Background:One of the key mechanisms in the pathogenesis of rheumatoid arthritis (RA) is the interaction of macrophages and synovial fibroblasts during joint inflammation. Increased synergistic proinflammatory activity of both cell types leads to the release of high levels of proinflammatory cytokines, especially of interleukin-6 (IL-6), and of matrix degrading enzymes. If this mechanism is uncontrolled, progressive destruction of articular cartilage and bone will take place.In active disease, immediate anti-inflammatory treatment with glucocorticoids is usually replaced by disease-modifying anti-rheumatic drugs (DMARDS), especially by methotrexate (MTX) and biologics such as TNF-α- or IL-6-inhibitors. This led to great improvements in prognosis and outcome for RA patients. However, about 40% of patients experience no remission or suffer from side effects of medication. To optimize established substances and to develop new treatment strategies, it is necessary to understand the mechanisms underlying the limited therapeutic effects.Objectives:Evaluation of the effect of prednisolone, MTX, adalimumab, tocilizumab on IL-6 secretion by RA synovial fibroblasts (RASF) and macrophages.Methods:RA synovium was used for RASF isolation. Peripheral blood mononuclear cells (PBMCs) were isolated from blood of healthy donors and RA patients by using Ficoll© medium followed by density gradient centrifugation. Mononuclear cells were seeded on six well plates (6x10^6/well) and incubated for one week. Then they were stimulated with Interferon-у (20 ng/ml) and LPS (50 ng/ml) for 48h to initiate differentiation into proinflammatory M1 macrophages. The M1 macrophages were co-cultured with RASF (100.000/well) and different treatments added (prednisolone: 10, 25, 50, 75, 100 nM, 1 µM; adalimumab: 100, 500 µg/ml; tocilizumab: 1, 5 µg/ml; MTX: 0,5, 1, 5, 10, 100 nM, 1µM). After 24h culture supernatants were collected and IL-6- and TNFα-ELISAs were performed.Results:IL-6 concentrations of untreated controls were comparable, regardless whether M1 macrophages from healthy donors or RA-patients were used for co-culture. Prednisolone reduced co-culture-induced IL-6 up to 56% (p<0.001) in co-culture of RASF and M1 macrophages of healthy donors and up to 60% (p<0.001) in co-culture of RASF and RA M1 macrophages. Adalimumab reduced IL-6 up to 28% (p<0.05) in M1 of healthy donors and up to 45% (p<0.01) in RA M1 macrophage co-cultures. A minor reduction by 10-20% of IL-6 was observed with tocilizumab and no significant effect could be achieved after treatment with MTX.Conclusion:Prednisolone and adalimumab clearly decrease but do not eliminate proinflammatory synergistic activity of RASF and M1 macrophages. These results confirm the clinical observation, that there is a large number of RA-patients that independent of anti-inflammatory treatment still suffer from low-level joint inflammation.The synergistic proinflammatory activity of M1 macrophages and RASF seems to be a complex and multifactorial mechanism that is difficult to eliminate by a single treatment substance. Since it is one of the key mechanisms in RA pathogenesis, there is a critical need to investigate how therapy effects could be optimized. This study confirmed RASFs as one of the leading effector cells of increased synergistic proinflammatory activity, thus underlining their promising role as a treatment target in rheumatoid arthritis.Disclosure of Interests:None declared
Hypoxia impairs mesenchymal stromal cell-induced macrophage M1 to M2 transition
