Elevation of SM/PC ratios is insufficient for Nef-mediated enhancement of virion infectivity. (A) Single round of infection analysis on TZM cells with cell culture supernatants from MT-4 T lymphocytes infected with the indicated viruses. The assay was performed analogous to that described in Fig. 1A. (B) Quantitative lipid analysis of virion SM/PC ratios. HIV particles purified from the cell culture supernatants analyzed in A were subjected to lipidome analysis. Depicted are the SM to PC ratios.