Enhanced synthesis of factor B induced by tumor necrosis factor in human skin fibroblasts is decreased by IL-4

IL-4 is a T cell-derived lymphokine that has multiple biologic functions, affecting B cells, T cells, mast cells, monocytes, macrophages, and hematopoietic progenitor cells. We report that IL-4 also affects human skin fibroblasts. These effects were primarily in modulating the effects of other mediators of inflammation on these cells, with IL-4 producing little or no effects by itself. Synthesis of C proteins in human skin fibroblasts is modulated by TNF and other mediators of inflammation. TNF increased synthesis of factor B by 18.6-fold; IL-4 reduced the TNF effect on factor B synthesis by 83%. This effect started with concentrations of IL-4 as low as 0.1 ng/ml. The effect of IL-4 on the TNF-induced increase in synthesis of factor B occurred after 2 h incubation, the time when the effects of TNF alone were first observed. IL-4 also abrogated the effects of IL-1 and LPS on factor B synthesis, but did not affect the increase in synthesis of factor B induced by IFN-gamma. In contrast to the pattern for effect of IL-4 on factor B synthesis, the TNF-induced rate of synthesis of C3 was augmented by IL-4. The specificity of the IL-4 effect was also apparent when comparing the effect of IL-4 on the TNF-induced synthesis of factor B to the effects on total protein synthesis (increased 1.5-fold) and the TNF-induced increases in synthesis in C1r, C1s, C1 inhibitor, C2, and factor H (no changes). The IL-4-induced decrease in synthesis of factor B was mediated at a pretranslational level and was dependent on synthesis of a new protein. This interaction between IL-4 and mediators of inflammation can potentially modulate the inflammatory response in the setting of activation of Th cells.     

Synthesis and regulation of C1 inhibitor in human skin fibroblasts

Proteins of the C1 complex, C1q, C1r, and C1s, of the classical pathway of complement activation are known to be synthesized in human skin fibroblasts. Using metabolic labeling with [35S]methionine, immunoprecipitation, and SDS-PAGE, we demonstrate that human skin fibroblasts synthesize and secrete C1 inhibitor with an apparent molecular mass of 78 kDa in the cell lysate and 102 kDa in the extracellular medium. This C1 inhibitor had the capacity to bind activated C1s. Fibroblasts synthesized 30- to 50-fold more C1 inhibitor than was synthesized in monocytes. As previously reported, fibroblasts also synthesized C1r and C1s. IFN-gamma, IFN-beta 1, and TNF had significant, but distinct, effects on synthesis of C1 inhibitor, C1r, and C1s. Incubation of the cells with IFN-gamma, 1000 U/ml, for 24 h induced increases in the synthesis of C1 inhibitor, C1r, and C1s by 4.2-, 1.9- and 1.6-fold, respectively. IFN-beta 1 had effects similar to IFN-gamma, although smaller in magnitude. TNF, 12.5 ng/ml, induced increases in the synthesis of C1 inhibitor, C1r, and C1s by 1.5-, 1.4- and 2.6-fold. IL-1, IFN-beta 2 (IL-6), and LPS did not affect synthesis of C1 inhibitor, C1r, or C1s. Fibroblasts are present in large amounts in most tissues. Synthesis of C1 inhibitor, C1r, and C1s by these cells could provide a source of these important proteins in body tissues. In addition, fibroblasts should be a good model for the in vitro study of genetic diseases involving the synthesis of these proteins.     

Modulation of IL-1 inflammatory and immunomodulatory properties by IL-6.

Among the major cytokines present in inflammatory lesions interleukin-1 (IL-1), tumor necrosis factor alpha (TNF alpha) and interleukin-6 (IL-6) share many biological activities. Since IL-1 alpha, IL-1 beta and TNF alpha have been previously demonstrated to play an important role in connective tissue destruction by stimulating the production of prostaglandin E2 (PGE2) and collagenase, these functions were investigated in the presence or absence of natural human IL-6 (nhIL-6) or recombinant human IL-6 (rhIL-6). IL-6 was found 1 degree to stimulate immunoglobulin A production by the CESS B cell line up to 19 fold without being affected by the presence of IL-1 beta and 2 degrees to stimulate murine thymocytes proliferation up to 2-4 fold, with an increase up to 60-fold in costimulation with either IL-1 alpha or beta. IL-6 alone, even at very high concentrations (up to 200 U/ml and 50 ng/ml), did not induce PGE2 production by fibroblasts and synovial cells. However, IL-1 alpha or beta induced PGE2 production by human dermal fibroblasts and by human synovial cells was inhibited (in 5/8 experiments) up to 62% by addition of IL-6. On the contrary in 2/4 experiments TNF alpha-induced PGE2 production was increased (approximately 2 fold) by the addition of IL-6. IL-1 and TNF alpha-induced collagenase production in synovial cells remained unchanged in the presence of IL-6.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endotoxemia elicits increased circulating beta 2-IFN/IL-6 in man

beta 2-IFN/hepatocyte stimulating factor/IL-6 is a cytokine secreted by monocytes, fibroblasts, and endothelial cells in cell culture that possesses diverse biologic activity including the stimulation of acute phase plasma protein synthesis and immunomodulation. The circulating levels of this cytokine in man in response to bacterial LPS (endotoxin) were studied. A single i.v. bolus of endotoxin (20 U/kg) produced a monophasic rise in circulating immunoreactive IFN-beta 2/IL-6 and IFN-beta 2/IL-6 bioactivity (hepatocyte stimulation and B cell differentiation assays) peaking 2 to 4 h after the endotoxin challenge. Peak IFN-beta 2/IL-6 levels ranged from 4.1 to 27.5 ng/ml. Associated with this was a rise in circulating C-reactive protein levels detected 20 h after the endotoxin bolus. Thus, IFN-beta 2/IL-6 is likely one of the endogenous mediators which is triggered in man during bacterial infection and likely participates in the metabolic and immune responses of the infected host.     

IL-6/IFN-beta-2 as a circulating hormone. Induction by cytokine administration in humans

IL-6/IFN-beta 2 is a family of phosphoglycoproteins ranging in size from 19 to 30 kDa which elicits a broad range of physiologic and immune responses. Several cytokines, including TNF, have been shown to stimulate IL-6 production in cell culture. In this report, we describe the rapid induction of circulating biologically active IL-6 by the systemic administration of rTNF to patients with cancer. Low levels of IL-6 activity could be detected in the sera of patients as early as 5 min after rTNF infusion. IL-6 levels peaked approximately 2 to 3 h after rTNF bolus administration and were undetectable in most cases within 8 h. IL-6 was detected in two separate bioassays--the hybridoma B9 proliferation and the hepatocyte-stimulating factor assay. Maximum detectable levels of IL-6 ranged from 160 to 310 hybridoma growth factor units and 11-82 ng/ml in the hepatocyte-stimulating factor assay. IL-6 induction decreased after serial, daily doses of rTNF. Serial serum samples of patients receiving IL-2 or IFN-alpha were also assayed for IL-6 production. IL-2-treated but not IFN-alpha-treated patients generated low levels of IL-6 (range less than 20 to 95 hybridoma growth factor units/ml). Interestingly, in patients treated with IL-2, serum levels of TNF were detectable and peak TNF activity preceded measurable IL-6 levels. Serum levels of acute phase plasma proteins and of corticosteroid rose in response to rTNF administration. C-reactive protein increased (2.5 to 4.0-fold) within 8 h of rTNF administration and cortisol levels rose (10- to 20-fold) within 4 h after rTNF injection. We conclude that rTNF administration in man leads to the induction of circulating IL-6 which, due to its broad range of activities, may be an important physiologic signal regulating the immune response.     

Regulation of osteoarthritis-associated key mediators by TNFα and IL-10: effects of IL-10 overexpression in human synovial fibroblasts and a synovial cell line

Synovial fibroblasts (SF) contribute to the pathogenesis of osteoarthritis (OA), but the effects of intra-articular cytokines on SF are not completely understood. The aim of this study was to characterize the interplay between tumor necrosis factor (TNF)α and the anti-inflammatory interleukin (IL)-10. Non-immortalized human SF and SF of the human cell line K4IM were stimulated with recombinant TNFα, IL-10, or TNFα?+?IL-10 (10 ng/ml each) for 24 h or transduced with an adenoviral vector overexpressing human IL-10 (hIL-10) and subsequently treated with 10 ng/ml TNFα for 24 h. Effects on the gene expression and protein synthesis of IL-6, IL-10, matrix metalloproteinases (MMP)-1, ?3, type I collagen, β₁-integrin, and CD44 were investigated via real-time detection polymerase chain reaction, immunofluorescence labeling, flow cytometry, and Western blotting. IL-10 release by transduced SF was confirmed with enzyme-linked immunosorbent assay. Both cell populations were activated by TNFα and by TNFα?+?IL-10, increasing their gene expression and protein synthesis of IL-6, IL-10, MMP-1, and MMP?3 and altering the synthesis of type I collagen, β₁-integrin, and CD44. hIL-10 overexpression greatly elevated the gene expression and protein synthesis of IL-10. However, transduction did not significantly affect the gene expression of IL-6, MMP-1, and MMP?3 in SF. The increased expression of pro-inflammatory and catabolic mediators in TNFα-activated SF indicates their role in OA pathogenesis, suggesting they are a potential therapeutic target. Although the vigorousness of the responses of non-immortalized SF and K4IM clearly differ, the K4IM cell line seems to be a suitable model for non-immortalized human SF.     

Induction of HLA class I mRNA by cytokines in human fibroblasts: comparison of TNF, IL-1 and IFN-beta.

Expression of HLA class I antigens is known to be regulated by various cytokines at both the mRNA and protein levels. We have examined the induction of HLA-B7 by tumor necrosis factor alpha (TNF), interleukin 1 alpha (IL-1) and interferon beta (IFN-beta) in normal human diploid FS-4 fibroblasts. Optimal induction of HLA-B7 by TNF at 24 h was shown to require a continuous presence of TNF. Since TNF also induces IFN-beta in these cells and the latter cytokine itself has the capacity to upregulate HLA class I expression, we investigated the role of autocrine IFN-beta in the induction of HLA-B7 by TNF. Experiments with neutralizing polyclonal antibodies to recombinant IFN-beta showed that the induction of HLA-B7 mRNA by TNF was partially dependent on autocrine IFN-beta. However, TNF and IFN-beta induced HLA-B7 mRNA with similar kinetics and treatment with saturating concentrations of both TNF and IFN-beta resulted in an additive or possibly synergistic response. The latter findings support the idea that induction of HLA class I by TNF is not mediated solely by autocrine IFN-beta produced in response to TNF. In addition, experiments with the protein synthesis inhibitor cycloheximide suggested that the induction of mRNAs for both the heavy and light (beta 2-microglobulin) chains of the HLA class I antigen by TNF did not require de novo protein synthesis. IL-1 was also shown to increase steady-state mRNA levels of HLA-B7 with kinetics similar to those of TNF and IFN-beta in FS-4 cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition by IL-1 of endothelial cell activation induced by tumor necrosis factor or lymphotoxin

Previous studies in this and other laboratories have demonstrated that IL-1, lymphotoxin (LT), and TNF rapidly stimulate a number of proinflammatory properties in cultured endothelial cells (EC) including cell-surface procoagulant activity and increased adhesivity for lymphocytes, monocytes, and polymorphonuclear leukocytes. In addition, we have demonstrated that LT and TNF, but not IL-1, stimulate increases in EC RNA synthesis, protein synthesis, and cellular volumes, changes which may correspond to the hypertrophy of EC seen at sites of inflammation in vivo. It is reported here that both human rIL-1 alpha and rIL-1 beta totally inhibit the increases in EC RNA synthesis, protein synthesis, and cell volumes induced by either TNF or LT. As little as 0.1 ng/ml of either IL-1 was sufficient to totally block the activation of EC induced by 100-fold higher concentrations (10 ng/ml) of either LT or TNF. The relevance of these findings to the regulation of inflammatory responses is discussed.     

Stimulation of EBV-activated human B cells by monocytes and monocyte products. Role of IFN-beta 2/B cell stimulatory factor 2/IL-6

EBV infects human B lymphocytes and induces them to proliferate, to produce Ig, and to give rise to immortal cell lines. Although the mechanisms of B cell activation by EBV are largely unknown, the continuous proliferation of EBV-immortalized B cells is dependent, at least in part, upon autocrine growth factors produced by the same EBV-infected B cells. In the present studies we have examined the influence of monocytes on B cell activation by EBV and found that unlike peripheral blood T cells and B cells, monocytes enhance by as much as 30- to 50-fold virus-induced B cell proliferation and Ig production. Upon activation with LPS, monocytes secrete a growth factor activity that promotes both proliferation and Ig secretion in EBV-infected B cells and thus reproduces the effects of monocytes in these cultures. Unlike a number of other factors, rIFN-beta 2/B cell stimulatory factor 2 (BSF-2)/IL-6 stimulates the growth of human B cells activated by EBV in a manner similar to that induced by activated monocyte supernatants. In addition, an antiserum to IFN-beta that recognizes both IFN-beta 1 and IFN-beta 2 completely neutralizes the B cell growth factor activity of activated monocyte supernatants. These findings demonstrate that IFN-beta 2/BSF-2/IL-6 is a growth factor for human B cells activated by EBV and suggest that this molecule is responsible for B cell growth stimulation induced by activated monocyte supernatants. We have examined the possibility that IFN-beta 2/BSF-2/IL-6 might also be responsible for B cell growth stimulation by supernatants of EBV-immortalized B cells and thus may function as an autocrine growth factor. However, IFN-beta 2/BSF-2/IL-6 is not detectable in supernatants of EBV-immortalized B cells by immunoprecipitation. Also, an antiserum to IFN-beta that neutralizes IFN-beta 2/BSF-2/IL-6 fails to neutralize autocrine growth factor activity. This suggests that autocrine growth factors produced by EBV-immortalized B cells are distinct from IFN-beta 2/BSF-2/IL-6. Thus, the continuous proliferation of EBV-immortalized B cells is enhanced by either autocrine or paracrine growth factors. One of the mediators with paracrine growth factor activity is IFN-beta 2/BSF-2/IL-6.     

Cytokine-induced production of IFN-beta 2/IL-6 by freshly explanted human endometrial stromal cells. Modulation by estradiol-17 beta

The cytokine IFN-beta 2/IL-6 has emerged as an important means of communication between cells--both within the immune system as well as outside it. In exploring the link between the endocrine and the immune systems, we have studied the secretion of IFN-beta 2/IL-6 by freshly explanted human endometrial stromal cells and its modulation by estrogens. Endometrial stromal cells produced IFN-beta 2/IL-6 in response to other inflammation-associated cytokines such as IL-1 alpha or beta, TNF, and IFN-gamma. This secretion was strongly inhibited by estradiol-17 beta at concentrations as low as 10(-9) M. Multiple species of stromal cell IFN-beta 2/IL-6 in the size range 23 to 30 kDa were detected using immunoprecipitation or immunoblotting procedures. The endometrial stromal cell IFN-beta 2/IL-6 species were phosphorylated and differentially glycosylated in a manner comparable to IFN-beta 2/IL-6 secreted by induced human peripheral blood monocytes or foreskin fibroblasts. However, in contrast to peripheral blood monocytes and fibroblasts, bacterial LPS did not induce IFN-beta 2/IL-6 production in endometrial stromal cells. Additionally, the IFN-beta 2/IL-6 identified in medium from IL-1 alpha-induced stromal cells is biologically active on hepatocytes. These observations, taken together with the observation that IFN-beta 2/IL-6 strongly inhibits the proliferation of human epithelial cells, suggest the possibility that stromal cell secreted IFN-beta 2/IL-6 may affect the physiology of the overlying epithelium in an hormonally modulated manner. Estrogen-regulated production of endometrial IFN-beta 2/IL-6 may participate in gender-specific systemic immunomodulation.     

Tumor necrosis factor stimulates DNA synthesis of mouse hepatocytes in primary culture and is suppressed by transforming growth factor beta and interleukin 6.

In a previous study, we revealed that tumor necrosis factor (TNF) was secreted in mouse liver at an early phase of liver regeneration after partial hepatectomy. Here, we investigated direct actions of TNF on the in vitro DNA synthesis of adult mouse hepatocytes in primary culture. TNF enhanced both 3H-TdR uptake and the number of 3H-TdR-labeled nuclei of hepatocytes. Their time courses were similar to those by epidermal growth factor (EGF) with about a 15 h lag period and a peak period of 24-48 h. This action of TNF was abrogated by DNA polymerase alpha inhibitor, aphidicolin and blocked specifically by anti-TNF antibody. The actions of rmTNF and rhTNF were not distinguishable; ED50 was about 7.5U/ml (5ng/ml) and 30U/ml (20ng/ml) for maximal response (about 2-fold or more of control). Other inflammatory monokines showed differential effects on in vitro DNA synthesis of hepatocyte. Neither type of interleukin 1 affected hepatocyte DNA synthesis in the range examined (up to 50 ng/ml). IL-6 markedly inhibited the hepatocyte DNA synthesis stimulated by TNF and EGF. The action of TNF was completely suppressed by transforming growth factor beta, which is known as a potent inhibitor of hepatocyte growth. Interferon gamma also blocked this TNF action when added simultaneously. These results indicate that the activation of tissue macrophages and local secretion of TNF in liver after partial hepatectomy is of physiological importance in liver regeneration, in part by a direct stimulation of hepatocyte DNA synthesis. Cytokines induced by TNF may also participate in the later termination of liver regeneration.     

Dexamethasone inhibits feedback regulation of the mitogenic activity of tumor necrosis factor, interleukin-1, and epidermal growth factor in human fibroblasts

Tumor necrosis factor (TNF), interleukin-1 (IL-1), and epidermal growth factor (EGF) were mitogenic for human diploid FS-4 fibroblasts. Dexamethasone amplified the growth-stimulating action of all three agents. Amplification of the growth-stimulating action was maximal when dexamethasone was added along with TNF or EGF; no amplification was seen if the addition of dexamethasone was delayed for more than 3 hr. Prolonged simultaneous treatment with TNF and EGF resulted in less growth stimulation than treatment with EGF alone. Dexamethasone abolished this apparent antagonistic interaction between TNF and EGF. Dexamethasone also inhibited the antiviral action of TNF against encephalomyocarditis (EMC) virus in FS-4 cells. TNF and IL-1 increased the steady state level of interferon (IFN)-beta 2 mRNA but failed to induce detectable levels of IFN-beta 1 mRNA in FS-4 cells. Dexamethasone inhibited the increase of IFN-beta 2 mRNA levels by IL-1 or TNF. Inhibition of IFN-beta synthesis is likely to be responsible for the inhibition of the TNF-induced antiviral state by dexamethasone. Since IFNs suppress cell growth, inhibition of endogenous IFN-beta synthesis may also be responsible for the amplification by dexamethasone of the growth-stimulating action of TNF and IL-1. Amplification of the mitogenic action of EGF by dexamethasone appears to be mediated by different mechanism.     

Tumor necrosis factor-alpha exerts interleukin-6-dependent and -independent effects on cultured skeletal muscle cells

In vivo studies have shown that cancer-associated skeletal muscle wasting (cachexia) is mediated by two cytokines, tumor necrosis factor-alpha (TNF) and interleukin-6 (IL-6). It has been unclear from these studies whether TNF exerts direct effects on skeletal muscle and/or whether these effects are mediated via IL-6. Previous studies from our laboratory have shown that TNF induces IL-6 mRNA expression in cultured skeletal muscle cells. To further investigate the relationship between TNF and IL-6, the effects of TNF and IL-6 on protein and DNA dynamics in murine C2C12 skeletal myotube cultures were determined. At 1000 U/ml, TNF induced 30% increases in protein and DNA content. The effects of TNF on protein accumulation were inhibited by aphidicolin, an inhibitor of DNA synthesis. IL-6 mimicked the effects of TNF on C2C12 cultures, inducing a 32% increase in protein accumulation and a 71% increase in the rate of protein synthesis. IL-6 also decreased expression of mRNA for several proteolytic system components, including ubiquitin 2.4 kb (51%) and 1.2 kb (63%), cathepsin B (39%) and m-calpain (47%), indicating that IL-6 acts on both protein synthesis and degradation. Incubation of murine C2C12 myotube cultures with TNF (1000 U/ml) in the presence of a polyclonal mouse anti-IL-6 antibody resulted in an abolishment of the effects of TNF on protein synthesis, but did not inhibit TNF-induced stimulation of DNA synthesis. These findings indicate that the effects of TNF on muscle protein synthesis are mediated by IL-6, but that TNF exerts IL-6-independent effects on proliferation of murine skeletal myoblasts.     

Compartmentalization of TNF and IL-6 in meningitis and septic shock

We examined the compartmentalization of bioactive tumour necrosis factor (TNF) and interleukin 6 (IL-6) to the subarachnoid space and systemic circulation in patients with meningococcal meningitis and septic shock/bacteraemia. In patients with meningitis, median levels of TNF in 31 paired samples of cerebrospinal fluid (CSF) and serum were respectively 783 pg/ml and below detection limit (p < 0.001) and median levels of IL-6 were 150 ng/ml and 0.3 ng/ml (p < 0.0001). In patients with septic shock without meningitis, median levels in paired samples of CSF and serum were respectively below detection limit and 65 pg/ml (not significant, (ns)) (TNF, eleven patients) and 1.3 ng/ml-3 ng/ml (ns) (IL-6, nine patients). The data show that TNF and IL-6 are localized to the subarachnoid space in patients with meningitis although the blood-brain barrier is penetrable to serum proteins. On the other hand, patients with septic shock tend to have cytokines in both serum and CSF.     

Tumor necrosis factor-α exerts interleukin-6-dependent and -independent effects on cultured skeletal muscle cells

In vivo studies have shown that cancer-associated skeletal muscle wasting (cachexia) is mediated by two cytokines, tumor necrosis factor-α (TNF) and interleukin-6 (IL-6). It has been unclear from these studies whether TNF exerts direct effects on skeletal muscle and/or whether these effects are mediated via IL-6. Previous studies from our laboratory have shown that TNF induces IL-6 mRNA expression in cultured skeletal muscle cells. To further investigate the relationship between TNF and IL-6, the effects of TNF and IL-6 on protein and DNA dynamics in murine C2C12 skeletal myotube cultures were determined. At 1000 U/ml, TNF induced 30% increases in protein and DNA content. The effects of TNF on protein accumulation were inhibited by aphidicolin, an inhibitor of DNA synthesis. IL-6 mimicked the effects of TNF on C2C12 cultures, inducing a 32% increase in protein accumulation and a 71% increase in the rate of protein synthesis. IL-6 also decreased expression of mRNA for several proteolytic system components, including ubiquitin 2.4 kb (51%) and 1.2 kb (63%), cathepsin B (39%) and m-calpain (47%), indicating that IL-6 acts on both protein synthesis and degradation. Incubation of murine C2C12 myotube cultures with TNF (1000 U/ml) in the presence of a polyclonal mouse anti-IL-6 antibody resulted in an abolishment of the effects of TNF on protein synthesis, but did not inhibit TNF-induced stimulation of DNA synthesis. These findings indicate that the effects of TNF on muscle protein synthesis are mediated by IL-6, but that TNF exerts IL-6-independent effects on proliferation of murine skeletal myoblasts.