(A) Non-suppurative encephalitis, represented by moderate, lymphocyte-dominated perivascular infiltration. (B) Small vein with mild perivascular infiltration and activated endothelial cells (arrow). (C) The presence of serum, indicated by staining for von Willebrandt factor, in the parenchyma surrounding vessels with perivascular infiltrates (arrows) indicates marked vessel leakage. (D) Degenerating neuron (arrow) surrounded by glial cells (satellitosis). (E) Microglial nodule with occasional apoptotic cells (black arrow). (F) Staining for GFAP highlights the presence of large numbers of activated astrocytes (reactive astrocytosis). A, B, D, E: Hematoxylin-eosin stain. C, F: Indirect peroxidase method, NovaRed (C), DAB (F), hematoxylin counterstain. Scale bars: A, C, F = 50 µm; B, D, E = 20 µm.