Labile coat: reason for noninfectious cell-free varicella-zoster virus in culture.

Experiments designed to determine why cell-free varicella-zoster virus replicated in cell culture is noninfectious were performed. Electron micrographs in which varicella-zoster virus (a herpesvirus) was compared to herpes simplex virus in primary human amnion cell cultures showed that the viruses were morphologically indistinguishable inside the nucleus. However, extranuclear varicella-zoster viruses were distinguished from herpes simplex virus by the presence of pleomorphism, incomplete coats, and a resultant loss of central dense cores. This result indicates that varicella-zoster virus possesses a labile coat which is degraded outside the nucleus. It is suggested that the labile coat is a principal reason for the lack of cell-free infectious virus in this system.