Figure 3.

Ultrastructure of alveolar type II cells infected with SARS-CoV. Cells were cultured as described in Materials and Methods under A/L conditions, inoculated with SARS-CoV on the apical surface, and then fixed and processed for electron microscopy 48 hours after inoculation. (A) A differentiated alveolar type II cell with its characteristic lamellar bodies (LB) and SARS-CoV virions are found in expanded, smooth-walled secretory vesicles in the cytoplasm of the infected cell. Several budding virions are indicated by arrows. (B) Several smooth-walled, double-membrane vesicles (V), which are the site of replication for SARS-CoV RNA, virions in secretory vesicles near the plasma membrane, and virions adsorbed to the apical plasma membrane. The inset depicts a higher magnification of one of these double-membrane vesicles.