A quantitative assay for cytolysis induced by Newcastle disease virus

We report here an assay for quantifying virus-induced lysis, in the absence of antibody and complement, produced within 2 hr after adsorption. This technique makes use of 51CrO4 release from cell monolayers pre-incubated overnight with the isotope. The release of 51Cr is specific for virus-induced lysis and is suppressible by 0.001 M-Ca2+. This assay clearly distinguishes between wild-type Chinese hamster ovary (CHO) cells, clone K and fusion-resistant mutant (CHO-15B), which was found to be resistant to virus-induced cytolysis. The stability of the association of isotope with monolayers of this cell type under the labelling conditions described makes this technique applicable to the study of the cytolytic effects of virus infection.