Furthermore, it was recently demonstrated that the receptor for CD40L, CD40, is upregulated during HIV infection, presumably via exposure to Tat [7], in a manner that promotes brain microvascular endothelial cell activation, monocyte recruitment [12], [13] and microglial activation [12], thus implying an important role for this receptor/ligand pair in the pathogenesis of HAND. Here, TAT is linked to HIV-associated neurocognitive disorder.