Isolation and characterization of biologically active murine interleukin-6 produced in Escherichia coli

Interleukin-6 in Siberian sturgeon (Acipenser baeri): Molecular characterization and immune functional activity

Interleukin-6 (IL-6) is a pleiotropic cytokine with crucial immunoregulatory functions in both innate and adaptive immune responses. However, the IL-6 sequence and function remain unknown in sturgeon, one chondrostean fish. In the present study, we identified an interleukin-6 homolog from Siberian sturgeon (Acipenser baeri), named AbIL-6. Its open reading frame (ORF) was 657 nucleotides in length, encoding a polypeptide of 218 amino acids, which contains a signal peptide and the IL-6 family domain. Phylogenetic analysis showed that sturgeon IL-6 had close relationship with both teleost and chondrichthyes IL-6s. Abil-6 mRNA was highly expressed in spleen, brain and liver tissues of healthy sturgeon, and significantly up-regulated in the spleen, head kidney and liver by A.hydrophila (A.h) challenge. Heat-killed A.h and LPS effectively stimulated Abil-6 transcripts in primary spleen cells in vitro. In order to understand the bioactivity and influence of AbIL-6 on immune responses, recombinant AbIL-6 (rAbIL-6) was synthesized by prokaryotes and demonstrated to promote the proliferation of spleen cells and head kidney cells in vitro. Additionally, intraperitoneal injection of rAbIL-6 induced significantly higher expression of four immuno-related genes including il-1β, cxcl10, mhcIIβ and igm. rAbIL-6 improved the survival rate and reduced the tissue bacterial load after A.h infection. Taken together, these results suggest that AbIL-6 plays an important role in inflammatory responses and immune defense against bacterial infection of sturgeon.

Expression Dynamics of Innate Immunity in Influenza Virus-Infected Swine

The current circulating swine influenza virus (IV) subtypes in Europe (H1N1, H1N2, and H3N2) are associated with clinical outbreaks of disease. However, we showed that pigs could be susceptible to other IV strains that are able to cross the species barrier. In this work, we extended our investigations into whether different IV strains able to cross the species barrier might give rise to different innate immune responses that could be associated with pathological lesions. For this purpose, we used the same samples collected in a previous study of ours, in which healthy pigs had been infected with a H3N2 Swine IV and four different H3N8 IV strains circulating in different animal species. Pigs had been clinically inspected and four subjects/group were sacrificed at 3, 6, and 21 days post infection. In the present study, all groups but mock exhibited antibody responses to IV nucleoprotein protein. Pulmonary lesions and high-titered viral replication were observed in pigs infected with the swine-adapted virus. Interestingly, pigs infected with avian and seal H3N8 strains also showed moderate lesions and viral replication, whereas equine and canine IVs did not cause overt pathological signs, and replication was barely detectable. Swine IV infection induced interferon (IFN)-alpha and interleukin-6 responses in bronchoalveolar fluids (BALF) at day 3 post infection, as opposed to the other non-swine-adapted virus strains. However, IFN-alpha responses to the swine-adapted virus were not associated with an increase of the local, constitutive expression of IFN-alpha genes. Remarkably, the Equine strain gave rise to a Serum Amyloid A response in BALF despite little if any replication. Each virus strain could be associated with expression of cytokine genes and/or proteins after infection. These responses were observed well beyond the period of virus replication, suggesting a prolonged homeostatic imbalance of the innate immune system.

Innate immune responses of young bulls to a novel environment

Animal welfare during transportation has been investigated in several studies, as opposed to post-transportation phases. In this study, we evaluated the effect of a novel environment after transportation on 26 Friesian bulls, 242 ± 42 day-old, from ten different dairy farms. Animals were shipped to a breeding center in different seasons, and selected parameters of innate immunity (serum bactericidal activity, hemolytic complement, serum albumin, α, β, and γ-globulins, interleukin-6, TNF-α) were monitored before and after the arrival at days--4/0/4/15/30. Our results showed significant differences of IL-6 and TNF-α protein levels at destination in December (94 ± 1.3 pg/ml) and June (+788 pg/ml), respectively. Moreover, the serum levels of these cytokines increased between days 0 and 15 after the arrival, the modulation of IL-6 being in agreement with established models of physical and/or psychological stress. Concerning the modulation of albumin, alpha and beta-globulins, the highest levels were detected in April, whereas a significant decrease was observed between day 15 and 30 after arrival; on the contrary, γ-globulin levels significantly increased after day 15. The results of this study highlight the occurrence of innate immune responses of young bulls to the combined effects of climate (season) and novel farming conditions.

IPEC-J2 cells as reporter system of the anti-inflammatory control actions of interferon-alpha

Interferon-alpha (IFN-α) shows potent immunomodulatory properties, which underlies its use for low-dose oral treatments of diverse viral infections and immunopathological conditions. The studies on oral administration have been hampered by the lack of recognized in vitro models, reproducing the in vivo control action of IFN-α over inflammatory cytokine responses. Owing to these reasons, the aim of our study was to validate IPEC-J2 (a continuous cell line of porcine intestinal epithelial cells) as a reporter system of the properties of IFN-α. Three different experimental conditions (oxidative stress, inflammatory response, and amplification of lymphoid cell signals) were selected to evaluate the effects of porcine recombinant IFN-α1 (rIFN-α) and 2 natural porcine IFN-α preparations (nIFN-α). The IFNs under study showed significantly different control actions in IPEC-J2 cells. In particular, rIFN-α was shown to down-regulate interleukin (IL)-8, IL-1β, tumor necrosis factor (TNF)-α, and β-defensin 1 genes either directly, or indirectly through second messengers released by IFN-α-treated lymphoid cells. With regard to IL-6, only second messengers from IFN-α-treated lymphoid cells could regulate the expression of this cytokine. Our results suggest that IPEC-J2 cells can be a useful tool for investigating the regulatory actions of type I IFNs and the second messengers thereof. The results provided by this model could be conveniently exploited in studies on enteric diseases sustained by infectious or noninfectious stressors.

Concordant and discordant interleukin-1-mediated signaling in lung fibroblast thy-1 subpopulations

Following lung injury or inflammation, fibroblasts mediate either restorative repair or disordered remodeling. Interleukin (IL)-1beta is a key mediator in the transition from injury/inflammation to tissue remodeling, in part through its regulation of platelet-derived growth factor alpha receptor (PDGFalphaR). Based on prior demonstration of differential PDGFalphaR expression, we hypothesized that subpopulations of fibroblasts would have heterogeneous responses to IL-1. We report that IL-1beta significantly increases expression of PDGFalphaR in Thy-1-, but not Thy-1+ fibroblasts. Higher baseline expression of PDGFalphaR in Thy-1- fibroblasts is partially abrogated by IL-1 receptor antagonist. There are no differences in IL-1beta binding, as determined by flow cytometry, or in the presence of the type I IL-1 receptor (IL-1RtI) or its associated protein (IL-1RacP) by immunoblotting. IL-1beta induces DNA binding of both nuclear factor kappaB (NF-kappaB) and CAATT-enhancer binding protein (C/EBP), and activation of p38 mitogen-activated protein kinase in both subpopulations. However, IL-1beta-induced proliferation and expression of IL-6 are significantly higher in Thy-1- fibroblasts. Heterogeneous responses to IL-1beta despite equivalent presence of both proximal and distal signaling components indicates that parallel signaling pathways are activated selectively in Thy-1- cells, suggesting a prominent role for this subset in the transition from inflammation to lung remodeling.

Interleukin 1β inhibits interleukin 6–mediated rat γ fibrinogen gene expression

Interleukin (IL)-1β and IL-6 are the 2 major inducers of a group of hepatic genes during acute inflammation; however, each cytokine uses different intracellular signaling molecules. In most instances, the 2 cytokines interact positively to enhance hepatic gene expression, but in one class of acute-phase reactants, which includes fibrinogen, IL-1β exerts a transient inhibitory effect over the IL-6 stimulatory signal. This study explored the effects of IL-1β/nuclear factor κB (NF-κB) and IL-6/signal transducer and activator of transcription 3 (STAT3) combinatory signaling on the transcriptional regulation of the rat γ fibrinogen gene. Northern blot and functional analyses employing luciferase reporter constructs driven by the rat γ fibrinogen promoter demonstrated that IL-1β inhibited the IL-6-mediated transcription of this gene. Exposing primary rat hepatocytes to IL-1β had no effect on IL-6-mediated STAT3 activation; instead, IL-1β-activated NF-κB associated with 2 IL-6 responsive elements (STAT3 binding site) on the rat γ fibrinogen promoter and blocked STAT3 binding to these regions. The competitive binding of NF-κB and STAT3 on the overlapping binding site provides a mechanism for the inhibition by IL-1β of the IL-6-mediated transactivation of rat γ fibrinogen.

Interleukin 1β inhibits interleukin 6–mediated rat γ fibrinogen gene expression

Interleukin (IL)-1β and IL-6 are the 2 major inducers of a group of hepatic genes during acute inflammation; however, each cytokine uses different intracellular signaling molecules. In most instances, the 2 cytokines interact positively to enhance hepatic gene expression, but in one class of acute-phase reactants, which includes fibrinogen, IL-1β exerts a transient inhibitory effect over the IL-6 stimulatory signal. This study explored the effects of IL-1β/nuclear factor κB (NF-κB) and IL-6/signal transducer and activator of transcription 3 (STAT3) combinatory signaling on the transcriptional regulation of the rat γ fibrinogen gene. Northern blot and functional analyses employing luciferase reporter constructs driven by the rat γ fibrinogen promoter demonstrated that IL-1β inhibited the IL-6-mediated transcription of this gene. Exposing primary rat hepatocytes to IL-1β had no effect on IL-6-mediated STAT3 activation; instead, IL-1β-activated NF-κB associated with 2 IL-6 responsive elements (STAT3 binding site) on the rat γ fibrinogen promoter and blocked STAT3 binding to these regions. The competitive binding of NF-κB and STAT3 on the overlapping binding site provides a mechanism for the inhibition by IL-1β of the IL-6-mediated transactivation of rat γ fibrinogen.

Expression of the interleukin-6 gene is constitutive and not regulated by estrogen in rat vascular smooth muscle cells in culture

Vascular smooth muscle cells (SMC) are major constituents of the medial layer of blood vessels and are involved in the development of atherosclerotic plaque. SMC secrete copious IL-6 under basal conditions that can be increased by cytokines such as tumor necrosis factor-alpha and interleukin-1beta (IL-1beta). The goal of our studies was to define the role of estrogen in IL-6 production by SMC. In a first series of experiments, the expression of specific messenger RNAs as well as the production of IL-6 bioactivity by rat SMC in culture could be demonstrated in basal and IL-1-stimulated conditions, but was unaffected by estrogen treatment. Different constructs containing deleted or mutated fragments of the human IL-6 promoter driving luciferase or chloramphenicol acetyltransferase reporter gene were then transiently transfected in these cells. A significant basal activity that was increased 2- to 4-fold after IL-1beta stimulation was observed with the total IL-6 promoter. Deletion analysis indicated that the -158/+11 region containing activator protein-1 and cAMP response element sites was apparently the minimal region of IL-6 promoter to confer both constitutive and IL-1-inducible activities. Site-directed mutagenesis experiments suggest that basal activity is dependent upon the promoter sequence -158 to -112 containing the nuclear factor (NF)-IL6(-153) and Sp1 sites, whereas IL-1beta stimulation would depend on the residual -112 nucleotides containing NF-IL6(-75) and NF-kappaB sites. In contrast to the down-regulation of IL-6 expression by estrogen described in osteoblasts, ethinyl estradiol as well as 17beta-estradiol did not influence stimulated IL-6 activity in our experimental conditions whatever the construct tested, even when either estrogen receptor alpha or beta was overexpressed. Thus, the atheroprotective properties of estrogen are probably not mediated through the regulation of IL-6 production by SMC.

Inhibition of nuclear factor kappa B attenuates proinflammatory cytokine and inducible nitric-oxide synthase expression in postischemic myocardium

We have previously reported that induction of nuclear factor-kappa B (NF-kappa B) occurs in a biphasic manner in postischemic myocardium. Because interleukin-1 (IL-1), IL-6, tumor necrosis factor-alpha (TNF-alpha), and inducible nitric-oxide synthase (iNOS) contain kappa B-response elements, and since transforming growth factor-beta 1 (TGF-beta 1) down-modulates both cytokine and iNOS expression, we studied their temporal expression during myocardial ischemia/reperfusion (I/R). Northern and Western analyses showed low levels of IL-6 and no signal for IL-1 beta, TNF-alpha and iNOS under basal conditions. Their expression rose significantly over sham-operated controls by 1 h reperfusion, and persisted high for various periods. Under basal conditions, low levels of TGF-beta 1 were detected, which rose significantly at 3 h reperfusion, and remained high until 24 h reperfusion. Administration of diethyldithiocarbamate (DDC) inhibited induction of NF-kappa B and concomitantly the expression of IL-1 beta, IL-6, TNF-alpha as well as iNOS. However, expression of TGF-beta was not altered. Our results indicate that ischemia/reperfusion induces NF-kappa B, and upregulates kappa B-response genes. Administration of DDC inhibits NF-kappa B levels, and attenuates expression of inflammatory cytokines and iNOS.

The competitive binding of STAT3 and NF-kappaB on an overlapping DNA binding site

Interleukin-1 (IL-1) and interleukin-6 (IL-6), two early-response cytokines expressed during an acute inflammatory reaction, regulate the expression of several acute phase proteins (APP) in the liver. IL-1 relays its signal to specific genes via NF-kappaB, whereas IL-6 sends its signal to the nucleus via STAT1alpha and STAT3. Interestingly, overlapping binding sites for STAT3 and NF-kappaB can be found on promoters of several APP genes. We show here that both STAT3 and NF-kappaB are active during inflammation and are capable of binding to a STAT3/NF-kappaB overlapping DNA motif derived from the alpha2-macroglobulin gene promoter. In vitro binding assays demonstrated that NF-kappaB competes with STAT3 binding on this probe. Our results suggest that these transcription factors regulate each others' function through competition for overlapping DNA binding sites.

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 the IL-6 responsive elements in the gamma fibrinogen gene promoter

Fibrinogen, a hepatically derived class II acute phase protein, is the product of three separate genes, (A alpha, B beta, and gamma). The fibrinogen genes are expressed constitutively; however, their transcription can be significantly up-regulated by interleukin-6 (IL-6) and glucocorticoid. Inspection of the promoter region of the fibrinogen gamma gene revealed three hexanucleotide clusters of CTGGGA that are recognized as class II IL-6 responsive elements. Functional analyses of these regions (designated here as site I, site II, and site III according to their position in the promoter) were performed using luciferase reporter constructs and show a hierarchy of IL-6 response in which site II was the preferred functional site, site I was the next important site, and site III was the site least responsive to IL-6. Gel mobility shift assays using 25-base pair oligonucleotide probes derived from these three regions with the CTGGGA positioned in the middle and nuclear extracts from IL-6-treated primary hepatocytes reveal the presence of IL-6-induced high molecular weight complexes appearing 5 min after cytokine treatment. Supershift assays using anti-Stat3 antibody indicate that Stat3 is part of the IL-6-induced complex formed on the three gamma chain probes. The binding of Stat3 to the IL-6 responsive elements of the gamma probes is significantly weaker than to an alpha 2-macroglobulin probe. These findings show for the first time that Stat3 is involved in associating with the IL-6 responsive elements of fibrinogen gamma chain, a class II acute phase gene other than alpha 2-macroglobulin.

Induction of interleukin 6 (IL-6) by hypoxia in vascular cells. Central role of the binding site for nuclear factor-IL-6

The pathologic picture in ischemic tissue injury shares features with the inflammatory response, including production of proinflammatory cytokines. Hypoxia-mediated induction of interleukin-6 (IL-6), a cytokine with anti-inflammatory properties, could set in motion mechanisms limiting inflammation in ischemia. Exposure of cultured endothelial cells (ECs) to H (pO2 approximately 12-16 torr) increased transcription of IL-6, elevated levels of IL-6 mRNA, and induced elaboration of IL-6 antigen in a time-dependent manner. Exposure of mice to hypoxia increased IL-6 transcripts in the lung, and immunostaining revealed a striking increase in IL-6 antigen in pulmonary vasculature. Transfection of ECs with deletion chimeric IL-6 promoter-chloramphenicol acetyl-transferase (CAT) constructs showed hypoxia-mediated 9-11-fold induction with -1200/+13, -596/+13, and -225/+13 but no induction with -111/+13. Electrophoretic mobility shift assays (EMSAs) using -225/-111 as the labeled probe demonstrated enhanced binding activity in nuclear extracts of hypoxic ECs and lung; the appearance of the gel shift band was prevented by excess unlabeled probe (-225/-111), and hypoxia-mediated enhancement of the band was blocked by a probe corresponding to the nuclear factor (NF)-IL-6 site (-158/-145). The hypoxia-enhanced band on EMSA displayed a supershift with antibody to CCAAT-enhancer-binding protein beta (C/EBP-beta), but antibody to C/EBP-alpha or -delta was without effect. Transfection of ECs with a construct comprising thymidine kinase promoter, -225/-111 in either the 5' to 3' to 5' orientation, and the reporter CAT showed this region to be an enhancer (approximately 8-fold) under hypoxia. EMSA with the NF-IL-6 probe revealed a prominent induction of binding activity with nuclear extracts from hypoxic ECs and whole lung. Constructs with -158/-145 and the CAT reporter gene showed induction when transfected into hypoxic ECs, whereas a similar construct with the NF-IL-6 motif mutationally inactivated failed to display hypoxia-induced expression. Furthermore, the tumor necrosis factor (TNF) gene, whose product contributes to ischemic pathology and contains a putative regulatory NF-IL-6 site, demonstrated enhanced binding activity for its NF-IL-6 motif and induction of TNF mRNA based on analysis of hypoxic lung. These data indicate that hypoxia induces expression of IL-6, most likely a result of hypoxic activation at the NF-IL-6 site, and suggest that other genes with regulatory NF-IL-6 sites may also be induced by a similar mechanism.

Phosphorylation and internalization of gp130 occur after IL-6 activation of Jak2 kinase in hepatocytes

Recent evidence has shown that members of the Jak kinase family are activated after IL-6 binds to its receptor complex, leading to a tyrosine phosphorylation of gp130, the IL-6 signal-transducing subunit. The different members of the IL-6 cytokine subfamily induce distinct patterns of Jak-Tyk phosphorylation in different cell types. Using monospecific antibodies to gp130, Jak2 kinase, and phosphotyrosine, we investigated the kinetics of IL-6 stimulation of members of this pathway in primary hepatocytes. Our findings show that Jak 2 is maximally activated within 2 min of exposure to IL-6, followed by gp130 phosphorylation that reaches its peak in another 2 min then declines to basal level by 60 min. In vitro phosphorylation experiments show that activated Jak 2 is able to phosphorylate both native gp130 and a fusion peptide containing its cytoplasmic domain, demonstrating gp130 is a direct substrate of Jak 2 kinase. Experiments designed to explore the cell surface expression of gp130 show that > or = 2 h are required to get a second round of phosphorylation after the addition of more cytokines. This finding suggests that activated gp130 is internalized from the cell surface after IL-6 stimulation. Additional experiments using protein synthesis inhibitors reveal that new protein synthesis is required to get a second cycle of gp130 phosphorylation indicating gp130 must be synthesized de novo and inserted into the membrane. These findings provide strong evidence that down regulation of the IL-6 signal in hepatocytes involves the internalization and cytosol degradation of gp130.

Differential regulation of interleukin-6 receptor and gp130 gene expression in rat hepatocytes

Interleukin-6 (IL-6) relays an important signal to hepatocytes during the early stages of an acute inflammatory response, causing an alteration in the expression of several major defense proteins. Additional regulation of this signal could occur either by altering the number of IL-6 receptors (IL-6-R) or of the signal transducing protein, gp130. We employed ribonuclease protection assays to measure the expression of IL-6-R and gp130 mRNA in primary rat hepatocytes in response to IL-6, interleukin-1, dexamethasone, and combinations thereof. Dexamethasone increases receptor mRNA levels 2.7-fold above controls but has no detectable effect on that of gp130. Such treatment increased surface expression of IL-6-R from 600 receptors per cell to greater than 6000, without a change in Kd (2.5-4.6 x 10(-10) M). In contrast to the stimulatory effect of the steroid signal, the inflammatory cytokines, individually and together, down-modulated both the mRNA and the cell surface expression of IL-6-R. These findings demonstrate for the first time that a sensitive control system exists between inflammatory mediators and IL-6-R.