A viral agent inducing syncytia formation in monolayer cul

A viral agent inducing syncytia formation in monolayer cul tures of bovine embryonic spleen cells and a rabbit cornea cell line was isolated from cattle with lymphosarcoma. The agent was strongly cell-associated and transmissible with cell-free ff1trates at very low dilutions. An antigen prepared from heavily infected cultures produced precipitin lines by immunodiffu sion when tested against sera from lymphosarcomatous and apparently normal cattle. Buffy coat cells and cellular dc ments present in milk from apparently normal cattle whose sera gave positive precipitin reactions contained the virus. Some nonreacting offspring of dams that reacted were also virus carriers. Fluorescent conjugates prepared with precipita ring sera stained infected cells specifically while nonprecipita ting sera failed to do so. Electron microscopic examination of ultrathin sections from infected cell cultures revealed virus-like particles budding at the cell membranes in a manner resem bling the avian and murine leukemia viruses. Morphologically, these virus-like particles bore some resemblance to the mouse mammary tumor virus. Evidence that the virus plays a role, if any, in inducing bovine lymphosarcoma has not been estab lished.