Fig. 8.

Three-dimensional reconstruction from 14 serial electron micrographs. a Overview of cell–cell interaction in viral propagation. b Detail of the membrane projections, where filopodial connections and viral surfing are observed. Numerous membrane projections from (at least) three different cells converge in a region of high viral load. We designate as 'viral extrusion' the region where the membrane of the extrusion vesicle fuses with the plasma membrane. c A vesicle with internalized viruses from cell 2 has been reconstructed. It is observed 12 viral particles that occupy practically the entire vesicle. It is probably an extrusion vesicle externalizing the virus. d A detail of viral extrusion has been reconstructed using eight micrographs. The micrographs have been selected to show how a vesicle fuses with the membrane to extrude viruses along a filopodium. This finding supports the hypothesis that filopodia are formed to promote the spread of the virus between cells. Scale bars represent 2 μm in a, 0.5 μm in b, and ~ 0.1 μm in c, d