Upon infection with virus lacking Nef (dNef), the percentage of infected cells that produced IL-2 after stimulation was significantly lower than in cells infected with virus encoding Nef and Vpu (NL4.3) (Fig. 8a, b), suggesting that the presence of Nef leads to increased activation, consistent with Nef’s previously reported role in T cell activation upon anti-CD3 and anti-CD28 treatment of Jurkat cells [57]. Here, CD28 is linked to infection.