Infectivity of recombinant viruses in different cell types. (A-C) The indicated target cells were cultured overnight in 96-well plates, infected with serial dilutions of supernatants containing each of the 7 indicated VSV pseudotyped envelope-deleted recombinant viruses (final concentrations 0.156 – 10 ng p24/ml), and luciferase activity (RLU) expressed by the target cells was determined 40 h after infection. The slope of the dose response curve was determined by linear regression. The slope obtained from infection of target cells by NL4-3 was measured on each 96-well plate, and the value used to normalize the slope of the other samples present on that plate, as described in the Materials and Methods. The results shown are the mean ± SEM for 4 independent experiments. (D-E) For each experiment, the results were also expressed as a ratio of the normalized slopes obtained for the two indicated target cell types. The results shown are the mean ± SEM for 4 independent experiments.