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

IL-6 inhibits the proliferation of fibroblastic synovial cells from rheumatoid arthritis patients in the presence of soluble IL-6 receptor

IL-6 and tumor necrosis factor (TNF)-alpha have been proven to play an important role in the development of rheumatoid arthritis (RA). It is well known that TNF-alpha induces IL-6 production from synovial cells as well as their proliferation. The effect of IL-6 on synovial cells, however, is not clear. An in vitrostudy was performed to determine the effect of IL-6 on the proliferation of synovial cells. Fibroblastic synovial cells isolated from the synovial tissues of eight RA patients were employed after the third to sixth passages. IL-6 in the presence of soluble IL-6 receptor (sIL-6R) inhibited the proliferation of synovial cells in a dose-dependent manner in seven cases without increasing the number of necrotic or apoptotic cells, while TNF-alpha increased synovial cell proliferation in all cases. The inhibitory effect of IL-6 was observed only in the presence of sIL-6R although small amounts of IL-6R were detected in these cells by RT-PCR analysis. However, anti-IL-6R or anti-gp130 mAb treatment increased spontaneous growth of synovial cells in all eight cases, suggesting that endogenous IL-6 and a small amount of IL-6R expressed in synovial cells suppressed their growth without exogenous IL-6 or sIL-6R. In addition, the IL-6-sIL-6R complex reduced the TNF-alpha-induced proliferation of synovial cells while TNF-alpha induced their IL-6 production. These data suggest that IL-6 may act as a negative feedback factor for TNF-alpha-induced synovial cell growth.

Animal models of rheumatoid arthritis and related inflammation

The major, extensively studied, experimentally-induced rat and mouse models of arthritis with features resembling rheumatoid arthritis are reviewed here. Etiopathogenetic studies that were recently published are emphasized. In summary, multiple triggering stimuli can induce disease in genetically-prone strains of inbred rats and mice. Multiple genetic loci, including both MHC and non-MHC, regulate disease expression in these animals. By comparison with other models of autoimmune disease, clustering of regulatory loci within and among species is increasingly becoming evident. At the cellular level, both innate and acquired immune systems are involved in the disease manifestations. At the molecular level, unbalanced chronic production of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1, IL-6 and IL-12, as opposed to IL-4 and IL-10, is correlated with arthritis disease susceptibility and severity.

Interleukin 6 knock-out mice are resistant to antigen-induced experimental arthritis

In order to assess the potential role of IL-6 in rheumatoid arthritis (RA), we have compared IL-6 deficient (IL-6 ko) mice and their wild-type (wt) counterpart for the capacity to develop methylated bovine serum albumin (mBSA)-induced arthritis. Our data show that IL-6 ko mice are not susceptible to antigen-induced arthritis (AIA). In fact, IL-6 ko mice treated by a standard protocol of immunization with mBSA did not develop joint swelling following intra-articular mBSA injection, nor revealed the characteristic joint lesions by histological examination. Conversely, wt mice treated according to the same protocol developed arthritis about 9 days after intra-articular injection, as detected by knee joint swelling and histological confirmation. We observed that the proliferative response of splenocytes to mBSA was impaired in ko mice following arthritis induction, as compared to the strong response observed in wt mice. Furthermore, anti-mBSA IgG levels were lower in ko mice as compared to wt mice. Finally, we show that sensitivity to AIA can be reconstituted in ko mice by subcutaneous injections of recombinant human IL-6 (rhIL-6). In addition, co-administration of IL-6 with mBSA by intra-articular injection into the joint was only partially effective in conferring sensitivity to AIA, suggesting the importance of a systemic effct for IL-6, but also that an additional role for this cytokine can be envisaged in the local inflammatory reaction during establishment of AIA.

Role of IL-6 in the Pleurisy and Lung Injury Caused by Carrageenan

In the present study we used IL-6 knockout mice (IL-6KO) to evaluate the role of IL-6 in the inflammatory response caused by injection of carrageenan into the pleural space. Compared with carrageenan-treated IL-6 wild-type (IL-6WT) mice, carrageenan-treated IL-6KO mice exhibited a reduced degree of pleural exudation and polymorphonuclear cell migration. Lung myeloperoxidase activity and lipid peroxidation were significantly reduced in IL-6KO mice compared with those in IL-6WT mice treated with carrageenan. Immunohistochemical analysis for nitrotyrosine and poly(A)DP-ribose polymerase revealed a positive staining in lungs from carrageenan-treated IL-6WT mice. No positive staining for nitrotyrosine or PARS was found in the lungs of the carrageenan-treated IL-6KO mice. Staining of lung tissue sections obtained from carrageenan-treated IL-6WT mice with an anti-cyclo-oxygenase-2 Ab showed a diffuse staining of the inflamed tissue. Furthermore, expression of inducible nitric oxide synthase was found mainly in the macrophages of the inflamed lungs from carrageenan-treated IL-6WT mice. The intensity and degree of the staining for cyclo-oxygenase-2 and inducible nitric oxide synthase were markedly reduced in tissue sections obtained from carrageenan-treated IL-6KO mice. Most notably, the degree of lung injury caused by carrageenan was also reduced in IL-6KO mice. Treatment of IL-6WT mice with anti-IL-6 (5 μg/day/mouse at 24 and 1 h before carrageenan treatment) also significantly attenuated all the above indicators of lung inflammation. Taken together, our results clearly demonstrate that IL-6KO mice are more resistant to the acute inflammation of the lung caused by carrageenan injection into the pleural space than the corresponding WT mice.

Enhanced Autoimmune Arthritis in IFN-γ Receptor-Deficient Mice Is Conditioned by Mycobacteria in Freund’s Adjuvant and by Increased Expansion of Mac-1+ Myeloid Cells

Induction of experimental autoimmune diseases often relies on immunization with the organ-specific autoantigens in CFA, which contains heat-killed mycobacteria. In several of these models, including collagen-induced arthritis, endogenous IFN-γ acts as a disease-limiting factor in the pathogenesis of the disease. Here we show that in collagen-induced arthritis the protective effect of IFN-γ depends on the presence of mycobacteria in the adjuvant. Omission of mycobacteria inverts the role of endogenous IFN-γ to a disease-promoting factor. Thus, the mycobacterial component of CFA opens a pathway by which endogenous IFN-γ exerts a protective effect that supersedes its otherwise disease-promoting effect. Extramedullary hemopoiesis and expansion of the Mac-1+ cell population accompanied the accelerated and more severe disease course in the IFN-γ receptor knockout mice immunized with CFA. Treatment of such mice with Abs against the myelopoietic cytokines IL-6 or IL-12 inhibited both disease development and the expansion of the Mac-1+ population. We postulate that mycobacteria in CFA stimulate the expansion of the Mac-1+ cell population by a hemopoietic process that is restrained by endogenous IFN-γ. These results have important implications for the validity of animal models of autoimmunity to study the pathogenesis and to evaluate cytokine-based therapy of autoimmune diseases.

Induction of alpha1-antitrypsin synthesis in human articular chondrocytes by interleukin-6-type cytokines: evidence for a local acute-phase response in the joint

OBJECTIVE

We have previously shown that human articular chondrocytes synthesize large amounts of interleukin-6 (IL-6) upon stimulation with proinflammatory cytokines and that they express the IL-6 receptor. The present study was undertaken to analyze whether different IL-6-type cytokines can induce synthesis of the acute-phase protein alpha1-antitrypsin in human articular chondrocytes.

METHODS

Chondrocytes from human articular cartilage, cultured in agarose, were stimulated with IL-6-type cytokines. Total RNA was isolated and analyzed by Northern blotting. Levels of alpha1-antitrypsin protein were determined by enzyme immunoassay.

RESULTS

Stimulation of chondrocytes with oncostatin M (OSM) and IL-6 led to a 5-10-fold increase in alpha1-antitrypsin synthesis. This increase was dose and time dependent. Furthermore, OSM and IL-6 induced IL-6 synthesis in chondrocytes, resulting in an autocrine amplification loop.

CONCLUSION

Our data strongly suggest the existence of a local acute-phase response in the joint. Synthesis of the acute-phase protein alpha1-antitrypsin, a major inhibitor of serine proteinases, may be an important protective mechanism of articular chondrocytes to prevent cartilage damage in inflammatory joint diseases.

Delayed onset and reduced severity of collagen-induced arthritis in interleukin-6-deficient mice

OBJECTIVE

To investigate the roles of interleukin-6 (IL-6) in the pathogenesis of rheumatoid arthritis (RA) by studying its effect on murine collagen-induced arthritis (CIA).

METHODS

IL-6-deficient (IL-6-/-) mice with a genetic background of susceptibility to CIA were generated by backcrossing them with DBA/1J mice for 8 generations. Clinical and immunologic features were compared between these mice and IL-6 wild-type (IL-6+/+) littermates with CIA.

RESULTS

Serum IL-6 levels increased during the development of CIA in IL-6+/+ mice. Two prominent peaks were observed. The first was coincident with the onset of arthritis, and the second one was observed during exacerbation of the disease. The onset of arthritis in IL-6-/- mice was delayed for 2 weeks compared with that in IL-6+/+ mice, and the severity of arthritis, as indicated by the arthritis score, remained significantly lower in IL-6-/- mice during the entire followup period (14 weeks), although all IL-6-/- mice developed definite arthritis as did the IL-6+/+ mice. Histologic severity was also reduced in IL-6-/- mice. In addition, radiologic changes such as osteopenia and bone erosion were reduced significantly in these animals. Both humoral and cellular responses to type II collagen (CII) in IL-6-/- mice were reduced to about half those in IL-6+/+ mice. In addition, enhanced production of IL-4 and IL-10 in response to concanavalin A stimulation was observed in IL-6-/- mice.

CONCLUSION

IL-6 plays an important role in the development of CIA, and both suppression of specific immune responses to CII and a tendency to a shift toward a Th2 cytokine profile might contribute in part to the attenuation of CIA in IL-6-/- mice. These findings suggest that blockade of IL-6 might be beneficial in the treatment of RA.

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

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

The effect of mesoporphyrin on the production of cytokines by inflammatory cells in vitro

This study was conducted to investigate a mechanism of the anti-inflammatory action of mesoporphyrin, especially the effect on the production of cytokines by some cultured inflammatory cells. Mesoporphyrin had no effect on lipopolysaccharide-induced tumor necrosis factor-alpha production by RAW 264.7 cells (murine macrophage-like cells). Mesoporphyrin inhibited interferon-gamma production by 1E10.H2 cells (murine T helper-1 cells), but not interleukin-4 production by D10.G4.1 cells (murine T helper-2 cells). Mesoporphyrin inhibited interleukin-6 production by human osteoblast-like MG-63 cells. This inhibition of interleukin-6 production is closely related to the suppression of prostaglandin E2 generation by interfering cyclooxygenase 1 and 2 enzyme activities. These data suggest that the inhibition of cytokine production is one of the anti-inflammatory mechanisms of mesoporphyrin.

Effect of Am-80, a synthetic derivative of retinoid, on experimental arthritis in mice

Am-80 is a newly snythesized retinoid with the structure of one aromatic amide among retinobenzoic acids. It exhibits specific biological activities of retinoic acid such as the activation of cellular differentiation and proliferation. We investigated the effect of Am-80 on collagen-induced arthritis (CIA) in mice and the immunopharmacological action on the production of several cytokines in the in vitro and in vivo models. Am-80, at doses of 0.3, 1 and 3 mg/kg, significantly inhibited the severity and development of the arthritis index, progression of foot pad swelling, bone damage and histopathological alterations. Am-80 also inhibited the production of anti-type II collagen (CII) IgG antibody, but did not affect the delayed-type hypersensitivity (DTH) response in arthritic mice. To determine the inhibitory mechanism of Am-80, we studied the effect of Am-80 on the production of cytokines. Am-80 did not affect the production of IFN-gamma by Th1 cells (1E10.H2 cells) and IL-4 by Th2 cells (D10.G4.1 cells), respectively. Am-80 selectively inhibited bacterial lipopolysaccharide (LPS)-induced IL-6, but not TNF-alpha and IL-1beta, production in mice. Moreover Am-80 inhibited IL-1beta induced IL-6 production and IL-6 mRNA expression in human osteoblast-like cells (MG-63). The inhibition of IL-6 production by Am-80 was due to downregulation of the pretranscription or the transcription of IL-6 in MG 63 cells. These findings suggest that the inhibitory effect of Am-80 on CIA is partially by modulating the production of the proinflammatory cytokine, IL-6.

Mice Lacking Mature T and B Lymphocytes Develop Arthritic Lesions after Immunization with Type II Collagen

Collagen-induced arthritis in DBA/1 mice is a widely used experimental model of rheumatoid arthritis. The induction phase of the disease is thought to be dependent upon MHC-restricted T and B cell-mediated immune responses to type II collagen, but an influence of additional non-MHC-restricted mechanisms has also been proposed. In this study, we report that type II collagen immunization of DBA/1 mice lacking mature T and B lymphocytes resulted in the development of arthritic lesions, which were characterized by synovial hyperplasia with occasional inflammation as well as cartilage and bone destruction. The specificity of disease induction to type II collagen was confirmed, because arthritis could not be induced when control preparations of OVA or adjuvant alone were administered. A delay in clinical disease onset and a reduction in severity between lymphocyte-positive and -negative DBA/1 mice confirmed that lymphocytes play an important role in disease; however, similar pathologic features and normal incidence suggest that lymphocyte-independent mechanisms of disease induction also operate in the standard collagen-induced arthritis model. We conclude that adaptive immune responses are not the only arthritogenic mechanism and hypothesize that the nonantigenic properties of type II collagen can also lead to arthritis.

In vivo priming of T cells against cryptic determinants by dendritic cells exposed to interleukin 6 and native antigen

T cells recognizing poorly displayed self determinants escape tolerance mechanisms and persist in the adult repertoire. The process by which these T cells are primed is not clear, but once activated, they can cause autoimmunity. Here, we show that dendritic cells treated with interleukin 6 (IL-6) process and present determinants from a model native antigen in a qualitatively altered hierarchy, activating T cells in vitro and in vivo against determinants that were previously cryptic because of poor display. IL-6 does not induce conventional maturation of dendritic cells but alters the pH of peripheral, early endosomal compartments and renders the cells more susceptible to killing by chloroquine. Acidification of endosomes by ouabain mimics the effect of IL-6 and allows processing of the same cryptic determinant. These results suggest that cytokines such as IL-6 could initiate and help to propagate an autoimmune disease process by differentiating dendritic cells into a state distinct from that induced by normal maturation.

Joint inflammation and cartilage destruction may occur uncoupled

Chronic arthritis is characterized by a persistent joint inflammation and concomitant joint destruction. Although the joint swelling is a major clinical problem, destruction of bone and cartilage may occur uncoupled to inflammation and it is of utmost importance to fully understand the elements of the destructive process. TNF and IL-1 are considered master cytokines in the process of human RA, with a claimed cascade of TNF inducing most of the IL-1 production. Studies in experimental models revealed that TNF is indeed a pivotal cytokine in joint swelling, yet IL-1 is the dominant cartilage destructive cytokine and its production may occur independent of TNF. This was found with anti-TNF/IL-1 neutralizing antibodies and the observations were recently backed up with similar data in arthritis models in TNF and IL-1 knockout mice. Apart from the absolute level of IL-1, the destructive potential of an arthritis is determined by the balance with regulatory cytokines and anabolic growth factors. IL-4, IL-6, and IL-10 can promote inflammation and tissue fibrosis, yet cartilage destruction is found to be greatly reduced by these cytokines, linked to a range of pathways which can reduce the IL-1 impact on the articular cartilage. Finally, the presence of anabolic growth factors in the inflamed synovium may have a major impact on net destruction. Endogenous transforming growth factor-beta (TGF-beta) is found in inflamed synovia, but local coadministration of TGF-beta further enhanced the degree of synovitis, yet almost fully prevented cartilage damage, providing another example of a major lack of correlation between inflammatory mass and destructive potential. It is suggested that novel therapy in RA patients should not only focus on reduction of outer signs of joint inflammation, but should also include attempts at reduction of cartilage destruction.

Blockage of interleukin-6 receptor ameliorates joint disease in murine collagen-induced arthritis

OBJECTIVE

To clarify the role of interleukin-6 (IL-6) in the pathogenesis of collagen-induced arthritis (CIA).

METHODS

CIA was induced by immunizing twice at a 3-week interval with bovine type II collagen (CII) emulsified with complete adjuvant. Rat anti-mouse IL-6 receptor (anti-IL-6R) monoclonal antibody MR16-1 or isotype-matched control antibody KH-5 was then injected once intraperitoneally. Symptoms of arthritis were evaluated with a visual scoring system, and serum anti-CII antibody and IL-6 levels were measured by enzyme-linked immunosorbent assay. In addition, the CII responsiveness of splenic lymphocytes from mice with CIA was examined.

RESULTS

In mice with CIA, excess production of IL-6 in sera was observed within 24 hours after the first CII immunization, and then rapidly decreased. Serum IL-6 increased again beginning 14 days after immunization, in conjunction with the onset of arthritis. When MR16-1 was injected immediately after immunization with CII, it inhibited the development of arthritis in a dose-dependent manner. Furthermore, MR16-1-treated mice exhibited lower serum levels of IgG anti-CII antibody and reduced responsiveness of lymphocytes to CII. This suppressive effect was observed when MR16-1 was injected on day 0 or 3, but not when injected on day 7 or 14.

CONCLUSION

IL-6 produced after CII immunization appears to play an essential role in the immunity to CII, and anti-IL-6R antibody reduces the development of CIA by suppressing IL-6 signal transduction.