HeLa (A) and 293T cells (B) were transfected with plasmids pNL4-3 VpuB, pNL4-3 Vpu BF, and pNL4-3 ΔVpu, separately. Viral production was evaluated, using an ELISA assay, by measuring the Gag p24 antigen content in cell culture supernatants 24 and 48 hours post-transfection. Jurkat cells (C) and CEM-GFP (D) were infected with equal MOI of NL4-3 Vpu B, NL4-3 Vpu BF and NL4-3 ΔVpu virus stock, and viral replication was monitored by measuring the virus-associated reverse transcriptase activity in culture supernatants. Error bars indicate standard errors. Results are representative of two independent experiments.