"Myeloid-related proteins" (MRP) 8 (S100A8) and MRP14 (S100A9) are endogenous ligands of Toll-like receptor (TLR) 41 that are highly expressed in granulocytes, monocytes, and activated keratinocytes. Both proteins belong to the alarmin family, which are danger signals released in response to cellular stress or damage. 10 Highly elevated serum concentrations of MRP8/14 complexes (calprotectin) have been found in patients with systemic juvenile idiopathic arthritis (SJIA), familial Mediterranean fever (FMF; OMIM #249100), and PAMI syndrome.