Topographic Changes in SARS Coronavirus–infected Cells at Late Stages of Infection

M.L Ng,M.L.N Leong,H.-C Tan,E.E Ooi,A.-E Ling,J.W.M Lee

doi:10.3201/eid1011.040195

Abstract

Scanning electron and atomic force microscopy was used for the first time to view the maturation of the severe acute respiratory syndrome-associated coronavirus at the cell surface. The surface form of the cells at advanced infection displayed prolific pseudopodia that, in addition to the rest of the plasma membrane, were also active sites of virus release. High magnification of the maturing virus particles showed a rosette appearance with short knoblike spikes under both the scanning electron and atomic force microscopes. The final expulsion step of the maturing virus particles seemed to result in some disruptions to the plasma membrane. The cytoskeletal network along the edge of the infected cells was enhanced and could be involved in transporting and expelling the progeny virus particles. Thickening of the actin filaments at the cell edge provided the bending force to extrude the virus particles.

Highlights

Scanning electron and atomic force microscopy was used for the first time to view the maturation of the severe acute respiratory syndrome–associated coronavirus at the cell surface
The scanning electron microscopy images showed a holistic view of severe acute respiratory syndrome (SARS)-CoV–infected cells compared to ultrathin sections in transmission electron microscopy
Another virus-induced change clearly demonstrated by using the scanning electron microscope was the proliferation of pseudopodia on the infected cells and in particular, at the edge of these cells (Figure 2A, arrows compared to Figure 1)

Summary

Introduction

Scanning electron and atomic force microscopy was used for the first time to view the maturation of the severe acute respiratory syndrome–associated coronavirus at the cell surface. The uncoated nucleocapsids are found within large, smooth, double-membrane vacuoles together with membrane whorls [11] These membrane whorls are postulated to be replication complexes for the virus since they appear very early (within 30 min) after infection. Other reports have described double-membrane vesicles as sites of replication for coronavirus (Linder strain) [13], mouse hepatitis virus [14], and SARS virus [15]. The aim of this study was to use scanning electron and atomic force microscopes to investigate changes in the surface topography of SARS-CoV–infected cells at late infection. The results can assist in further understanding how SARS-CoV interacts with infected cells at late infection

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Conclusion