High-titer replication of nondefective Sendai virus in MDBK cells

Egg-grown Sendai virus was adapted to growth in a bovine kidney cell line (MDBK cells) by serial passage under defined conditions. The adapted virus contained only 50S RNA and was highly infectious for MDBK cells. Infection of these cells with a high multiplicity of adapted virus resulted in a yield of 10(8) MDBK-infectious units/ml by 18 h, accompanied by severe cytopathic changes in the host. Cell fusion did not occur. Examination of the proteins of the adapted virus revealed that despite the high infectivity of this virus for MDBK cells the virions contained considerable quantities of Fo, the precursor to the F glycoprotein that is responsible for cell fusion and high infectivity in other systems.