BK virus in cell culture: infectivity quantitation and sequential expression of antigens detected by immunoperoxidase staining.

We applied an indirect immunoperoxidase staining method for the detection of BK virus (BKV) antigens in Vero cells. By immunoperoxidase staining of sequential samples, expression of BKV T- and structural antigens was first detectable 72 h postinfection (pi). The initial low number of antigen positive cells was slowly increasing until 6 d pi. Thereafter, a steady progression was observed until total cytopathogenic effect 30 d pi. Viral hemagglutinins were detected 11 d pi in both the culture medium and in the cell lysate. Passage of the preparations into fresh Vero cells and immunoperoxidase detection demonstrated the presence of infectious virions in both the cell lysates and the medium from 2 d pi. The number of infectious particles in both media and cell lysates correlated to the number of IP stained cells in the sequential staining. We suggest that this type of assay might be used to examine the effects, in vitro, of interferons and other virostatic drugs of BKV and other viruses.