Serum IFN-γ, TNF-α, IL-4, IL-6, IL-10, and IL-18 were found to be valuable in early identification, disease progression, and outcome prediction of HLH, especially in pediatric patients, EBV-related HLH, and MAS associated with sJIA or KD (8, 15, 18, 35–38). Here, IL4 is linked to macrophage activation syndrome.