As a first step, we examined the expression of cell cycle proteins (Ki-67, cyclin D1, and p16INK4a), by immunohistochemistry, in the frontal and/or temporal cortices and brainstems of uninfected control macaques (n = 3), SIV-infected macaques without encephalitis (SIVnoE, n = 4), and SIV-infected macaques with encephalitis (SIVE, n = 4) (Table 1). This evidence concerns the gene CDKN2A and encephalitis.