S100A8 and juvenile idiopathic arthritis: There are attempts to develop more specific laboratory biomarkers, such as serum proteins, the neutrophil activation marker S100A12, and the phagocyte activation marker myeloid-related proteins 8 and 14 heterocomplexes (MRP8/14), which were found to be more specific in predicting response to methotrexate and JIA flare than other clinical and laboratory data [32, 33].