LCN2 and juvenile idiopathic arthritis: The serum concentrations of HNL, S100A8/A9 and MPO, were significantly higher in untreated children with JIA than in healthy children, p = 0.001 for HNL (Fig. 3), p = 0.01 for S100A8/AA9 (Fig. 4), p = 0.01 for MPO (Fig. 5).