CXCL9 and macrophage activation syndrome: In conclusion, serum cytokines might in the future inform therapeutic stratification for Still’s–MAS since CXCL9 was already suggested as a biomarker to stratify patients towards IFN-γ-blockade [3]; Shimizu et al. found that tocilizumab-treated systemic JIA patients with high IL-18 levels (>47 750 pg/mL) were prone to develop MAS, suggesting IL-1 blockade may be preferred for these cases [7]; and patients with inactive MAS but persistently high IL-18 may be prone to develop Still’s-associated lung disease [8].