Figure 1

Histological evidence of rapid immune cell infiltration into the hippocampus of mice acutely infected with Theiler's murine encephalomyelitis virus (TMEV). C57BL/6J mice were injected intracerebrally with 2 × 10⁵ PFU TMEV in 10 μL of RPMI (B, D, H-J) or with 10 μL RPMI (SHAM) (A, C, E-G). The animals were killed by intracardiac perfusion of 4% paraformaldehyde 24 h after infection. Brain was processed for paraffin embedding and sectioning, and stained with hematoxylin and eosin. Robust inflammatory infiltrate is present above the hippocampus and throughout the corpus callosum in the TMEV-infected mice (B, D). Sham-infected mice exhibit no signs of infiltrate (A, C). Higher magnification confirms the presence of infiltrate throughout the corpus callosum and alveus (H), within the CA1 pyramidal neuron cell layer (I), and within the perivascular space along the hippocampal fissure (J) in virus-infected mice but not in sham-infected mice (E-G). Scale bar in B is 500 μm and refers to (A); scale bar in (D) is 100 μm and refers to (C); scale bar in (J) is 20 μm and refers to (E-I). Abbreviations: alv = alveus; CA1 and CA3 = cornu ammonis fields of the hippocampus; cc = corpus callosum; DG = dentate gyrus; fi = fimbria; hf = hippocampal fissure. Findings are representative of more than 20 animals per group.