ACOT8 (Acyl-CoA thioesterase 8) also designated, TEII p35 or hTE, is a novel human thioesterase that has been found to interact with the HIV protein Nef using yeast two-hybrid screening. Nef is an auxiliary gene of the human immunodeficiency virus (HIV) which facilitates virus replication and enhances infectivity. The roles of Nef in HIV-infected cells are likely to be mediated by specific interactions with cellular proteins. The interaction between Nef and ACOT8 is correlated with CD4 downregulation, suggesting that ACOT8 may be involved in Nef-mediated CD4 downregulation in HIV-infected cells. ACOT8 is 42% identical to thioesterase II from Escherichia coli, and it has no significant homology with the two types of animal thioesterases that have previously been cloned (type I and type II thioesterases).