Rheumatoid synovial cell morphologic changes induced by a mononuclear cell factor in culture

The turnover and degradation of collagen

The interstitial collagens are degraded predominantly extracellularly, by specific collagenases (metalloproteinases) capable of cleaving the helical region across the three chains at a similar locus, solubilizing the cleaved products from the fibril. Other neutral proteinases may also function in this role by cleaving near cross-links in the fibril. Collagen type, molecular aggregation and small changes in temperature all markedly affect rates of collagenolysis in the fibril. Regulation of collagenolysis is also modulated at the levels of (1) cellular production of latent collagenase (procollagenase), (2) activation of latent collagenase, and (3) production of collagenase inhibitors. Fibroblastic cells and certain macrophages are probably the predominant sources of collagenases in inflammation; an enzyme in polymorphonuclear leucocytes (neutrophils) is distinct from the tissue enzyme. Molecules such as mononuclear cell factor (MCF), homologous with interleukin 1, which augment cellular collagenase production in inflammation, are derived from monocytes. The mechanisms of augmented collagenase production involve new protein synthesis and, if this augmentation is analogous to that produced by urate crystals, it is probably associated with increased levels of procollagenase mRNA. MCF production is itself controlled by products of lymphocytes as well as by interactions of monocytes with the Fc portion of immunoglobulins and components of the extracellular matrix. Activation of latent (pro)collagenase probably occurs in vivo through the action of neutral proteinases such as plasmin (through plasminogen activator). These effects may be indirect and exerted through proteolytic activation of a procollagenase activator. Tissue inhibitors act to regulate the active collagenase.

A role for parathyroid hormone-related protein in the pathogenesis of inflammatory/autoimmune diseases

Our increased understanding of the critical role of cytokines in chronic inflammatory/autoimmune diseases has led to the recent development of effective anti-cytokine treatments. In particular, agents blocking the function of TNF-alpha, a cytokine first identified as an endotoxin-inducible mediator of tumor cell necrosis, are now licensed for the treatment of rheumatoid arthritis (RA) and inflammatory bowel disease. However, TNF-alpha is but one member of a cytokine network that is responsible for mediating these inflammatory disorders. Therefore, as our understanding of the pathophysiologic role of other members of this inflammatory network increases, other cytokines may similarly be identified as effective targets for treatment. In this article, we will review evidence which suggests that parathyroid hormone-related protein (PTHrP), a peptide which, like TNF-alpha, was first identified because of its effects in the setting of malignancy, may in fact serve an important non-neoplastic, physiologic function by mediating the inflammatory/autoimmune host response. Data identifying PTHrP as a member of the cytokine network induced in multi-organ inflammation and rheumatoid arthritis will be summarized, initial evidence comparing the therapeutic efficacy of PTHrP- vs. TNF-alpha-blockade in the treatment of endotoxemia will be reviewed, and potential future areas of research, including assessment of the effects of PTHrP blockade in the treatment of RA, will be discussed.

Myofibroblasts. I. Paracrine cells important in health and disease

Myofibroblasts are a unique group of smooth-muscle-like fibroblasts that have a similar appearance and function regardless of their tissue of residence. Through the secretion of inflammatory and anti-inflammatory cytokines, chemokines, growth factors, both lipid and gaseous inflammatory mediators, as well as extracellular matrix proteins and proteases, they play an important role in organogenesis and oncogenesis, inflammation, repair, and fibrosis in most organs and tissues. Platelet-derived growth factor (PDGF) and stem cell factor are two secreted proteins responsible for differentiating myofibroblasts from embryological stem cells. These and other growth factors cause proliferation of myofibroblasts, and myofibroblast secretion of extracellular matrix (ECM) molecules and various cytokines and growth factors causes mobility, proliferation, and differentiation of epithelial or parenchymal cells. Repeated cycles of injury and repair lead to organ or tissue fibrosis through secretion of ECM by the myofibroblasts. Transforming growth factor-beta and the PDGF family of growth factors are the key factors in the fibrotic response. Because of their ubiquitous presence in all tissues, myofibroblasts play important roles in various organ diseases and perhaps in multisystem diseases as well.

Synovium as a source of increased amino-terminal parathyroid hormone-related protein expression in rheumatoid arthritis. A possible role for locally produced parathyroid hormone-related protein in the pathogenesis of rheumatoid arthritis

Proinflammatory cytokines, including tumor necrosis factor (TNF) and interleukin 1 (IL-1), mediate the joint destruction that characterizes rheumatoid arthritis (RA). Previous studies have shown that parathyroid hormone-related protein (PTHrP) is a member of the cascade of proinflammatory cytokines induced in parenchymal organs during lethal endotoxemia. To test the hypothesis that NH2-terminal PTHrP, a potent bone resorbing agent, could also be a member of the synovial cascade of tissue-destructive cytokines whose expression is induced in RA, PTHrP expression was examined in synovium and synoviocytes obtained from patients with RA and osteoarthritis (OA). PTHrP production, as determined by measurement of immunoreactive PTHrP(1-86) in tissue explant supernatants, was increased 10-fold in RA versus OA synovial tissue. Synovial lining cells and fibroblast-like cells within the pannus expressed both PTHrP and the PTH/PTHrP receptor, findings that were confirmed by in vitro studies of cultured synoviocytes. TNF-alpha and IL-1beta stimulated PTHrP expression in synoviocytes, while dexamethasone and interferon-gamma, agents with some therapeutic efficacy in the treatment of RA, inhibited PTHrP release. Treatment of synoviocytes with PTHrP(1-34) stimulated IL-6 secretion. These results suggest that proinflammatory cytokine-stimulated production of NH2-terminal PTHrP by synovial tissue directly invading cartilage and bone in RA may mediate joint destruction through direct effects on cartilage or bone, or, indirectly, via the induction of mediators of bone resorption in the tumor-like synovium.

Primary cultivation of human synovial cells from nonrheumatic synovial tissue and fluid

Cultures were established from adherent cells of synovial fluid and from collagenase-dispersed specimens of synovial tissue. In cultures derived from synovial tissue, prolyl hydroxylase-positive cells of fibroblast-like morphology were identified as the predominant cell type. In cultures from synovial fluid the majority of adherent cells was macrophage-like in appearance and strongly positive for CD 68. Cells with a stellate morphology could rarely be observed in cultures from synovial tissue. Their relations to other forms will be discussed. Several simple methods for cultivating adherent synovial cells are presented.

Inflammatory cytokines in the herniated disc of the lumbar spine

STUDY DESIGN

Tissues in the area of herniated lumbar discs were examined for inflammatory cytokines to elucidate the causes of sciatic pain in lumbar disc herniation.

OBJECTIVES

To determine the role of inflammatory cytokines in the stimulation of sciatic pain in lumbar disc herniation.

SUMMARY OF BACKGROUND DATA

It is postulated that in addition to mechanical compression of lumbar nerve roots and sensory root ganglia by herniated discs, there is a chemical stimulus to the production of sciatic leg pain. The exact mechanisms of chemical stimulation are not clearly defined.

METHODS

During surgery, cases of lumbar disc herniation in 77 patients were classified macroscopically into protrusion, extrusion, and sequestration types. Tissues adjacent to nerve roots at the herniation were excised and analyzed biochemically and immunohistochemically for the presence of inflammatory cytokines and for the production of these cytokines and prostaglandin E2 in vitro.

RESULTS

The homogenates of samples were analyzed for interleukin-1 alpha, interleukin-1 beta, interleukin-6, tumor necrosis factor-alpha, and granulocyte-macrophage colony stimulating factor, which were detectable. Most of the cytokine-producing cells were histiocytes, fibroblasts, or endothelial cells in extrusion and sequestration types, and chondrocytes in protrusion type. The secretion of these cytokines and prostaglandin E2 was decreased by the addition of betamethasone. The prostaglandin E2 production was dramatically enhanced by additional interleukin-1 alpha, but decreased by the addition of tumor necrosis factor-alpha.

CONCLUSION

The results demonstrate that at the site of lumbar disc herniation, inflammatory cytokines such as interleukin-1 alpha are produced, which increases prostaglandin E2 production. Further studies are required to elucidate the role of inflammatory cytokines in causing sciatic pain.

Distribution of macrophages in rheumatoid synovial membrane and its association with basic activity

Rheumatoid arthritis (RA) is an inflammatory disease of the synovial membrane, which results in the destruction of joints by inflammatory pannus. The synovial membrane shows proliferation and cellular infiltrates on microscopy with signs of chronic and acute inflammation. Macrophages are thought to play a central role in the pathogenesis of RA. We examined synovial membrane specimens of 21 RA patients using morphological, immunohistological and enzyme histochemical methods for number and distribution of macrophages. We were able to identify 41.5 +/- 8.8% of lining cells as macrophages, depending on the method used. In abundant diffuse lymphocellular infiltrates, 23.4 +/- 11.1% of mononuclear cells were macrophages. In addition, most cells in the region of tumorlike proliferation and a stromal population of fibroblastlike cells were detected by macrophage markers. Although cell number in synovial membrane increases drastically, we did not find correlations between the relative amount of macrophages in these regions and basic activity. Basic activity includes proliferative reaction as well as lymphoplasmacellular and mononuclear infiltration--both signs of an immunopathological process. In contrast, using enzymes or activation markers, there was a clear correlation. We consider that a constant high percentage of macrophages in RA synovial membrane is present regardless of any actual inflammatory process.

Contribution of synovial mesenchymal cells to the pathogenesis of rheumatoid arthritis

Rheumatoid joint destruction is caused by (1) enzymatic digestion from articular surfaces of cartilage, (2) pannus formation, and (3) lysis of the matrix by activated chondrocytes. Pannus, a vascular and fibrous granulation tissue arising from the perichondral synovial membrane, extends onto cartilage surfaces as a layer of morphologically quiescent fibroblastic mesenchymal cells. Pannus subsequently starts invasion into cartilage matrix with the appearance of macrophagelike cells. Synovial mesenchymal cells are thought to play important roles in the pathogenesis of rheumatoid joint destruction in relation to la expression and antigen presentation as well as the elaboration of inflammatory cytokines such as interleukin (IL)-1, IL-6, and tumor necrosis factor-alpha. By experimentally inducing antigen-induced arthritis in H-2-c-fos transgenic mice whose immunoglobulin G antibody response against immunizing antigen was defective, the investigators produced destructive arthritis without lymphocyte infiltration. The only cells invading the joints in these mice were similar to a previously recognized subset of human synovial cells that had a mesenchymal appearance. These mesenchymal cells invaded the cartilage matrix upon in vitro culture. The role of synovial mesenchymal cells in the pathogenesis of rheumatoid joint destruction is discussed.

Mediators of joint swelling and damage in rheumatoid arthritis and pristane induced arthritis

Joint swelling and tenderness in rheumatoid arthritis (RA) probably result from IgG aggregates activating complement with the consequent attraction of polymorphonuclear leucocytes (PMNs) and the liberation of their granule enzymes such as kininogenases. By contrast IL-1 and TNF are the major stimulants of cartilage and bone loss although other agents contribute. The fundamental drive for the production of these mediators is unknown but a role for heat shock proteins is suggested from work on pristane induced arthritis.

Influence of interleukin-1 on the morphology and proteoglycan metabolism of cultured bovine articular chondrocytes

Bovine articular chondrocytes cultured in agarose gel in the presence of serum elaborated a highly organized extracellular matrix rich in proteoglycans and collagens. The cultures were evaluated quantitatively by radiosulfate labeling of proteoglycans, and by densitometry following staining with alcian blue. In addition, immunohistochemical methods were used to demonstrate the presence of several components of cartilage proteoglycan molecules. Treatment with Interleukin-1 (Il-1) or retinol resulted in diminished synthesis and enhanced catabolism of matrix proteoglycans, but the chondrocytes were more sensitive to human recombinant Il-1 alpha than to Il-1 beta. Treatment with Il-1 alpha or retinol resulted in a profound disorganization of the residual matrix around the majority of the chondrocytes, while Il-1 beta caused much less severe changes. Some variation in cellular response to Il-1 alpha may result from the heterogeneity previously reported among articular chondrocytes.

Intracellular localization of group II phospholipase A2 in rat vascular smooth muscle cells and its possible relationship to eicosanoid formation

We investigated the localization of group II phospholipase A2 (PLA2-II) in rat vascular smooth muscle cells (VSMCs) by applying immunofluorescence and immunoelectron microscopy with its polyclonal antibody. In unstimulated cells, no immunolabelling was detected in the cells. On the other hand, in the cells stimulated with tumor necrosis factor (TNF) and/or forskolin (FK), intense fluorescence was detected in the cytoplasm. The immunoperoxidase reactions were detected in the cisternae of rough endoplasmic reticulum (rER), trans-cisternae of Golgi apparatus, and small vesicles beneath the plasma membrane. Western blot analysis showed VSMCs secrete PLA2-II after stimulation. Secreted PLA2-II was associated with the plasma membrane and extracellular matrix. Colchicine inhibited PLA2-II synthesis and its secretion to the extracellular space. These observations indicate that in VSMCs PLA2-II is synthesized at rER. transported to Golgi apparatus, discharged into extracellular space via the small vesicles, and microtubules may concern with its process. Furthermore, in VSMCs treated with TNF or TNF + FK, prostaglandin E2 formation was also increased. Actinomycin D and cycloheximide inhibited the potentiation of the prostaglandin E2 formation induced by TNF or TNF + FK, indicating that both RNA and protein synthesis are required for the potentiation. These results suggest an involvement of PLA2-II in the prostaglandin formation.

Human synovial cells secrete a 39 kDa protein similar to a bovine mammary protein expressed during the non-lactating period

By SDS/PAGE analysis we have observed that human synovial cell monolayers secrete a prominent 39 kDa protein which could not be detected in skin and lung fibroblasts. This protein was purified to homogeneity by heparin-Sepharose chromatography and reverse-phase h.p.l.c. The N-terminal sequence was found to be almost identical to that of a recently described bovine protein detected in the mammary secretions during the involutionary phase of the lactational cycle. Characterization of this 39 kDa protein may provide a useful marker for classification of connective tissue cells.

Mechanisms of matrix degradation in rheumatoid arthritis

In the inflammatory synovium production of collagenase is probably responsible for the degradation of collagen in the extracellular matrix and distortion of the architecture and function of the joints. Major collagenase-producing cells are mesenchymal cells such as fibroblasts and chondrocytes, which synthesize and secrete the enzyme influenced by the action of cytokines produced by adjacent mononuclear cells. The cytokines act primarily through cell-surface receptors, whose signal is probably then mediated by complexes of nuclear oncoproteins, to activate transcription of the procollagenase gene. The increased production of collagenase ultimately is the result of a cascade of cellular effects involving complex interactions of different ligands in a system characterized by amplification and feedback loops.

Cellular basis and oncogene expression of rheumatoid joint destruction

A new animal model for human rheumatoid arthritis is described, and the unsolved questions regarding the mechanism of primary joint destruction are discussed. Following an analysis of the types of cells and antibodies found in joints affected by rheumatoid arthritis, it is concluded that both expression of oncogenes and the presence of retroviral sequences detectable by monoclonal antibodies to HTLV I p19 and p24 sequences are associated with early abnormal proliferation of apparently transformed cells at the site of initial cartilage and/or bone destruction.

A natural interleukin 1 (IL-1) inhibitor counteracts the inhibitory effect of IL-1 on insulin production in cultured rat pancreatic islets

Several lines of evidence suggest that autoimmune processes are involved in the pathogenesis of Type I diabetes mellitus. Monocyte-macrophages are among the first mononuclear cells to invade the islets of Langerhans in various murine diabetic syndromes, and blockade of monocyte-macrophage functions by injection of silica particles in these animals prevents the development of the disease. Monokines such as interleukin 1 (IL-1) are known to mediate tissue lesions by inducing collagenase and prostaglandin E2 (PGE2) production. In addition, IL-1 has been demonstrated to inhibit proinsulin biosynthesis and secretion in pancreatic islet cells. Using 3-d cultured rat islets we have found that (a) the lowering of insulin release induced by human recombinant IL-1 (rIL-1) is dose-dependent with a decrease to 21% of control value at the higher rIL-1 tested concentration (500 pg/ml), and about two times more pronounced than the decrease in cellular insulin content, which reached 44% of control value at the highest rIL-1 concentration; (b) rIL-1 stimulates islets to secrete PGE2 but the addition of indomethacin, which blocks PGE2 production, does not affect the decrease in insulin release and content caused by IL-1, suggesting a limited role of endogenous PGE2 as a mediator in this system; and (c) a specific, noncytotoxic IL-1 inhibitor, shown in other cell systems to block the binding of IL-1 to its receptor, prevents the rIL-1 lowering of insulin content and minimizes the decrease of insulin release.

Identification of a high-affinity receptor for interleukin 1 alpha and interleukin 1 beta on cultured human rheumatoid synovial cells

In this report the binding of recombinant human interleukins 1 alpha and 1 beta (rIL-1 alpha and rIL-1 beta) to primary cultures of human rheumatoid synovial cells is measured and compared to the concentrations of these mediators required for stimulation of PGE2 production by these same cells. The average concentration of IL-1 alpha required for half-maximal stimulation of PGE2 was 4.6 +/- 1.5 pM (+/- SEM) (n = 6), whereas for IL-1 beta half-maximal stimulation was observed at a concentration of 1.3 +/- 0.24 pM (n = 6). Both direct and competitive binding experiments were performed. In direct binding experiments, IL-1 alpha bound with a Kd of 66 pM (n = 1), while IL-1 beta bound with a Kd of 4 pM (n = 2). In competitive binding experiments, IL-1 alpha inhibited binding of 125I-IL-1 alpha with a Ki of 33-36 pM (n = 2) and binding of 125I-IL-1 beta with a Ki of 51-63 pM (n = 2). IL-1 beta inhibited binding of 125I-IL-1 alpha with a Ki of 2-3 pM (n = 2) and binding of 125I-IL-1 beta with a Ki of 7 pM (n = 2). The binding data were best fit by a model specifying a single class of receptors with homogeneous affinity for either IL-1 alpha or IL-1 beta and with an abundance of 3,000-14,000 sites per cell. Autoradiography showed that the vast majority of the synoviocytes within the cultures possessed IL-1 receptors. Comparison of biological response curves with the binding curves indicates that the observed receptors exhibit sufficiently high affinity to mediate the response of human synoviocytes to low picomolar concentrations of IL-1 alpha and IL-1 beta.

Morphology of surface synoviocytes in situ at normal and raised joint pressure, studied by scanning electron microscopy

The synovial surface in rabbit knees was examined by scanning electron microscopy (SEM) to define normal surface contour, cell shape, and interstitial exposure. Comparison was made between specimens excised before immersion fixation (I), fixed in situ by vascular perfusion (V) before excision, or fixed in situ under an effusion pressure of 5-25 cmH2O (E). The deeply convoluted appearance of rabbit areolar-muscular synovium fixed after excision (I) was found to be an artefact; areolar-muscular synovium fixed in situ (V) was much smoother. The well documented cobblestone contour of immersion fixed adipose synovium was present after fixation in situ, but may be exaggerated by the SEM preparative process. At higher magnification the synoviocytes showed evidence of considerable surface activity (smooth granules, larger cauliflower-like excrescences, thin lamelliform filopodia). Cell shape was variable but many synoviocytes extended long cytoplasmic processes along the surface, producing fibroblastoid and even stellate outlines. At an intra-articular pressure of 25 cmH2O (E) the cytoplasmic processes were elongated and branched, creating a highly dendritic outline. Also, the exposure of interstitium increased markedly at the higher pressure. It is concluded that extension of lengthy cytoplasmic processes is a feature of normal healthy synoviocytes, and that an increase in interstitial area with joint pressure contributes to the increased hydraulic permeability of synovium at raised pressure.

Dendritic cells in the pathogenesis of rheumatoid arthritis

The cause of rheumatoid arthritis is unknown. It appears that abnormal or overstimulated cell-mediated immune mechanisms are operating. Dendritic cells, with their potent antigen presenting and immunostimulatory properties, have been found in increased numbers of rheumatoid synovial fluids and membranes. It is postulated that these cells play a key role in inducing and perpetuating the immune response with subsequent synovial proliferation and joint destruction.

Peripheral blood and synovial fluid monocyte activation in inflammatory arthritis. II. Low levels of synovial fluid and synovial tissue interferon suggest that gamma-interferon is not the primary macrophage activating factor

Because synovial fluid monocytes (SFM) in patients with inflammatory arthritis bear an activated phenotype (i.e., high expression of HLA-DR and low expression of the monocyte differentiation antigen Mo2), we assessed the role of gamma-interferon (gamma-IFN) in the activation of these cells. Sensitive and specific radioimmunoassays detected only 0.40 +/- 0.20 units/ml of gamma-IFN in the SF of patients with rheumatoid arthritis (RA) and 0.61 +/- 0.67 units/ml of gamma-IFN in the SF of patients with other forms of chronic inflammatory arthritis. There was no detectable alpha-IFN in any SF studied by radioimmunoassay. Bioassays failed to detect nonimmunoreactive IFN. Synovial tissue (ST) explants produced very little gamma-IFN (0.14 +/- 0.091 units/ml), and production was not increased by the presence of indomethacin in the cultures or by removal of adherent cells. However, gamma-IFN was produced if ST was cultivated in the presence of phytohemagglutinin. In SF and ST supernatants, gamma-IFN-mediated induction of HLA-DR on monocytes was inhibited, even though the amount of immunoreactive IFN was not affected. Prostaglandin E2 was shown to be one possible inhibitor. We demonstrated that a factor that induces HLA-DR on some individuals' peripheral blood monocytes, and cannot be neutralized by monoclonal anti-gamma-IFN antibody, is present in SF and ST supernatants. These data suggest that activation of SFM may occur by mechanisms other than gamma-IFN.

Histamine H1 receptors on adherent rheumatoid synovial cells in culture: demonstration by radioligand binding and inhibition of histamine-stimulated prostaglandin E production by histamine H1 antagonists

Histamine H1 receptors have been demonstrated on adherent rheumatoid synovial cells using biochemical and radioligand binding assays in vitro. The addition of histamine (17.8 mumol/l) to nine primary cultures of adherent rheumatoid synovial cells resulted in a two- to 21-fold increase in the production of prostaglandin E (PGE). This increase was inhibited by three H1 receptor antagonists (mepyramine, tripelennamine, and chlorpheniramine) in a dose related manner at concentrations below 10(-6) mol/l. Competitive binding assays with [3H]mepyramine gave ED50 values of approximately 10(-5) mol/l for the three H1 antagonists. H2 receptor antagonists (cimetidine and ranitidine) did not inhibit the histamine induced increase in PGE and did not compete effectively with the binding of H1 antagonists.

Comparative studies of adherent rheumatoid synovial cells in primary culture: characterisation of the dendritic (stellate) cell

Primary cultures of adherent rheumatoid synovial cells contain variable proportions of fibroblasts, macrophages, and dendritic cells, as judged by morphological appearance. Comparative studies using various enzymic and histochemical staining procedures showed the dendritic cells to lack many of the characteristic features of macrophages, e.g. the failure to express HLA-DR (Ia) antigen. The dendritic cells and fibroblasts had several similarities, but differed to some extent in their nonspecific esterase activity, phagocytic and proliferative potential. As the proportions of dendritic cells and fibroblasts varied in relation to specific culture conditions, we examined the possibility that these morphologies might represent different functional states rather than distinct cellular origins. Using subcultured synovial fibroblasts with a uniform bipolar appearance, we have shown that exposure to interleukin-1 or mast cell products resulted in a transformation to dendritic morphology. This change in cell shape was prevented by the presence of indomethacin, but was subsequently achieved by the addition of exogenous PGE2. Thus it appears that the latter is the factor that modulates the morphological change of fibroblastic to dendritic cells. This study has also demonstrated the complete and reversible interchange of fibroblast/dendritic morphology, thereby confirming that these different shapes are manifest by the same cell. The changes in phenotypic expression associated with the dendritic appearance include increased production of collagenase, prostaglandin E, and nonspecific esterase, as well as an apparent inability to exhibit phagocytosis and to proliferate in culture. We conclude from our in vitro studies that the phenotypic behaviour of the synovial fibroblast (or synoviocyte) is very variable and dependent to a large extent upon local stimuli, but the identity and hierarchy of such stimulating and suppressive factors in relation to cellular interactions requires further study.

Diverse morphological responses of normal human synovial fibroblasts to mononuclear leukocyte products: relationship to prostaglandin production and plasminogen activator activities, and comparison with the effects of purified interleukin 1

Supernatant media from cultured human mononuclear blood leukocytes (MCCM) induced morphological changes in normal human synovial fibroblasts in culture, including the formation of cells with a dendritic or stellate morphology and, less frequently, cells with a striking fenestrated appearance. These changes were fully reversed within 1 h of removing the MCCM. They were inhibited by indomethacin, the glucocorticoids hydrocortisone, prednisolone and dexamethasone, and by colcemid, but not by actinomycin D and only weakly by cycloheximide. The morphological responses to MCCM could be reproduced by MCCM fractions containing interleukin 1-like activity and by purified forms of human interleukin 1 (IL-1), including monocyte-derived IL-1 beta and recombinant IL-1 alpha. These responses were also inhibited by indomethacin, indicating a link with prostanoid production. However, the morphological responses were not related to the stimulation of plasminogen activator activity due to MCCM, MCCM fractions, or IL-1.

Connective tissue components in synovial fibroblast cultures exposed to interleukin 1 and prostaglandin E2

Long-term synovial fibroblast cultures were exposed to interleukin 1 (IL-1) or prostaglandin E2 (PGE2). The normally spindle-shaped fibroblasts changed to stellate-shaped cells, resembling the HLA-DR-positive, collagenase-producing cells which are normally seen only in primary cultures from enzyme-digested rheumatoid synovial tissue. However, the IL-1- or PGE2-induced fibroblasts were not HLA-DR-positive. This suggests that these cell populations represent originally different cell lines or that the expression of HLA-DR antigens is not induced by the agents used. For further characterization of these stellate cells, the location of fibronectin and type I collagen was studied by specific antibodies and the pericellular coat around fibroblasts was visualized by the erythrocyte exclusion method. Both IL-1 and PGE2 treatments destroyed the intercellular fibronectin network. Type I collagen was detected as intracellular granules. The stellate fibroblasts were usually full of these granules in contrast to intact fibroblasts in which the number of collagen fluorescence granules varied greatly. The pericellular coat known to be formed mainly by hyaluronic acid was similar around spindle and stellate-shaped fibroblasts. Rheumatoid arthritis-derived fibroblasts did not differ from their non-rheumatoid counterparts in any of the experiments. The effect of IL-1 and PGE2 on fibroblasts simulates the interaction between mononuclear cells and fibroblasts in synovial stroma and also potentially the interactions between different cell types in synovial lining.

Specific bioactivities of monocyte-derived interleukin 1 alpha and interleukin 1 beta are similar to each other on cultured murine thymocytes and on cultured human connective tissue cells

In this report we compare the bioactivities of pure, human monocyte-derived interleukin 1 (IL-1) alpha and beta in the standard murine thymocyte proliferation assay, a human dermal fibroblast proliferation assay, and in an assay measuring stimulation of prostaglandin E2 (PGE2) release from human rheumatoid synoviocytes. In each case the different species of IL-1 produced saturable stimulation and gave similar dose response curves. Half-maximal stimulation was observed at average IL-1 concentrations of 29 pM in the thymocyte assay, 2 pM in the dermal fibroblast proliferation assay, and 5 pM in the synovial cell assay. Our results show that native, monocyte-derived IL-1 alpha and IL-1 beta are both potent stimulators of connective tissue cells and that the specific bioactivities of these molecules are similar to each other in tests on human connective tissue cells, as well as on murine lymphoid cells.

Pathogenesis of rheumatoid arthritis

Many types of cells are activated and transformed in rheumatoid synovium, thereby contributing to amplification of the disease process. The immune response in rheumatoid arthritis is probably initiated by an antigen, although there is some evidence that anticollagen antibodies develop in response to tissue destruction, after rheumatoid arthritis has evolved clinically. Early inflammation in the synovium is characterized by a striking vascular proliferation, occurring in response to angiogenesis factors released by activated macrophages. Generalized activation of macrophages and lymphocytes typical of the immune reaction in the synovium generates antibody production, including production of rheumatoid factor. Data suggest that immune complexes deposited within cartilage attract polymorphonuclear leukocytes, which then release enzymes onto the cartilage surface. Many products of inflammation act as mediators, driving proliferation of synovial cells. Stellate cells, macrophages, and fibroblasts have been found along the pannus/cartilage junction; by various interactions, these contribute to destruction of cartilage and bone.

Rheumatoid arthritis: clinical features and pathogenetic mechanisms

Rheumatoid arthritis is a disorder characterized by chronic inflammation affecting predominantly articular tissues, leading in some instances to disruption of the normal structure and function of the joint. In some patients extra-articular manifestations are also present. In the joints, the pathologic lesion consists of synovial cell proliferation with infiltration by inflammatory cells. The complex interaction among these cells is likely responsible for the connective tissue abnormalities that characterize the rheumatoid lesion. The factors responsible for inducing the inflammatory process are unknown.

Hyaluronic acid production in vitro by synovial lining cells from normal and rheumatoid joints

Organ cultures and primary cell cultures were established from synovial tissue collected from patients with rheumatoid arthritis. Hyaluronic acid measured by the incorporation of [3H]glucosamine into the polysaccharide was found to be synthesised in the cultures immediately after transfer from in-vivo to in-vitro conditions. This was in contrast to the primary cultures established from cells isolated from normal joints. The latter cells did not synthesise any detectable hyaluronate. 90-100% of the cells in primary culture were found to be esterase positive, indicating their macrophage nature. The molecular weight of the hyaluronate produced by the pathological cells was low (approximately 50 000) compared with the molecular weight of hyaluronate found in joint fluid from normal or rheumatoid joints. Cell lines of fibroblasts established from rheumatoid joints and studied after four or seven passages also produced hyaluronate of low molecular weight. It is known that similar cell lines from normal joints produce a high molecular weight polymer.

Influences of gamma interferon on synovial fibroblast-like cells. Ia induction and inhibition of collagen synthesis

The shape and function of adherent cells cultured from rheumatoid synovial membranes are influenced by immune cells, and their products. The synovial cells produce collagenase and prostaglandin E2 (PGE2), the levels of which are increased when the cells are incubated with the monokine, mononuclear cell factor/interleukin 1. The majority of adherent synovial cells are fibroblastlike in appearance and synthesize collagens and fibronectin; the synthesis of collagens and fibronectins are also increased by a monocyte factor. In the present study we found that the fibroblastlike cells expressed major histocompatibility complex class II (Ia-like) antigens after initial dispersion from the synovial membrane. Monocyte lineage antigens were detected on some round cells in early passage, but no T lymphocytes were identified in established cultures. There was loss of Ia expression on the fibroblastlike cells with age and passage in culture. The addition of the lymphokine, gamma interferon (recombinant), induced class II antigen (DR and DS/DQ) expression in early or late passage cells in a time- and dose-dependent manner and required protein synthesis. Furthermore, the adherent synovial fibroblastlike cells continued to be Ia-positive when examined as long as 10 d after the removal of gamma interferon. Ia expression was also induced by gamma interferon in normal skin fibroblasts. Synovial cells that could be induced to express Ia also bound a monoclonal antibody to type III collagen (a fibroblast marker). Gamma interferon, while inducing Ia expression, decreased the binding of type III collagen antibody on unstimulated as well as monokine-stimulated cells. Analysis of [3H]proline-labeled medium by SDS polyacrylamide gel electrophoresis showed that gamma interferon decreased the synthesis of type I and III collagens and fibronectin by adherent synovial cells in a dose-dependent manner. These findings suggest that Ia expression by synovial tissue cells is not cell-specific, but reflects one or several related events, such as the degree of T lymphocyte infiltration, the presence of factors that stimulate gamma interferon release, or an increased sensitivity of the cells to gamma interferon. Whereas the synthesis of class II antigens is enhanced by the lymphokine gamma interferon, and a monocyte factor(s) stimulates collagen, collagenase and PGE2 synthesis by the same cells, gamma interferon inhibits basal and monokine-induced collagen synthesis. Thus, lymphokines and monokines may influence the extent of fibrosis as contrasted to matrix destruction at various stages of the rheumatoid lesion by affecting the function of fibroblastlike synovial cells.

Identification of immunostimulatory dendritic cells in the synovial effusions of patients with rheumatoid arthritis

Dendritic cells in the circulation are leukocytes that are rich in Ia antigens and that actively stimulate T cell replication. We have identified dendritic cells in the joint effusions of patients with rheumatoid arthritis. By phase-contrast and immunofluorescence microscopy, synovial mononuclear cells contained 1-5% dendritic profiles that were rich in HLA-DR and DQ, had small amounts of C3bi receptor, and lacked a battery of monocyte and lymphocyte markers. These dendritic cells could be enriched to 60-80% purity by cytolytic depletion of monocytes and lymphocytes with a group of monoclonal antibodies (MAb) and complement. By transmission electron microscopy, the dendritic cell processes were bulbous in shape and lacked organelles. The cytoplasm had few lysosomes or endocytic vacuoles but contained a well-developed smooth reticulum that was comparable to that previously described in the Ia-rich interdigitating cells of lymphoid tissues. The growth of sodium periodate-modified T lymphocytes was used as a rapid quantitative assay of accessory cell function. Synovial mononuclear cells were some ten times more active than normal blood cells. Treatment with alpha-Ia MAb and complement ablated stimulatory function. In contrast, removal of monocytes (MAb, 3C10) or monocytes and B (MAb, BA-1) plus T (MAb, OKT3, or T101) lymphocytes did not significantly alter total activity, and the function per viable cell increased four- to eightfold. We conclude that rheumatoid arthritis synovial fluids contain cells that are comparable in function, phenotype, and structure to blood dendritic cells, although the frequency (1-5%) is 10 times greater in joints. The reason for their accumulation in the articular cavity is not known, but dendritic cells may be important in perpetuating the joint inflammation characteristic of this disease.

Osteoarthritis. Emerging evidence for cell interactions in the breakdown and remodeling of cartilage

Interactions among the cells of joint components appear to contribute to the dynamic events associated with breakdown of the cartilage matrix and remodeling of the articular surface in osteoarthritis. The mediator interleukin-1 may be one of the stimuli that induce release of hydrolytic factors from synovial membrane cells and chondrocytes, which contribute to the degradation of collagen and proteoglycans in the cartilage matrix. The remodeling process is associated with chondrocyte proliferation and vascular and cellular ingrowth from subchondral bone with osteophyte formation. It is postulated that growth factors isolated from cartilage and bone may contribute to repair and remodeling of the articular end of the joint.

Arachidonic acid metabolism by rabbit synovial cells in culture. Studies of non-cyclooxygenase pathways

We have investigated arachidonic acid (20:4) metabolism by rabbit synovial cells in culture. The lipoxygenase products 5-HETE, 12-HETE and 15-HETE were not detected, despite the presence of a cyclooxygenase inhibitor sodium meclofenamate (20 microM), nor after incubation with ionophore A23187 (1 microM), 20:4 (10 microM), prostaglandin E2, (1 microM), N-formylmethionylleucylphenylalanine (0.01 microM), or murine spleen cell-conditioned medium. [3H]20:4 (10 microM) was incorporated into phospholipids, triacylglycerols and diacylglycerols. A majority of the 3H content of phosphatidylinositol/phosphatidylserine and of diacylglycerols was already present at 1 min, in contrast to the slower accumulation of 3H in triacylglycerols, phosphatidylcholine and phosphatidylethanolamine. The diacylglycerol fraction contained sn-glycerol-1-acyl-2-20:4. These observations are consistent with phospholipase C activity in synovial cells under those culture conditions. The products generated by these enzymes may play important roles in the physiological processes of synovium.

Phospholipase C activity in plasma membranes isolated from lapine synovial cells in monolayer culture

Plasma membranes were isolated from lapine synovial cells grown in monolayer culture using discontinuous sucrose gradient centrifugation techniques. 5'nucleotidase was detected in great abundance while glucose-6 phosphate dehydrogenase and cytochrome oxidase were present at low to undetectable levels. Plasma membranes incubated at 37 degrees C for 60 min with [3H]-arachidonyl-phosphatidylinositol/phosphatidylserine synthesized [3H]-diacylglycerides. Little if any [3H]-diacylglyceride synthesis was measured when [3H]-arachidonyl-phosphatidylcholine or [3H]-arachidonyl-phosphatidylethanolamine were used as substrates. These results are consistent with a plasma membrane-associated phosphatidylinositol-specific phospholipase C from lapine synovial cells in culture.