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

Evidence that a humoral immune response to autologous cartilage proteoglycan can participate in the induction of cartilage pathology

We examined antiproteoglycan antibodies as an autoimmune response for induction of synovitis. This hypothesis was studied by monitoring humoral antiproteoglycan antibody following IgG induction of experimental immune synovitis, localization in the articular cartilage of an autologous immune response, and loss of proteoglycan from cartilage following intravenous administration of antiproteoglycan monoclonal antibodies. The data support the hypothesis that autoimmunity to cartilage macromolecules may play a role in the etiopathogenesis of arthritis.

The relationship between cell-mediated immunity and cartilage degradation in antigen-induced arthritis in the rabbit

The relative contributions of cellular and humoral immunity to cartilage destruction in chronic arthritis has been investigated in a model of chronic synovitis in the rabbit. In this model, antigen-induced arthritis, immunization with ovalbumin in Freund's complete adjuvant (FCA) followed by intra-articular injection of this protein produces a chronic synovitis associated with loss of proteoglycan from articular cartilage. In addition, the synovial lining cell population is metabolically activated. Similar treatment of animals immunized with ovalbumin in Freund's incomplete adjuvant (FIA) produced a resolving arthritis which initially (over the first 7 days) appears to be identical to that in FCA-immunized animals, apart from the lack of activation of synovial lining cells. Following this initial synovitis the joints return to apparent normality apart from a persistent 'low grade' synovitis consisting mainly of a plasma cell infiltrate. The most striking finding in the FIA-immunized animals is the rapid loss (greater than 30% by day 7) and recovery of proteoglycan from the matrix of articular cartilage. These findings show that the perpetuation of chronic destructive synovitis in the rabbit requires the presence of active cellular immunity.

Crystallization of purified recombinant human interleukin-1 beta

The gene for human interleukin-1 beta was cloned from SK-hep-1 hepatoma cellular RNA and expressed at high levels in Escherichia coli both as the naturally processed form (rIL-1 beta) and as a variant with an additional sequence of three amino acids on the N-terminus (rIL-1 beta +). Expressed protein was purified to homogeneity by a sequence of steps, which included low pH incubation, adsorption and desorption from Procion Red Sepharose, sizing on a Superose 12 fast-performance liquid chromatography (FPLC) column, and anion exchange chromatography on QAE Sepharose. The final step provided a biologically active protein that migrates on two-dimensional (2-D) gels as a single spot with a pI of 6.7 +/- 0.2 and a molecular mass of 17,500 daltons. Concentrated solutions of rIL-1 beta have produced crystals by ammonium sulfate precipitation. The crystals are tetragonal, show the symmetry of space group P4(1) or its enantiomer, have lattice constants of a = 58.46 (1) and c = 77.02 (3) A, and scatter to at least 2 A resolution. A structure determination based on these crystals is under way.

Effects of interleukin-1 and anti-inflammatory drugs on the degradation of human articular cartilage

It has been suggested that metalloproteases produced by chondrocytes play an important role in cartilage breakdown in joint diseases. The aim of this study was to investigate changes in enzyme activities in human rheumatoid and osteoarthritic articular cartilage. Cartilage fragments were incubated with various drugs for 48 hours. The concentrated culture media were used as enzyme solutions. Collagenase was assayed using FITC-collagen as the substrate. Proteoglycanase (PGase) was measured either by the release of 35S-labelled proteoglycans from cartilage into the medium, or by enzyme assay using proteoglycan monomer bound to fluorescein-conjugated hyaluronic acid as the substrate. Collagenase and proteoglycanase were found only in trace amounts in the concentrated media of healthy cartilage. Interleukin-1 (IL-1) enhanced the enzyme activities significantly. Marked increases of enzyme activities were observed in the concentrated media of rheumatoid (RA) and osteoarthritic (OA) cartilage. The sensitivity to interleukin-1 was also higher in OA and RA cartilage compared with healthy cartilage. Dexamethasone (10(-6) mol/L) markedly depressed enzyme activity. Tiaprofenic acid (4 x 10(-5) mol/L) also decreased enzyme activity, whereas indomethacin (4 x 10(-6) mol/L) and naproxen (3 x 10(-4) mol/L) had no effect.

Role of cytokines in rheumatoid synovitis

Although the chronic inflammatory reaction in rheumatoid synovitis appears to be stimulated by an as yet unidentified antigen, the mononuclear cell infiltration is to a large extent accomplished through the nonspecific action of cytokines and growth factors acting as (1) chemotactic agents for the emigration and ecotaxis of monocytes and lymphocytes, (2) upregulators of endothelial cells for the binding of lymphocytes and monocytes to the endothelium of postcapillary venules prior to emigration and (3) angiogenic agents for the proliferation of the microvasculature, and as a result, the proliferation of the synovial membrane. The synovial lining layer may play an important part in this process by stimulating the infiltration of the synovial tissue with "exudate macrophages" as a necessary step in the development of lining layer hyperplasia. Evidence for the capacity of the cytokines to mediate chronic synovitis is provided by the well-known observation that intraarticular injection of cytokines, particularly IL-1, produces both acute and chronic synovitis in the experimental animal.

Differential responses of old human cartilage explants to synovial- and mononuclear-cell factors

To investigate mechanisms of cartilage destruction that may apply to rheumatoid arthritis, young and old human, and young porcine, articular cartilage was cultured for 8 days and the effects on proteoglycan (PG) metabolism of normal synovium supernatant (NSS), rheumatoid synovial fluid (RFL), and blood mononuclear cell supernatant (MCF) were studied. The effects were chondrocyte-mediated. An inverse correlation was found between baseline net PG synthesis and the effect of NSS on PG synthesis. Responses of young (porcine and human) cartilage were similar. In young cartilage the three agents induced PG depletion by suppression of net PG synthesis. In old cartilage NSS and RFL induced PG depletion, whereas MCF did not. In cartilage of low baseline net PG synthesis, NSS and MCF stimulated both PG release and PG synthesis; NSS stimulated predominantly PG release, and MCF predominantly PG synthesis. In conclusion, young and old human cartilage differ in the quality of their in vitro response to potentially catabolic factors. This may be due to the difference in baseline net PG synthesis. Synovial extracts differ from mononuclear-cell supernatants in their effects on old cartilage. It is suggested that this is caused by the presence, in different relative amounts, of factors that influence either PG synthesis or PG release.

Enchondral cartilage rests collagen-induced autoimmunity: a possible pathogenetic mechanism of otosclerosis

Collagen autoimmunity has been suggested as one etiologic mechanism to otosclerosis. Although substantial studies relating this disease to collagen autoimmunity have been reported, a basic understanding of the pathogenic mechanism involved is lacking. Some otosclerosis patients have a high level of antibody to type II collagen. In addition, complement and antibody were deposited in the stapes from otosclerosis patients. Furthermore, the otic capsule and stapes have been found to contain type II collagen by immunohistologic studies and biochemical analysis. Otospongiosis-like lesions have also been produced in rats by immunizing them with type II collagen. This finding led us to postulate a hypothesis of an autoimmunity to type II collagen as an etiopathogenesis of this illness. Our initial hypothesis has been updated to incorporate new findings in the field of cell biology. The role of interleukin 1, osteoclasts, osteoblasts, bone resorption, and other factors such as minor collagens, calcitonin, vitamin D, parathyroid hormone, collagenase, and prostaglandins are incorporated in this updated hypothesis.

Inflammatory responses to intraocularly injected interleukin 1

Intraocular injection of highly purified human interleukin 1 into the anterior chamber of the rabbit eye resulted in the accumulation of inflammatory cells. Peak cellular infiltration occurred at 4hr and cells were still present at 24h. Examination of ocular blood vessels in IL-1-injected eyes revealed no abnormalities. IL-1 had no effect on the protein content of the aqueous humour confirming that this monokine has no direct action on the blood-aqueous barrier. Comparison of the potency of IL-1 as a chemoattractant with the 5-lipoxygenase product, leukotriene B4 demonstrated that the former agent was more active by several orders of magnitude.

PAF-acether in chronic arthritis

Platelet activating factor (PAF-acether) is a potent pro-inflammatory mediator. The possible involvement of this molecule in the pathogenesis of chronic erosive arthritis has been investigated using an animal model, antigen-induced arthritis in the rabbit, which closely resembles rheumatoid arthritis. The arthritic joint fluids from rabbits with antigen-induced arthritis contained low levels of PAF-acether in the acute stages of the disease. However, PAF-acether was not detectable in the chronic stages of the lesion. The biologically inactive precursor/metabolite of PAF-acether, lyso-PAF-acether, was detectable in both control and arthritic joint washes. However, the levels of lyso-PAF-acether in the arthritic joint fluids were significantly elevated above those of control in the acute stages of the disease, but not in the chronic stages. Intra-articular injection of PAF-acether at doses up to 100 times the levels detected in the acute stages of this model did not induce joint swelling or leucocyte accumulation in normal rabbits. This study suggest that PAF-acether may contribute to the acute phase of antigen-induced arthritis but is less likely to be involved in the chronic processes.