LCMV-infected pfp^–/– mice display histopathologic features of HLH. (A) Tissue sections from uninfected wild-type mice or LCMV-infected pfp^–/– mice were stained with hematoxylin and eosin. All images are of paraffin-embedded tissue, except the high-power views of spleen and bone marrow cells, which are cytospins. All pfp^–/– samples were taken from mice 12 days after infection, except for the central nervous system (CNS) sections which were taken from mice infected 30 days previously and treated with anti-LCMV antibodies (Figure 6). (B) Tissues from wild-type mice (with and without LCMV infection) and LCMV-infected pfp^–/– mice were analyzed by flow cytometry for the relative content of macrophage-lineage cells (% CD68⁺). Error bars represent SEM. (C) CD68⁺ cells from the bone marrow of wild-type and pfp^–/– mice infected with LCMV 12 days previously were stained for MHC class II. Data (± standard error) are representative of at least 2 experiments with at least 3 mice in each group.