Background Systemic onset Juvenile Idiopathic Artritis (sJIA), also known as Still’s disease, is characterised by arthritis with symptoms of systemic inflammation such as spiking fever, rash and serositis. It is considered an autoinflammatory disease with a major role for the innate immune system. The S100-proteins S100A8, S100A9 and S100A12 interleukin (IL)-18 in plasma are extremely elevated in sJIA patients and have been proposed to be useful biomarkers for diagnosis, disease activity and response to therapy. However, the relationship between S100-proteins and IL-18 in sJIA and the role of S100 proteins in pathogenesis is still unknown.

Objective To study the relation between S100-proteins and IL-18 in sJIA.

Materials and methods Peripheral blood mononuclear cells (PBMCs) from sJIA patients during active disease and during remission and PBMCs from healthy controls were stimulated with S100A8, S100A9, S100A12 or LPS (positive control) for four hours. As a second signal for NLRP3 inflammasome activation, ATP was added during the last 30 min. Cytokine levels in supernatant were measured by Luminex; cell frequencies and TLR-expression were analysed by flow cytometry.

Results Upon stimulation with S100-proteins, PBMCs from healthy donors produced inflammasome dependent IL-1b, IL-18 as well as inflammasome independent IL-6 and TNF-a; IL-18 and IL-1b production was further enhanced when ATP was added. S100 proteins are known to bind to TLR4 and RAGE; blocking TLR4 by adding CLI-095 decreased cytokine production to near normal levels, while blocking RAGE did not have an effect on cytokine production. When compared to healthy controls, PBMCs from sJIA patients produced less IL-18 upon S100 stimulation. The addition of ATP enhanced this differential effect. PBMCs from patients with active disease were less responsive to S100 stimulation than PBMCs from the same patient in remission. The same trend of hyporesponsiveness was seen when PBMCs from sJIA patients were stimulated with TLR2 or TLR7/8 ligands, suggesting cross-tolerance in these patient cells.

Conclusions S100-proteins serve as a first signal via TLR4 to establish NLRP3 inflammasome activation and thereby induce production of IL-1b and IL-18. Interestingly, PBMCs from sJIA patients with active disease are hyporesponsive to S100-proteins compared to sJIA patients in remission and healthy controls. We are currently investigating whether this hyporesponsiveness can be explained by stress tolerance of PBMCs after prolonged elevation of serum S100-proteins.

Acknowledgments for providing S100 proteins Holzinger D¹, Vogl T², Foell D¹, Roth J²

¹University Hospital Muenster and University Children’s Hospital Muenster, Muenster, Germany ² University of Muenster, Institute of Immunology, Muenster, Germany