Interleukin 1 induces leukocyte infiltration and cartilage proteoglycan degradation in the synovial joint

Cytokine abnormalities in inflammatory arthritis

Cytokines are soluble molecules which control communication between cells of the immune and non-immune systems. Studies on their role in the pathogenesis of inflammatory arthritis have been increased with the discovery of new cytokines and the development of assays for their detection. Conditions such as rheumatoid arthritis are characterized by increased production of proinflammatory cytokines in association with reduced control by regulatory cytokines produced by T lymphocytes. The inadequate inhibition of proinflammatory cytokines by anti-inflammatory cytokines and other regulatory mechanisms contributes to this cytokine imbalance. This situation is responsible for the enhanced degradation, without sufficient repair activity. These results have provided the rationale for the use of cytokines as well as for drug targeting of the cytokine network in rheumatoid arthritis. This also includes the modulation of the cytokine network by targeting the level of the receptors as well as the effects and/or the responding cells.

N-terminal sequence of proteoglycan fragments isolated from medium of interleukin-1-treated articular-cartilage cultures. Putative site(s) of enzymic cleavage

Bovine articular cartilage was cultured both in the presence and in the absence of human recombinant interleukin-1 alpha (IL-1) (100 units/ml). Addition of this cytokine stimulated matrix degradation approx. 3-fold. This increased degradation permitted characterization of the large chondroitin sulphate proteoglycan (aggrecan) fragments accumulating in the media. When compared with controls, the proteoglycans isolated from the medium of cultures treated with IL-1 exhibited a decrease in the Kav. (control 0.25; IL-1-treated 0.37), determined by Sepharose CL-2B chromatography. This decrease in proteoglycan size was accompanied by a decreased ability of these monomers to associate with hyaluronic acid. Thus only 20% of the proteoglycans isolated from the medium of IL-1-treated cultures, compared with 39% for control cultures, had the capacity to form high-M(r) aggregates with hyaluronic acid. SDS/PAGE analysis of the proteoglycans from the media of IL-1-treated cultures demonstrated several large proteoglycan protein-core bands (M(r) 144,000-380,000). The protein-core bands with M(r) 144,000-266,000 exhibited a significantly decreased reactivity with monoclonal antibody 1-C-6 (specific for domains G1 and G2). The N-terminal amino acid sequence of four of these protein-core bands (M(r) 144,000, 173,000, 214,000 and 266,000) yielded sequences LGQRPPV-Y-PQLF(E), AGEGP(S)GILEL-GAP(S)-AP(D)M, GLG-VEL-LPGE and (A)RGSVIL-AKPDFEV-P-A. A comparison of these N-terminal amino acid sequences with the published proteoglycan sequence for bovine nasal cartilage [Oldberg, Antonsson & Heinegård (1987) Biochem. J. 243, 255-259], rat chondrosarcoma [Doege, Sasaki, Horigan, Hassell & Yamada (1987) J. Biol. Chem. 262, 17757-17769] and human articular cartilage [Doege, Sasaki, Kimura & Yamada (1991) J. Biol. Chem. 266, 894-902] permitted assignment of their relative positions on the core protein. Furthermore, on the basis of this similarity to published sequence, putative sites of enzymic cleavage were constructed. These theoretical cleavage sites revealed a glutamic acid residue in the P1 position and an uncharged polar or non-polar residue in the P1' position.

Involvement of platelet-activating factor and tumour necrosis factor in the pathogenesis of joint inflammation in rabbits

We have studied the participation of platelet-activating factor (PAF) in antigen-induced arthritis in rabbits, as well as the possible co-operation between PAF and tumour necrosis factor (TNF) in their ability to induce joint inflammation when injected into the knees of healthy rabbits. The administration of two structurally different PAF receptor antagonists, BN52021 and Alprazolam, from 4 h before the intra-articular injection of ovalbumin in preimmunized rabbits, induced an important reduction in the synovial fluid volume, in the amount of cells infiltrating the articular cavity and the synovial membrane, as well as in the prostaglandin E2 (PGE2) concentration. Furthermore, proteoglycans of the articular cartilage, which were found diminished in animals with non-treated arthritis, were well preserved in rabbits treated with PAF antagonists. All the synovial fluids from joints with arthritis had detectable amounts of PAF. The injection of either TNF or PAF into the joints of normal rabbits induced a mild inflammation. When TNF was administered 1 h before PAF, a synergistic response was noted in the synovial fluid volume, in the accumulation of leucocytes, and in the amount of PGE2. The administration of BN50726, a hetrazepine with a potent PAF-receptor antagonist effect, induced a diminution in those parameters. Our results suggest that PAF may be an early and important mediator of joint damage, and that TNF can amplify the inflammatory response induced by PAF. PAF receptor antagonists could play some role in the treatment of inflammatory joint diseases.

Gene transfer to synoviocytes: prospects for gene treatment of arthritis

Joints are difficult organs to target therapeutically. Intravenous, intramuscular, and oral routes of drug delivery provide poor access to the joint, and expose the body systemically to the therapeutic agent. Although intraarticular injection provides direct access to the joint, most injected materials have a short intraarticular half-life. We propose to circumvent these problems by introducing into the synovium gene(s) coding for proteins with antiarthritic properties. Two methods of gene delivery to synovium are under development. In the direct approach, in situ transduction of synoviocytes follows the injection of suitable vectors into the joint. In the indirect approach, synovium is removed from the joint, its synoviocytes are isolated, and the cells transduced in vitro. Genetically modified cells are subsequently transplanted back into the synovium. Using retroviral vectors, we have been able to express the lacZ and neo genes in lapine synovial fibroblasts in vitro. Following neoselection, all cells became LacZ+. Neo-selected cells carrying the lacZ marker gene were transplanted back into the knees of recipient rabbits to examine the persistence and expression of these genes in vivo. Islands of LacZ+, transplanted cells persisted in the recipient joints for at least 3 months. Furthermore, Neo+ cells could be grown from synovia recovered from these joints. Initial attempts to use retroviruses for the direct, in situ transduction of synovium have failed, probably because synoviocytes in the normal synovium are mitotically inactive. Present efforts are directed towards further development of our techniques for transferring genes to joints, and using these techniques to antagonize the intraarticular actions of interleukin-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic studies on connective tissue collagens in bone and tendon of adjuvant arthritic rat

The metabolic alterations in the matrix of connective tissue collagen were investigated in bone and tendon of rats with adjuvant-induced arthritis. Adjuvant arthritis was induced in rats with the immunization of Freund's adjuvant containing heat-killed Mycobacterium tuberculosis. The changes in the metabolism of collagen were studied using radioactive isotopic measurements with (3H)-proline. Tissue specimens were fractionated individually into soluble and insoluble collagens. The synthesis of collagen was examined by measuring the total collagen content and the radioactivity of (3H)-hydroxyproline in soluble collagen fraction within 24 hours after the administration of tritiated proline. The conversion of soluble to insoluble collagen was analyzed by measuring the radioactivity of (3H)-hydroxyproline in both soluble and insoluble collagens. The catabolism of soluble and insoluble collagens was studied by estimating the radioactivity of urinary (3H)-hydroxyproline 24 hours after the injection of tritiated proline. It was observed that the total collagen content and the total radioactivity of (3H)-hydroxyproline in bone and tendon were decreased significantly in adjuvant arthritic rats. The specific and total radioactivities of (3H)-hydroxyproline in soluble collagen were found to be reduced, indicating the decreased de novo synthesis of collagen during the diseased state. The conversion of soluble to insoluble collagen was impaired in tissues as evidenced by the increased content of soluble collagen in arthritic disease. In addition, an enhanced excretion of hydroxyproline was found in urine of arthritic rats, indicating the increased degradation of collagen in arthritic disease. These observations could, therefore, explain in part the changes in synthesis and degradation of collagen in bone and tendon during the development of experimentally induced adjuvant arthritis in rats.

Production of interleukin 8 by cultured synovial cells in response to interleukin 1 and tumor necrosis factor

Both interleukin 1 alpha (IL-1 alpha) and tumor necrosis factor alpha (TNF alpha) stimulated the production of interleukin 8 (IL-8) by synovial cells in time and dose dependent manners. Enhanced chemotactic activity of polymorphonuclear cells (PMN) in culture supernatants of synovial cells was neutralized with anti-IL-8 antibody, thus showing synovial cells to be capable of secreting IL-8 which may contribute to PMN accumulation in rheumatoid inflamed joints.

Influence of continuous infusion of interleukin-1 alpha on the core protein and the core protein fragments of the small proteoglycan decorin in cartilage

Decorin, a collagen-binding small proteoglycan, is considered to have a specific function in the organization or stability of the collagen network. Therefore, alteration of its molecular properties may be of pathophysiological relevance during the development of cartilage damage. It is shown here that normal cartilage from rabbit knee-joint contains glycosaminoglycan chain-bearing core protein fragments of 39, 23, and 18 kDa, each one amounting to approximately 5-6% of the intact decorin core protein. Continuous infusion of human recombinant interleukin-1 alpha for 14 days (200 ng/day) into a knee-joint led in condylar cartilage to a reduction in the amount of intact core protein from 2 micrograms/mg wet tissue to about 1.1 micrograms/mg. The increase in its quantity found after infusion of heat-inactivated interleukin-1 was not statistically significant. The concentration of all three core protein fragments became reduced to a similar extent as the intact core protein under the influence of the cytokine, and additional fragments were not found. Surprisingly, there was a much smaller response to interleukin-1-treatment in patellar cartilage.

Flare-up of experimental arthritis in mice with murine recombinant IL-1

Intra-articular injections of murine recombinant IL-1 (mrIL-1) during the chronic phase of antigen-induced arthritis (AIA) induced a flare-up of the smouldering inflammation. The exacerbation was characterized by acute and transient joint swelling and this coincided with the extravascular accumulation of neutrophils. IL-1 injected into arthritic joints of neutropenic mice demonstrated that joint swelling was independent of the neutrophil influx into the joint. Both phenomena were absent when IL-1 was injected into a naive joint. The IL-1-induced flare-up was not T cell mediated as in the antigen-induced flare-up, and suggestive evidence is presented that IL-1 sensitivity depended on the resident macrophage population. This explained why the hypersensitivity is not restricted to the immunologically mediated arthritis but reflects a more general hypersensitivity of previously injured joints, e.g. zymosan-induced arthritis and IL-1-affected joints. In addition, IL-1 could also potentiate the antigen-specific flare-up of chronic AIA and prolongs the duration of the exacerbation. Our data indicate that joints bearing a chronic infiltrate are at risk from exacerbations in two ways: a T cell mediated rechallenge with antigen, and a non-specific reactivation by systemic and local IL-1 generation.

Intra-articular administration of interleukin-1 causes prolonged suppression of cartilage proteoglycan synthesis in rats

The effect of IL-1 on proteoglycan synthesis was studied after intraarticular injection of IL-1 into the knee joints of rats. IL-1 reduced the sulfated glycosaminoglycan synthesis in the articular cartilage of rats in a dose-dependent fashion. Analysis of the sulfated molecules by chondroitinase ABC digestion followed by composite agarose/acrylamide gel electrophoresis confirmed the proteoglycan nature of the molecules. Immunoprecipitation of the methionine-labeled extracts with a polyclonal antibody against the core protein indicated that the reduction in glycosaminoglycan synthesis was due to an inhibition of the core protein synthesis after IL-1 treatment. IL-1 induced inhibition occurred in both young and old rats and was independent of the prostaglandin pathway, as non-steroidal anti-inflammatory drugs failed to block the inhibition of proteoglycan synthesis by IL-1. The cartilage of rats injected with IL-1 was able to recover with time and synthesize normal amounts of total proteoglycan. However, administration of successive doses resulted in a much delayed return to normal synthesis. These results suggest that IL-1, if available locally in a cyclical fashion, could significantly interfere with the ability of cartilage to repair by causing a prolonged suppression of proteoglycan synthesis.

Reduction of tumor necrosis factor alpha and interleukin-1 beta levels in human synovial tissue by interleukin-4 and glucocorticoid

The effects of recombinant human interleukin-4 (IL-4) and the glucocorticoid, dexamethasone, on tumor necrosis factor alpha (TNF alpha) and interleukin-1 beta (IL-1 beta) levels in cultures of rheumatoid and osteoarthritic synovial tissue were studied. Low concentrations of IL-4 and dexamethasone suppressed the levels of both cytokines in the supernatants of both types of tissue after stimulation with lipopolysaccharide (LPS); the IL-1 beta and TNF alpha levels were measured by ELISA. It is suggested that it is the monocyte/macrophage in the synovial tissues that is responsive to the inhibitors. It is proposed that glucocorticoids may act on synovial tissue in this manner in vivo and IL-4 may do so if administered intraarticularly.

A proteolytic fragment from human link protein is taken up and processed by monocytes and B cells

Mild digestion of 125I-labelled human proteoglycan aggregates with trypsin or stromelysin produced specific peptides that were taken up rapidly by THP-1 monocytes. SDS/PAGE of undigested aggregate showed that the three components of molecular mass 48, 44 and 41 kDa, corresponding to isoforms of link protein originally present, had been converted into a single component of 41 kDa by trypsin treatment, and that fragments of 6-12 kDa were present in fractions containing the high-uptake peptide. Separate proteolysis of isolated proteoglycan monomer and link protein confirmed that the specific high-uptake fragment was derived from link protein. Uptake of the link fragment was rapid, reaching a maximum after 5 min, and specific, since it was blocked by metabolic or serine proteinase inhibitors and at 4 degrees C. After uptake the cleaved fragment was processed further, with 50% of the radiolabel being released as degraded peptides within 5 min. In contrast, accumulation of whole aggregate reached a maximum after 45 min and only 50% had been released after 2 h. Uptake of aggregate was less affected by inhibitors or at low temperature, suggesting that a separate mechanism existed for its turnover. The aggregate was transported to lysosomes after uptake, although the link fragment did not sediment with either lysosomes or plasma membranes, suggesting that it was present in the cytoplasm or in very labile vesicles. However, the mode of handling of the peptide by the cells remains unclear. The link fragment was taken up by several different monocytic and B cell lines, but not by mouse fibroblasts or peritoneal macrophages. These data suggest that a surface serine proteinase on monocytes and B cells enables them to process and take up a fragment of link protein derived by extracellular proteolysis.

Pro- and anti-inflammatory roles of interleukin-1 in recurrence of bacterial cell wall-induced arthritis in rats

A specific interleukin-1 (IL-1) receptor antagonist (IL-1ra) was used to examine the roles of IL-1 in an experimental model designed to analyze the reactivation phase of erosive arthritis, induced in rats with peptidoglycan-polysaccharide polymers (PG-APS) isolated from cell walls of group A streptococci. Monoarticular arthritis was initiated by injection of a small dose of PG-APS into an ankle joint, and reactivation was induced by intravenous injection of PG-APS 20 days later. Human recombinant IL-1ra given at a dose of 2 to 3 mg/kg at the time of reactivation of arthritis and at 6-h intervals inhibits the increase in joint swelling by at least 60%. Joint swelling is suppressed 30 to 50% when the initial treatment with IL-1ra is delayed until 6 h after reactivation. IL-1ra is not effective when the initial injection is delayed 12 or 24 h. With an injection schedule of IL-1ra given at the time of reactivation and every 6 h, treatment can be stopped at 24 h and the suppression of swelling is no different from that in rats for which injections are continued for 4 days. The results indicate that IL-1 has a prominent, although not exclusive, role in initiating inflammation in this model and is involved in the amplifying processes in progressive inflammation and chronic erosive disease. An anti-inflammatory function of IL-1 is also indicated from data showing that IL-1ra treatment limited to 6 h or less after the induction of reactivation enhances joint swelling, whereas intravenous injection of human recombinant IL-1 beta 24 h before reactivation suppresses the reactivation of arthritis.

Tumour necrosis factor alpha and interleukin-2 in plasma from rheumatoid arthritis patients in relation to disease activity

Tumour necrosis factor alpha (TNF alpha) and interleukin-2 (IL-2) are potential immunological mediators of pathogenetic changes in rheumatoid arthritis. We measured the concentrations of TNF alpha and IL-2 in plasma from 2 groups of patients suffering from rheumatoid arthritis (RA). One group had high and one had low disease activity. In addition, in connection with steroid treatment in the high disease activity group, TNF alpha was significantly increased in plasma from RA patients with high disease activity compared with those of low disease activity (p = 0.0009). Furthermore, TNF alpha decreased significantly in relation to steroid medication, parallel to clinical improvement (p = 0.016). All IL-2 concentration measurements were within the estimated normal range. The increased TNF alpha plasma levels in patients with rheumatoid arthritis with high disease activity, might result from activated white mononuclear cells in the inflamed joints. This might, in part, support the theory that TNF alpha is a possible mediator of pathogenetic changes known to occur in rheumatoid arthritis.

Substrate specificity and activation mechanisms of collagenase from human rheumatoid synovium

Substrate specificity studies of collagenase extracted from human rheumatoid synovium suggest that synovial pannus tissue overlying articular cartilage may not be particularly active in degradation of cartilage type II collagen, which, considering the poor inherent healing capacity of the articular hyaline cartilage, may exert a protective function against inadvertant tissue damage. Rheumatoid synovial tissue was also used to establish synovial fibroblast cell lines. Treatment of these cells in monolayer cultures with IL-1 leads to collagenase gene activation, increased collagenase production and an almost complete autoactivation of secreted collagenase. Interleukin-1 also activated stromelysin gene suggesting this as a possible mechanism effecting autoactivation. Latent human fibroblast and macrophage collagenase purified from culture medium were efficiently activated by phenylmercuric chloride but also by gold thioglucose, gold sodium thiomalate and HCIO. These new observations support the Cys73 switch activation mechanism. In contrast to neutrophil collagenase, the activation by gold(I) compounds and HCIO was associated with a change in the apparent molecular weight of the fibroblast procollagenase. In addition, gold(I) compounds rendered collagenase more susceptible to thermal denaturation. Thus the fibroblast-type interstitial collagenase, probably derived from fibroblast- and macrophage-like synoviocytes, seems to provide the predominant collagenolytic potential in human rheumatoid synovial tissue. Furthermore, the conditions in synovitis tissue may be such as to favor at least initial activation of collagenase synthesized and secreted in situ.

Tumor necrosis factor alpha and epidermal growth factor regulation of collagenase and stromelysin in adult porcine articular chondrocytes

Chondrocyte-derived metalloproteases have been postulated to play a role in the degradation of articular cartilage during the development of chronic arthritic disorders. TNF alpha (tumor necrosis factor alpha), an inflammatory mediator released by activated macrophages, has been detected in the synovial fluid of patients with rheumatoid diseases. We have found that TNF alpha is a potent stimulator of collagenase and stromelysin mRNA accumulation, collagenase activity, and immunoprecipitable stromelysin in monolayer cultures of adult porcine articular chondrocytes. In contrast EGF (epidermal growth factor), which stimulates collagenase and/or stromelysin synthesis in fibroblast systems, stimulated minimal amounts of these enzymes at both the message and protein levels. Nuclear run-on transcription analysis demonstrated that the TNF alpha-stimulated increase in stromelysin and collagenase message levels was, at least partially, due to increased transcription. Elevated transcription of these genes, in response to TNF alpha, was apparent by at least 2 hours post-stimulation. The degree of c-fos and c-jun stimulation by TNF alpha or EGF did not correlate with the levels of collagenase and stromelysin message stimulated by these factors. EGF stimulated significant accumulation of both c-fos and c-jun mRNAs while only very low amounts of these messages were stimulated by TNF alpha. Our data suggests that TNF alpha may contribute to articular cartilage degradation by stimulating chondrocyte-derived matrix metalloproteases. In addition the regulation of metalloprotease genes in chondrocytes may be different from their regulation in fibroblasts.

Elevation of synovial plasminogen activator activity after injection of interleukin-1 alpha into rabbit knee joint

We investigated production of plasminogen activator (PA) and cartilage degradation induced by injection of recombinant human interleukin-1 (rhIL-1 alpha) in rabbit knees. Rabbits were injected intra-articularly (i.a.) with 100 ng rhIL-1 alpha and necropsied at 0, 3, 6, 18 and 54 h and synovial lavage and articular cartilage were collected. PA activity in the joint lavage was measured using Z-Lys-thiobenzyl ester as a substrate. Cartilage degradation was assessed by quantitating sulfated glycosaminoglycan (S-GAG) to hydroxyproline (Hyp) and appearance of keratan sulfate (KS) in synovial lavage by and ELISA. The PA activity in the lavage of IL-1 injected knees at 3, 6, and 18 h was elevated 8 to 10 fold compared to vehicle controls. At 54 h the activity declined to approximately one third of that seen at the earlier time points. KS in the joint lavage was highest at 18 h, suggesting proteoglycan degradation. The maximal loss of cartilage proteoglycan (S-GAG/Hyp) occurred by 54 h. These observations demonstrate that i.a. injection of IL-1 stimulated the production of PA activity within the rabbit joint. Since elevation of PA activity is followed by cartilage degradation, we investigated effect of anti-inflammatory agents on PA activity and cartilage degradation in this model. We found that triamcinolone, indomethacin and dexamethasone were able to suppress PA activity but not the cartilage degradation. These observations suggest that in this model of cartilage degradation suppression of PA is not sufficient to inhibit cartilage degradation.

Effects of anti-arthritic drugs on IL-1 induced inflammation in rats

Intra-articular injection of IL-1 in rats results in profound changes in the synovial joints including edema, synovitis, cartilage degeneration and fibroblast proliferation. We have tested the efficacy of several anti-arthritic drugs in this model to characterize the mechanism of IL-1 induced inflammatory lesions. The response to IL-1 was evaluated by measurement of soft-tissue swelling and by histological scoring. Dexamethasone, and several NSAIDS were effective in reducing the soft tissue swelling but only some were effective in improving the histological lesions. The slow-acting antirheumatic D-penicillamine and immunosuppressive agents such as cyclosporine A were ineffective. These observations provide further evidence that in vivo, at least some aspects of IL-1 induced changes in rat knee joints are likely to be prostaglandin mediated.

Synergism of basic fibroblast growth factor and interleukin-1 beta to induce articular cartilage-degradation in the rabbit

Interleukin-1 beta (IL-1) and basic fibroblast growth factor (bFGF) synergistically induce proteases in vitro. To investigate this synergy in vivo, we injected IL-1 and bFGF alone and in combination into the lapine knee. Three days later, we compared the glycosaminoglcan (GAG) content of tibial cartilage of cytokine-treated and contralateral control-knees. IL-1 caused significant increases of granulocytes and GAG in the synovial fluid but minor cartilage-GAG losses of 11, 11 & 16% at 5kU, 10 kU and 100 kU IL-1/knee, respectively. bFGF at 2 and 10 micrograms/knee caused no changes. 10 micrograms bFGF in combination with 10 kU IL-1 induced a 33% GAG loss (p less than 0.01) that lasted 21 days. IL-1/bFGF induced cartilage degradation may be useful to 1) evaluate agents which modulated proteoglycan catabolism and 2) assess factors that accelerate cartilage-repair.

Modulation of interleukin-1-induced alterations in cartilage proteoglycan metabolism by activation of protein kinase C

Interleukin-1 (IL-1) stimulates proteoglycan degradation and prostaglandin E2 (PGE2) release and inhibits proteoglycan synthesis by cartilage in organ culture. Addition of the protein kinase C (PKC) activator, mezerein, resulted in the concentration-dependent inhibition of IL-1 activity on proteoglycan metabolism. Similar effects were seen with other compounds which stimulated PKC, such as teleocidin B4 and phorbol dibutyrate (PDBu), but not with a phorbol analog that is inactive in stimulating PKC. Simultaneous addition of the PKC antagonist, staurosporine, blocked the mezerein-induced inhibition of IL-1 activity on both proteoglycan degradation and synthesis in a concentration-related manner. In contrast to its inhibition of the effect of IL-1 on proteoglycan metabolism, mezerein did not block the release of PGE2 by cartilage in response to IL-1 but caused a synergistic stimulation of PGE2 release. Importantly, in cultures made deficient in PKC by prolonged incubation with PDBu, the effects of this PKC agonist on proteoglycan breakdown and PGE2 were blocked, while stimulation by IL-1 persisted. These data indicate that the effects of IL-1 on proteoglycan metabolism and prostaglandin production are mediated by an intracellular signal distinct from PKC and suggest that activation of PKC in chondrocytes may play a role in modulating the action of IL-1 on proteoglycan metabolism.

Cytokines in rheumatoid arthritis

Joints with rheumatoid arthritis are a site for chronic inflammation involving T cells, B cells, macrophages and dendritic cells. When these cells interact cytokines are likely to be produced. The presence of different cytokines in the synovial fluid of patients with rheumatoid arthritis has been studied and the macrophage derived cytokines such as IL-1, IL-6, TNF-alpha, TGF-beta and PDGF have usually been detected in large quantities, whereas T cell produced cytokines (IL-2, IL-4, IFN-gamma) are absent or present in small quantities. IL-1, IL-6 and TNF-alpha have several functions which suggest that they participate in the chronic disease process of rheumatoid arthritis, such as increasing production of eicosanoid, collagenase and prostaglandin E2. Many synovial B cells are activated and produce large amounts of immunoglobulins. We searched for a B cell stimulatory activity in rheumatoid synovial fluid and found a B cell differentiation and helper activity. Cytokines in the joints of patients with rheumatoid arthritis seem central for the propagation of the disease process. Specific intervention in cytokine production or in its effects might help to relieve symptoms in rheumatoid patients.

Interleukin 1 induces the expression of a heat-shock gene in chondrocytes

The presence of T cells and antibodies reactive with heat-shock proteins (hsps) in the joints of patients with rheumatoid arthritis may indicate a role of hsps in this disease. In the present study we examined whether increased temperature and interleukin 1 (IL 1), both of which are elevated in arthritic joints, induced the expression of two hsp70 genes in bovine chondrocyte cultures. We found that heat shock resulted in increased expression of constitutive and inducible hsp70 mRNA species. IL 1 and phorbol 12-myristate 13-acetate (PMA) also induced an increase in the constitutive hsp70 mRNA species, but without affecting the expression of the inducible hsp70 gene. The increase induced by IL 1 was observed only after 3 h, whereas increases induced by PMA were observed within 1 h. For all treatments, the hsp70 mRNA decreased by 24 h. Heat treatment of chondrocytes did not affect levels of collagenase and caseinase activity in the medium, nor did it alter proteoglycan synthesis by these cells.

In vivo effects of interleukin-1 on articular cartilage. Prolongation of proteoglycan metabolic disturbances in old mice

We investigated the effects of intraarticular injections of interleukin-1 alpha (IL-1 alpha) into the knee joints of young (3-month-old) and old (18-month-old) C57Bl/10 mice. In this in vivo study, 35S-sulfate incorporation and release were used to compare the effects of IL-1 on patellar cartilage proteoglycan metabolism. IL-1-induced stimulation of proteoglycan degradation was confined to the first 24 hours after injection in both young and old animals, and was only slightly lower in old cartilage than in young. In old patellar cartilage, IL-1-induced suppression of proteoglycan synthesis appeared to be more prolonged. Also, the amount of time needed to restore the cartilage matrix, characterized by proteoglycan synthesis above normal levels, was longer in old animals. Histologic analysis confirmed the retarded recovery in the cartilage of old mice. Autoradiography showed that the chondrocytes of the medial side of the femorotibial area were most vulnerable to IL-1-induced suppression of proteoglycan synthesis, especially the medial tibial plateau. As with the patellar cartilage, IL-1-induced suppression of proteoglycan synthesis in this area of articular cartilage was more prolonged in old animals. Our data indicated that the impact of IL-1 on articular cartilage is higher in old mice and that, consistent with certain loci found to be at risk in experimental osteoarthritis, there are sites at which IL-1 is more likely to act.

Cytokine enhancement of monocyte/synovial cell attachment to the surface of cartilage: a possible trigger of pannus formation in arthritis

When rheumatoid articular cartilage samples were incubated with normal peripheral blood monocytes and cultured synovial cells in the presence of recombinant human interleukin-1 (IL-1) in vitro, large numbers of monocytes were seen to be attached to the articular surface. Significant numbers of monocytes invaded the cartilage tissue when the rheumatoid cartilage samples were pre-incubated with 10 U/ml of IL-1. Considerable numbers of monocytes were also attached to normal cartilage when these were pre-incubated with IL-1. It is of interest that recombinant human gamma interferon (gamma-IFN) did not enhance monocyte attachment. However, there was a significantly greater attachment of monocytes to rheumatoid than to normal cartilage. When normal cartilage was exposed to collagenase and then incubated with monocytes or synovial cells in the presence of 10 U/ml of IL-1, large numbers of cells were attached to the natural cartilage surface but not to the cut surface. These phenomena were much more intense when the rheumatoid cartilage was pre-incubated with collagenase. These results indicate that increased levels of IL-1 in the rheumatoid joint may play an important role in joint destruction by stimulation of pannus formation by inducing synovial cell attachment to the articular surface.

Interactions between interleukin-1 and basic fibroblast growth factor on articular chondrocytes. Effects on cell growth, prostanoid production, and receptor modulation

The interactions of interleukin-1 beta (IL-1 beta) and basic fibroblast growth factor (bFGF) with monolayer cultures of rabbit articular chondrocytes were examined. Both agonists resulted in a synergistic increase in prostanoid production, to levels higher than the maximal level for either protein alone. The synergy was time- and dose-dependent, was augmented in serum-free medium, and was blocked by indomethacin or a polyclonal antibody to IL-1 beta. The proteins had opposite effects on cell growth, and IL-1 beta completely blocked the mitogenic effect of bFGF. Pretreatment of cells with IL-1 beta induced a down-regulation in the number of the bFGF high-affinity receptors. Pretreatment of cells with bFGF increased the number of IL-1 receptors, which was dependent on messenger RNA synthesis.

In vivo studies of cartilage regeneration after damage induced by catabolin/interleukin-1

The response of the rabbit knee joint to a brief episode of cytokine induced damage is described. After three intra-articular injections of catabolin/interleukin-1 all joint cartilages showed an immediate extensive loss of proteoglycan (glycosaminoglycan), which was gradually replaced over three to four weeks. Glycosaminoglycan biosynthesis (measured by 35SO4 uptake) was initially depressed, but at one week had almost doubled its rate as compared with the normal side. This increased synthetic activity was further maintained throughout the duration of the experiment (28 days), though the rate gradually fell. Histological cartilage metachromasia to toluidine blue mirrored the glycosaminoglycan changes. No disturbance of the articular cartilage collagen network was found. It is considered, therefore, that during treatment for arthritis the indigenous chondrocyte must continue to be capable of carrying out regenerative matrix repair and that antiarthritic agents should first be screened for interference with that process.

Cytokine assays: role in evaluation of the pathogenesis of autoimmunity

Cytokines are protein mediators involved in inflammation, the immune response, cell growth, repair and fibrosis. All of these processes are ongoing in active autoimmune diseases such as rheumatoid arthritis (RA), and so it would be expected that many cytokines would be actively produced in RA joints or Graves' disease (GD) thyroid glands. The cDNA cloning of cytokines has permitted the generation of pure recombinant molecules, and of newer more sensitive assays, and spurred the rapid development of knowledge in this field. Here we review the molecular strategies devised to study the possible role of cytokines in the pathogenesis of RA and GD, and describe some of the initial results. After 'cataloguing' the relative abundance of various cytokines, we sought to discover which cytokines are of major importance in pathogenesis. For that purpose we used neutralizing anti-cytokine antibodies and found that TNF alpha is one of the major signals regulating the production of IL-1 in the RA but not in the osteoarthritic (OA) joint. In order to further understand the dynamics of the cytokine network, the localization of the cytokine-producing cells by immunostaining and in situ hybridization has also been performed. The latter techniques are particularly valuable for attempting to establish the role of the target cell, such as thyroid epithelium, in the pathogenesis of disease. Cytokines act on cells via binding to high-affinity receptors. The last two years has been the cDNA cloning of many molecules encoding cytokine receptor chains, and it is now possible to begin to evaluate the other half of the cytokine pathway. Taken together, there are now exciting opportunities for the molecular dissection of the cytokine events occurring in auto-immune tissues.

Lack of adjuvanticity of human recombinant interleukin-1 beta in collagen induced arthritis in rats

We investigated the influence of human recombinant interleukin-1 beta (hrIL-1 beta) on the time-course of collagen induced arthritis (CIA) when injected concomitantly with the arthritogenic emulsion. Three sensitizing procedures were compared. The control group received type II collagen only. The other groups differed by the adjunction of demonstrated (MDP) or potential (IL-1 beta) adjuvant. No adjuvant effect of IL-1 was observed as judged on clinical or radiological scores. On the contrary, MDP significantly worsened the lesions of the injected right hindpaw, and increased the incidence of CIA. Surprisingly, humoral response to type II collagen was decreased in the group receiving IL-1 beta. This might be explained by a non specific increase of antigen clearance.

Human cartilage is degraded by rheumatoid arthritis synovial fluid but not by recombinant cytokines in vitro

Rheumatoid arthritis (RA) synovial fluid (SF) stimulated significant loss of glycosaminoglycans (GAG) from normal and pathological human cartilage biopsies over 2 days as compared with normal human serum. By contrast, 15 RA SFs failed to degrade killed normal cartilage, and degraded killed RA cartilage less effectively than living RA cartilage. Four RA SFs were treated with neutralizing anti-cytokine antisera prior to incubation with normal cartilage. The degrading effects of two of the fluids were reversed by anti-interleukin-1 alpha (IL-1 alpha) while degradation by the third and fourth fluids were reversed by anti-interleukin-1 beta (IL-1 beta) and anti-tumour necrosis factor-alpha (TNF-alpha), respectively. However, recombinant human IL-1 alpha, IL-1 beta, TNF alpha or a combination of all three cytokines had no degrading effect in this 2-day culture system. It is concluded that RA SF degrades cartilage by a mechanism involving a synergistic interaction between cytokines and some other component of SF.

Modulation of the effects of interleukin-1 on glycosaminoglycan synthesis by the urine-derived interleukin-1 inhibitor, but not by interleukin-6

Interleukin-1 (IL-1) has been shown to regulate glycosaminoglycan (GAG) synthesis. We therefore investigated whether an IL-1 inhibitor or IL-6 modulates IL-1 biologic activities in human synovial cells and cultured articular cartilage. We found that in the presence of a constant amount of IL-1 beta, stimulation of hyaluronic acid (HA) synthesis by the IL-1 inhibitor was inhibited in a dose-dependent manner. Similarly, the decrease in sulfated GAG synthesis induced by IL-1 was reversed by the addition of the IL-1 inhibitor. In contrast, IL-6 did not affect the production of HA, prostaglandin E2, or collagenase in synovial cells, nor did it affect GAG in organ cultures when tested in the presence or absence of IL-1 beta. Hence, IL-6 was ineffective in modulating IL-1 bioactivities on HA or sulfated GAG synthesis. These results emphasize the importance of IL-1 and IL-1 inhibitor in connective tissue destruction and raise questions concerning the role of IL-6 in this pathogenesis.

Absence of correlations between indices of systemic inflammation and synovial fluid interleukin 1 (alpha and beta) in rheumatic diseases

There are two forms of the cytokine interleukin 1 (IL1), produced by two distinct genes encoding a neutral (IL1 beta) and an acidic (IL1 alpha) peptide. They have powerful pro-inflammatory, immunopotentiating, catabolic and arthritogenic properties in vivo and have been implicated in the pathogenesis of rheumatic diseases. In this study, using specific immunoassays, we have measured both IL1 alpha and IL1 beta levels in synovial fluids (SF) from a large number of patients with different rheumatic diseases. Biologically significant levels of both cytokines were found in SF from patients with different forms of arthritis, but no correlations were found with any of the measures of disease activity that we tested. We also describe the presence in joint exudates of biological inhibitor(s) that neutralize IL1-induced T-cell activation. This is the first report of IL1 alpha and IL1 beta measurements in the same synovial exudates and also of the comparison of local levels of these cytokines with conventional indices of systemic inflammation.

Inhibition of interleukin-1-induced collagenase production in human articular chondrocytes in vitro by recombinant human interferon-gamma

The production of collagenase by human articular chondrocytes in response to interleukin-1 beta is inhibited in a dose-dependent manner by interferon-gamma (1-1,000 units/ml). The analysis of culture medium samples by Western blotting and the measurement of levels of tissue inhibitor of metalloproteinases suggest that the decrease in measurable collagenase activity is primarily due to the inhibition of procollagenase production. These results provide evidence of a role for interferon-gamma in limiting connective tissue degradation.

Interleukin 1 beta in synovial fluid is related to local disease activity in rheumatoid arthritis

Interleukin 1 beta (IL-1 beta) is a polypeptide with pro-inflammatory and immunopotentiating effects in vivo and in vitro. With relevance to rheumatoid arthritis (RA) IL-1 augments release of prostanoids, proteinases and oxygen metabolites and is a potent inducer of bone and cartilage resorption. Although high levels of IL-1 have been found in rheumatoid synovial fluids, intra-individual variation in IL-1 production has made it difficult to correlate these levels with disease activity. To overcome this problem we have studied patients with symmetrical and asymmetrical knee joint inflammation. Local disease activity was documented using Ritchie score and joint circumference; IL-1 beta levels were quantitated in synovial fluid by ELISA. In patients with symmetrical joint involvement almost identical levels of IL-1 beta were detected in the right and left knee joints. In contrast, in patients exhibiting asymmetrical knee joint involvement, IL-1 beta levels in the inflamed joints were significantly higher than in the contralateral joints. The study provides further evidence for the role of IL-1 in the pathogenesis of rheumatoid inflammation.

Antigen induced arthritis in beige (Chediak-Higashi) mice

Mice with the beige mutation, which are known to be deficient for leucocyte elastase and cathepsin G, were used to investigate the role of neutral proteases in a model for antigen induced arthritis. Surprisingly, it was shown that in this model of arthritis, using methylated bovine serum albumin as an antigen, C57/black/6 'beige' mice (deficient for leucocyte neutral proteases) developed a more severe form of arthritis than the control mice ('black' mice), resulting in a higher degree of tissue damage. The incidence and degree of bone apposition and destruction of articular cartilage at day 21 after induction of arthritis were significantly higher in the beige mice. These findings could not be ascribed to differences in the cellular immune response to methylated bovine serum albumin. Autoradiographic detection of radiolabelled methylated bovine serum albumin suggested that more antigen is retained in the joints of beige mice than in black mice, which might account for the sustained arthritis and the concomitant tissue damage. These findings do not support the contention that leucocyte elastase and cathepsin G contribute to the pathogenesis of joint destruction in this model.

Inverse correlation between tyrosine phosphorylation and collagenase production in chondrocytes

Collagenase production by chondrocytes appears to play a major role in the development of osteoarthritis. Although the mechanisms regulating collagenase production by chondrocytes are not known, incubation of bovine chondrocytes in serum markedly decreases collagenase production. Since serum has been demonstrated to increase levels of phosphotyrosine (P-Tyr) in several cell types, we determined the effect of altering intracellular levels of P-Tyr on collagenase production. Both orthovanadate, a potent inhibitor of tyrosine phosphatases, and serum caused a marked increase in tyrosine phosphorylation. The increase in P-Tyr was associated with a decrease in the production of collagenase, suggesting that two processes may be linked. Orthovanadate caused an increase in P-Tyr in the absence of serum, suggesting that P-Tyr levels in resting chondrocytes are regulated through activity of both tyrosine kinases and phosphatases. Orthovanadate and serum induced a synergistic increase in P-Tyr levels, suggesting that serum functions through increasing kinase activity rather than decreasing phosphatase activity. In the absence of serum, concentrations of orthovanadate which maximally inhibited collagenase production primarily increased phosphorylation of a 36 kDa protein, suggesting that the phosphorylation of this protein may play a major role in regulating collagenase production. Orthovanadate had limited effects on chondrocyte proteoglycan synthesis, morphology or viability in the presence or absence of serum, suggesting that the decrease in collagenase production was not due to non-specific inhibition of protein synthesis or cellular toxicity. Inhibition of tyrosine phosphatases by orthovanadate or activation of tyrosine kinases by addition of serum correlated with the inhibition of collagenase production.

Elevated substance P and accelerated cartilage degradation in rabbit knees injected with interleukin-1 and tumor necrosis factor

Cytokines, interleukin-1 (IL-1), tumor necrosis factor alpha, and the neurotransmitter, substance P, have been implicated in the pathogenesis of arthritis because they stimulate synovial cells to secrete prostaglandin E2 and collagenase in vitro. We investigated in vivo changes in intraarticular substance P and the degradation of cartilage proteoglycan in response to intraarticular cytokine injections in rabbits. Twenty-four hours after a single injection of 10 ng, 30 ng, or 100 ng of recombinant human IL-1 alpha (rHuIL-1 alpha) per joint, the mean +/- SEM levels of substance P detected in the cell-free joint lavage fluid were 250 +/- 67 fmoles, 480 +/- 60 fmoles, and 530 +/- 130 fmoles (n = 4-5), respectively. The level of substance P in the contralateral knees injected with diluent was 58 +/- 8 fmoles (n = 12). The level of substance P had increased by 2 hours after IL-1 injection and remained elevated in the joint 48 hours after injection. Cytokine-induced proteoglycan depletion was also time- and dose-dependent. Proteoglycan concentrations in articular cartilage dissected from the weight-bearing condyles were calculated as the ratio of sulfated glycosaminoglycan measured using 1,9-dimethylmethylene blue: hydroxyproline. After 48 hours, 10 ng, 30 ng, or 100 ng of rHuIL-1 alpha per joint decreased proteoglycan levels by 9 +/- 4%, 14 +/- 4%, and 21 +/- 3% (n = 8), respectively. Likewise, the injection of recombinant human tumor necrosis factor alpha induced depletion of intraarticular substance P and cartilage proteoglycan.

Co-operation between interleukin-1 and the fibrinolytic system in the degradation of collagen by articular chondrocytes

1. The interaction between interleukin 1 (IL-1) and the fibrinolytic system in the control of collagen degradation by rabbit chondrocytes has been investigated in a tissue-culture system where cells are grown on a 14C-labelled collagen matrix. 2. Culture of rabbit chondrocytes in the presence of human recombinant IL-1 beta at a concentration of 57pM for 48 h led to the presence of procollagenase but not active collagenase in the medium. The latent collagenase could be activated by incubation with an organomercurial, aminophenylmercuric acetate (APMA). 3. Addition of IL-1 beta to chondrocytes grown on a 14C-labelled collagen matrix did not increase the degradation of the matrix compared to control over a 48 h period. However, in the presence of plasmin (200 micrograms ml-1) or plasminogen (100 micrograms ml-1), IL-1 beta (57 pM) caused almost complete degradation of the collagen matrix. Plasmin or plasminogen alone caused only slight degradation of the collagen matrix. 4. Tissue inhibitor of metalloproteinases (TIMP) or the selective metalloproteinase inhibitor, SC44463, inhibited the degradation induced by IL-1 beta and plasminogen in a concentration-related manner and at concentrations that were correlated with inhibition of collagenase. 5. When concentrations of IL-1 beta which caused only minimal degradation of the matrix in the presence of plasminogen were combined with fibrin (1 microgram ml-1), there was almost total degradation of the matrix by 48 h. 6. These results indicate there is a synergistic interaction between IL-1 and the fibrinolytic system in the degradation of collagen by rabbit chondrocytes in culture.

Recombinant interleukin-1 and tumor necrosis factor induce neutrophil migration "in vivo" by indirect mechanisms

The alpha and beta forms of recombinant interleukin-1 (IL-1 alpha and IL-1 beta) and of recombinant Tumor Necrosis Factor (TNF alpha and TNF beta) induced dose-dependent neutrophil migration into rat peritoneal cavities. Migration induced by both IL-1s showed a bell-shaped dose-response curve and IL-1 beta was 3-fold more potent than IL-1 alpha. Pretreatment of the animals with dexamethasone or depletion of the peritoneal macrophage population, abolished the neutrophil migration induced by the four cytokines. "In vitro" stimulation of macrophage monolayers with IL-1 beta and the TNFs released a factor into the supernatant which, unlike these cytokines, induced neutrophil migration in dexamethasone pretreated animals. These results suggest that the neutrophil migration induced by IL-1 alpha, IL-1 beta, TNF alpha and TNF beta is not due to a direct effect on neutrophils, but occurs via the release of a chemotactic factor(s) from resident macrophages.

Immobilization aggravates cartilage damage during antigen-induced arthritis in mice. Attachment of polymorphonuclear leukocytes to articular cartilage

The early and late effects of short-term immobilization on arthritic joints have been studied. Knee joints of mice in which an antigen-induced unilateral arthritis was elicited were immobilized in extension for 3, 5, and 7 days. After 5 and 7 days' immobilization, arthritis was significantly more severe. More leukocytes infiltrated the periarticular tissues and more cellular exudate was found in the joint space. A striking observation was that large numbers of polymorphonuclear leukocytes (PMN) attached to the surface of the cartilage, a phenomenon not found in mobile arthritic joints. Electron-microscopy confirmed PMN adhesion and showed severe ruffling of the cartilage surface under immobilized conditions. Further examination of factors determining PMN sticking revealed that attachment is rapid when the cartilage surface is already damaged, and that retained immune complexes and complement play a pivotal role. The late effects of immobilization were studied after a remobilization period of 2 weeks. Enhanced matrix depletion and chondrocyte death persisted in arthritic joints that were previously immobilized for 5 and 7 days, and the latter also showed significantly increased osteophyte formation. Although these results are speculative for the human situation, this study indicates that treatment of arthritic joints by complete rest should be applied with caution.

Concentrations of glycosaminoglycans in synovial fluids and their relation with immunological and inflammatory mediators in rheumatoid arthritis

The dimethylmethylene blue assay showed higher concentrations of glycosaminoglycans in many synovial fluids from patients with rheumatoid arthritis (RA) than in autologous sera or sera or synovial fluids from normal subjects. These results were taken to suggest that the glycosaminoglycans in RA synovial fluid were abnormally raised and derived from cartilage. To discover what stimulated such glycosaminoglycan release in RA joints relations were sought between synovial fluid concentrations of glycosaminoglycans and immunological and inflammatory mediators. It was shown that RA synovial fluid glycosaminoglycan concentrations correlated with synovial fluid C3d concentrations but not with synovial fluid rheumatoid factor concentrations, polymorphonuclear leucocyte numbers, myeloperoxidase concentrations, or the ability of the synovial fluids to release free radicals from normal polymorphonuclear leucocytes. A correlation was found between synovial fluid C3d and interleukin 1 concentrations as judged by both lymphocyte activating factor activity and immunoassay, but no significant correlation was detected between interleukin 1 and glycosaminoglycan concentrations. It is suggested that in the rheumatoid joint locally produced cytokines, in addition to interleukin 1, together stimulate glycosaminoglycan release from cartilage and render it vulnerable to attack by other processes.

Colony stimulating factor occurs in both inflammatory and noninflammatory synovial fluids

Synovial fluids (SF) from patients with osteoarthritis (OA) and rheumatoid arthritis (RA) and various other arthritides were examined for the presence of colony stimulating factors (CSF). CSF was found in 7 of 13 (54%) SF from OA patients and in 8 of 12 (67%) SF from RA patients. It was also found in SF from patients with other arthropathies including 5 of 5 samples from patients with septic arthritis. Inhibition studies employing monospecific antisera indicated that in both RA and OA, CSF was of the macrophage type (M-CSF). While CSF was found in both inflammatory and noninflammatory effusions, significantly greater numbers of colonies were stimulated by RA SF than by OA SF and in general greater numbers of colonies correlated with higher SF leukocyte counts. Our data suggest that CSF as well as other cytokines may be involved in the perpetuation of joint destruction that occurs in various rheumatological conditions.

Effects of murine recombinant interleukin 1 on synovial joints in mice: measurement of patellar cartilage metabolism and joint inflammation

Murine recombinant interleukin 1 was injected intra-articularly into mice. It induced a clear effect on patellar cartilage within 24 hours. A low dose of interleukin 1 (1 ng) elicited a significant reduction in [35S]sulphate incorporation (50%) into proteoglycans and an accelerated breakdown (twofold) of 35S prelabelled proteoglycan. Proteoglycan breakdown returned to normal rates (approximately 10%/day) 48 hours after a single interleukin 1 injection. Recovery of proteoglycan synthesis was delayed by up to 72 hours, however, which implies that repair of the depleted cartilage matrix is retarded. Interleukin 1 induced only minor joint inflammation, too slight to be held responsible for the strong suppression of proteoglycan synthesis. Vehement joint inflammation was found after repeated interleukin 1 injections. The plasma extravasation and massive infiltration and exudation of leucocytes, predominantly polymorphonuclear leucocytes, were not a mere summation of single interleukin 1 effects, but point to interleukin 1 induced local hypersensitivity. The cartilage matrices of patella and femur were heavily depleted. Measurement of the extent of loss of 35S prelabelled proteoglycan and the prolonged inhibition of [35S]sulphate incorporation indicate that both inhibition of proteoglycan synthesis and enhanced loss of proteoglycan contributed substantially to this depletion.

Cytokines and cytokine inhibitors or antagonists in rheumatoid arthritis

This review has summarized some of the evidence suggesting that cytokines may play an important role in mediating pathophysiologic events in RA. However, these proteins are capable of mediating both stimulatory (agonist) and inhibitory (antagonist) effects in the rheumatoid synovium. GM-CSF, IL-1, TNF alpha, and PDGF are all produced in the rheumatoid synovium and may function to induce inflammation, enzyme release, fibroblast proliferation, and tissue destruction. Local release of IL-6 may alter the effects of IL-1 and TNF alpha, as well as induce Ig production and hepatic synthesis of acute-phase proteins. However, specific inhibitors of IL-1 and TNF alpha exist, which, if also released into the synovium, may antagonize the proinflammatory effects of these cytokines. In addition, IL-1 may have antiinflammatory effects, such as the induction of the synthesis of collagen and enzyme inhibitors by chondrocytes and synovial fibroblasts. Stimulation of these latter cells by TGF beta also may result in decreased matrix degradation and increased formation of scar tissue. The developing scenario is one of cell-cell interactions that are influenced in positive and negative manners by the local release of various mediators. A further understanding of cytokines and cytokine inhibitors in the rheumatoid synovium may lead to the development of more specific and effective therapeutic agents.

The role of stromelysin in the cartilage destruction that accompanies inflammatory arthritis

Articular cartilage from arthritic joints of rats immunized with type II collagen is severely depleted of proteoglycans. Depletion begins within 48 hours after the onset of inflammation, prior to extensive pannus formation, and may represent a critical first step in cartilage destruction. We have immunolocalized stromelysin, an enzyme that is believed to play a major role in the pathologic degradation of proteoglycans, in the joints of rats with collagen-induced arthritis. Immunoperoxidase staining of frozen tissue sections demonstrated the presence of stromelysin in both the synovium and chondrocytes. In contrast, collagenase was localized primarily to the pannus-cartilage junction. Neither enzyme was detectable in joints from normal animals. To test the hypothesis that chondrocytes respond directly to inflammatory mediators by increasing the production of stromelysin, isolated chrondrocytes were incubated with various concentrations of interleukin-1. The culture media were also assayed for the presence of stromelysin by immunoreactivity on Western blots and by analysis of enzymatic activity on casein substrate gels. A 3-fold increase in a doublet of proteins synthesized in response to 10 units/ml of interleukin-1 was observed. These proteins also immunoreacted with the stromelysin antibody and degraded casein. Northern blotting results established that the increased levels of stromelysin were accompanied by increases in stromelysin-specific messenger RNA levels. These results suggest that stromelysin is responsible for proteoglycan degradation in early inflammatory arthritis, and that chondrocytes may play a direct role in the earliest stages of the degradation of their own matrices.