S100A8 and systemic-onset juvenile idiopathic arthritis: The innate TLR4 ligand myeloid related protein 8/14 (MRP8/14 or S100A8/9), originally found to be elevated in patients with systemic-onset juvenile idiopathic arthritis (JIA), correlated moderately to strongly with global and muscle disease activity in a large cohort of 56 JDM patients (rs = 0.55–0.65) (98, 141).