An anti-inflammatory selective glucocorticoid receptor modulator preserves osteoblast differentiation.

Glucocorticoids (GCs) are in widespread use to treat inflammatory bone diseases, such as rheumatoid arthritis (RA). Their anti-inflammatory efficacy, however, is accompanied by deleterious effects on bone, leading to GC-induced osteoporosis (GIO). These effects include up-regulation of the receptor activator of NF-κB ligand/osteoprotegerin (RANKL/OPG) ratio to promote bone-resorbing osteoclasts and include inhibition of bone-forming osteoblasts. We previously identified suppression of osteoblast differentiation by the monomer glucocorticoid receptor (GR) via the inhibition of Il11 expression as a crucial mechanism for GIO. Here we show that the GR-modulating substance compound A (CpdA), which does not induce GR dimerization, still suppresses proinflammatory cytokines in fibroblast-like synovial cells from patients with RA and in osteoblasts. In contrast to the full GR agonist dexamethasone, it does not unfavorably alter the RANKL/OPG ratio and does not affect Il11 expression and subsequent STAT3 phosphorylation in these cells. Notably, while dexamethasone inhibits osteoblast differentiation, CpdA does not affect osteoblast differentiation in vitro and in vivo. We describe here for the first time that selective GR modulators can act against inflammation, while not impairing osteoblast differentiation.

Systemic levels of IL-23 are strongly associated with disease activity in rheumatoid arthritis but not spondyloarthritis.

OBJECTIVES: Th17 cells are an effector T-cell population that plays a role in chronic inflammatory conditions and is dependent on IL-23 for their survival and expansion. More recently, a genetic association was discovered between polymorphisms in the gene coding for the IL-23 receptor and spondyloarthritis. This study aimed to evaluate the role of Th17-associated cytokines in spondyloarthritis pathogenesis by measuring their levels in the joints and circulation as well as correlating them with disease activity parameters. METHODS: Paired synovial fluid (SF), serum and synovial biopsies were obtained from 30 non-PsA (psoriatic arthritis) spondyloarthritis, 22 PsA and 22 rheumatoid arthritis (RA) patients. IL-17, IL-23 and CCL20 were measured by ELISA in the SF and serum of patients and correlated with systemic and local parameters of disease activity. RESULTS: Concentrations of CCL20, a major Th17-attracting chemokine, tended to be higher in the joints of RA than in spondyloarthritis patients. Interestingly, levels of CCL20 were markedly higher in SF as opposed to serum. In addition, there was a remarkable association between the expression of the Th17 cytokine system and the presence of intimal lining layer hyperplasia in RA. Also in the serum, there was a tendency for higher IL-23 levels in RA, which correlated strongly with disease activity parameters. CONCLUSIONS: Th17-related cytokines are expressed in joints of spondyloarthritis as well as RA patients. IL-23 levels, however, correlate with disease activity parameters in RA only. These results point towards a differential regulation of the Th17 cytokine system in spondyloarthritis compared with RA.

Synovial and mucosal immunopathology in spondyloarthritis.

Chronic inflammation ofmusculoskeletal structures is the most prominent disease manifestation of SpA. More specifically, the axial disease affects the spine, the sacroiliac joints and the hips. Peripheral disease includes peripheral arthritis, with a preference for asymmetrical inflammation ofjoints of the lower limbs and enthesitis, which is the presence of inflammation at the sites were ligaments and tendons attach to the bone. Additionally, SpA is often characterized by subclinical inflammation of the gut which partially resembles inflammatory bowel disease. Here, we will review the immunopathology of these different disease manifestations and relate them to clinical applications as well as emerging pathogenic concepts.

In vitro spontaneous osteoclastogenesis of human peripheral blood mononuclear cells is not crucially dependent on T lymphocytes.

OBJECTIVE: In vitro spontaneous osteoclastogenesis from peripheral blood mononuclear cells (PBMCs) is increased in diseases with excessive bone loss. The purpose of this study was to reassess the role of T lymphocytes in this process. METHODS: Fresh or cryopreserved PBMCs obtained from healthy subjects and from patients with rheumatoid arthritis, psoriatic arthritis, and non-psoriatic spondylarthritis were cultured at high density and stained for tartrate-resistant acid phosphatase (TRAP). Resorption of mineralized matrix was assessed by a dentin disc assay. CD14+ monocytes and CD3+ T cells were selected using magnetically labeled antibodies. RESULTS: Numerous multinucleated, TRAP+, dentin-resorbing osteoclasts developed spontaneously from fresh PBMCs from healthy individuals. This process was abrogated by T cell depletion and was restored by exogenous macrophage colony-stimulating factor (M-CSF) and RANKL, indicating the important role of T cells in spontaneous osteoclastogenesis in vitro. Using physiologic freezing and thawing as a model for the activation of PBMCs, spontaneous osteoclastogenesis was significantly increased in cryopreserved versus fresh cells. Under these conditions, spontaneous osteoclastogenesis was not dependent on T lymphocytes, since it was not influenced by T cell depletion and persisted in purified CD14+ cell cultures supplemented with M-CSF and RANKL. In contrast to studies with fresh PBMCs, spontaneous osteoclastogenesis under these conditions did not appear to be clearly different between healthy subjects and patients with arthritis. CONCLUSION: Spontaneous osteoclastogenesis in vitro is dependent on T lymphocytes or on the direct activation of monocytic cells, depending on the test conditions. This variability warrants better validation of the relevance of this functional test for in vivo osteoclastogenesis.

Absence of a classically activated macrophage cytokine signature in peripheral spondylarthritis, including psoriatic arthritis.

OBJECTIVE: Peripheral spondylarthritis (SpA) is characterized by macrophages that express CD163, a marker of alternative activation (M2). The purpose of this study was to assess whether this differential infiltration with macrophage subsets was associated with a different local inflammatory milieu in SpA as compared with rheumatoid arthritis (RA). METHODS: The effect of SpA and RA synovial fluid (SF) on macrophage polarization was tested in vitro on normal peripheral blood monocytes. SF levels of classically activated macrophage (M1)-derived and alternatively activated macrophage (M2)-derived mediators were analyzed by enzyme-linked immunosorbent assay and multiparameter Luminex bead assay in 47 patients with non-psoriatic SpA, 55 with RA, and 15 with psoriatic arthritis (PsA). Paired synovial biopsy samples were analyzed histologically. RESULTS: SF from SpA patients promoted preferential expression of the M2 markers CD163 and CD200R in vitro, even if SF levels of the prototypical M2-polarizing factors (interleukin-4 [IL-4], IL-13, and IL-10) were not increased as compared with those in RA SF. Despite a similar degree of overall joint inflammation in SpA and RA, SpA synovitis displayed strongly reduced SF levels of M1-derived, but not M2-derived, mediators, such as tumor necrosis factor alpha (TNFalpha), IL-1beta, IL-12p70, and interferon-gamma-inducible protein 10. SF levels of M1-derived mediators correlated well with peripheral joint inflammation in RA, but neither these mediators nor IL-1alpha and IL-17 did so in SpA. Of interest, the SF cytokine profile in PsA, a more destructive subtype of SpA, was similar to that in non-psoriatic SpA. CONCLUSION: The local inflammatory milieu is clearly different in SpA as compared with RA peripheral arthritis. Synovitis in SpA, including that in PsA, is characterized by a selective decrease in M1-derived proinflammatory mediators, such as TNFalpha and IL-1beta.

Tumor necrosis factor alpha drives cadherin 11 expression in rheumatoid inflammation.

OBJECTIVE: Cadherin 11 expressed on fibroblast-like synoviocytes (FLS) plays a key role in normal synovial architecture. The purpose of this study was to examine the expression of cadherin 11 in human synovitis. METHODS: Cadherin 11 expression in synovial biopsy samples from patients with various types of arthritis and in lung biopsy samples from patients with interstitial pneumonitis (IP) was examined by immunostaining. The regulation of cadherin 11 expression in human FLS was assessed by quantitative reverse transcription-polymerase chain reaction analysis and Western blotting. Therapeutic modulation of synovial cadherin 11 was assessed before and after effective antiinflammatory therapy. RESULTS: Abundant staining for cadherin 11 was seen in the intimal lining layer and the synovial sublining in inflamed tissues, with discrete staining in noninflammatory osteoarthritic (OA) tissues. The pattern and degree of immunostaining were similar in tissues from patients with rheumatoid arthritis (RA), nonpsoriatic spondylarthritis (SpA), psoriatic arthritis (PsA), and inflammatory OA. Clear staining for cadherin 11 was also observed in lung tissues from RA-associated IP and idiopathic IP patients, but was very limited in normal lung tissue. Cadherin 11 staining correlated strongly with the degree of inflammatory infiltration of the tissue, as well as with the C-reactive protein level and the erythrocyte sedimentation rate in RA patients. In vitro, cadherin 11 expression by FLS was consistently up-regulated by tumor necrosis factor alpha (TNFalpha) at the protein, but not the messenger RNA, level. Cadherin 11 staining in vivo was strongly down-regulated by prednisone treatment in RA patients and by TNFalpha blockade in SpA patients. CONCLUSION: Cadherin 11 expression is regulated by mediators of inflammation, such as TNFalpha. Since cadherin 11 plays an important role in cartilage destruction in experimental arthritis, down-modulation of cadherin 11 by potent antiinflammatory therapies in humans with arthritis may contribute to halting cartilage damage.

B lymphocyte autoimmunity in rheumatoid synovitis is independent of ectopic lymphoid neogenesis.

B lymphocyte autoimmunity plays a crucial role in the pathogenesis of rheumatoid arthritis. The local production of autoantibodies and the presence of ectopic lymphoid neogenesis in the rheumatoid synovium suggest that these dedicated microenvironments resembling canonical lymphoid follicles may regulate the initiation and maturation of B cell autoimmunity. In this study, we assessed experimentally the relevance of ectopic lymphoid neogenesis for B cell autoimmunity by a detailed structural, molecular, and serological analysis of seropositive and seronegative human synovitis. We demonstrate that synovial lymphoid neogenesis is a reversible process associated with inflammation which is neither restricted to nor preferentially associated with autoantibody positive rheumatic conditions. Despite the abundant expression of key chemokines and cytokines required for full differentiation toward germinal center reactions, synovial lymphoid neogenesis in rheumatoid arthritis only occasionally progresses toward fully differentiated follicles. In agreement with that observation, we could not detect Ag-driven clonal expansion and affinity maturation of B lymphocytes. Furthermore, ectopic lymphoid neogenesis is not directly associated with local production of anti-citrullinated protein Abs and rheumatoid factor in the rheumatoid joint. Therefore, we conclude that synovial lymphoid neogenesis is not a major determinant of these rheumatoid arthritis-specific autoantibody responses.

The abundant synovial expression of the RANK/RANKL/Osteoprotegerin system in peripheral spondylarthritis is partially disconnected from inflammation.

OBJECTIVE: Spondylarthritis (SpA) and rheumatoid arthritis (RA) have different patterns of bone damage, with more pronounced bone erosions in RA. The RANK/RANKL/osteoprotegerin (OPG) system plays a central role in bone resorption by promoting the maturation and activation of osteoclasts. To assess the potential role of this system in the distinct bone phenotype, we studied the synovial expression of these mediators in SpA and RA peripheral synovitis. METHODS: Synovial biopsy specimens were obtained from the actively inflamed peripheral joints of 35 patients with SpA and 19 patients with RA. Paired synovial biopsy samples were obtained from 24 patients with SpA after tumor necrosis factor alpha (TNFalpha) blockade. Synovial tissue sections were immunostained for RANKL, OPG, RANK, and TRAP and assessed by semiquantitative scoring and digital image analysis. RESULTS: After extensive validation of the reactivity and specificity of the antibodies, we demonstrated the abundant expression of RANKL and OPG in SpA synovitis. RANKL was expressed by both fibroblast-like synoviocytes and sublining T lymphocytes. RANK-positive osteoclast precursors but no mature TRAP-positive osteoclasts were present in the inflamed tissue. The expression of these mediators was not different between patients with nonpsoriatic SpA, patients with psoriatic SpA, and patients with RA, was not related to the degree of systemic or local inflammation, and was not significantly modulated by highly effective treatment with TNFalpha blockers. Only the subset of patients with the best systemic response to TNFalpha blockade had decreased RANKL expression in the intimal lining layer. CONCLUSION: The relative protection against bone erosions in SpA cannot be explained by qualitative or quantitative differences in the synovial expression of RANKL, OPG, and RANK. The abundant expression of these factors in SpA peripheral synovitis is largely disconnected from systemic and local inflammation.

Distinct synovial immunopathologic characteristics of juvenile-onset spondylarthritis and other forms of juvenile idiopathic arthritis.

OBJECTIVE: To characterize the synovial immunopathologic features of juvenile-onset spondylarthritis (SpA) in relation to adult SpA and other forms of juvenile idiopathic arthritis (JIA). METHODS: Synovial biopsy samples were obtained from 10 patients with juvenile-onset SpA, 23 with adult SpA, 19 with rheumatoid arthritis (RA), 8 with juvenile polyarthritis, and 12 with juvenile oligoarthritis. Synovial immunopathologic features were studied by extensive histologic and immunohistochemical analyses. RESULTS: Synovitis in juvenile SpA was characterized by marked lining layer hyperplasia, clear hypervascularity, and pronounced inflammatory cell infiltration with lymphocytes and macrophages, independent of disease duration or time of sampling. The immunopathologic features of juvenile SpA resembled those of adult SpA in terms of hypervascularity and absence of RA-specific intracellular citrullinated proteins and HLA-DR4/human cartilage glycoprotein 39(263-275) complexes, but differed markedly by a stronger lining layer hyperplasia and lower numbers of CD163+ macrophages. Accordingly, class prediction analysis failed to classify juvenile SpA synovitis in the SpA group. Comparison of juvenile SpA with other JIA subtypes showed a broad overlap, with the exception of slightly lower vascularity in juvenile polyarthritis and higher inflammatory cell infiltration in juvenile oligoarthritis. Unsupervised clustering analysis identified a subgroup of samples characterized by high plasma cell infiltration, which corresponded with active, longstanding JIA, mostly of the oligoarthritis subtype. CONCLUSION: Despite some similarities with adult SpA, the findings with regard to lining layer hyperplasia and CD163+ macrophage infiltration are indicative of important differences in the synovial immunopathologic features of juvenile-onset SpA. The partial overlap with other JIA subtypes emphasizes the need for further biologic characterization of JIA in order to define pathophysiologic, rather than phenotypic, subgroups.

Pathogenesis of spondyloarthritis: insights from synovial membrane studies.

Here, we review histopathologic studies of the cellular and molecular pathways of spondyloarthritis (SpA) synovial inflammation. In contrast with lymphocytes, specific macrophage subsets and polymorphonuclear cells selectively increase in SpA synovitis, correlate with global disease activity, decrease rapidly upon effective treatment with tumor necrosis factor (TNF)-alpha blockers, and serve as valuable biomarkers for treatment response in SpA. Functionally, increased Toll-like receptor triggering may be responsible for the proinflammatory response of these cells. Therefore, we propose that an exaggerated response of the innate immune system in genetically susceptible patients rather than a classic, lymphocyte-mediated autoimmune process is involved in the pathogenesis of SpA.

Identification of synovial biomarkers of response to experimental treatment in early-phase clinical trials in spondylarthritis.

OBJECTIVE: To identify biomarkers for effective treatment in early-phase clinical trials of spondylarthritis (SpA), by analyzing which synovial features can be reliably identified in patients with SpA. METHODS: Synovial biopsies were performed at weeks 0 and 12 in 20 SpA patients treated with infliximab, 20 treated with etanercept, and 12 who were not treated. Primary clinical outcome measures were patient and physician global assessment of disease activity. Extensive histologic evaluation included assessment of lining layer hyperplasia, vascularity, markers of cellular infiltration, and metalloproteinases (MMPs) in the lining and sublining layers. RESULTS: Changes in levels of CD163 (resident tissue macrophages) in the lining, and CD163, MMP-3, and myeloid-related protein 14 (MRP-14; infiltrating myeloid cells) in the sublining correlated significantly with changes in the primary clinical outcomes. Comparison between responders (n = 35) and nonresponders (n = 17) showed differences in the degree of change in the levels of CD163 in the lining and CD163, MMP-3, and CD3 in the sublining, whereas trends in change in the levels of MRP-8 and MRP-14 in the lining and sublining were similar in the 2 groups. Accordingly, the highest differences in standardized response means (SRMs) between the 2 groups were found for CD163 in the lining, MMP-3, CD163, CD3, and MRP-8 in the sublining, and the level of polymorphonuclear cells (PMNs). When comparing treated and untreated patients, high differences in SRMs were again found for CD163 in the lining, MMP-3, CD163, and MRP-8 in the sublining, and PMNs. These parameters performed prognostically as well as the erythrocyte sedimentation rate and better than the C-reactive protein level. Class prediction analysis yielded a 90% correct prediction using 8 synovial parameters, as follows: lining and sublining CD163, MRP-8, and MRP-14, sublining MMP-3, and PMNs. In validation analyses with independent samples, effective treatment was correctly predicted in 24 of 30 SpA patients and in 2 of 2 placebo-treated patients. CONCLUSION: Changes in synovial macrophage subsets, PMN levels, and MMP-3 expression reflect response to treatment in SpA. The ability of these parameters to correctly identify effective therapy makes them interesting biomarkers for use in early-phase clinical trials in SpA.

Tumor necrosis factor alpha blockade treatment down-modulates the increased systemic and local expression of Toll-like receptor 2 and Toll-like receptor 4 in spondylarthropathy.

OBJECTIVE: Abnormal host defense against pathogens has been implicated in the pathogenesis of spondylarthropathy (SpA), a disease characterized by abundant synovial infiltration with innate immune cells. Given the role of Toll-like receptors (TLRs) in activation of innate inflammation and the occurrence of TLR-dependent infections after tumor necrosis factor alpha (TNFalpha) blockade treatment, the present study was undertaken to analyze TLRs and their modulation by TNFalpha blockade in SpA. METHODS: Peripheral blood mononuclear cells (PBMCs) were obtained from SpA and rheumatoid arthritis (RA) patients during infliximab therapy, and from healthy controls. TLR-2 and TLR-4 expression and TNFalpha production upon lipopolysaccharide (LPS) stimulation were analyzed by flow cytometry on different monocyte subsets. Synovial biopsy specimens from 23 SpA patients before and after infliximab or etanercept treatment, from 15 RA patients, and from 18 osteoarthritis (OA) patients were analyzed by immunohistochemistry. RESULTS: Expression of TLR-4, but not TLR-2, was increased on PBMCs from patients with SpA, whereas both TLRs were increased in RA patients. TLR expression was particularly increased on the CD163+ macrophage subset. Infliximab reduced TLR-2 and TLR-4 expression on monocytes of SpA and RA patients, leading to lower levels than in controls and to impaired TNFalpha production upon LPS stimulation. In inflamed synovium, the expression of both TLRs and of CD163 was significantly higher in patients with SpA than in those with RA or OA. Paralleling the systemic effect, TLRs in synovium were down-regulated following treatment with infliximab as well as etanercept, indicating a class effect of TNFalpha blockers. CONCLUSION: Inflammation in SpA is characterized by increased TLR-2 and TLR-4 expression, which is sharply reduced by TNFalpha blockade. These findings suggest a potential role of innate immunity-mediated inflammation in SpA and provide an additional clue regarding the mechanism of action as well as the potential side effects of TNFalpha blockade.

Synovial histopathology of psoriatic arthritis, both oligo- and polyarticular, resembles spondyloarthropathy more than it does rheumatoid arthritis.

At present only few biological data are available to indicate whether psoriatic arthritis (PsA) is part of the spondyloarthropathy (SpA) concept, whether it is a separate disease entity or a heterogeneous disease group with oligoarticular/axial forms belonging to SpA and polyarticular forms resembling rheumatoid arthritis (RA). To address this issue with regard to peripheral synovitis, we compared the synovial characteristics of PsA with those of ankylosing spondylitis (AS)/undifferentiated SpA (USpA) and RA, and compared the synovium of oligoarticular versus polyarticular PsA. Synovial biopsies were obtained from patients with RA, nonpsoriatic SpA (AS + USpA), and oligoarticular and polyarticular PsA. The histological analysis included examination(s) of the lining layer thickness, vascularity, cellular infiltration, lymphoid aggregates, plasma cells and neutrophils. Also, we performed immunohistochemical assessments of CD3, CD4, CD8, CD20, CD38, CD138, CD68, CD163, CD83, CD1a, CD146, alphaVbeta3, E-selectin, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, S100A12, intracellular citrullinated proteins and major histocompatibility complex (MHC)-human cartilage (HC) gp39 peptide complexes. Comparing SpA (PsA + AS + USpA) with RA, vascularity, and neutrophil and CD163+ macrophage counts were greater in SpA (P < 0.05), whereas lining layer thickness and the number of CD83+ dendritic cells were greater in RA (P < 0.05). In RA, 44% of samples exhibited positive staining for intracellular citrullinated proteins and 46% for MHC-HC gp39 peptide complexes, whereas no staining for these markers was observed in SpA samples. We excluded influences of disease-modifying antirheumatic drug and/or corticosteroid treatment by conducting systematic analyses of treated and untreated subgroups. Focusing on PsA, no significant differences were observed between PsA and nonpsoriatic SpA. In contrast, vascularity (P < 0.001) and neutrophils were increased in PsA as compared with RA (P = 0.010), whereas staining for intracellular citrullinated proteins and MHC-HC gp39 peptide complexes was exclusively observed in RA (both P = 0.001), indicating that the same discriminating features are found in PsA and other SpA subtypes compared with RA. Exploring synovial histopathology between oligoarticular and polyarticular PsA, no significant differences were noted. Moreover, intracellular citrullinated proteins and MHC-HC gp39 peptide complexes, which are specific markers for RA, were observed in neither oligoarticular nor polyarticular PsA. Taken together, these data indicate that the synovial histopathology of PsA, either oligoarticular or polyarticular, resembles that of other SpA subtypes, whereas both groups can be differentiated from RA on the basis of these same synovial features, suggesting that peripheral synovitis in PsA belongs to the SpA concept.

Diagnostic classification of spondylarthropathy and rheumatoid arthritis by synovial histopathology: a prospective study in 154 consecutive patients.

OBJECTIVE: To explore prospectively the value of synovial histopathology in comparison with the value of classic parameters for diagnostic classification of spondylarthropathy (SpA) and rheumatoid arthritis (RA) in patients with an atypical disease presentation. METHODS: Synovial biopsy samples were obtained from 154 consecutive patients presenting for diagnostic evaluation; 67 patients fulfilled the classification criteria for RA, SpA, or other well-defined disease at the time of arthroscopy (cohort 1), and an additional 53 patients were classified after a full diagnostic reevaluation at 6 months (cohort 2). Synovial parameters with diagnostic value were identified in cohort 1 and were compared prospectively with classic diagnostic parameters in cohort 2. RESULTS: Staining with anticitrulline, staining with monoclonal antibody 12A (recognizing HLA-DR shared epitope-human cartilage glycoprotein 39(263-275) complexes), and crystal deposition had positive predictive values (PPVs) for diagnosis of >90% in patients with an atypical disease presentation (cohort 2). Using these 3 parameters, a diagnosis was predicted by synovial histopathology in 39.6% of cohort 2 patients and turned out to be correct in 90.5% of these patients at 6 months of followup. Using a multiparameter model rather than single histopathologic parameters, even better results were obtained, with a diagnostic prediction in 79.2% of samples and a PPV of 81.0%. In comparison, a similar multiparameter model using classic diagnostic criteria rather than synovial histopathology performed poorly in cohort 2; the sensitivity was 56.6% and the PPV was 73.3%, with an inferior capacity to predict SpA. Especially for the presence of crystals and anticitrulline staining, the analysis of synovial tissue had a clear added value to the analysis of synovial fluid or serum in patients with an atypical presentation. CONCLUSION: This proof-of-concept study indicates that synovial histopathology can contribute to the multiparametric diagnostic classification of inflammatory arthritis in patients with an atypical presentation.

Involvement of matrix metalloproteinases and their inhibitors in peripheral synovitis and down-regulation by tumor necrosis factor alpha blockade in spondylarthropathy.

OBJECTIVE: To investigate the role of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) in spondylarthropathy (SpA) synovitis. METHODS: Paired samples of synovial biopsy tissue as well as serum and synovial fluid (SF) from 41 patients with SpA and 20 patients with rheumatoid arthritis (RA) and serum samples from 20 healthy controls were analyzed by immunohistochemistry and enzyme-linked immunosorbent assay for the presence of MMPs 1, 2, 3, and 9 and TIMPs 1 and 2. In addition, sera from 16 patients with ankylosing spondylitis (AS) and peripheral synovitis and 17 patients with AS and exclusively axial involvement were analyzed. An additional cohort of SpA patients was analyzed at baseline and after 12 weeks of infliximab treatment. RESULTS: Staining for MMPs and TIMPs showed a cellular and interstitial pattern in the synovial lining and sublining layers that was similar between the RA and SpA patients. Involvement of MMPs and TIMPs in SpA synovitis was suggested by the correlation with cellular infiltration, vascularization, and cartilage degradation. Higher serum levels of MMPs 3 and 9 were revealed in SpA and RA patients as compared with healthy controls. Production of MMP-3, but not MMP-9, in the serum reflected the presence of peripheral synovitis, as indicated by 1) the correlation between serum levels, SF levels (which were 1,000-fold higher than the serum levels), and synovial expression of MMP-3, 2) the increased levels of MMP-3 in AS patients with peripheral disease and not exclusively axial involvement, and 3) the correlation of serum and SF MMP-3 with parameters of synovial, but not systemic, inflammation. The modulation of the MMP/TIMP system by tumor necrosis factor alpha (TNFalpha) blockade was confirmed by the down-regulation of all MMPs and TIMPs in the synovium and a pronounced and rapid decrease of serum MMP-3. CONCLUSION: MMPs and TIMPs are highly expressed in SpA synovitis and mirror both the inflammatory and tissue-remodeling aspects of the local disease process. Serum MMP-3, originating from the inflamed joint, represents a valuable biomarker for peripheral synovitis. Modulation of the MMP/TIMP system by infliximab could contribute to the antiinflammatory and tissue-remodeling effects of TNFalpha blockade in SpA.