Electron microscopic observations of vesicular stomatitis virus particles penetration in human fibroblasts.

The penetration of vesicular stomatitis virus (VSV) into the target cells is known to depend on the acid triggered receptor-mediated endocytosis pathway (RME). However, the possible contribution of phagocytosis and macropinocytosis both at early and late stages of infection and of plaque-forming process is unknown. Electron microscopic images of fibroblasts obtained one hour after VSV adsorption at 37 degrees C showed RME vesicles as well as clusters of particles in cytoplasmic inlets and phagocytic vacuoles which are morphologically similar with macropinosomes. Therefore, the possibility that VSV can use, in addition to RME, phagocytosis and macropinocytosis is discussed with respect to the wide range of host cell VSV infectivity and binding as well as to pseudotype formation.