Mouse hepatitis virus (MHV-2). Plaque assay and propagation in mouse cell line DBT cells.

Various factor sinfluencing the plaque formation of mouse hepatitis virus (MHV-2) in DBT cell monolayers were studied and a practical method for plaque assay was developed. Infected DBT cells yielded high-titered virus and were a satisfactory source of complement-fixing viral antigen. The predominant cytopathic effect of MHV-2 in DBT cells was cell rounding and detachment, but no syncytial formation was observed. Fluorescent antibody staining revealed specific fluorescence only in the cytoplasm of infected DBT cells. In one-step growth experiment, newly formed virus was first recognized within 4-hr postinfection and showed subsequently a rapid exponential increase. Release of newly formed virus from the cell was rapid, and a continuous release lasted for a certain period of time. The average per-cell yield of active virus was estimated to be about 6-7 X 10(2) plaque-forming units.