IFITMs incorporation into HIV-1 viral particles affects viral infectivity by interfering with entry of the virus in target cells. Normalized NL4-3 Env bearing HIV-1 virions produced in the presence or absence of IFITMs were bound to HeLaP4 cells at 4°C prior to extensive cell washing. The temperature was then raised at 37°C to induce entry. The extent of entry was then measured according to the two assays schematically depicted in A. B) Two hours after entry, cells were extensively washed, treated with trypsin to remove external virion particles and then lysed. The amount of cell-associated p24 was measured by ELISA. C) After exo-RT normalization, equal amounts of viruses incorporating Vpr-BLAM were used to challenge HeLaP4 cells for 2 hours. Cells were then incubated with the fluorescent dye CCF2 prior to FACS analysis. Graphs present averages obtained from 3 to 8 independent experiments. *p≤0,05, according to a Student t test.