TNF and encephalitis: Microglial activation was identified by higher levels of HLA‐DR, TNF‐α and IL‐1 expression.Severe microglial activation was only found in AIDS participants.Microglial activation was less pronounced but obvious in pre‐AIDS cases and weak or absent in seronegative patients.There was no clear distinction in the level of microglia activation between the HIVE/HIV‐associated dementia (HAD) compared to HIV non‐encephalitis (HIVnE) cases.