Isolation of a cell line for rapid and sensitive histochemical assay for the detection of herpes simplex virus.

A cell line which can be used in a simple, sensitive, and rapid histochemical assay was isolated for detection of herpes simplex virus (HSV). The cell line was derived by selection of G418 resistant colonies following co-transfection of baby hamster kidney cells with a plasmid which contains a G418 antibiotic resistance marker and a plasmid which contains the Escherichia coli LacZ gene placed behind an inducible HSV promoter. The promoter is from HSV-1UL39 which encodes ICP6, the large subunit of ribonucleotide reductase (RR1). This promoter has a number of features which make it ideal for the detection of HSV. First, there is no constitutive expression from this promoter in uninfected cells. Second, activation of the promoter appears to be specific for HSV. Third, expression from this promoter occurs within hours after infection. Fourth, this promoter is strongly transactivated by the virion associated trans-activator protein VP16. As early as six hours after infection HSV-infected cells can be detected by histochemical staining for beta-galactosidase activity. Infected cells stain intensely blue whereas uninfected cells show no staining, and a single infected cell can easily be recognized in a microscopic field of uninfected cells. Both HSV-1 and HSV-2 are detected with this cell line, but after infection with human cytomegalovirus (HCMV), varicella zoster virus (VZV), adenovirus, and sindbis virus no blue cells were detected. Quantitation of HSV-1 stocks on this cell line by counting blue cell forming units (BFU) reveals that the number of BFU/ml closely approximates the number of plaque forming units (PFU)/ml as determined by plaque assays on the parent cell line. This cell line should provide a useful adjunct in the diagnostic virology laboratory for the rapid detection of HSV in clinical specimens.