A comparative phenotypical analysis of rheumatoid nodules and rheumatoid synovium with special reference to adhesion molecules and activation markers

OBJECTIVES—(1)To analyse the in situ expression of adhesion molecules in rheumatoid nodules. (2) To compare the endothelial expression of adhesion molecules in synovial tissue and subcutaneous nodules obtained from the same patients. (3) To compare the expression of adhesion molecules and activation markers on T cell lines from nodules and synovium.
METHODS—(1) Immunohistochemical analysis by APAAP technique of E selectin, CD44, ICAM-1, PECAM-1, and VCAM-1 was performed on 10 rheumatoid nodules from seven patients with rheumatoid arthritis (RA); nodules and synovium were simultaneously analysed from three patients. (2) T cell lines were generated from RA nodules (n=7) and synovium (n=7) by interleukin 2 expansion, and subsequently characterised by flow cytometry for surface expression of αEβ7, α4β7, CD44, L selectin, LFA-1a, PECAM-1, and CD30.
RESULTS—(1) In rheumatoid nodules, the palisading layer strongly stains for ICAM-1 and PECAM-1, but less pronounced for CD44. VCAM-1 staining was usually negative. ICAM-1 is upregulated in the vessels surrounding the central zone of fibrinoid necrosis. The immunohistological picture in different nodules derived from the same patient was similar. (2) The endothelial expression of adhesion molecules is comparable in RA nodules and synovium on an individual level, except for E selectin, which is overexpressed in nodule endothelium. (3) T cell lines from nodules and synovium display similar adhesion molecule profiles. However, the expression of CD30, a T cell activation marker linked with Th2 subsets, is higher in nodules compared with synovium.
CONCLUSION—These data support a recirculation hypothesis of T cells between articular and extra-articular manifestations in RA, although the activation state of the T cells in each of these localisations may differ.

Keywords: T cells; adhesion molecules; rheumatoid nodules; rheumatoid synovium     

Differential expression and functional behaviour of the αv and β3 integrin subunits in cytokine stimulated fibroblast-like cells derived from synovial tissue of rheumatoid arthritis and osteoarthritis in vitro

OBJECTIVE—The aim of this study was to investigate in situ the expression of the classic vitronectin (VN) receptor consisting of the αv and β3 subunits in synovial lining cells (SLC) of chronic synovitis occurring in osteoarthritis (OA) and in rheumatoid arthritis (RA). The expression and function of αv and β3 as VN receptor in cultured fibroblast-like synoviocytes (FBS) derived from patients with OA and RA was also compared.
METHODS—Expression of αv and β3 was examined immunohistochemically in normal synovial tissue and in synovial tisssue from patients with OA and RA. The effect of proinflammatory cytokines and of a synovial fluid of a patient with RA on the expression of the αv and β3 subunits of cultured FBS was determined by flow cytometry. Binding of OA and RA-FBS to VN was quantified using adhesion assays and the effect of interleukin 1β (IL1β) and tumour necrosis factor α (TNFα) on adhesion was measured. The specifity of the adhesion was tested by inhibition studies using monoclonal antibodies to integrin subunits.
RESULTS—In in situ studies normal SLC showed a parallel distribution of αv and β3 subunits. OA-SLC strongly and uniformly expressed αv whereas RA-SLC showed heterogeneous expression of αv. In situ both OA-SLC and RA-SLC lacked the expression of the integrin subunit β3. In in vitro studies, OA-FBS and RA-FBS did not differ as regards expression of αv and β3, and VN attachment. Binding of RA-FBS to VN was partially blocked by antibodies against αv, β1, and β3 subunits, whereas only antibodies against αv and β3 inhibited the binding of OA-FBS to VN. The proinflammatory cytokines TNFα and IL1β increased the expression of αv and β3, and the VN binding of OA-FBS, whereas αv and β3 expression, and VN binding were downregulated in RA-FBS. Similar effects were found when the synovial fluid of an RA patient was used.
CONCLUSION—The integrin subunit β3 seems to be one partner but not the major one with which the subunit αv forms functional vitronectin receptors in OA-FBS and RA-FBS. The interaction between synovial cells and inflammatory cytokines seems to be different for OA and RA; the basis for this difference, however, remains to be established.

     

Expression of sentrin, a novel antiapoptotic molecule, at sites of synovial invasion in rheumatoid arthritis

OBJECTIVE: Sentrin, a novel antiapoptotic molecule, has been shown to interact with the signal-competent form of Fas/APO-1 and tumor necrosis factor receptor I (TNFRI), and thereby, to protect cells against anti-Fas/APO-1- and TNF-induced cell death. Since reduced apoptosis in the synovial lining is supposed to contribute to synovial hyperplasia in rheumatoid arthritis (RA), we searched for the expression of sentrin-1 messenger RNA (mRNA) in synovium from patients with RA. METHODS: The expression of sentrin-1 mRNA was examined by in situ hybridization on snap-frozen sections of normal and RA synovial tissues as well as on paraffin-embedded RA synovial specimens, including the interface of cartilage-bone and invading synovium. Immunohistochemical double labeling after in situ hybridization was performed to further characterize sentrin-1 mRNA-expressing cells. In addition, quantitative analysis of sentrin-1 mRNA expression in RA synovial fibroblasts (RASF), osteoarthritis synovial fibroblasts (OASF), and normal fibroblasts was performed by quantitative real-time polymerase chain reaction. Expression levels were standardized to the expression of GAPDH. The in vivo maintenance of sentrin expression in RASF aggressively invading human cartilage was explored in the SCID mouse model of RA. RESULTS: A marked expression of sentrin-1 mRNA could be seen in all RA synovial specimens, predominantly in SF of the lining layer and at sites of invasion of RA synovium into cartilage. In normal synovial tissues, no sentrin-1 mRNA was detectable. RASF showed a maximum 32.5-fold (mean +/- SD 14.9 +/- 11.6) increase of sentrin-1 mRNA expression compared with normal fibroblasts and a maximum 31.4-fold (mean +/-SD 14.3 +/- 10.9) increase compared with OASF. When coimplanted with normal human cartilage in the SCID mouse model, invading RASF maintained their sentrin-1 mRNA expression for at least 60 days in vivo. CONCLUSION: The marked expression of sentrin in rheumatoid synovial tissue, but not in normal or OA synovial tissue, may contribute to the modulation of Fas- and TNFR-mediated apoptosis in RA synovium, and thereby extend the lifespan of invasive, cartilage-destructive SF.     

Local production of complement proteins in rheumatoid arthritis synovium

OBJECTIVE: Complement has been repeatedly implicated in the pathogenesis of rheumatoid arthritis (RA) based on studies showing reduced levels of native complement components and increased levels of complement metabolites in plasma, synovial fluid (SF), and synovial tissue (ST) of RA patients. However, there is limited information on local production and activation of key factors of the complement cascade in RA synovium and their potential modulation by novel anticytokine therapies. This study was undertaken to characterize the expression of complement proteins and receptors in RA SF and ST. METHODS: Using in situ hybridization, immunohistochemistry, and Western blot techniques, we assessed the presence of complement proteins C3, factor B (FB), and C5b-9, as well as the expression of complement receptors C3aR and C5aR in rheumatoid synovium. C3 and FB levels in SF were determined by enzyme-linked immunosorbent assay. Functional assessment was performed by examining the effects of soluble tumor necrosis factor receptor (sTNFR) p55 gene transfer in the SCID mouse model of RA. RESULTS: Complement proteins and receptors could be localized in all RA synovial specimens, whereas in osteoarthritis (OA) synovium, only a few, single cells expressed complement proteins and receptors. No differences were noted in the concentration of C3 between RA and OA in SF; however, FB levels were markedly reduced in RA versus OA SF. In RA synovium, in contrast to OA synovium, local expression of complement factor and complement receptor messenger RNA was found throughout the various ST compartments, suggesting that activation of the complement cascade occurs in all parts of the rheumatoid synovium. Moreover, C5aR expression was up-regulated following overexpression of sTNFR p55 by adenovirus-based gene transfer. CONCLUSION: In summary, local complement production and activation may play an important role in RA, and specific modulation and inhibition of local complement production could be an attractive therapeutic target for RA.     

Transforming growth factor β1 and interleukin 4 induced α smooth muscle actin expression and myofibroblast-like differentiation in human synovial fibroblasts in vitro: modulation by basic fibroblast growth factor

OBJECTIVE—To discover if α smooth muscle actin expression and myofibroblastic differentiation are induced in synovial fibroblasts by cytokines found in the inflamed RA joint.
METHODS—Immunofluorescent microscopy and western blotting were used to examine different cultures of human synovial fibroblasts for expression of α actin in the presence of the cytokines transforming growth factor β (TGFβ1), interleukin 1α (IL1α), IL4, IL6, tumour necrosis factor α (TNFα), and basic fibroblast growth factor (FGF).
RESULTS—A small but significant population of cells (14.4 ± 12.9%) expressed α actin under standard culture conditions. Upon treatment with TGFβ1 there was a pronounced increase in the number of cells expressing α actin (68.1 ± 5.49%), accompanied by a change in morphology to a myofibroblast-like phenotype. Other cytokines found within the inflamed joint such as IL1, TNFα , IL6, and basic FGF failed to induce α actin expression. However, IL4, which is normally absent or only present at low concentrations in the RA joint had a similar effect to TGFβ1. It was also found that basic FGF inhibited the induction of α actin expression by TGFβ1 and IL4.
CONCLUSION—In the presence of TGFβ1 or IL4, fibroblasts derived from synovial tissue or synovial fluid are induced to differentiate into myofibroblast-like cells containing the α smooth muscle form of actin. This differentiation is inhibited by basic FGF. It is suggested that the balance between these particular cytokines may be important in the modulation of fibroblast behaviour, which could have significant effects on joint repair mechanisms and the generation of fibrous tissue within the rheumatoid joint.

     

Determination of cytokines in synovial fluids: correlation with diagnosis and histomorphological characteristics of synovial tissue.

In a study aimed at correlating cytokine levels in synovial fluid with the pathology of rheumatoid arthritis (RA), tumour necrosis factor alpha, interleukin 1 beta and interferon gamma were immunoassayed in 27 patients with RA, 16 patients with other arthritides, 23 with osteoarthritis, 13 patients with trauma, and 18 patients at necropsy without inflammatory disease and not known to have had joint disease (median 27 hours after death). The results for interleukin 1 beta clearly show higher cytokine levels in patients with RA and other arthritides than in patients with osteoarthritis, trauma, or the patients at necropsy. Interferon gamma levels in patients with osteoarthritis and the patients at necropsy, however, were significantly greater than in patients with RA, and tumour necrosis factor alpha levels were also greater in the patients at necropsy compared with patients with RA. This study also correlated histomorphological patterns of synovitis and indicators of local inflammatory activity with synovial fluid cytokine levels, showing, for example, a positive association of interleukin 1 beta titre and a negative association of interferon gamma titre with ulcerogranulomatous synovitis (itself associated with RA). Taken together, these results extend and strengthen data suggesting a possible part played by increased synovial fluid levels of interleukin 1 beta in joint destruction in RA, but provide no evidence for increases in levels of tumour necrosis factor alpha or interferon gamma affecting the disease pathology.     

Ceramide, a mediator of interleukin 1, tumour necrosis factor α, as well as Fas receptor signalling, induces apoptosis of rheumatoid arthritis synovial cells

OBJECTIVES—To examine the effects of ceramide, which is a lipid second messenger of cell surface receptors, including tumour necrosis factor α (TNFα), interleukin 1 (IL1), and Fas receptors, on rheumatoid arthritis (RA) synovial cells.
METHODS—Synovial cells from RA patients and normal skin fibroblasts were cultured with cell permeable ceramide (C2-ceramide). Apoptosis was assessed by microscopic observation of morphological changes, nuclear staining, and DNA electrophoresis. DNA synthesis was examined by thymidine incorporation.
RESULTS—C2-ceramide induced reversible morphological changes of synovial cells such as cell rounding within four hours. Subsequently, irreversible nuclear changes characteristic to apoptosis were observed at 48 hours. DNA synthesis was not promoted. The addition of ceramide exerted similar effects on cultured dermal fibroblasts.
CONCLUSION—Ceramide induced apoptosis in RA synovial cells. Ceramide could be a second messenger specific for apoptosis of RA synovial cells.

Keywords: ceramide; apoptosis; rheumatoid arthritis     

Expression and proinflammatory role of proteinase-activated receptor 2 in rheumatoid synovium: ex vivo studies using a novel proteinase-activated receptor 2 antagonist

OBJECTIVE: Serine proteinases activate the G protein-coupled receptor, proteinase-activated receptor 2 (PAR-2), via cleavage and exposure of a tethered ligand. PAR-2 is known to exert proinflammatory actions in a murine model of arthritis, since PAR-2-deficient mice exhibit strikingly reduced articular inflammation. This study was undertaken to examine synovial PAR-2 expression and to determine the effect of a novel PAR-2 antagonist on synovial cytokine production, in order to investigate the hypothesis that PAR-2 plays a critical role in the pathogenesis of rheumatoid arthritis (RA). METHODS: Using a monoclonal antibody to human PAR-2, expression in RA synovium and cultured synovial fibroblasts was characterized. The novel PAR-2 antagonist, ENMD-1068, was added to primary cultures of RA synovial tissue, from which spontaneous cytokine release was measured. RESULTS: PAR-2 was substantially up-regulated in RA synovium compared with control synovial tissue from patients with osteoarthritis or seronegative inflammatory arthritis, neither of which exhibited significant PAR-2 expression. Importantly, spontaneous release of tumor necrosis factor alpha and interleukin-1beta from RA synovium was substantially inhibited by ENMD-1068, in a dose-dependent manner. CONCLUSION: These findings identify PAR-2 as a novel upstream regulator of proinflammatory cytokine production in RA and indicate its potential as a novel therapeutic target in inflammatory arthritis.     

Expression and proinflammatory role of proteinase‐activated receptor 2 in rheumatoid synovium: Ex vivo studies using a novel proteinase‐activated receptor 2 antagonist

Objective

Serine proteinases activate the G protein–coupled receptor, proteinase‐activated receptor 2 (PAR‐2), via cleavage and exposure of a tethered ligand. PAR‐2 is known to exert proinflammatory actions in a murine model of arthritis, since PAR‐2–deficient mice exhibit strikingly reduced articular inflammation. This study was undertaken to examine synovial PAR‐2 expression and to determine the effect of a novel PAR‐2 antagonist on synovial cytokine production, in order to investigate the hypothesis that PAR‐2 plays a critical role in the pathogenesis of rheumatoid arthritis (RA).

Methods

Using a monoclonal antibody to human PAR‐2, expression in RA synovium and cultured synovial fibroblasts was characterized. The novel PAR‐2 antagonist, ENMD‐1068, was added to primary cultures of RA synovial tissue, from which spontaneous cytokine release was measured.

Results

PAR‐2 was substantially up‐regulated in RA synovium compared with control synovial tissue from patients with osteoarthritis or seronegative inflammatory arthritis, neither of which exhibited significant PAR‐2 expression. Importantly, spontaneous release of tumor necrosis factor α and interleukin‐1β from RA synovium was substantially inhibited by ENMD‐1068, in a dose‐dependent manner.

Conclusion

These findings identify PAR‐2 as a novel upstream regulator of proinflammatory cytokine production in RA and indicate its potential as a novel therapeutic target in inflammatory arthritis.

     

Wnt1 inducible signaling pathway protein-3 regulation and microsatellite structure in arthritis

OBJECTIVE: Rheumatoid arthritis (RA) synovial tissue expresses several embryonic gene families, including wingless (wnt) and their receptors, frizzled (fz). The Wnt proteins, including Wnt-1, activate the Wnt inducible signaling pathway proteins (WISP), which are members of the CCN family that regulate cell growth and differentiation. WISP3 is of particular interest because it contains a microsatellite region in its coding region that is susceptible to frameshift mutations and leads to a truncated protein. To investigate the contribution of WISP3 to synovial inflammation, we evaluated its expression and regulation in arthritis. METHODS: mRNA and protein expression of WISP3 were determined by quantitative real-time polymerase chain reaction (PCR) and Western blot analysis, respectively. For mutation analysis, PCR product amplified from genomic DNA of synovial tissue and cultured fibroblast-like synoviocytes (FLS) was subcloned and sequenced. RESULTS: WISP3 mRNA is expressed in synovial tissue, but is 11-fold higher in RA than osteoarthritis (OA) or normal samples. Surprisingly, WISP3 protein levels are similar in RA, OA, and normal synovium samples. Immunohistochemistry of synovial tissue reveals that WISP3 protein is located primarily in the synovial intimal lining. WISP3 mRNA expression is also 6-fold higher in RA FLS compared with OA FLS and 50-fold higher in RA than in normal FLS. When RA FLS are stimulated with interleukin 1 or tumor necrosis factor-a, WISP3 mRNA is significantly increased. The cytokines also increase WISP3 mRNA in OA FLS, but the maximal level in stimulated OA FLS is still less than medium-treated RA FLS. Mutation analysis in the coding region microsatellite of the WISP3 gene in RA and OA synovium and FLS shows a limited number of insertion and deletion mutations. CONCLUSION: WISP3 gene expression is higher in RA synovium and FLS compared with OA and normal synovial tissue and is further induced by proinflammatory cytokines in vitro. Protein levels are not increased, indicating discoordinate regulation of WISP3 protein and mRNA. Although functionally relevant mutations were observed in genomic DNA, they were noted in both OA and RA samples.     

Characterization of the newly established human type B synovial lining cell line, RAMAK-1: expression of adhesion molecules and cytokine production

RAMAK-1, a new spontaneously immortalized synovial cell line consisting of type B lining cells, was recently derived from a patient with rheumatoid arthritis (RA). The present study was designed to characterize RAMAK-1 cells in terms of expression of adhesion molecules and cytokine production. RAMAK-1 cells constitutively express intercellular adhesion molecule-1. In contrast, vascular cell adhesion molecule-1 (VCAM-1) expression by the cells was not observed in the absence of stimulation. However, when stimulated by tumor necrosis factor-α, VCAM-1 expression was readily apparent and sustained over 48 h. RAMAK-1 cells spontaneously produced interleukin (IL)-6, IL-8 and granulocyte macrophage colony stimulating factor, but not IL-1α nor IL-1β. However, when stimulated with IL-1β, the cells expressed IL-1α and IL-1β mRNA. This cell line presents functional responses when stimulated with pro-inflammatory cytokines and may be useful in elucidating the initial lesions of the synovial lining layer of RA.     

Characterization of the newly established human type B synovial lining cell line,RAMAK-1: expression of adhesion molecules and cytokine production

Abstract

RAMAK-1, a new spontaneously immortalized synovial cell line consisting of type B lining cells, was recently derived from a patient with rheumatoid arthritis (RA). The present study was designed to characterize RAMAK-1 cells in terms of expression of adhesion molecules and cytokine production. RAMAK-1 cells constitutively express intercellular adhesion molecule-1. In contrast, vascular cell adhesion molecule-1 (VCAM-1) expression by the cells was not observed in the absence of stimulation. However, when stimulated by tumor necrosis factor-α, VCAM-1 expression was readily apparent and sustained over 48 h. RAMAK-1 cells spontaneously produced interleukin (IL)-6, IL-8 and granulocyte macrophage colony stimulating factor, but not IL-1α nor IL-1β. However, when stimulated with IL-1β, the cells expressed IL-1α and IL-1β mRNA. This cell line presents functional responses when stimulated with pro-inflammatory cytokines and may be useful in elucidating the initial lesions of the synovial lining layer of RA.     

Identification of the epidermal growth factor-TM7 receptor EMR2 and its ligand dermatan sulfate in rheumatoid synovial tissue

OBJECTIVE: EMR2 and CD97 are closely related members of the epidermal growth factor (EGF)-TM7 family of adhesion class 7-span transmembrane (TM7) receptors. Chondroitin sulfates (CS) have recently been identified as ligands for EMR2 and CD97. CS have been implicated in the pathogenesis of rheumatoid arthritis (RA). We undertook this study to determine the expression of EMR2 and the distribution of EMR2 and CD97 ligands within RA synovial tissue (ST). METHODS: ST samples were obtained by arthroscopy from 19 patients with RA, 13 patients with inflammatory osteoarthritis (OA), and 13 patients with reactive arthritis (ReA). Immunohistochemistry was performed with a monoclonal antibody against EMR2, and stained STs were analyzed by digital image analysis. Coexpression of EMR2 with cell lineage- and activation-specific markers was determined by double immunofluorescence microscopy. To evaluate the expression of EMR2 and CD97 ligands in RA synovium, binding assays were performed using EMR2- and CD97-specific multivalent fluorescent probes. RESULTS: EMR2 expression in the synovial sublining was found to be significantly higher in RA patients compared with OA and ReA control patients. Most EMR2+ cells were macrophages and dendritic cells expressing costimulatory molecules and tumor necrosis factor alpha. Dermatan sulfate was shown to be the ligand of the largest isoforms of EMR2 and CD97 in rheumatoid synovium. In addition, the smaller isoforms of CD97, but not those of EMR2, bound CD55 on fibroblast-like synoviocytes. CONCLUSION: The EGF-TM7 receptors EMR2 and CD97 are abundantly expressed on myeloid cells in ST of RA patients where their cognate ligands dermatan sulfate and CD55 are detected. These results suggest that these interactions may facilitate the retention of activated macrophages in the synovium.     

Loss of laminin and of the laminin receptor integrin subunit α6 in situ correlates with cytokine induced down regulation of α6 on fibroblast-like synoviocytes from rheumatoid arthritis

OBJECTIVE—To investigate in situ the expression of the integrin receptor subunits α6 and β1 and the distribution of the ligand laminin in the synovia from osteoarthritis (OA) and rheumatoid arthritis (RA) patients and to study the effect of cytokines and antirheumatic drugs on the expression of the α6 and β1 integrin subunits on long term cultures of fibroblast-like synoviocytes (FBS) derived from OA and RA.
METHODS—The expression of the α6 and β1 integrin subunits and the distribution of laminin were examined immunohistochemically in normal synovia and in synovia from patients with OA and RA. The effect of proinflammatory cytokines (IL1β and TNFα), and of antirheumatic drugs (salicylic acid, dexamethasone, and methotrexate) on the α6 and β1 expression of cultured normal FBS and FBS from patients with OA and RA was determined by flow cytometry.
RESULTS—In normal synovia and in OA synovia samples with a low grade of inflammation, synovial lining cells (SLC) showed a parallel expression and distribution of α6 and laminin. In synovia samples of OA with a higher grade of inflammation and in the majority of RA synovia samples laminin was pericellularly distributed in a low number of SLC, whereas α6 was expressed on the surface of a high number of SLC. In RA synovia samples with severe inflammatory changes the gradual loss of laminin generally corresponded to a decrease of the α6 integrin subunit. β1 was always strongly expressed in all synovia samples detected. Proinflammatory cytokines up regulated the expression of α6 and β1 on OA-FBS, whereas these effectors decreased α6 and β1 on RA-FBS. In contrast, antirheumatic drugs, in particular methotrexate and dexamethasone, reduced the expression of α6 and β1 on OA-FBS, whereas the same treatment on RA-FBS stimulated the expression of these integrin subunits.
CONCLUSION—The gradual loss of laminin in chronic synovitis may contribute to the altered expression of α6 in SLC. IL1β and TNFα down regulated the expression of the α6 and β1 integrin subunits on long term cultures of FBS derived from RA. Therefore, these cytokines may be among the effectors regulating the expression of the α6 integrin subunit in SLC in vivo. As antirheumatic drugs increase the expression of α6 on RA-FBS, the presence of the laminin receptor may confer a protective effect on the synovia in vivo.

Keywords: laminin; alpha 6; integrins; rheumatoid arthritis; osteoarthritis     

T cell derived cytokines in psoriatic arthritis synovial fluids

OBJECTIVE—The aim of this study was to investigate the concentrations of T cell derived cytokines in the synovial fluids (SFs) of patients with psoriatic arthritis (PsA) in comparison with rheumatoid arthritis (RA) and osteoarthritis (OA).
METHODS—Th1 type cytokines (interleukin 2 (IL2), tumour necrosis factor β (TNFβ), and interferon γ (INFγ)) and Th2 type cytokines (IL4, IL10) were measured by means of enzyme linked immunosorbent assays.
RESULTS—IL2 was usually not detectable in any of the disease groups. TNFβ was found in 3 of 31 PsA SFs (mean (SEM) 11.1 (2.3) pg/ml) and in a significantly lower concentration than in 20 of the 40 RA SFs (42.2 (15.6) pg/ml; p < 0.002). INFγ was measurable in 2 of 10 PsA and 6 of 16 RA SFs (p > 0.05). IL4 was present at low concentrations in 4 of 22 PsA SFs (0.41 (0.8) pg/ml), and in 15 of 20 RA SFs (0.63 (0.09) pg/ml; p < 0.01). IL10 was found in 4 of 27 PsA SFs (12.3 (0.9) pg/ml) and in 27 of 32 RA SFs (37.3 (4.9) pg/ml; p < 0.0001). In all OA SFs cytokine concentrations were below the limit of detection.
CONCLUSION—The pattern of T cell derived cytokines in PsA SFs was similar to that of RA SFs. However, both the frequency and the concentrations of cytokines were lower in PsA SFs than in RA SFs, while OA SFs generally lacked any detectable T cell cytokines altogether. The presence of Th1 and Th2 cell derived cytokines in PsA SFs suggests the presence of activated T cells in the inflamed joint tissues and their participation in the immunoinflammatory events.

Keywords: psoriatic arthritis; rheumatoid arthritis; cytokines; T cells; synovial fluids