Background Systemic onset Juvenile Idiopathic Artritis (sJIA) is a systemic autoinflammatory disease, characterised by arthritis, spiking fever and rash and elevation of serum S100-proteins and interleukin (IL)-18. The role of monocytes and neutrophils in the inflammatory cascade of sJIA is still unclear.
Objective To study the role of monocytes and neutrophils in the inflammatory cascade of sJIA.
Methods We determined neutrophil activation ex vivo (phenotype and cell membrane markers) and after stimulation (ROS-production and degranulation) of cells derived from sJIA with disease onset or in remission, compared to healthy donors (HDs). To investigate the role of monocytes, we assessed cytokine production of PBMCs from sJIA patients and HDs after stimulation with TLR-4 activating S100-proteins (+/- ATP) or other TLR-ligands. In a cohort of sJIA patients at onset and during inactive disease, we evaluated cell counts and serum levels of cytokines, chemokines and other analytes. Cytokine concentrations in supernatant and serum were determined by multiplex immunoassay.
Results Twenty-one of 23 patients with onset sJIA had elevated neutrophil counts, while monocyte counts were elevated in only 5/23 patients. Many inflammatory markers were significantly elevated in serum of onset sJIA patients, among which several neutrophil specific proteins indicating the importance of this cell type. Neutrophils from onset sJIA patients showed an activated phenotype, reflected by higher ex vivo cell membraneexpression of FC-gamma receptors (CD32 and CD64), markers of secretory vesicles (CD35) and specific granules (CD66b). ROS production and degranulation were also enhanced in onset sJIA. Neutrophil phenotypenormalized when patients were in remission. In contrast to the hyperactivated status of neutrophils in active sJIA, PBMCs from these patients produced less Il-1b, IL-18, IL-6 and TNF-a upon TLR-stimulation compared to PBMCs from remission patients or HDs, suggesting tolerance after exposure to high TLR4 stimulating S100-levels in vivo.
Conclusions We show here that monocytes from onset sJIA patients produce less cytokines upon stimulation, while the neutrophils are hyperactivated, reflected by increased cell membrane activation markers, ROS production and degranulation. The exact role of each cell type and activity and their interaction in sJIA pathology is currently under investigation.