A subgroup of lupus patients with nephritis, innate T cell activation and low vitamin D is identified by the enhancement of circulating MHC class I-related chain A.

The major histocompatibility complex (MHC) class I-related chain A (MICA) is induced upon stress, and labels malfunctioning cells for their recognition by cytotoxic lymphocytes. Alterations in this recognition and also abnormal natural killer (NK) functions have been found in systemic lupus erythematosus (SLE). MICA can be shed from cells, subsequently acting as a soluble decoy receptor (sMICA). Our purpose was to study circulating sMICA levels in relationship with the activation of innate pathways in PBMC in a cohort of lupus patients. NK cells were characterized by flow cytometry. Gene expression of Toll-like receptors (TLR), interferon (IFN)-I sensitive genes and MICA were separately analyzed in monocytes, T cells and B cells. Serum sMICA was measured with enzyme-linked immunosorbent assay (ELISA). In our cohort, NK cell counts dropped in relationship with disease activity. sMICA showed an inverse trend with NK cell counts, as well as a significant association with activity indices, but not with complement decrease. Levels of sMICA associated to proteinuria and active nephritis. A multivariate regression model revealed anti-nuclear antibody (ANA) titres, the up-regulation of TLR-4 in T cells and lower vitamin D as predictors of sMICA enhancement. Interestingly, vitamin D showed an inverse association with proteinuria and a strong correlation with T cell MICA mRNA levels. According to our data, circulating sMICA identifies a subgroup of lupus patients with low vitamin D, innate activation of T cells and nephritis. We propose that lymphocyte shedding could account for the enhancement of sMICA and reflect an immune evasion mechanism driving disease activation in lupus.

Chondrocyte enlargement is a marker of osteoarthritis severity.

OBJECTIVE: We aimed to assess whether an increase in chondrocyte size might be a feature of the articular cartilage (AC) hypertrophic-like phenotype both in experimental and in human osteoarthritis (OA). The anatomical location of these enlarged cells in the cartilage layers was also evaluated. METHODS: Experimental OA was carried out in female rabbits alone or in combination with osteoporosis (OPOA). The rabbits were subjected to destabilization knee surgery to develop OA. Osteoporosis was induced with ovariectomy and methylprednisolone administration. Human OA samples obtained from knee replacement surgery were also studied. Cartilage lesions and chondrocyte size were assessed in AC sections. Immunostaining of type-X collagen and metalloproteinase-13 were used as markers of the AC hypertrophic transformation. Both the cell size and the gene expression of type-X collagen were further analyzed in primary murine chondrocyte cultures. RESULTS: Compared to healthy AC, chondrocyte size was increased both in experimental and in human OA, in correlation with the severity of cartilage damage. No differences in chondrocyte size were found between deeper or more superficial regions of AC. In cell cultures, accretion of hypertrophic markers and cell enlargement were found to occur synchronized. CONCLUSIONS: We observed an enhancement in the mean size of chondrocytes at the OA cartilage, which showed correlation with cartilage damage, both in human and in experimental OA. The enlarged chondrocytes were homogeneously distributed throughout the AC. Our results suggest that chondrocyte size could be a reliable measure of disease progression, of potential use in the histopathological assessment of OA cartilage.

Effects of PTH [1-34] on synoviopathy in an experimental model of osteoarthritis preceded by osteoporosis.

PURPOSE: Synoviopathy contributes to cartilage degradation in osteoarthritis (OA). Intermittent parathyroid hormone (PTH) [1-34] administration inhibits terminal differentiation of human chondrocytes and prevents cartilage damage. We aimed to determine whether PTH [1-34] could modify synovial changes in experimental OA preceded by osteoporosis (OP). METHODS: Twenty osteoporosis (OP) rabbits underwent knee surgery to induce OA. They were administered either saline vehicle or PTH for 10 weeks. Ten healthy rabbits were used as controls. Following sacrifice, synovial changes were assessed by Krenn synovitis score, immunohistochemistry for macrophages (RAM-11), B and T lymphocytes, type I collagen, parathyroid hormone 1 receptor (PTH1R), and anti-proliferating cell nuclear antigen (PCNA). Synovial mRNA levels of Col1A1, IL-1ß, cyclooxygenase 2 (COX-2), matrix-degrading metalloproteinases (MMP-9, MMP-13), and monocyte chemotactic protein-1 (MCP-1), as well as protein expression of PTH1R were also determined. Cartilage damage was analyzed by Mankin score. RESULTS: OPOA + vehicle rabbits showed an increase in synovitis score vs controls (P = 0.003), mainly due to synovial hyperplasia and fibrosis, while PTH reduced these changes (P = 0.017). Mankin and Krenn scores were well correlated in all groups (r = 0.629, P = 0.012). Immunostaining for RAM-11 and B lymphocytes was increased (P ≤ 0.05), whereas PTH1R protein levels tended to be higher in OPOA + vehicle animals vs controls. PTH did not modify RAM-11 staining or PTH1R levels; however, it restored PTH1R localization to the vicinity of synovial vessels. PTH also decreased type I collagen, MCP-1, and MMP-13 expression (P < 0.05), as well as PCNA staining compared to vehicle-treated OPOA rabbits. CONCLUSIONS: In our model of OA aggravated by previous OP, synoviopathy correlated well with cartilage damage. Intermittent PTH [1-34] administration ameliorated both hyperplasia and fibrosis.

Recurrent Anterior Non-necrotizing Scleritis as an Adverse Event of ChAdOx1 nCoV-19 (Vaxzevria) Vaccine.

PURPOSE: To describe a case of anterior scleritis related to SARS-CoV-2 vaccine. SARS-CoV-2 vaccines appear safe; however vaccination has triggered thromboembolic events in predisposed patients. METHODS: A retrospective case report of anterior scleritis in a woman following administration of both ChAdOx1nCoV-19 vaccine doses was studied by complete ophthalmologic examination and complementary tests. RESULTS: The patient has overcome SARS-CoV-2 infection a year prior. Ancillary tests including autoimmune and infectious diseases were negative. The chronology between ChAdOx1nCoV-19 vaccine and the sequential episodes of scleritis may have a cause-and-effect relationship. CONCLUSION: Ophthalmologists may be aware of scleritis as an ocular manifestation following ChAdOx1nCoV-19 vaccine, in otherwise healthy patients.

Pharmacologic Treatment of Anti-MDA5 Rapidly Progressive Interstitial Lung Disease.

Purpose of the Review: Idiopathic inflammatory myopathies are a heterogeneous group of autoimmune disorders. The presence of different autoantibodies allows clinicians to define distinct phenotypes. Antibodies against the melanoma differentiation-associated protein 5 gene, also called anti-MDA5 antibodies, are associated with a characteristic phenotype, the clinically amyopathic dermatomyositis with rapidly progressive interstitial lung disease. This review aims to analyze the different pharmacological options for the treatment of rapidly progressive interstitial lung disease in patients with anti-MDA5 antibodies. Recent Findings: Evidence-based therapeutic recommendations suggest that the best initial approach to treat these patients is an early combination of immunosuppressive drugs including either glucocorticoids and calcineurin inhibitors or a triple therapy adding intravenous cyclophosphamide. Tofacitinib, a Janus kinase inhibitor, could be useful according to recent reports. High ferritin plasma levels, generalized worsening of pulmonary infiltrates, and ground-glass opacities should be considered predictive factors of a bad outcome. In this scenario, clinicians should consider rescue therapies such as therapeutic plasma exchange, polymyxin-B hemoperfusion, veno-venous extracorporeal membrane oxygenation, or even lung transplantation. Summary: Combined immunosuppressive treatment should be considered the first-line therapy for patients with anti-MDA5 rapidly progressive interstitial lung disease. Aggressive rescue therapies may be useful in refractory patients.

Chondroitin sulfate improves synovitis in rabbits with chronic antigen-induced arthritis.

OBJECTIVE: Our aim was to explore the effect of chondroitin sulfate (CS), a natural glycosaminoglycan with attributed anti-inflammatory properties, on synovitis in a rabbit model of chronic arthritis with intense systemic inflammation bolstered by endothelial lesion and atherosclerotic diet. METHODS: Chronic arthritis was induced by intraarticular injections of ovalbumin in immunized rabbits. Systemic inflammation was boosted in these rabbits by receiving a hyperlipidemic diet after producing an endothelial lesion in the femoral arteries. A group of these rabbits were treated with CS (100mg/kg/day). At sacrifice, synovial membranes were isolated, and cyclooxygenase-2 (COX-2) and chemokine (C-C motif) ligand 2 (CCL2) mRNA, as well as protein expression were assayed by quantitative real-time polymerase chain reaction (RT-PCR) and western blot studies. Histological synovial examination was also carried out employing the histopathological synovitis score (Krenn scale). RESULTS: CS diminished both gene expression and protein synthesis of COX-2 and CCL2, and the histopathological score of the synovial membrane, when compared to untreated rabbits. In fact, CS partially prevented the intimal layer proliferation and the inflammatory cell infiltration in the synovial membrane, which was observed in non-treated animals. CONCLUSION: CS reduced the inflammatory response of the synovial membrane, as well as decreased the synovial histopathological lesions in our animal model. Further studies are warranted to demonstrate whether CS might be beneficial in the treatment of inflammatory arthritis.

Recommendations for the treatment of anti-melanoma differentiation-associated gene 5-positive dermatomyositis-associated rapidly progressive interstitial lung disease.

OBJECTIVES: The study aimed to develop evidence-based recommendations for the treatment of rapidly progressive interstitial lung disease (RPILD) associated with the anti-Melanoma Differentiation-Associated Gene 5-positive dermatomyositis (DM) syndrome. METHODS: The task force comprised an expert panel of specialists in rheumatology, intensive care medicine, pulmonology, immunology, and internal medicine. The study was carried out in two phases: identifying key areas in the management of DM-RPILD syndrome and developing a set of recommendations based on a review of the available scientific evidence. Four specific questions focused on different treatment options were identified. Relevant publications in English, Spanish or French up to April 2018 were searched systematically for each topic using PubMed (MEDLINE), EMBASE, and Cochrane Library (Wiley Online). The experts used evidence obtained from these studies to develop recommendations. RESULTS: A total of 134 studies met eligibility criteria and formed the evidentiary basis for the recommendations regarding immunosuppressive therapy and complementary treatments. Overall, there was general agreement on the initial use of combined immunosuppressive therapy. Combination of high-dose glucocorticoids and calcineurin antagonists with or without cyclophosphamide is the first choice. In the case of calcineurin antagonist contraindication or treatment failure, switching or adding other immunosuppressants may be individualized. Plasmapheresis, polymyxin B hemoperfusion and/or intravenous immunoglobulins may be used as rescue options. ECMO should be considered in life-threatening situations while waiting for a clinical response or as a bridge to lung transplant. CONCLUSIONS: Thirteen recommendations regarding the treatment of the anti-MDA5 positive DM-RPILD were developed using research-based evidence and expert opinion.

Effect of chondroitin sulphate in a rabbit model of atherosclerosis aggravated by chronic arthritis.

BACKGROUND AND PURPOSE: Among the agents employed to manage osteoarthritis, chondroitin sulphate (CS) is a natural glycosaminoglycan with an anti-inflammatory effect on joint cells. CS might also influence the inflammatory component of atherosclerosis. Our aim was to examine the effect of CS administration on vascular injury and on markers of systemic inflammation in a rabbit model of atherosclerosis aggravated by systemic inflammation provoked by chronic antigen-induced arthritis. EXPERIMENTAL APPROACH: Atherosclerosis was induced in rabbits by maintaining them on a hyperlipidaemic diet after producing an endothelial lesion in the femoral arteries. Simultaneously, chronic arthritis was induced in these animals by repeated intraarticular injections of ovalbumin in previously immunized rabbits. A group of these rabbits were treated prophylactically with CS (100 mg kg(-1)day(-1)) and when the animals were killed, serum and peripheral blood mononuclear cells (PBMC) were isolated. Furthermore, femoral arteries and thoracic aorta were used for gene expression studies and histological examination. KEY RESULTS: CS administration reduced the concentration of the proinflammatory molecules C-reactive protein and IL-6 in serum. Likewise, CS inhibited the expression of CCL2/monocyte chemoattractant protein (MCP)-1 and cyclooxygenase (COX)-2 in PBMC, and reduced the nuclear translocation of nuclear factor-kappaB. In the femoral lesion, CS also diminished the expression of CCL2 and COX-2, as well as the ratio of the intima/media thickness. Moreover, CS decreased the percentage of rabbits with atherosclerosis and chronic arthritis that developed vascular lesions in the aorta. CONCLUSIONS AND IMPLICATIONS: These findings suggest that CS treatment may to some extent impede the progression of atherosclerosis.

Diacerein has a weak effect on the catabolic pathway of human osteoarthritis synovial fibroblast--comparison to its effects on osteoarthritic chondrocytes.

OBJECTIVES: Synoviocytes play a crucial role in the inflammatory response leading to structural damage in OA. Our aim was to assess the effects of diacerein and NSAIDs on cellular responses of synoviocytes associated with inflammation and structural integrity of cartilage in OA. METHODS: The effects of diacerein, celecoxib, diclofenac, meloxicam and indomethacin on prostaglandin (PG) E2 production, cyclo-oxygenase-2 (COX-2) protein expression, nitrite levels, presence of MMP-1 and -13, and activation of nuclear factor-kappaB (NF-kappaB) were studied on stimulated OA synoviocytes and chondrocytes. RESULTS: Diacerein and NSAIDs inhibited IL-1beta-stimulated NF-kappaB activation in synoviocytes and chondrocytes except indomethacin in synoviocytes. Diacerein further increased COX-2 protein expression and PGE2 synthesis in synoviocytes stimulated with IL-1beta, while no effect was observed on stimulated chondrocytes. NSAIDs diminished until almost basal levels PGE2 release in both cells and, surprisingly, these drugs also diminished COX-2 protein expression both in synoviocytes and chondrocytes. With regard to structural mediators, diacerein decreased MMP-13 levels in synoviocytes but did not modify MMP-1 presence. NSAIDs induced a significant increase in MMP-1 levels in both cell types and in MMP-13 levels in chondrocytes. CONCLUSIONS: Diacerein does not seem to reduce but rather increase inflammatory mediators in synoviocytes, while it does not overall affect chondrocyte inflammatory profile.

Cartilage oligomeric matrix protein (COMP) is modified by intra-articular liposomal clodronate in an experimental model of arthritis.

OBJECTIVE: High-dose liposomal bisphosphonates exert apoptotic effects. This work studies the chondroprotective and anti-inflammatory properties of intra-articularly administered low-dose, non-cytotoxic liposomal clodronate. METHODS: Antigen induced arthritis in rabbits was treated with intra-articular injections of liposomal clodronate. Drug effects on cartilage oligomeric matrix protein COMP was assessed using immunohistochemistry and morphometry of synovial membrane and hyaline articular cartilage. RESULTS: COMP remained close to normal in liposomal clodronate treated superficial articular cartilage compared to a significant loss of COMP in arthritis controls treated with empty liposomes. The middle and deep layers of the hyaline articular cartilage were characterized by highly increased COMP expression in liposomal clodronate treated AIA joints compared to controls. In contrast to cartilage, synovial COMP expression was slightly decreased as a result of liposomal clodronate treatment. CONCLUSION: Low-dose, non-cytotoxic liposomal clodronate exerts a dichotomous effect on synovial membrane and articular cartilage COMP in the AIA model. COMP is a useful inflammation marker in the synovial tissue, but it also contributes to the structural integrity of the hyaline articular cartilage forming bridges between type II and IX collagens. Enhancement of COMP in clodronate treated AIA cartilage suggests a chondroprotective and anti-inflammatory effect in the inflammatorily damaged and mechanically strained cartilage.

Prevalence, characteristics, and outcome of asthmatic patients with type 2 diseases in hospitalized patients with COVID-19 in Madrid, Spain

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Cartilage and bone biological markers in the synovial fluid of osteoarthritic patients after hyaluronan injections in the knee.

OBJECTIVE: To evaluate synovial fluid levels of cartilage and bone biological markers after repetitive intra-articular injections of sodium hyaluronate (HA) in knee osteoarthritis (OA) patients. METHODS: Twenty patients with knee OA were evaluated before and after 5 weekly injections of HA. To study cartilage and bone biological markers, synovial fluid and urine samples were collected simultaneously with the first (FI=week 0) and before the last injection (LI=week 4) of HA. Not commercially available markers (cartilage oligomeric matrix protein (COMP), proteoglycan monomers and cyanogen bromide peptide 11 of the type II collagen chains (alpha (II) CA11B)) were determined by an indirect inhibition ELISA developed and standardized in our laboratory. RESULTS: We found a significant reduction in levels of proteoglycan monomers (30+/-16 vs. 22+/-10 microg/ml, p<0.05), an increase in COMP concentration (2.9+/-0.9 vs. 3.6+/-0.9 microg/ml, p<0.05) and osteocalcin (BGP) levels (8.7+/-8 vs. 11.9+/-9 ng/ml, p<0.05). No significant changes were observed in the levels of alpha (II)CB11B), metalloproteinase-1 (MMP-1) or pyridinium cross-link/creatinine (Pyr/Cr). CONCLUSIONS: HA could elicit an indirect response on the cartilage and bone metabolism due to the increased overuse of the joint caused by the analgesic effect of HA. However, a direct HA action on the metabolism of chondrocytes must not be ruled out.

Pharmacological modulation by celecoxib of cachexia associated with experimental arthritis and atherosclerosis in rabbits.

BACKGROUND AND PURPOSE: Non-steroidal anti-inflammatory drugs improve inflammatory cachexia in several conditions. Thus, we have explored inhibition of cyclooxygenase-2 (COX-2) in an experimental model of rheumatoid cachexia in rabbits. EXPERIMENTAL APPROACH: Chronic arthritis was induced in immunized rabbits by repeated intra-articular injections of ovalbumin. To increase the degree of systemic inflammation and also to induce atherosclerotic lesions, the animals were fed a hyperlipidaemic diet (2% cholesterol and 6% peanut oil) and were given an endothelial injury of the femoral artery. Rabbits were randomized to receive the COX-2 inhibitor celecoxib (10 mg·kg⁻¹ ·day⁻¹) or no treatment. After 4 weeks, sera, peripheral mononuclear cells and vessel specimens were collected. KEY RESULTS: Inhibition of COX-2 by celecoxib modulated the systemic inflammatory response and increased total cholesterol and triglyceride levels. Celecoxib also minimized weight loss and prevented serum albumin fall. At a vascular level, celecoxib reduced COX-2 protein in the femoral arterial wall, but did not modify size or the macrophage infiltration of femoral lesions nor the percentage of rabbits with spontaneous aortic plaques. CONCLUSIONS AND IMPLICATIONS: Our animal model induced a severe inflammatory cachexia, comparable to that of persistently active rheumatoid arthritis. The inhibition of COX-2 by celecoxib improves this state, suggesting that COX products play an important role in its development, without affecting the development or the progression of vascular lesions. Overall, these results suggest that celecoxib might be considered as a new therapeutic tool for the treatment of rheumatoid cachexia.

A sonographic enthesitic index of lower limbs is a valuable tool in the assessment of ankylosing spondylitis.

BACKGROUND: Enthesitis is a remarkable feature of ankylosing spondylitis (AS) not specifically approached by the available measuring tools for the disease. Ultrasonography (US) has proved to be an excellent technique for the assessment of tendon pathology. OBJECTIVE: To test a Sonographic Entheseal Index (SEI) of the lower limbs in a cohort of patients with AS, as a potential measuring tool. METHODS: 44 patients with AS and 10 healthy controls were enrolled. Bath Ankylosing Spondylitis Functional Index and Bath Ankylosing Spondylitis Disease Activity Index, pain at entheseal points, severity of symptoms, acute-phase reactants, Schober's test and stage of sacroiliitis were recorded. Patients underwent US examination of five entheseal regions from both lower limbs by two experts. Hypoechogenicity, increased tendon thickness, peritendinous oedema and bursitis were considered signs of active inflammation. Insertional bone erosions, intratendinous calcifications, decreased thickness and tears were considered signs of chronic injury. Each alteration independently scored one point. Data were analysed with Spearman's correlation method. RESULTS: A significant interobserver correlation in SEI scores (p<0.001) and a fine discriminative power between controls and patients were observed. Acute entheseal lesions predominated (63% vs 37%), the most frequent alteration being tendon hypoechogenicity (43%). 72% of all lesions were located at the foot. The SEI correlated with reduction of Schober's test (p<0.02), but not with other activity or severity parameters. CONCLUSIONS: A scoring method such as the SEI may be of help in characterising entheseal injury in AS, and for decision making in these patients.

Long term NSAID treatment inhibits COX-2 synthesis in the knee synovial membrane of patients with osteoarthritis: differential proinflammatory cytokine profile between celecoxib and aceclofenac.

OBJECTIVE: To compare the effect of celecoxib with that of a classic non-steroidal anti-inflammatory drug (NSAID) on synovial inflammation and on the synovial expression of proinflammatory genes in patients with knee osteoarthritis (OA). METHODS: 30 patients with severe knee OA scheduled for total knee replacement surgery were included in a 3 month clinical trial. They were randomised to two groups: patients treated with celecoxib (CBX) (200 mg/24 h) and patients treated with aceclofenac (ACF) (100 mg/12 h). Those patients with OA who did not want to be treated with NSAIDs served as a control group. During knee surgery, synovial fluid (SF) and synovial membrane (SM) were collected. A SM specimen was fixed and embedded in paraffin and another part was frozen for molecular biology studies. RESULTS: At the end of study both CBX and ACF treated patients showed a significant improvement in pain and knee function compared with controls. Both drugs significantly reduced prostaglandin E(2) (PGE(2)) SF concentration and down regulated COX-2 mRNA and protein expression at the SM. However, synovial macrophage infiltration (CD68 antigen staining) and expression of proinflammatory mediators, such as interleukin 1beta and tumour necrosis factor alpha, were decreased only by CBX treatment. CONCLUSION: Both drugs improved joint pain and function, inhibited SF PGE(2) concentration, and induced a decrease in synovial COX-2 expression and synthesis not related to the tissue inflammatory status. These data suggest that PGE(2) blocking agents may decrease PGE(2) production not only by direct COX-2 inhibition but also by down regulating COX-2 expression and synthesis. However, CBX and ACF appear to have different anti-inflammatory profiles in controlling OA synovial macrophage infiltration and proinflammatory expression.

Expression of the peptide C4b-binding protein beta in the arthritic joint.

BACKGROUND: C4b-binding protein (C4BP) is a plasma oligomeric glycoprotein that participates in the regulation of complement and haemostasis. Complement-regulatory activity depends on the C4BPalpha-polypeptide, whereas the C4BPbeta-polypeptide inactivates protein S, interfering with the anti-coagulatory protein C-dependent pathway. OBJECTIVE: To investigate the expression of C4BPbeta in the rheumatoid joint. METHODS: Expression of C4BP was studied in synovial explants from patients with rheumatoid arthritis, osteoarthritis and healthy controls, using immunohistochemistry and in situ hybridisation. C4BP isoforms and free C4BPbeta were studied in synovial effusions from patients with rheumatoid arthritis, osteoarthritis and microcrystalline arthritis (MCA) by immunoblotting; total and free protein S levels were studied by enzyme immunoassay. RESULTS: C4BPbeta was overexpressed in the synovial membranes of patients with rheumatoid arthritis, in close association with the severity of synovitis and the extension of interstitial fibrin deposits. As many as 85% fluids from patients with rheumatoid arthritis contained free C4BPbeta, whereas this unusual polypeptide was present in 50% fluids from patients with MCA and 40% fluids from patients with osteoarthritis. Free protein S at the effusions was pathologically reduced in patients with rheumatoid arthritis and MCA, and remained normal in patients with osteoarthritis. CONCLUSION: C4BPbeta is expressed by the inflamed synovial tissue, where it can participate in processes of tissue remodelling associated with invasive growth.

A platelet activating factor receptor antagonist prevents the development of chronic arthritis in mice.

OBJECTIVE: To examine the effect of treatment with the platelet activating factor (PAF) receptor antagonist BN 50730 on the clinical and morphological evolution of collagen induced arthritis in mice. METHODS: Mice with collagen induced arthritis were treated with BN 50730 (0.3, 1, 3 mg/kg) or vehicle (0.1% Tween-20 in saline) once a day, from 3 days before the induction of the arthritis to 70 days after. Disease evolution was followed daily by inspection of inflammatory signs and measurement of the knee joint diameter on Days 0, 40, and 70. At the end of the treatment period, the morphological evaluation of the synovial membrane, the immunodetection of fibronectin, and the content of cartilage proteoglycans were studied. RESULTS: On Day 40, mice receiving the highest dose of BN 50730 (3 mg/kg) showed a reduction in the knee joint diameter in comparison with untreated (2.1 +/- 0.2 vs 2.8 +/- 0.4 mm, p < 0.01). On Day 70, animals receiving 1 and 3 mg/kg had a normal knee diameter, while it remained enlarged in the untreated ones. In BN 50730 treated mice (3 mg/kg) we also observed a significant reduction of the inflammation score (0.1 +/- 0.1 vs 2.5 +/- 0.2 in the untreated) and deposition of fibronectin. Depletion of cartilage proteoglycans was also reversed with BN 50730. CONCLUSION: The beneficial effects in this model of joint injury after administration of the PAF antagonist BN 50730 suggest that PAF could be implicated in the pathogenesis of chronic arthritis.