RESPIRATORY SYNCYTIAL VIRUS MATURES AT THE APICAL SURFACES OF POLARIZED EPITHELIAL-CELLS

Respiratory syncytial (RS) virus infects the epithelium of the respira tory tract. We examined the replication and maturation of RS virus in two polarized epithelial cell lines, Vero C1008 and MDCK. Electron mic roscopy of RS virus-infected Vero C1008 cells revealed the presence of pleomorphic viral particles budding exclusively from the apical surfa ce, often in clusters. The predominant type of particle was filamentou s, 80 to 100 nm in diameter, and 4 to 8 mu m in length, and evidence f rom filtration studies indicated that the filamentous particles were i nfectious. Cytopathology produced by RS virus infection of polarized V ero C1008 cells was minimal, and syncytia were not observed, consisten t with the maintenance of tight junctions and the exclusively apical m aturation of the virus. Infectivity assays with MDCK cells confirmed t hat in this cell line, RS virus was released into the apical medium bu t not into the basolateral medium. In addition, the majority of the RS virus transmembrane fusion glycoprotein on the cell surface was local ized to the apical surface of the Vero C1008 cells. Taken together, th ese results demonstrate that RS virus matures at the apical surface of polarized epithelial cell lines.