Phagocyte-derived S100 proteins in autoinflammation: Putative role in pathogenesis and usefulness as biomarkers

The cytoplasmic S100 proteins derived from cells of myeloid origin are promising new markers of (auto-)inflammation. S100A8/A9 and S100A12 are released from monocytes and granulocytes during activation of the innate immune system. Tissue and serum concentrations correlate to disease activity, both during local and systemic inflammation. In autoinflammatory diseases such as Familial Mediterranean Fever (FMF) and Systemic onset Juvenile Idiopathic Arthritis (SJIA), a dysregulation of alternative secretory pathways may be involved in pathogenesis and lead to hypersecretion of S100 proteins. Since autoinflammatory diseases can be difficult to diagnose, phagocyte-derived S100 proteins are valid tools in the diagnosis of autoinflammatory diseases. In addition, they may help achieve a better understanding of the pathophysiology of autoinflammatory disorders including SJIA and FMF, and even provide novel therapeutic targets in the future.

► S100A8/A9 and S100A12 are released from activated phagocytes.
► S100 proteins are released via alternative secretory pathways.
► Dysregulated alternative secretion may be involved in autoinflammation.
► S100A8/A9 and S100A12 are valid biomarkers for autoinflammatory diseases.