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Osteoarthritis (OA) is a destructive disease of the joint with age and obesity being its most important risk factors. Around 50% of OA patients suffer from inflammation of the synovial joint capsule, which is characterized by increased abundance and activation of synovial macrophages that produce reactive oxygen species (ROS) via NADPH-oxidase 2 (NOX2). Both ROS and high blood levels of low-density lipoprotein (LDL) are implicated in OA pathophysiology, which may interact to form oxidized LDL (oxLDL) and thereby promote disease. Therefore, targeting NOX2 could be a viable treatment strategy for OA. Collagenase-induced OA (CiOA) was used to compare pathology between wild-type (WT) and Nox2 knockout (Nox2−/−) C57Bl/6 mice. Mice were either fed a standard diet or Western diet (WD) to study a possible interaction between NOX2-derived ROS and LDL. Synovial inflammation, cartilage damage and ectopic bone size were assessed on histology. Extracellular ROS production by macrophages was measured in vitro using the Amplex Red assay. Nox2−/− macrophages produced basal levels of ROS but were unable to increase ROS production in response to the alarmin S100A8 or the phorbol ester PMA. Interestingly, Nox2 deficiency reduced cartilage damage, synovial lining thickness and ectopic bone size, whereas these disease parameters were not affected by WD-feeding. These results suggest that NOX2-derived ROS are involved in CiOA development.

Background: Injection of adipose-derived mesenchymal stromal cells (ASCs) into murine knee joints after induction of inflammatory collagenase-induced osteoarthritis (CiOA) reduces development of joint pathology. This protection is only achieved when ASCs are applied in early CiOA, which is characterized by synovitis and high S100A8/A9 and IL-1β levels, suggesting that inflammation is a prerequisite for the protective effect of ASCs. Our objective was to gain more insight into the interplay between synovitis and ASC-mediated amelioration of CiOA pathology.Methods: CiOA was induced by intra-articular collagenase injection. Knee joint sections were stained with hematoxylin/eosin and immunolocalization of polymorphonuclear cells (PMNs) and ASCs was performed using antibodies for NIMP-R14 and CD271, respectively. Chemokine expression induced by IL-1β or S100A8/A9 was assessed with qPCR and Luminex. ASC-PMN co-cultures were analyzed microscopically and with Luminex for inflammatory mediators. Migration of PMNs through transwell membranes toward conditioned medium of non-stimulated ASCs (ASCNS-CM) or IL-1β-stimulated ASCs (ASCIL-1β-CM) was examined using flow cytometry. Phagocytic capacity of PMNs was measured with labeled zymosan particles.Results: Intra-articular saline injection on day 7 of CiOA increased synovitis after 6 h, characterized by PMNs scattered throughout the joint cavity and the synovium. ASC injection resulted in comparable numbers of PMNs which clustered around ASCs in close interaction with the synovial lining. IL-1β-stimulation of ASCs in vitro strongly increased expression of PMN-attracting chemokines CXCL5, CXCL7, and KC, whereas S100A8/A9-stimulation did not. In agreement, the number of clustered PMNs per ASC was significantly increased after 6 h of co-culturing with IL-1β-stimulated ASCs. Also migration of PMNs toward ASCIL-1β-CM was significantly enhanced (287%) when compared to ASCNS-CM. Interestingly, association of PMNs with ASCs significantly diminished KC protein release by ASCs (69% lower after 24 h), accompanied by reduced release of S100A8/A9 protein by the PMNs. Moreover, phagocytic capacity of PMNs was strongly enhanced after priming with ASCIL-1β-CM.Conclusions: Local application of ASCs in inflamed CiOA knee joints results in clustering of attracted PMNs with ASCs in the synovium, which is likely mediated by IL-1β-induced up-regulation of chemokine release by ASCs. This results in enhanced phagocytic capacity of PMNs, enabling the clearance of debris to attenuate synovitis.

Directional migration of leukocytes is orchestrated by the regulated expression of chemokine receptors and their ligands. The receptor CXCR6 is abundantly expressed by Th1‐polarized effector/memory lymphocytes accumulating at inflammatory sites. This study was undertaken to examine the presence of CXCR6+ T cells and of CXCL16, the only ligand for CXCR6, in the joints of patients with rheumatoid arthritis (RA).Flow cytometry analysis of the expression of CXCR6 by peripheral blood and synovial fluid (SF) T cells. In addition, by performing conventional and real‐time reverse transcriptase–polymerase chain reaction, immunohistochemistry, and enzyme‐linked immunosorbent assay, we determined the expression of CXCL16 and its protease ADAM‐10 within synovium and by cultured macrophages. SF T cell migration was studied with the Transwell system.Accumulation of CXCR6+ T cells within RA SF coincided with highly elevated levels of CXCL16+ macrophages. In vitro studies revealed that monocytes started to express CXCL16 upon differentiation into macrophages, and that RA SF and tumor necrosis factor (TNF) enhanced CXCL16 expression. Moreover, RA patients responding to anti‐TNF therapy showed a strongly decreased CXCL16 expression, whereas nonresponding patients did not. Interestingly, ADAM‐10, a recently identified protease of CXCL16, was abundantly expressed by CXCL16+ macrophages in vitro and in RA in vivo, which resulted in increased levels of cleaved CXCL16 in RA SF relative to controls. Finally, CXCR6+ T cells from RA SF were attracted by CXCL16.These data provide evidence that enhanced production of CXCL16 in RA synovia leads to recruitment of CXCR6+ memory T cells, thereby contributing to the inflammatory cascade associated with RA pathology. [ABSTRACT FROM AUTHOR]

To evaluate Fcγ receptor (FcγR) expression on synovial macrophages from rheumatoid arthritis (RA) patients and to determine whether this expression correlates with the production of the proinflammatory cytokines tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), IL-12, and matrix metalloproteinase 1 (MMP-1). We also sought to determine whether mature macrophages from RA patients express aberrant levels of FcγRI, FcγRII, and FcγRIII, and to determine the production of inflammatory mediators after immune complex (IC) stimulation. Immunohistochemistry was performed on cryostat sections of synovial biopsy specimens obtained from 27 RA patients and 5 controls. FcγR I, II, and III were detected, as well as the proinflammatory mediators IL-1, TNFα, IL-12, and MMP-1. Monocytes were isolated from the blood of 10 RA patients and 10 healthy controls and cultured for 7 days with macrophage colony-stimulating factor to obtain macrophages. Using fluorescence-activated cell sorting, the expression of FcγRI, FcγRII, and FcγRIII was determined. On day 7, macrophages were stimulated with heat-aggregated gamma globulins (HAGGs) for 24 hours. Production of cytokines was measured using enzyme-linked immunosorbent assay, and production of gelatinases/collagenases was measured by degradation of fluorescent gelatin. Immunohistochemistry showed higher FcγRII and FcγRIII expression in RA synovium than in controls. FcγRII and FcγRIII, but not FcγRI, were highly correlated with the number of synovial macrophages. Consistent with this, TNFα expression correlated positively with FcγRIII expression. Moreover, MMP-1 expression strongly correlated with FcγR I, II, and III expression. Mature macrophages from RA patients showed significantly enhanced expression of FcγRII and FcγRIII compared with controls. Twenty-four hours after stimulation of RA macrophages with HAGGs, significantly higher production of TNFα and gelatinase/collagenase was measured. RA synovium and mature RA macrophages express significantly elevated levels of FcγRII and FcγRIII, resulting in much higher production of TNFα and gelatinase/collagenase after IC stimulation. These data suggest that disturbed expression of FcγR on mature synovial macrophages is involved in the pathology of RA. [ABSTRACT FROM AUTHOR]