IL-18BP and CXCL9 are both biomarkers of Interferon (IFN, particularly IFN-γ) and, this finding corroborates previous findings of relatively lower CXCL9 and sIL-2Ra in Stills/MAS patients when compared to primary HLH patients [28]. Here, CXCL9 is linked to hemophagocytic syndrome.