Lack of syncytium formation by a type C virus-producing XC cell line in the mixed culture cytopathogenicity test.

XC cells, derived from a Rous sarcoma virus-induced Wistar strain rat tumor, form syncytia when cultured in the presence of murine leukemia virus-producing mouse cells. However, one XC cell culture (designated as XC-v cells), found to produce type C virus particles, fails to form syncytia in the presence of murine leukemia virus-producing mouse cells. Coculture of XC-v cells and XC cells negative for type C virus particles leads to a moderate degree of syncytium formation. Infection of XC cells with either the Moloney (M) strain of mouse leukemia virus or type C virus particles released by XC-v cells results in the loss of ability of XC cells to form syncytia in the mixed culture cytopathogenicity test. The syncytium-forming ability of XC cells, therefore, is altered by the presence of a type C virus in these cells.