Clinical significance of serum CXCL9 levels as a biomarker for systemic juvenile idiopathic arthritis associated macrophage activation syndrome.

To clarify cytokines involved in the development of systemic juvenile idiopathic arthritis (s-JIA) associated macrophage activation syndrome (MAS) and to identify the serum biomarkers for the diagnosis of s-JIA associated MAS, we employed an antibody array that simultaneously detects 174 cytokines. Fifteen s-JIA patients including 5 patients receiving tocilizumab (TCZ) were analyzed. The levels of five cytokines were significantly elevated in MAS phase compared to those in the active phase of s-JIA. CXCL9 showed the most significant increase following the development of s-JIA associated MAS. Next, to confirm clinical significance of serum CXCL9 levels as a biomarker for s-JIA associated MAS, serum CXCL9 levels in 56 patients with s-JIA including 20 with MAS were analyzed. Results were compared with the clinical features of s-JIA associated MAS. Serum CXCL9 levels correlated positively with disease activity. Monitoring of serum CXCL9 is useful for the evaluation of disease activity in s-JIA associated MAS.