Biologic Properties of Two Plaque Variants of Vesicular Stomatitis Virus (Indiana Serotype)

Large plaque (LP) and small plaque (SP) variants were cloned from stock cultures of Indiana serotype, San Juan strain of vesicular stomatitis (VS) virus. Both variants bred true in cultures of chick embryo (CE) and L cells. Differences in infectivity, cytopathogenicity and growth potential were more pronounced when the two variants were compared in cultures of L cells. The LP and SP variants did not appear to differ significantly in the following properties: adsorption on CE or L cells, release from infected L cells, thermostability, growth in the presence of agar extracts, plaque size and growth under conditions of reduced bicarbonate concentrations, inactivation of infectivity by ultraviolet irradiation and cytotoxicity. Slight variations could be detected in neutralization by antibody and buoyant density in a cesium chloride density gradient. The LP variant was not conclusively inferior in its capacity to induce formation of interferon during the course of infection. However, definite evidence was obtained that the SP variant is more susceptible to the action of an exogenous interferon produced by infected L cells. Persistent infection of L cells could be established only with the SP variant. During an observation period of 5 months, carrier L cell cultures underwent periodic cycles of SP virus multiplication and cell destruction alternating with cycles of virus quiescence and slow repopulation of cultures by surviving L cells. No interferon could be detected in SP carrier cultures, but the L cells became more resistant to superinfection with the LP variant.