We subjected Perf1 KO mice to infection with MCMV, which induces IFN-γ and TNF-α (Van Dommelen et al., 2006) and observed that these mice indeed developed a lethal condition similar to HLH, with pancytopenia, hemophagocytosis in the bone marrow and severe inflammation in the liver and spleen. Here, TNF is linked to hemophagocytic syndrome.