Immunorecognition of chondrocytes in articular cartilage activated by synovial interleukin 1

Effects of copper and zinc on proteoglycan metabolism in articular cartilage

Co-Cultures of porcine articular cartilage and synovium or synovial conditioned medium were used as an in vitro model to mimic inflammatory events at the cartilage/synovial junction in degenerative joint disease. This model provides a useful tool to assess the anti-inflammatory and antiarthritic properties of pharmacological agents. In this study the effects of copper and zinc on (i) PG synthesis by cartilage and (ii) synovial-induced PG depletion have been investigated. Copper sulphate at a concentration of 0.01 mM did not stimulate PG synthesis significantly in cultured cartilage explants but completely abrogated the inhibitory effects of synovial tissue in co-culture experiments. This finding was supported by the histological demonstration of copper-dependent reversal of the PG depletion in cartilage exposed to synovial conditioned medium. Zinc sulphate at 0.01 mM had no effect on PG synthesis and was unable to protect cartilage against synovialinduced PG depletion. These results reveal possible mechanisms by which copper exerts its anti-inflammatory and anti-arthritic actions.

ICAM-1 expression on chondrocytes in rheumatoid arthritis: induction by synovial cytokines

The intercellular adhesion molecule-1 (ICAM-1) was found by immunostaining chondrocytes in cartilage from three patients with rheumatoid arthritis. Expression of ICAM-1 was restricted to chondrocytes in areas of erodedcartilage adjacent to the invading synovial tissue. Toluidine blue staining of these areas demonstrated severe depletion of the cartilage extracellular matrix. In areas of undamaged cartilage there was no ICAM-1 expression. Since ICAM-1 is not constitutively expressed on normal human articular cartilage, but could be induced in vitro by exogenous IL-1alpha, TNFalpha and IFNgamma or by co-culturing cartilage with inflammatory rheumatoid synovium, we conclude that the induction of ICAM-1 on rheumatoid chondrocytes results from the synergistic action of a variety of cytokines produced by the inflammatory cells of the invading pannus.

Expression of ICAM-1 on intact cartilage and isolated chondrocytes

A major factor in cellular cytotoxicity is the interaction between LFA-1 on leukocytes and ICAM-1 on targets. Because several inflammatory cartilage diseases are characterized by the presence of leukocyte infiltrates, the expression of ICAM-1 on human cartilage, cultured chondrocytes, and transplanted cartilage was investigated using monoclonal antibodies. Frozen tissue sections, chondrocytes in suspension, as well as total cellular mRNA were prepared from human cartilage samples. ICAM-1 expression was studied with two different monoclonal antibodies directed against ICAM-1 by immunohistochemical APAAP-staining and additional flow cytometric analyses. The expression of ICAM-1-mRNA in cartilage tissue was analyzed using the northern blot hybridization technique. Furthermore, chondrocytes were treated in culture with interleukin-1 (IL-1) and gamma-interferon (gamma-IFN). ICAM-1 expression after culture was quantified using flow cytometric analysis. We could detect ICAM-1 mRNA in cartilage tissue, however, the immunostaining of tissue sections using monoclonal antibodies did not give clear positive reactions. Isolated chondrocytes showed strongly positive staining patterns in comparison with adequate negative controls as assessed by flow cytometry. A dose-dependent increase of the expression of ICAM-1 on chondrocytes was observed when stimulated with IL-1 and gamma-IFN. Finally, two of the three studied transplanted autologous cartilage samples with advanced resorption showed the presence of ICAM-1 molecules as assessed by immunohistochemistry. This expression of ICAM-1 suggests that the molecule plays a role in severe cartilage inflammatory processes, where tissue damage leads to the exposure of chondrocyte surfaces.

Intercellular adhesion molecule-1 (ICAM-1) and MHC class II on chondrocytes in arthritic joints from pigs experimentally infected with Erysipelothrix rhusiopathiae

This study set out to investigate the in vivo expression and distribution of the porcine homologues of the intercellular adhesion molecule-1 (ICAM-1) and MHC Class II as markers of chondrocyte activation during the development of chronic polyarthritis, which was experimentally induced in Landrace pigs by intra-articular injection of Erysipelothrix rhusiopathiae. ICAM-1 was found to be strongly expressed in vivo on chondrocytes and synovial cells in arthritic joints but was not detected in cartilage from unaffected joints. Although the majority of ICAM-1 positive chondrocytes did not co-express MHC Class II, chondrocyte-type cells expressing both molecules were detected in the transition zone as the disease progressed, particularly at 5 months post-infection. At this stage infiltration of CD4+ T lymphocytes into the damaged cartilage was also apparent. ICAM-1 and MHC Class II are not constitutively expressed on porcine chondrocytes but appeared to be induced as arthritis progressed. The detection of these markers in the pig helps to establish the validity of this animal model for immunopathological studies.

Degradation of human articular cartilage by neutrophils in synovial fluid

OBJECTIVE

To determine whether surface-adherent immunoglobulins are capable of mediating synovial fluid (SF) neutrophil degradation of proteoglycan and collagen in intact, normal human articular cartilage, and to define the respective roles of neutrophil serine proteases and metalloproteases in degrading these cartilage constituents.

METHODS

Pellet explants of normal human articular cartilage pretreated with bovine serum albumin (BSA) or IgG were incubated with polymorphonuclear cells suspended in SF (PMN-SF), or with supernatants derived from neutrophils stimulated with surface-associated IgG. Proteoglycan degradation was measured by assaying release of 35S-proteoglycan fragments from cartilage explants prelabeled with 35S-sulfate. Collagen degradation was measured by assaying hydroxyproline content in the PMN-SF preparations or neutrophil supernatants following their incubation with unlabeled explants.

RESULTS

Significant release of both 35S fragments and hydroxyproline was noted following incubation of PMN-SF with IgG-treated pellets, compared with pellets treated with BSA. IgG preparations derived from pooled normal serum or rheumatoid arthritis SF were equally efficacious in mediating PMN degradation of cartilage collagens. Explant release of 35S fragments during incubation with PMN supernatant was completely inhibited when serine proteases were inactivated by diisopropyl fluorophosphate (DFP); however, release of 35S fragments was enhanced when metalloprotease activity was present in the supernatant. Release of hydroxyproline during incubation of explants with PMN supernatant was comparable in the presence of DFP or EDTA, but was markedly enhanced when both serine and metalloprotease activity were present in the supernatant.

CONCLUSION

Neutrophils in SF are capable of degrading both proteoglycans and collagens in intact human articular cartilage. Degradation of these cartilage constituents is facilitated by immunoglobulins adherent to the cartilage surface and by the synergistic action of PMN serine and metalloproteases released during activation of neutrophils with surface-associated immunoglobulin.

Detection of cytokine activated chondrocytes in arthritic joints from pigs infected with Erysipelothrix rhusiopathiae

Chronic polyarthritis was induced in pigs by injection of Erysipelothrix rhusiopathiae and the in vivo activation of chondrocytes by cytokines was then investigated in the affected joints by immunocytochemistry. A polyclonal antiserum which recognises surface markers on in vitro interleukin 1 activated porcine chondrocytes was used to detect activated chondrocytes in all zones of the cartilage from diseased joints. In contrast, cartilage removed from an unaffected joint in the same animal showed no chondrocyte activation. Inflammatory synovial tissue removed from diseased joints and cocultured with cartilage from the unaffected joint induced activation of adjacent chondrocytes. The presence of interleukin 1 in the inflammatory cells of the synovium was confirmed and major histocompatibility complex (MHC) class II antigens were detected as a marker of synovial activation. Chondrocytes were found not to express class II antigens in cartilage from either the diseased or the unaffected joint. These observations show that the porcine erysipelas model of arthritis will be useful in facilitating a novel approach to monitoring the behaviour of individual chondrocytes under pathophysiological conditions.

Expression of intercellular adhesion molecule 1 (ICAM-1) on human articular cartilage chondrocytes

Monoclonal antibodies have been used to demonstrate the induction of intercellular adhesion molecule 1 (ICAM-1) on chondrocytes in human articular cartilage. ICAM-1 was found not to be constitutively expressed but could be induced by exogenous interleukin 1 alpha(IL1- alpha) at concentrations ranging from 0.01 to 20 ng/ml during in vitro culture. Maximum expression was observed with 2-5ng/ml. In time-course experiments ICAM-1 was not expressed after 4h in culture with IL1 alpha. Expression was induced by 16h and was sustained for a minimum of 6 days in the continued presence of the cytokine. The endothelial leukocyte adhesion molecule (ELAM-1) was not expressed on chondrocytes and was not induced by IL1-alpha.