LCMV-infected pfp^–/– mice display clinical and laboratory features of HLH. Wild-type and pfp^–/– mice were infected with LCMV-WE. Eight to 12 days after infection, these animals and uninfected wild-type mice were assayed for (A) temperature, (B) plasma fibrinogen, (C) serum triglycerides, (D) spleen size, (E) peripheral blood neutrophil counts, (F) platelet counts, and (G) hemoglobin. The spleen photo in panel D portrays uninfected wild-type spleens and infected pfp^–/– spleens. (H) Survival of mice was monitored after LCMV infection of wild-type, RAG^–/–, β2m^–/–, and pfp^–/– mice. Data shown (± standard error) are representative of at least 2 experiments with at least 3 mice in each group.