SPP1 and Cognitive impairment: Because of their central role in the development of HIV-associated cognitive impairment, and to gain an understanding of the impact of activated HIV-infected macrophages on the expression of OPN in the context of the central nervous system (CNS), we used double-label immunochemistry for cells of the human brain and OPN to test the hypothesis that resident macrophages/microglia are the major sources of this proinflammatory cytokine associated with HAND.