Improvement in HLH-like manifestations in Prf1-reconstituted Rag2^−/− mice depends on NK cells.Rag2^−/− mice were reconstituted with BM from Prf1^−/− donors. After 8 weeks, T^Prf1−NK^Prf1+ (black bars/black circles) and T^Prf1−NK^Prf1+ injected with anti-NK1.1–depleting antibody (dashed bars/open circles) 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 and hematocrit counts on day 14 postinfection. (D) Spleen size expressed as percentage of body weight on day 14 postinfection. (E) MNC infiltration in liver on day 14 postinfection. (F) Quantification of absolute numbers of CD64⁺ Ly6C⁺ in liver on day 14 postinfection. Data (mean ± SEM) are representative of 2 independent experiments with at least 3 mice in each group. Statistical analysis was performed using Student t test. Dotted lines represent minimal normal values for control mice. *P < .05; **P < .01.