MMP3 and juvenile idiopathic arthritis: In this regard, proteomics has identified that serum levels of matrix metalloproteinase-3 are high in JIA patients, and seem to be a biomarker of disease activity.9, 10, 11 Myeloid-related protein 8/14 and the neutrophil-derived S100A12 were also reported to be biomarkers of JIA disease activity and to predict a subgroup of patients who will improve after Methotrexate (MTX) use.12