Concerning the response to canakinumab in sJIA, a differential regulation of the IL-18–IFN-γ–CXCL9 axis has been proven in patients with sJIA, and the higher the IL-18/CXCL9 and IFN-γ/CXCL9 ratios, the better the clinical response to canakinumab treatment [146,147]. This evidence concerns the gene CXCL9 and systemic-onset juvenile idiopathic arthritis.