Investigation On The Clinical Significance And Underlying Mechanisms Research Of Extracellular Histones In Systemic-onset Juvenile Idiopathic Arthritis

Objective: Systemic-onset juvenile idiopathic arthritis(So JIA) is a systemic inflammatory disease, the pathogenesis of which is still not clear. So JIA is always characterized by chronic, recurrent episodes, and some children are difficult to cure. The present study aims to investigate the correlation of serum histone levels of So JIA patients with the disease progression, as well as the clinical significance and underlying mechanisms of serum histones in So JIA, in order to provide theoretical basis for the treatment of refractory SoJIA.Methods: A total of 26 So JIA patients were recruited, and the peripheral blood samples and clinical information were collected. The serum histone levels of the patients were determined by ELISA. Neutrophils were incubated with patient serum, Fe Cl3 or histones in the presence or absence of heparin, and the percentage of neutrophils that released NETs was calculated under confocal microscope. In addition, a retrospective analysis on 12 refractory So JIA patients treated with etanercept at our hospital in the past 5 years was performed. The analysis included their clinical symptoms(such as high fever, inflammatory arthropathy, eruption rash, hydrohymenitis), as well as the changes in the levels of laboratory inflammatory markers(i.e., the white blood cell count, erythrocyte sedimentation rate, levels of C-reactive protein and serum ferritin).Results: The serum histone levels of the active group(0.90±0.90) were significantly higher than those of the remission group(0.17±0.10) or healthy controls(0.14±0.09), but no significant difference was observed between the remission group and healthy controls. The percentages of neutrophils releasing NETs were 31.93%, 12.32% and 11.31%, respectively, when treated with serum from active patients, remission patients or healthy controls; were 6.71%, 24.70%, 33.33% and 56.28%, respectively, when treated with 0mg/ml, 1mg/ml, 2mg/ml or 5mg/ml Fe Cl3; were 32.02%, 32.51% and 45.96%, respectively, when treated with 10mg/ml, 20mg/ml, or 50mg/ml histones. Addition of heparin could significantly reduce NETs production from neutrophils in vitro. During etanercept treatment, except that one patient was withdrawn from the corticosteroid-dependent group and the treatment-ineffective group, respectively, the remaining 10 patients completed the entire therapy until etanercept was discontinued. After treatment, the clinical symptoms and laboratory inflammatory markers of the 10 patients were within normal range, and compared to the baseline, the average doses of prednisone decreased by 81%. No patient relapsed.Conclusions: The serum histones in So JIA patients may be from the NETs released by activated neutrophils, and the histone levels are significantly correlated with the disease activities of So JIA. Free iron could induce NETs generation from neutrophils, which might be one of the causing reasons for the elevated histone levels in the So JIA patients. Histones can further promote the NETs generation, leading to the formation of a positive-feedback loop of histone generation. Addition of heparin could significantly reduce NETs production from neutrophils in vitro. Etanercept is an important and effective candidate in such combined treatment strategies for refractory So JIA patients.