FIG 3.

Infectious internalization of FPC-HPV16 is faster and more synchronous than that of HPV16. (A) In an add-on experiment, HPV16 (dotted) or FPC-HPV16 (solid) was used to infect HeLa (left) or HaCaT (right) cells. At indicated times postinfection, extracellular virus was inactivated by a high-pH wash (pH 10.5). Depicted are the half-times of infectious internalization and the difference in the half-time between the two viruses in hours and percentages. (B) A seed-over experiment was performed as described for panel A. Infectious internalization values were normalized to the 48-h samples and are depicted in percentages ± standard errors of the means (SEM) for all experiments. Curves were fitted with the nonlinear regression function of GraphPad Prism v6. Statistical significance was tested by two-tailed unpaired Student's t test in GraphPad Prism v6; P values are indicated by asterisks: *, P < 0.05; **, P < 0.01. (C) pHrodo-HPV16 and pHrodo-FPC-HPV16 particles were added to cells, and the pHrodo signal was imaged at different time points p.i. and analyzed as relative intensity per cell.