CXCL9 and systemic-onset juvenile idiopathic arthritis: This term is used by rheumatologists to describe the aggressive, life-threatening complications in patients with sJIA or AOSD, and is phenotypically associated with secondary hemophagocytic lymphohistiocytosis (sec-HLH), in which IFN-γ and CXCL9 play essential roles as biomarkers.