Plaque formation of Newcastle disease virus in primary chicken kidney cells.

Using primary chicken kidney (PCK) cells, a plaque assay was carried out with an avirulent strain of Newcastle disease virus (NDV) without adding trypsin to the agar overlay medium. The plaque assay was done in less than 4 days in PCK cells, by 3 days earlier than in primary chicken embryo (CE) cells maintained in the presence of trypsin. The curves of the progeny virus production began to rise 6 h after the infection and reached a plateau at 12 h. Equal amounts of virus were produced in PCK cells both in the presence and absence of trypsin in the culture medium. Viral peptide analysis revealed that a large portion of the HN and F precursor envelope glycoproteins of the NDV-Ulster strain remained uncleaved in PCK-grown virions. This suggests that a marginal proteolytic cleavage of these glycoprotein suffices for the full growth of the progeny virus in PCK cells. A higher shut-off in the host protein synthesis occurred in the virus-infected PCK cells than in the infected CE cells.