A recent study using macaques infected with a neuropathogenic SIV clone, CL757, that results in progression to SIV-induced encephalitis (SIVE) in 50% of those infected, showed increased numbers of memory CD4+ T cells (mCD4s) and macrophages in the brains of macaques with SIVE (47). The gene discussed is CD4; the disease is viral encephalitis.