculation with OVA prepared in either FCA or in Alum. Furthermore, analysis of cytokine production by spleen cells revealed that both Th1 and Th2 cytokine production was higher in IL-6-deficient mice compared with control mice. As the majority of the effects of TNF-alpha are mediated via TNFR-1, we conclude that this cytokine inhibits the adjuvant activities of FCA. Furthermore, the results also imply that immunopotentiating effects of FCA or Alum adjuvant are both inhibited by IL-6.

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.

IL-1 beta mediates leptin induction during inflammation

Interleukins (IL) are key mediators of the host response to infection and inflammation. Leptin is secreted by adipose tissue and plays an important role in the control of food intake. Administration of lipopolysaccharide (LPS), tumor necrosis factor (TNF), or IL-1 acutely increases leptin mRNA and protein levels. To investigate the role of IL-1 beta and IL-6 in leptin expression during inflammation, we used IL-1 beta-deficient (-/-) and IL-6 -/- mice. Mice were injected intraperitoneally with LPS or subcutaneously with turpentine, as models of systemic or local inflammation, respectively. In IL-1 beta +/+ mice, both LPS and turpentine increased leptin mRNA and circulating leptin. In contrast, neither LPS nor turpentine increased leptin levels in IL-1 beta -/- mice. In IL-6 +/+ or IL-6 -/- mice, turpentine increased leptin protein to comparable levels. We conclude that IL-1 beta is essential for leptin induction by both LPS and turpentine in mice, but IL-6 is not.

Interleukin-6 and CAAT/enhancer binding protein beta-deficient mice act as tools to dissect the IL-6 signalling pathway and IL-6 regulation

Interleukin-6 (IL-6) is a pleiotropic cytokine playing important roles in immunity, hemopoiesis and inflammation. IL-6 signalling is known to involve the activation of two independent transcription factors: Stat3 (through phosphorylation by Jak kinases) and C/EBP beta (through activation of the ras pathway). In addition, C/EBP beta is believed to act as a transcriptional activator of the IL-6 gene itself. Making use of IL-6-deficient mice, we have recently demonstrated that IL-6 is essential for the induction of acute phase mRNAs in the liver upon localized tissue damage, but not upon systemically induced inflammation. Here we show that the defective mRNA induction is paralleled by a defective activation of Stat3, thus establishing a direct relationship between IL-6 function, Stat3 activation and acute phase genes induction. On the other hand, making use of C/EBP beta-deficient mice, we show that the induction of IL-6 by a variety of stimuli does not require C/EBP beta activity. In contrast to the predicted activating role of C/EBP beta, IL-6 levels are increased in the C/EBP beta-deficient mice, suggesting that C/EBP beta may act as a down-modulator of the IL-6 gene. Through the generation of C/EBP beta, IL-6 double mutant mice we show that IL-6 hyperproduction is responsible for the development of the Castleman's like lymphoproliferative disease described in the C/EBP beta-deficient mice, since the disorder is completely blocked by inactivating the IL-6 gene.

Safety and kinetic properties of a humanized antibody to human interleukin-6 receptor in healthy non-human primates

A monoclonal antibody, hPM-1, was constructed by grafting the complementarity determining regions to human interleukin-6 (IL-6) receptor, raised in mouse, onto a human antibody backbone (humanized antibody). It is expected to be useful as a therapeutic agent for IL-6-related diseases such as multiple myeloma. To investigate the toxicological and kinetic properties of hPM-1 preliminarily, normal cynomolgus monkeys, which showed cross-reactivity with hPM-1, were intravenously administered with hPM-1 at doses of 0 (vehicle), 4 or 40 mg/kg once a week for 13 weeks. Upon toxicological examination, there were no changes in clinical signs, food consumption, body weights, urinalyses, body temperatures, electrocardiograms, hematological and biochemical parameters including blood platelet counts, serum levels of immunoglobulin G and C-reactive protein, and pathological findings. In a kinetic study, serum concentrations of hPM-1 showed a linearity between doses of 4 and 40 mg/kg. The serum concentrations, even at a dose of 4 mg/kg, were maintained at a high enough level to inhibit the IL-6 functions throughout the period of the study. Concentrations of hPM-1 in bone marrow were almost equal to those in serum. The antibodies against hPM-1 were detected only in one of four monkeys receiving hPM-1. This study suggests that blockage of the IL-6 receptor by hPM-1 does not induce any influence on a healthy living body, and hPM-1 is not toxic under the conditions of this investigation.

Interleukin-6-dependent and -independent regulation of the human C-reactive protein gene

We have investigated the function of different mediators of the regulation of the human C-reactive protein (hCRP) gene in transgenic mice. hCRP was induced by lipopolysaccharide and wounding in interleukin-6 (IL-6) +/+ mice, but not in IL-6 -/- mice. This finding suggested that IL-6 is necessary for the induction of hCRP. However, injection of IL-6 did not induce the hCRP gene. Thus, the induction of hCRP by IL-6 seems to require an additional cofactor. Therefore, we screened different cytokines for their activity in IL-6 +/+ and IL-6 -/- mice. Surprisingly, interleukin-1beta, as well as oncostatin M or leukaemia inhibitory factor, led to an induction of hCRP in both genetic backgrounds. These results indicate an IL-6-dependent and -independent regulation of hCRP. These hCRP transgenic mice therefore represent a novel model system for defining the cytokine network involved in the regulation of acute-phase genes during the course of inflammation.

IL-6 and APPs: anti-inflammatory and immunosuppressive mediators

Acute inflammation is accompanied by changes in the concentrations of acute phase proteins (APPs). While much is known about the cytokines involved in the initiation of inflammation, less is known about the mediators involved in its resolution. Recent data suggest that interleukin 6 (IL-6) and IL-6-regulated APPs are anti-inflammatory and immuno-suppressive, and may negatively regulate the acute phase response.

Defective development of pristane-oil-induced plasmacytomas in interleukin-6-deficient BALB/c mice

Interleukin (IL)-6 is known to be an essential growth factor for myeloma cells, both in vitro and in vivo. In mice, IL-6 is required for development of B cell tumors upon infection with a retrovirus expressing the myc/raf oncogenes. In the present study, we used the pristane-oil-induced plasmacytoma model, which more closely mimics tumor transformation and progression in human multiple myeloma. Also using this system, we found that IL-6-deficient BALB/c mice are protected against tumor development. Although the pristane-induced inflammatory reaction was less pronounced in IL-6-deficient mice versus their wild-type littermates, both B cell differentiation and plasma cell formation took place, and even morphological evidence of plasma cell transformation was detected, albeit at a low frequency. However, in the absence of IL-6, there were never signs of uncontrolled proliferation of either normal B lymphocytes or tumor cells, suggesting that the role of IL-6 in murine plasmacytoma and possibly also in human multiple myeloma is to ensure abnormal survival and proliferation of previously transformed tumor cells and therefore tumor development and progression.

Interleukin-6 is necessary, but not sufficient, for induction of the humanC-reactive protein gene in vivo

We have investigated the involvement of interleukin-6 (IL-6) in the induction of the gene encoding the acute-phase protein human C-reactive protein (hCRP). In transgenic mice the hCRP gene can be induced by lipopolysaccharide (LPS), but not by IL-6. In contrast, hCRP was inducible by IL-6 in primary human hepatocytes and in primary hepatocytes isolated from transgenic mice. To further evaluate the role of IL-6, we introduced the hCRP transgene into animals lacking endogenous IL-6 (IL-6-negative mice). Here, hCRP was not inducible by LPS, but was induced by a combination of LPS and IL-6. These results clearly demonstrate that IL-6 is necessary, but not sufficient, for the induction of hCRP expression. These animal models will allow further dissection of the cytokine network responsible for the regulation of the major human acute-phase reactant CRP.

Interleukin-6 reduces cartilage destruction during experimental arthritis. A study in interleukin-6-deficient mice

Using interleukin (IL)-6-deficient (IL-6(0/0) mice or wild-type mice, we investigated the controversial role of IL-6 in joint inflammation and cartilage pathology during zymosan-induced arthritis (ZIA). Monoarticular arthritis was elicited by injection of zymosan into the right knee joint cavity. Production of IL-1, tumor necrosis factor (TNF), IL-6, and nitric oxide by the inflamed knee was assessed in washouts of joint capsule specimens. Plasma corticosterone was measured using a radioimmunoassay. Proteoglycan synthesis was assessed using [35S]sulfate incorporation into patellas ex vivo. Joint swelling was quantified by joint uptake of circulating 99mTechnetium pertechnetate. Histology was taken to evaluate cellular infiltration and cartilage damage. Zymosan caused a rapid increase in articular IL-1, IL-6, TNF, and NO levels. Except for IL-6, the released amounts and time course of these mediators were comparable in the IL-6-deficient mice and the wild-type mice. Elevated plasma corticosterone levels were measured during the first day of arthritis in both strains. At day 2 of ZIA, joint inflammation (joint swelling and cell exudate) in IL-6-deficient mice was comparable with that in the wild-type mice. The marked suppression of chondrocyte proteoglycan synthesis and proteoglycan degradation were on the average higher in the IL-6-deficient mice. Together this resulted in a more pronounced proteoglycan depletion in the IL-6-deficient mice as compared with the wild-type mice during the first week of arthritis. Injection of recombinant IL-6 into the joint cavity corrected the IL-6 deficiency and significantly reduced cartilage destruction. Inflammation was more chronic in the wild-type mice, and these mice also showed a higher prevalence for osteophyte formation. In ZIA, IL-6 plays a dual role in connective tissue pathology, reducing proteoglycan loss in the acute phase and enhancing osteophyte formation in the chronic phase. The latter could be related to the more severe joint inflammation as seen in the normal (IL-6-producing) animals during the chronic phase of arthritis.

Induction of interleukin 6 by ionizing radiation in a human epithelial cell line: control by corticosteroids

The cutaneous radiation syndrome after therapeutic or accidental exposure of human skin to ionizing radiation (IR) is accompanied by inflammatory processes which are controlled partly by proinflammatory cytokines. Besides tumour necrosis factor (TNF)-alpha and interleukin (IL)1, the pluripotent cytokine IL-6 belongs to the key mediators of inflammation. So far, there are no reports about the regulation of IL-6 by IR in epidermal cells. As an in vitro model to study the effects of IR on IL-6 gene expression, we treated the human epithelial HeLa cell line with different single X-ray doses between 1 and 20 Gy. Twenty-four hours after irradiation the IL-6 secretion was dose-dependently enhanced as measured by ELISA. At the transcriptional level, a slight increase of IL-6 transcripts was already detectable 1 h after irradiation, with maximum levels at 2 h, and a decline to baseline levels between 8 and 24 h. Addition of the transcriptional inhibitor actinomycin D inhibited the inducibility of IL-6 mRNA by TPA and IR. As the IL-6 promoter contains multiple binding sites for activated glucocorticoid receptors within the 5' regulatory region, the potential modulation of IL-6 expression by the corticosteroids hydrocortisone, dexamethasone and mometasone furoate was included in our study to modify the radiation-induced stress response. All corticosteroids applied could efficiently downregulate TPA- or radiation-induced IL-6 expression on both gene expression and protein levels. Mometasone furoate, followed by dexamethasone, was found to be most effective at low concentrations (1 nM), whereas hydrocortisone had to be applied at about 100-fold higher concentrations to achieve comparable inhibition. This experimental model is aimed at understanding the molecular circuits following IR, and thus to provide a basis for the treatment of radiation effects in skin.

The decrease in nonsplenic interleukin-6 (IL-6) production after splenectomy indicates the existence of a positive feedback loop of IL-6 production during endotoxemia in dogs

The spleen is involved in endotoxin-induced interleukin-6 (IL-6) production. To quantitate the relative contribution of the spleen to endotoxin-induced IL-6 production, we studied the effect of endotoxin (1.0 microg/kg of body weight) in control dogs (n = 7) and splenectomized dogs (n = 7). Blood for analysis of tumor necrosis factor (TNF) and IL-6 was sampled from the femoral artery and the portal, hepatic, and splenic (only in controls) veins. Arterial plasma endotoxin and cortisol levels were also measured. Whole-body IL-6 production was calculated by a deconvolution technique. Splenic IL-6 production in control dogs was measured from splenic blood flow and arteriovenous concentration differences. Endotoxin levels were higher in splenectomized dogs (P < 0.05) because of a decreased distribution volume (P < 0.05) and decreased clearance of endotoxin (P < 0.05). Endotoxin-induced plasma IL-6 levels were decreased by approximately 75% in splenectomized dogs (P < 0.01), and whole-body IL-6 production rates were severalfold lower (median of 8.7 mg/4 h and range of 3.9 to 11.4 mg/4 h versus a median of 32.3 mg/4 h and a range of 22.7 to 70.2 mg/4 h) (P < 0.05). However, in control dogs splenic IL-6 production (0.6 +/- 0.2 mg/4 h) was only approximately 2% of whole-body IL-6 production. Plasma TNF levels increased in both groups (P < 0.01) but were not different between the groups. Plasma cortisol levels were slightly higher in splenectomized dogs than in control dogs (P < 0.05). In conclusion, splenectomy decreases the distribution volume and clearance rate of endotoxin. Splenectomy results in decreased endotoxin-induced IL-6 production, which is caused not by the absence of splenic IL-6 production, but by a decrease in nonsplenic IL-6 production. Therefore, the spleen is an important mediator in the complete activation of nonsplenic IL-6 production by endotoxin.

Interleukin-6: structure-function relationships

Interleukin-6 (IL-6) is a multifunctional cytokine that plays a central role in host defense due to its wide range of immune and hematopoietic activities and its potent ability to induce the acute phase response. Overexpression of IL-6 has been implicated in the pathology of a number of diseases including multiple myeloma, rheumatoid arthritis, Castleman's disease, psoriasis, and post-menopausal osteoporosis. Hence, selective antagonists of IL-6 action may offer therapeutic benefits. IL-6 is a member of the family of cytokines that includes interleukin-11, leukemia inhibitory factor, oncostatin M, cardiotrophin-1, and ciliary neurotrophic factor. Like the other members of this family, IL-6 induces growth or differentiation via a receptor-system that involves a specific receptor and the use of a shared signaling subunit, gp130. Identification of the regions of IL-6 that are involved in the interactions with the IL-6 receptor, and gp130 is an important first step in the rational manipulation of the effects of this cytokine for therapeutic benefit. In this review, we focus on the sites on IL-6 which interact with its low-affinity specific receptor, the IL-6 receptor, and the high-affinity converter gp130. A tentative model for the IL-6 hexameric receptor ligand complex is presented and discussed with respect to the mechanism of action of the other members of the IL-6 family of cytokines.

Characterization of early cytokine responses and an interleukin (IL)-6-dependent pathway of endogenous glucocorticoid induction during murine cytomegalovirus infection

Early infection with murine cytomegalovirus (MCMV) induces circulating levels of interleukin (IL)-12, interferon (IFN)-gamma, and tumor necrosis factor (TNF). Studies presented here further characterize these responses by defining kinetics and extending evaluation to include IL-1, IL-6, and glucocorticoids. IL-12 p40, IFN-gamma, TNF, IL-1alpha, and IL-6 were shown to be increased, but IL-1beta was undetectable, in serum of MCMV-infected mice. The IL-12 p40, IFN-gamma, TNF, and IL-6 responses were dramatic with peak levels reaching >150-10,000 pg/ml at 32-40 h after infection and rapidly declining thereafter. Glucocorticoid induction, peaking at 36 h and reaching 30-fold increases above control values, accompanied the cytokine responses. Mice with cytokine deficiencies or neutralized cytokine function demonstrated that IL-6 was the pivotal mediator of the glucocorticoid response, with IL-1 contributing to IL-6 production. The IL-6 requirement appeared to be specific for virus-type stimuli as the synthetic analogue of viral nucleic acid, polyinosinic-polycytidylic acid, also induced IL-6-dependent glucocorticoid release, but treatments with the bacterial product lipopolysaccharide and a non-immune physical restraint stressor elicited IL-6-independent responses. Collectively, the results identify IL-6 as a primary mediator of glucocorticoid induction, and elucidate specific pathways of interactions between immune and neuroendocrine systems during viral infection.

Impact of knockout mice in toxicology

Knockout mice obtained by homologous recombination technology may be valuable tools for in vivo investigations in toxicopathogenesis. A short review is given on the phenotype of mice with distinct deletions of cytokines and related genes. The application of these mice in pharmacological and toxicological research is discussed, with emphasis in endotoxic shock, hepatic toxicity, and myelotoxicity. The use of such knockout mice will be valuable for mechanistic studies in toxicology.

Cytokines and the hepatic acute phase response

The acute phase response is an orchestrated response to tissue injury, infection or inflammation. A prominent feature of this response is the induction of acute phase proteins, which are involved in the restoration of homeostasis. Cytokines are important mediators of the acute phase response. Uncontrolled and prolonged action of cytokines is potentially harmful, therefore mechanisms exist which limit the activity of cytokines; these include soluble cytokine receptors and receptor antagonists. The cytokine signal is transmitted into the cell via membrane-bound receptors. Different intracellular signalling pathways are activated by different cytokine-receptor interactions. Eventually, cytokine-inducible transcription factors interact with their response elements in the promotor region of acute phase genes and transcription is induced. Systemic inflammation results in a systemic acute phase response. However, local inflammatory or injurious processes in the liver may also induce an acute phase response, for example after partial hepatectomy and during hepatic fibrosis. The acute phase proteins induced in these conditions probably act to limit proteolytic and/or fibrogenic activity and tissue damage. The possible function of the acute phase protein alpha 2-macroglobulin in hepatic fibrosis is discussed in some detail.

Role of IL-6 and its soluble receptor in induction of chemokines and leukocyte recruitment

IL-6-/- mice showed impaired leukocyte accumulation in subcutaneous air pouches. Defective leukocyte accumulation was not due to a reduced migratory capacity of IL-6-/- leukocytes and was associated with a reduced in situ production of chemokines. These observations led to a reexamination of the interaction of IL-6 with endothelial cells (EC). EC express only the gp130 signal transducing chain and not the subunit-specific IL-6R and are therefore unresponsive to IL-6. However, EC are responsive to a combination of IL-6 and soluble IL-6R as measured by the activation of STAT3, chemokine expression, and augmentation of ICAM-1. Activation by IL-6-IL-6R complexes was inhibited by an IL-6 receptor antagonist and potentiated by a superagonist. Hence, in vivo and in vitro evidence supports the concept that the IL-6 system plays an unexpected positive role in local inflammatory reactions by amplifying leukocyte recruitment.

Interleukin 6 causes growth impairment in transgenic mice through a decrease in insulin-like growth factor-I. A model for stunted growth in children with chronic inflammation

Stunted growth is a major complication of chronic inflammation and recurrent infections in children. Systemic juvenile rheumatoid arthritis is a chronic inflammatory disorder characterized by markedly elevated circulating levels of IL-6 and stunted growth. In this study we found that NSE/hIL-6 transgenic mouse lines expressing high levels of circulating IL-6 since early after birth presented a reduced growth rate that led to mice 50-70% the size of nontransgenic littermates. Administration of a monoclonal antibody to the murine IL-6 receptor partially reverted the growth defect. In NSE/hIL-6 transgenic mice, circulating IGF-I levels were significantly lower than those of nontransgenic littermates; on the contrary, the distribution of growth hormone pituitary cells, as well as circulating growth hormone levels, were normal. Treatment of nontransgenic mice of the same strain with IL-6 resulted in a significant decrease in IGF-I levels. Moreover, in patients with systemic juvenile rheumatoid arthritis, circulating IL-6 levels were negatively correlated with IGF-I levels. Our findings suggest that IL-6-mediated decrease in IGF-I production represents a major mechanism by which chronic inflammation affects growth.

Salmonella typhi stimulation of human intestinal epithelial cells induces secretion of epithelial cell-derived interleukin-6

Interleukin 6 (IL-6) is a multifunctional cytokine that has been shown to be associated with both systemic and tissue-specific responses within the host. Moreover, IL-6 is produced by both lymphoid and nonlymphoid cells and has been identified as a growth-inducing, growth-inhibiting, and differentiation-inducing factor for these cells. Recent studies of uropathogenic and upper respiratory pathogens have suggested that epithelial cell-derived IL-6 plays a role in mucosal host-parasite interactions. Since many mucosal enteric pathogens enter the host through the epithelial cells of the distal small intestine, a role for intestinal epithelial cell-derived IL-6 in the initial interaction between bacteria and host might also be predicted. However, no studies to date have determined whether the interaction of any bacteria with the epithelial cells that line the small intestine of the host can induce IL-6. To address this issue, we have established an in vitro model to evaluate the capacity of the gram-negative bacterium Salmonella typhi to induce IL-6 in the small intestine epithelial cell line Int407 and in other intestinal epithelial cell lines. The results demonstrate that both wild-type and live, attenuated S. typhi vaccine strains induce small and large intestine epithelial cells to secrete IL-6, and kinetic analysis suggests that IL-6 may be one of the earliest responses following adherence and invasion of enteric organisms. Thus, these studies suggest a physiologic role for epithelial cell-derived IL-6 in the initial interactions between host and bacterium in the small intestine.

Acute phase proteins and transformed cells

Acute phase proteins (APP) are plasma proteins whose concentration and glycosylation alters in response to tissue injury, inflammation, or tumor growth. Significant interspecies and sex differences in APP response exist. APP are produced mainly by hepatocytes, and their synthesis and glycosylation are controlled by a network consisting of cytokines, their soluble receptors, and glucocorticoids. The major cytokines involved in these processes belong to a group of interleukin-6-type cytokines that act through the hematopoietin receptor complex on hepatocytes and JAK-STAT signal transduction pathway. Transformed cells (hepatoma) display significant differences in synthesis of APP, cytokine responsiveness, expression of cytokine-receptor subunits and signal-transduction machinery. The most striking variability relates to the glycosylation alterations induced by cytokines. However, transformed cells (hepatoma) form a basic model for studying and understanding mechanisms controlling the synthesis and glycosylation of APP. Furthermore, APP may be secreted by transformed (tumor) cells of various origins and may display a growth factor-like function in certain cancer types.

Cardiotrophin-1 inhibits tumor necrosis factor production in the heart and serum of lipopolysaccharide-treated mice and in vitro in mouse blood cells

Cardiotrophin-1 (CT-1) is a member of the gp130 family of cytokines that includes interleukin-6, interleukin-11, ciliary neurotrophic factor, leukemia inhibitory factor, and oncostatin M. As interleukin-6, leukemia inhibitory factor, and ciliary neurotrophic factor were previously reported to inhibit the production of tumor necrosis factor (TNF), we studied the effect of CT-1 on serum and heart TNF levels in mice treated with lipopolysaccharide (100 ng/mouse, iv). Co-treatment with CT-1 (5 micrograms/mouse intravenously) markedly inhibit TNF production both in serum and in the heart. The effect of CT-1 seems to be direct as it also inhibited TNF production when added to whole mouse blood cultured with lipopolysaccharide. Thus, CT-1 might play a protective role in some TNF-mediated diseases.

Estriol: a potent regulator of TNF and IL-6 expression in a murine model of endotoxemia

The increased incidence of autoimmune disease in premenopausal women suggests the involvement of sex steroids in the pathogenesis of these disease processes. The effects of estrogen on autoimmunity and inflammation may involve changes in the secretion of inflammatory mediators by mononuclear phagocytes. Estradiol, for example, has been reported to regulate TNF, IL-6, IL-1 and JE expression. In the present study the effects of the estrogen agonist, estriol, on cytokine expression have been investigated in mice administered a sublethal lipopolysaccharide, LPS, challenge. Pretreatment of mice with pharmacologic doses of estriol, 0.4-2 mg/kg, resulted in a significant increase in serum TNF levels in both control and autoimmune MRL/lpr mice, following LPS challenge. This increase in TNF over the placebo group was blocked by the estrogen antagonist tamoxifen. Estriol treated mice also exhibited a rapid elevation in serum IL-6 levels following LPS challenge with the peak increase occurring 1 hr post LPS. This contrasted with the placebo group in which maximal serum IL-6 levels were detected at 3 hrs post challenge. This shift in the kinetics of IL-6 increase by estriol was inhibited by tamoxifen. The estriol mediated effects of TNF and IL-6 serum levels were consistent with the changes in TNF and IL-6 mRNA observed ex vivo in elicited peritoneal macrophages. Macrophage cultures from estriol treated animals however, did not demonstrate significant differences from the placebo group for TNF or NO secretion following in vitro LPS challenge. These results suggest that the estrogen agonist estriol can have significant quantitative, TNF, and kinetic, IL-6, effects on inflammatory monokines produced in response to an endotoxin challenge.

Liver failure and defective hepatocyte regeneration in interleukin-6-deficient mice

Liver regeneration stimulated by a loss of liver mass leads to hepatocyte and nonparenchymal cell proliferation and rapid restoration of liver parenchyma. Mice with targeted disruption of the interleukin-6 (IL-6) gene had impaired liver regeneration characterized by liver necrosis and failure. There was a blunted DNA synthetic response in hepatocytes of these mice but not in nonparenchymal liver cells. Furthermore, there were discrete G1 phase (prereplicative stage in the cell cycle) abnormalities including absence of STAT3 (signal transducer and activator of transcription protein 3) activation and depressed AP-1, Myc, and cyclin D1 expression. Treatment of IL-6-deficient mice with a single preoperative dose of IL-6 returned STAT3 binding, gene expression, and hepatocyte proliferation to near normal and prevented liver damage, establishing that IL-6 is a critical component of the regenerative response.

Interleukin-6 in the injured patient. Marker of injury or mediator of inflammation?

OBJECTIVE

The effects of interleukin (IL)-6 in the injured patient are examined in an attempt to clarify the potential pathophysiologic role of IL-6 in the response to injury.

SUMMARY BACKGROUND DATA

Interleukin-6 is an integral cytokine mediator of the acute phase response to injury and infection. However, prolonged and excessive elevations of circulating IL-6 levels in patients after trauma, burns, and elective surgery have been associated with complications and mortality. The mechanistic role of IL-6 in mediating these effects is unclear.

METHODS

A review of current literature is performed to summarize the origins, mechanisms of action, and biologic effects of IL-6 and to characterize the IL-6 response to injury.

RESULTS

Interleukin-6 is a multifunctional cytokine expressed by a variety of cells after a multitude of stimuli, under complex regulatory control mechanisms. The IL-6 response to injury is uniquely consistent and related to the magnitude of the insult. Moreover, the early postinjury IL-6 response correlates with complications as well as mortality.

CONCLUSIONS

Interleukin-6 appears to play an active role in the postinjury immune response, making it an attractive therapeutic target in attempts to control hyperinflammatory provoked organ injury.

Inhibition of liver RNA breakdown during acute inflammation in the rat

Liver RNA- and protein-degradation rates were measured after the induction of acute inflammation in the rat. A preliminary study determined changes in hepatic RNA and protein content 12, 18 and 24 h after a turpentine oil injection. The RNA content in turpentine-treated rats compared with pair-fed animals increased significantly and sharply from 12 h (+ 11%) to 18 h (+ 32%) and slightly thereafter (+ 37% at 24 h). The liver protein content was significantly enhanced only at 24 h (+ 11%) in response to inflammation. RNA-degradation rates were determined in livers perfused cyclically in situ for 15 min by measuring the accumulation of radioactive cytidine in the medium 60 h after in vivo labelling of RNA by [5-3H]cytidine instead of [6-14C]orotic acid, the most commonly used radioactive marker. Several validation procedures showed that the method employed was a valid alternative to the use of radioactive orotic acid. RNA-degradation rates, which mainly reflect rRNA breakdown, were significantly lower in the turpentine-treated rats than in respective pair-fed animals at 18 and 24 h (57 and 45% decrease respectively). Proteolysis rates measured at 24 h together with RNA breakdown by valine accumulation in the perfusion medium were not modified after turpentine treatment. The main factors known to regulate RNA degradation (amino acids, insulin/glucagon ratio) were measured in the portal blood 24 h after induction of acute inflammation. Of the known regulatory amino acids, only glutamine and to a lesser extent methionine were increased in the turpentine-treated rats as compared with their pair-fed counterparts. The insulin/glucagon molar ratio was similar in both groups. In conclusion, the reduced breakdown of RNA, especially rRNA, is largely responsible for the accumulation of hepatic RNA during acute inflammation. This inhibition of RNA degradation could possibly be related to the increase in glutamine.

Interleukin-6 is required for a protective immune response to systemic Escherichia coli infection

Interleukin-6 (IL-6) is a multipotential cytokine detected in the serum of patients or experimental animals undergoing bacterial sepsis. To date, the role of IL-6 in gram-negative sepsis models has been controversial. We have used IL-6-deficient mice to investigate the role of IL-6 during virulent Escherichia coli infection and in lipopolysaccharide (LPS)-induced mortality. In this report we describe an increased susceptibility of IL-6-deficient mice to E. coli infection in terms of mortality and accumulation of viable bacteria in tissues, indicating a protective role for IL-6 during the immune response against E. coli. In contrast, mortality rates of IL-6-deficient mice and control animals undergoing LPS-induced shock did not differ, indicating that IL-6 was inconsequential for survival in this model. Furthermore, we have shown that neutrophils were crucial for resistance to E. coli in normal mice. IL-6-deficient mice were unable to efficiently induce neutrophilia in the bloodstream immediately following challenge with E. coli, in contrast to a characteristic neutrophilia induced in control animals. Prophylactic treatment of the mutant animals with recombinant IL-6 protein reverted both the deficit of neutrophilia and the accumulation of bacteria in tissues. These data clarify the role of IL-6 as protective in virulent E. coli infection and suggest that the protective effect may be at least partially mediated through neutrophils.

Impaired neutrophil response and CD4+ T helper cell 1 development in interleukin 6-deficient mice infected with Candida albicans

To define the role of interleukin (IL)6 in Candida albicans infection, IL-6 deficient mice were assessed for susceptibility to systemic or gastrointestinal infection, as well as for parameters of elicited T helper cell (Th) immunity. IL-6-deficient mice were more susceptible than wild-type mice to either type of infection caused by virulent C. albicans. In response to systemic challenge with a live vaccine strain of yeast, IL-6-deficient mice failed to mount Th1-associated protective immunity, but the resulting Th2-biased response could be redirected to the Th1 phenotype by IL-10 neutralization. Severe impairment of the macrophage and neutrophil response to infection was observed in IL-6-deficient mice, but administration of IL-6 would increase both neutrophil response and resistance to infection. IL-6 seems to oppose the Th2-promoting role of IL-10 in candidiasis, its early regulatory activity involving effects on neutrophil function.

Thymus-dependent effects of a traditional Chinese medicine, ren-shen-yang-rong-tang (Japanese name; Ninjin-youei-to), in autoimmune MRI/MP-lpr/lpr mice

Autoimmune MRL/lpr mice were i.p. treated with 200 mg/kg Ren-shen-yang-rong-tang (Japanese name: Ninjin-youei-to, NYT), a traditional Chinese herbal medicine (Japanese name: Kampo), from 8 weeks of age every 3 days before the onset of autoimmune disease Compared to age-matched control MRL/lpr mice, the serum IL-6 concentration in NYT-treated mice was decreased, their serum IFN-gamma concentration was increased, and the proliferative responses of whole and enriched CD4+ cells in their spleen and lymph nodes stimulated with ConA in vitro were restored. FACS analysis revealed that the rate of decreased CD4+CD8+ T-cell population in the thymus was decreased in MRL/lpr mice but recovered by NYT treatment. Further, adult thymectomized (ATX) MRL/lpr mice were treated with 200 mg/kg NYT similarly. NYT treatment prolonged the survival of sham-operated MRL/lpr mice and ameliorated their proteinuria but did not improve such autoimmune manifestations in ATX-MRL/lpr mice. These findings suggest that NYT plays an important role in the abrogation of autoimmune-prone T cell differentiation and that the therapeutic effect of NYT is dependent on the thymus in MRL/lpr mice.

Trace metal, acute phase and metabolic response to endotoxin in metallothionein-null mice

Accumulation of hepatic zinc via metallothionein (MT) induction during infection/inflammation is postulated to benefit a range of metabolic processes. The metabolic consequences of two doses of endotoxin (LPS) (1 and 5 mg/kg, intraperitoneally) were examined in normal (MT+/+) and MT-null (MT-/-) mice (all results means =/- S.E.M., n=6). At 16 h after 1 mg/kg LPS, hypozincaemia was pronounced in the MT+/+ mice (4.4+/-0.2 microM), concomitant with a 36% increase in hepatic Zn and a > 10-fold increase in hepatic MT. Plasma Zn (16.6+/-0.7 microM) and total hepatic Zn were unchanged in MT -/- mice, confirming the importance of MT in altering plasma and hepatic Zn during inflammation. Plasma iron was lower in LPS-treated MT-/- mice, whereas plasma copper increased to a similar extent in both groups of mice. Plasma fibrinogen more than doubled, and was similar in both groups of mice, which questions the importance of MT in acute-phase protein synthesis. Blood and liver glucose concentrations were not significantly different between groups before or after LPS, whereas blood and liver lactate concentrations were significantly lower (31% and 24% respectively) in MT-/- mice after LPS. At 16 h after 5 mg/kg LPS, plasma Zn was decreased even further in MT+/+ mice (2.6+/-0.3 microM), but remained unchanged in MT-/- mice at concentrations significantly above those in 16-h fasted MT-/- mice (15.8+/-0.5 versus 11.3+/-0.3 microM). Total liver Zn was 17% lower than fasting values in MT-/- mice, in contrast with 32% higher in MT+/+ mice. Synthesis of MT (in MT+/+ mice) and fibrinogen in all mice was not further enhanced by the higher LPS dose. Blood glucose was significantly decreased by 18% in MT+/+ mice and by 38% in MT-/- mice after 5 mg/kg LPS. There was a marked 44% decrease in liver glucose in MT-/- mice; that in MT+/+ mice was unchanged from fasting levels, implying a deficit in hepatic gluconeogenesis in LPS-treated MT-/- mice. In the absence of any indication of major hepatotoxicity, the results of this study indicate that energy production, and not acute-phase protein synthesis, may be most influenced by Zn supply during endotoxaemia, suggesting that MT has a role in maintaining hepatic and blood glucose in this metabolic setting.

Epidermal cytokine and neuronal peptide modulation of contact hypersensitivity reactions

Cellular and molecular mechanisms underlying contact hypersensitivity reactions have been, and still are, fields under intense investigation, not only for the importance of these reactions in clinical medicine, but also because they are considered prototypic of a vast group of T cell-mediated immune diseases of the skin. Interestingly, potent contributions by non-bone marrow-derived cells have been shown clearly, demonstrating that epidermal cells are far more than mere spectators of these reactions, and undergo a functional activation after contact with the hapten causing the hypersensitivity reaction. In particular, keratinocyte contribution to the onset as well as modulation of contact hypersensitivity reactions through the release of a plethora of cytokines, has been widely documented. Moreover, an important control over these reactions is exerted by local release of neuropeptides by nerve endings. This review paper focuses on epidermal cytokine and neuronal peptide modulation of contact hypersensitivity reactions, trying to document the complexity of the regulatory systems, active during these immune processes of the skin.

In vivo role of IL-6 on the viral load and on immunological abnormalities of HIV-infected patients

In vitro experiments have suggested that interleukin (IL)-6 may contribute to human immunodeficiency virus (HIV) burden and to immunological abnormalities in HIV-infected patients. We had the opportunity to directly address this question in vivo through the virological and immunological monitoring of HIV-infected patients treated with an anti-IL-6 monoclonal antibody (mAb) for a lymphoma (ANRS 018 trial). Sixteen courses of anti-IL-6 mAb administration, performed in 11 patients, were studied. All patients were at a late stage of HIV infection. The HIV load and the immunological status were determined at the initiation of each course and at its end, 21 days later. The mAb induced no significant change of HIV load, as evaluated by p24 antigenemia, plasma viremia, and quantification of circulating HIV RNA by reverse transcriptase-polymerase chain reaction and branched DNA techniques. The anti-IL-6 mAb also did not affect CD4+, CD8+, and CD19+ circulating cell counts, nor the serum concentrations of sIL-2R and of sCD8. In contrast, the mAb completely abrogated acute-phase reaction, as demonstrated by the normalization of C-reactive protein and fibrinogen circulating levels (p = 0.013 and p = 0.008, respectively). It increased serum albumin concentration. The latter effect was restricted to patients with a spontaneously low albuminemia (p = 0.01). It decreased B-lymphocyte hyperactivity, as reflected by decreased IgG and IgA serum levels (p = 0.008 and p < 0.001, respectively), and by a decreased production of IgG in vitro (p = 0.017). In contrast, the IgM hyperproduction was not affected by the mAb. Therefore, increased IL-6 production in HIV-infected patients at a late stage of the infection may not stimulate HIV replication in vivo, but it may represent a key mechanism contributing to the metabolic and immunological dysbalance of the disease.

Interleukin (IL)-6 gene expression in the central nervous system is necessary for fever response to lipopolysaccharide or IL-1 beta: a study on IL-6-deficient mice

Interleukin (IL)-6, IL-1 beta, and tumor necrosis factor alpha (TNF-alpha) are considered to act as endogenous pyrogens. Because of the complex pattern of cross-inductions between these cytokines, the relative role of the central and peripheral production of these cytokines in eliciting the fever response has not yet been clarified. The purpose of this study was to determine the role of IL-6 in the fever response by making use of mice carrying a null mutation in the IL-6 gene. The intraperitoneal injections of lipopolysaccharide (LPS) (50 micrograms/kg) and recombinant murine (rm) IL-1 beta (10 micrograms/kg), respectively, failed to evoke fever response in IL-6-deficient mice, whereas the same doses of LPS and rmIL-1 beta caused fever response in wild-type mice. The fever response could be induced in the IL-6-deficient mice by intracerebroventricular injection of recombinant human (rh) IL-6 (500 ng/mouse), whereas intracerebroventricular injection of rmIL-1 beta (100 ng/mouse) failed to produce fever response in the IL-6-deficient mice. These results suggest that central IL-6 is a necessary component of the fever response to both endogenous (IL-1 beta) and exogenous (LPS) pyrogens in mice and that IL-6 acts downstream from both peripheral and central IL-1 beta.

Role of proinflammatory cytokines in a toxic response: application of cytokine knockout mice in toxicological research

The toxic effect of xenobiotics may be direct or mediated through the release of secondary toxic mediators such as proinflammatory cytokines. Knockout mice (KO or -/-) with discrete gene deletions obtained by homologous recombination may prove the function of a given cytokine in general and in toxico-pathogenesis. The technology is briefly described, and a short review of the phenotype of mice with deletions of several proinflammatory cytokines is given. The emphasis of this presentation is on the role of tumor necrosis factor, interleukins and interferon-gamma in endotoxic shock and acute phase response. The future application of these mice for mechanistic studies in toxicological research is discussed.

The acute phase protein response in patients receiving subcutaneous IL-6

IL-6, tumour necrosis factor-alpha (TNF-alpha) and IL-1 are thought to be the key mediators of the acute phase response although much of the evidence is based on in vitro studies. It is not clear to what extent each of the acute phase proteins are regulated in vivo by each of these cytokines. The aim of this study was to examine the effects of IL-6 treatment in eight patients with cancer on the concentrations of an extensive range of positive and negative acute phase proteins. It was part of a larger investigation to assess the value of IL-6 in the management of chemotherapy-induced thrombocytopenia. IL-6 was administered by a daily subcutaneous injection for 7 days at a dose level of 1, 3, or 10 micrograms/kg/day. Increases in the positive acute phase proteins, serum amyloid A, C-reactive protein, alpha 1-acid glycoprotein, alpha 1-antichymotrypsin, haptoglobin, alpha 1-antitrypsin, fibrinogen, complement component C3, and caeruloplasmin, were observed, with the greatest incremental changes and fastest responses being seen for C-reactive protein and serum amyloid A protein. The negative acute phase proteins transferrin, transthyretin and retinol binding protein all fell to a nadir within 48-96 h after the first IL-6 injection. Increases in complement component C4 were only found in two patients, which may be related to the increase in circulating TNF-alpha concentrations found only in these patients. This study has therefore shown that IL-6 is capable of causing changes in the majority of acute phase proteins in vivo. Although secondary induction of TNF-alpha was not observed in the majority of patients examined, it is still possible however that other cytokines involved in regulation of the acute phase response, such as IL-1, may have been induced and contributed to the overall response.

In vivo modulation of murine serum tumour necrosis factor and interleukin-6 levels during endotoxemia by oestrogen agonists and antagonists

Oestrogen has been reported to modulate tumour necrosis factor (TNF), interleukin (IL)-1 and IL-6 cytokine levels in human mononuclear cell cultures. In the present study, the effects of exogenous oestrogen administration on the cytokine response to an endotoxin challenge was investigated in a murine model of endotoxemia. Animals pretreated for 4 days with 17 alpha ethinyl oestradiol exhibited divergent regulation of TNF and IL-6 levels in sera from endotoxin-stimulated mice. Oestrogen treatment resulted in a significant increase in serum TNF while serum IL-6 levels, relative to the placebo group, decreased in response to an endotoxin challenge. These oestrogenic effects were dose dependent with maximal elevations observed in TNF at 1 mg/kg and maximal reduction in IL-6 at 0.1 mg/kg of 17 alpha ethinyl oestradiol. The increase in TNF levels by ethinyl oestradiol was blocked by co-administration of the oestrogen receptor antagonist tamoxifen. Oestrogen-mediated modulation of the TNF and IL-6 response to endotoxin was also apparent in animals implanted with 17 beta oestradiol pellets. The oestrogen-mediated effects on serum IL-6 were consistent with a reduction in IL-6 mRNA in peritoneal macrophages from oestrogen-treated mice. The effects of oestrogen on TNF and IL-6 production were also investigated in vitro. Oestradiol-treated macrophage cultures produced three- to fourfold lower amounts of IL-6 without any significant modulatory effects on TNF secretion. The combined in vivo and in vitro results demonstrate the modulation of IL-6 and TNF during endotoxemia by oestrogen analogues through an oestrogen receptor-dependent mechanism.

Ciliary neurotrophic factor inhibits brain and peripheral tumor necrosis factor production and, when coadministered with its soluble receptor, protects mice from lipopolysaccharide toxicity

BACKGROUND

The receptor of ciliary neurotrophic factor (CNTF) contains the signal transduction protein gp130, which is also a component of the receptors of cytokines such as interleukin (IL)-6, leukemia-inhibitory factor (LIF), IL-11, and oncostatin M. This suggests that these cytokines might share common signaling pathways. We previously reported that CNTF augments the levels of corticosterone (CS) and of IL-6 induced by IL-1 and induces the production of the acute-phase protein serum amyloid A (SAA). Since the elevation of serum CS is an important feedback mechanism to limit the synthesis of proinflammatory cytokines, particularly tumor necrosis factor (TNF), we have investigated the effect of CNTF on both TNF production and lipopolysaccharide (LPS) toxicity.

MATERIALS AND METHODS

To induce serum TNF levels, LPS was administered to mice at 30 mg/kg i.p. and CNTF was administered as a single dose of 10 micrograms/mouse i.v., either alone or in combination with its soluble receptor sCNTFR alpha at 20 micrograms/mouse. Serum TNF levels were the measured by cytotoxicity on L929 cells. In order to measure the effects of CNTF on LPS-induced TNF production in the brain, mice were injected intracerebroventricularly (i.c.v.) with 2.5 micrograms/kg LPS. Mouse spleen cells cultured for 4 hr with 1 microgram LPS/ml, with or without 10 micrograms CNTF/ml, were also analyzed for TNF production.

RESULTS

CNTF, administered either alone or in combination with its soluble receptor, inhibited the induction of serum TNF levels by LPS. This inhibition was also observed in the brain when CNTF and LPS were administered centrally. In vitro, CNTF only marginally affected TNF production by LPS-stimulated mouse splenocytes, but it acted synergistically with dexamethasone (DEX) in inhibiting TNF production. Most importantly, CNTF administered together with sCNTFR alpha protected mice against LPS-induced mortality.

CONCLUSIONS

These data suggest that CNTF might act as a protective cytokine against TNF-mediated pathologies both in the brain and in the periphery.

Resistance to fever induction and impaired acute-phase response in interleukin-1 beta-deficient mice

We used gene targeting in embryonic stem cells to introduce an IL-1 beta null allele in mice. The IL-1 beta-deficient mice develop normally and are apparently healthy and fertile. The IL-1 beta null mice responded normally in models of contact and delayed-type hypersensitivity or following bacterial endotoxin LPS-induced inflammation. The IL-1 beta-deficient mice showed equivalent resistance to Listeria monocytogenes compared with wild-type controls. In contrast, when challenged with turpentine, which causes localized inflammation and tissue injury, the IL-1 beta mutant mice exhibited an impaired acute-phase inflammatory response and were completely resistant to fever development and anorexia. These results highlight a central role for IL-1 beta as a pyrogen and a mediator of the acute-phase response in a subset of inflammatory disease models, and support the notion that blocking the action of a single key cytokine can alter the course of specific immune and inflammatory responses.