Electron Microscopic Observations on the Mechanisms of Entry of Simian Foamy Virus in HEp-2 Cells

Early electron microscopic studies of virus uptake by tissue culture cells, reviewed by Dales (1965), demonstrated the ingestion of virus particles by phagocytosis, a mode of uptake which necessitates the release of ingested virus particles from the phagocytic vacuoles before the infection cycle can proceed. Alternative means of entry, whereby infection is more direct, have more recently been demonstrated for a number of viruses by examination of samples harvested at short intervals after virus adsorption (Morgan & Howe, 1968; Morgan, Rose & Mednis, 1968; Dunnebacke, Levinthal & Williams, 1969; Morgan, Rosenkranz & Mednis, 1969; Heine & Schnaitman, 1971) but as yet it has not been shown which of these methods leads to initiation of infection. In this paper we describe and illustrate the adsorption and various methods of entry of a simian foamy agent (mk5) into HEp-2 cells and the early intracellular events which could lead to infection.