Porcine Mx1 expression inhibits the centripetal traffic of endocytic vesicles containing incoming influenza A virus particles. Twenty minutes after addition of the lipophilic dye DiD to the medium, an inoculum drawn from the H1N1 influenza A virus stock and corresponding to a multiplicity of infection of ~ 200 was added to induced and non-induced V50 cells. Infection was stopped 40 min after infection by thorough PBS washings and fixation of cell monolayers with 4% paraformaldehyde. No additional staining was done, so the only visible fluorescence signals are from endocytosed fragments of plasma membrane and viral particles. Forty minutes after infection, non-induced cells displayed endocytosed material concentrated around the cell nuclei. Induced cells, in contrast, reproducibly displayed a diffuse, punctate, “dusty” pattern compatible with a block in the normal centripetal traffic of endocytosed materials.