Although this result may be due to differences between the cell types in which these analyses were performed (primary human macrophages for HIV infection and murine macrophage cell line RAW 264.7 for Nef transfection), it is also possible that the primary effect of Nef is to sequester ABCA1 at the plasma membrane, and some other HIV protein may cooperate with Nef to stimulate down-regulation of sequestered ABCA1. This evidence concerns the gene S100B and HIV infectious disease.