Tissue sections of frontal cortex, hippocampus and cerebellum from uninfected (SIV-, n = 3), SIV-infected animals with encephalitis (SIVE, n = 3), SIV-infected animals without encephalitis (SIV+ No ART, n = 3), and SIV-infected animals treated with ART (SIV+ART+, n = 3) were used to detect SIV Nef protein in vivo through immunohistochemistry. This evidence concerns the gene S100B and encephalitis.