Myeloid-related protein 8/14 in plasma and serum in patients with new-onset juvenile idiopathic arthritis in a real-life setting

Abstract Objective: The aim of this study was to analyze the usefulness of myeloid-related protein 8/14 (MRP8/14) in the prediction of disease course in a real-life setting for patients with new-onset juvenile idiopathic arthritis (JIA), to identify the relationship between MRP8/14 and disease activity using the physician’s global assessment of disease activity (PGA), and determine whether the MRP8/14 levels measured in serum and plasma are equally useful.Methods: In this prospective follow-up study, 87 new-onset non-systemic JIA patients were studied. Blood and synovial fluid samples were collected prior to any antirheumatic medication use. MRP8/14 was measured from serum (S-MRP8/14), plasma (P-MRP8/14), and synovial fluid samples using ELISA. Results: The baseline MRP8/14 blood levels were significantly higher in patients using synthetic antirheumatic drugs than in patients with no systemic medications at one year after diagnosis in serum (mean 298 vs. 198 ng/ml, P<0.001) and in plasma (mean 291 vs. 137 ng/ml, P=0.001). MRP8/14 levels at the time of JIA diagnosis were higher in patients who started methotrexate during 1.5-year follow-up compared to those who achieved long-lasting inactive disease status without systemic medications (serum: mean 298 vs. 219 ng/ml, P=0.006 and plasma: 296 vs. 141 ng/ml, P=0.001). P-MRP8/14 was the most effective predictive variable for disease activity (by PGA) in linear multivariate regression model (combined to ESR, CRP, leukocytes, and neutrophils), whereas S-MRP8/14 was not significant. Conclusions: Blood MRP8/14 levels at baseline seem to predict disease course in new-onset JIA patients. P-MRP8/14 might be superior to S-MRP8/14 in assessing disease activity at the time of JIA diagnosis.