IL2RA and isolated hyperferritinemia: ≥5/8 of the following: 1. Fever 2. Splenomegaly 3. Cytopenias (≥2 lineages) 4. Hypertriglyceridemia, hypofibrinogenemia 5. Hemophagocytosis 6. Low/absent NK cell activity 7. Hyperferritinemia 8. Elevated sIL-2R (CD25)