Presence of NK-cell cytotoxic activity reduces biological features of HLH-like syndrome.Rag2^−/−Il2rg^−/− and Rag2^−/− mice were reconstituted with BM from Prf1^−/− and control B6 donors. After 8 weeks, T^Prf1−NK^Prf1− (open bars), T^Prf1−NK^Prf1+ (gray bars), and T^Prf1+NK^Prf1+ mice (black bars) were infected with 200 PFU of LCMV-WE. (A) Spleen size expressed as percentage of body weight on day 14 postinfection. (B) Mononuclear cell (MNC) infiltration in liver on day 14 postinfection. (C) Absolute numbers of CD8⁺ and NK1.1⁺ in liver. (D) FACS analysis of MNC from liver gated on CD3⁻ CD19⁻ NK1.1⁻ (left panel). Quantification of absolute numbers of CD64⁺ Ly6C⁺ in liver on day 14 postinfection. (E) Serum alanine and aspartate aminotransferase (alanine aminotransferase and aspartate aminotransferase, respectively) levels in infected mice were analyzed on day 14 postinfection. (F) Serum IFN-γ on day 8 postinfection. (G) Serum IL-6 (left panel), CCL2 (middle panel), and CCL5 levels (right panel) on day 14 postinfection. Data (mean ± SEM) are representative of 3 to 4 independent experiments with at least 3 mice in each group. Dotted lines represent minimal normal values for control mice. Statistical analysis was performed using 1-way ANOVA or Student t test. *P < .05; **P < .01.