A rapid virus neutralization assay for Newcastle disease virus with the swine testicular continuous cell line

Five continuous cell lines, swine testicular (ST), human rectal tumor (HRT 18), fetal rhesus monkey kidney (MA104), bovine turbinate (BT), and quail t racheal (QT35), were evaluated and compared with chicken embryo fibroblasts (CEFs) for their ability to propagate B1 or Texas GB strains of Newcastle disease virus (NDV). The NDV Texas GB strain replicated in all the continuo us cell lines used in this study Only the ST and QT35 cells produced a cyto pathic effect (CPE) similar to that produced in CEFs. However, the ST cell line remained attached while displaying CPE, whereas infected QT35 cells de tached, as did the CEFs. The B1 strain of NDV replicated in ST cells, MA104 cells, and CEFs bur with less CPE as compared with the Texas GB strain. Pr etreatment with trypsin did not enhance CPE with either NDV strain at the l evel tested. Sera evaluated for neutralizing antibody titers co NDV were si gnificantly higher in titer when the ST cell line was used and compared wit h CEFs. A high correlation was found between the microscopic examination an d the tetrazolium dye (MTT) microassay methods for determining the viral ne utralization endpoint, thus suggesting the ST cell line and MTT microassay could be used as an alternative to CEFs and microscopic examination for eva luating neutralizing antibodies titers to NDV.