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Changes in expression of membrane TNF, NF-κB activation and neutrophil apoptosis during active and resolved inflammation

Background Tumour necrosis factor (TNF) is central to the pathophysiological process of rheumatoid arthritis (RA), whether as soluble cytokine or membrane-expressed pro-TNF (mTNF). Objectives To determine whether neutrophils, which can express TNF, are activated in the blood of patients with RA compared with healthy controls. To investigate, by focusing on mTNF expression, if the functions of RA neutrophils change in response to therapeutic TNF inhibition. Methods TNF was measured by flow cytometry and qPCR in neutrophils from 20 patients with RA before and after the start of TNF inhibitor therapy. Apoptosis was measured by morphology, and western blotting of pro- and antiapoptotic proteins in cell lysates. Nuclear factor κB (NF-κB) activation was determined by western blotting of phosphorylated NF-κB (p65). Results Before treatment RA neutrophils exhibited increased TNF mRNA expression, elevated mTNF levels and NF-κB activity compared with controls. They also underwent delayed apoptosis as shown by altered expression of anti- and proapoptotic proteins, such as Mcl-1 and caspases. Neutrophil TNF expression returned to baseline levels during successful treatment with anti-TNF biological agents, and there was a close correlation between clinical disease improvement and changes in neutrophil function. Conclusions Neutrophils express elevated levels of TNF in RA and the transcription factor, NF-κB, a target of TNF, is activated. This mechanism could lead to a self-sustained inflammatory process. These data point to an important role of neutrophils in the abnormal TNF signalling pathways activated in RA and provide new evidence that neutrophils actively contribute to altered cytokine signalling in inflammatory diseases.