Lemon balm extract does not inhibit HIV-1 Env-mediated cell-cell fusion. (A) Schematic of assay used for the quantification of Env-mediated cell-cell fusion. The fusion efficiencies of TZM-bl target cells, expressing the HIV receptor complex, cocultured with CHO Tat cells, transiently expressing the JR-FL Env proteins, were determined via β-galactosidase enzyme activity in relation to the protein concentration. (B) Following overnight transfection, CHO Tat cells expressing JF-FL Env were treated either with different concentrations of lemon balm extract (0.6% (highest non-toxic concentration), 0.1%, or 0.06%), solvent, or enfuvirtide (positive control) for 1 h prior to addition of TZM-bl cells and during the coculture period. The relative fusion efficiency of untreated cells was set to 100% and the arithmetic mean ± SD (n = 4) are given. The experiment shown is representative for three independent experiments. *** Student's t-test; p < 0.001.