CD4 and infection: In contrast, significantly more killing of bystander CD4+ T lymphocytes (Fig. 6C and 6D) was observed in HIV-1 wt-infected cultures when compared to infections with the Δnef or the LLAA and Δ12–39 Nef mutant viruses [wt: 154.6 ± 34.2% (p = 0.0079 compared to mock); Δnef: 92.8 ± 6.5% p = 0.0317; LLAA: 107 ± 5.3% p = 0.0556; Δ12–39: 99.7 ± 5.9% p = 0.0159, data expressed as percentage relative to mock that was arbitrarily set to 100%].