Presence of NK-cell cytotoxic activity reduces HLH-like manifestations in mice.Rag2^−/−Il2rg^−/− and Rag2^−/− mice were reconstituted with BM from Prf1^−/− and control B6 donors. After 8 weeks, T^Prf1−NK^Prf1− (open bars/open squares), T^Prf1−NK^Prf1+ (gray bars/gray circles), and T^Prf1+NK^Prf1+ mice (black bars/black squares) were infected with 200 PFU of LCMV-WE. Clinical and biochemical parameters were determined after infection. (A) Survival, body weight, and body temperature. (B) White blood cell counts were analyzed on day 14 postinfection. (C) Red blood cell, hematocrit, and platelets counts on day 14 postinfection. (D) The time course of neutrophils counts. Data (mean ± standard error of the mean [SEM]) are representative of 3 to 4 independent experiments with at least 3 mice in each group. For survival experiments T^Prf1−NK^Prf1− (n = 10), T^Prf1−NK^Prf1+ (n = 9), and T^Prf1+NK^Prf1+ (n = 12) mice. Dotted lines represent minimal normal values for control mice. Statistical analysis was performed using log-rank test or 1-way ANOVA. **P < .01; ***P < .001.