Schematic of the general model to describe the relationship between Tax+ and Tax- infected cells in vivo. Death of silently infected CD4+ cells will include all normal cell death processes such as necrosis and apoptosis. Death of Tax-expressing CD4+ cells is divided into two: that which can be directly attributed to CTL (e.g. perforin mediated lysis or Fas-mediated apoptosis) and that which is independent of CTL (including normal cell necrosis and apoptosis as well as Tax-induced apoptosis and activation induced cell death). Natural proliferation describes the normal background rate of CD4+ cell turnover. Tax-driven proliferation describes the extra proliferation that may be caused by Tax expression due to its upregulation of cellular genes involved in cell proliferation and deregulation of cell cycle checkpoints [15–17, 33].