reviewed the various extracellular effects of HIV-1 Tat. The authors pointed out that Tat plays a crucial role in many pathological processes, which might contribute to nonimmune and immune dysfunctions during HIV infection and AIDS. Moreover, they underlined that Tat can block Ca 2+ channels in dendritic cells and natural killer (NK) cells and that this could be one molecular mechanism of the immunosuppressive effects mediated by exogenous Tat, such as inhibition of T-cell proliferation and phagocytosis, as well as interleukin 12 (IL-12) secretion and NK-cell activity. However, most of the immunosuppressive effects described could also be explained by a second mechanism: the Tat-mediated induction of the multifunctional, immunoinhibitory cytokine, transforming growth factor β1 (TGF-β1)