Studies on vaccinia virus plaque formation and its inhibition by interferon: II. Dynamics of plaque formation by vaccinia virus in the presence of interferon

The effect of interferon on the dynamics of vaccinia virus plaque formation in chick embryo cell monolayers was investigated. Preincubation of cells with interferon only slightly affected inhibition as compared to simultaneous addition of interferon and challenge virus. Within limits, a linear relationship was found when the following parameters were plotted against log interferon concentration: (a) Plaque counts; (b) average plaque diameters; (c) logarithm of total plaque area. Plaques in interferon-treated cultures emerged at a slower rate into visibility and took longer to reach a plateau in numbers than did controls. As a consequence, the amount of inhibition as estimated from plaque counts decreased after primary control plaques had reached their maximum number. The growth rate of treated plaques was reduced but remained independent of plaque size or time. Some of the infected cells seemed to be permanently prevented from yielding plaques.