Characterization of productive and non-productive AcMNPV infection in selected insect cell lines

We have investigated the process of productive and non-productive AcMNPV infection in a variety of cultured insect cells including lines derived from Spodoptera frugiperda (IPLB-SF21), Mamestra brassicae (SES-MaBr-3), Choristoneura fumiferana (IPRL-CF-1), Bombyx mori (BmN-4), Lymantria dispar (IPLB-Ld652Y), Helicoverpa zea (Hz1b3), and Drosophila melanogaster (Dm). In each cell line, we have examined viral utilization of an early, a late, and a very late promoter, the replication of viral DNA and the production of budded virus (BV) and polyhedral inclusion bodies (PIBs). Analysis of promoter use on the single cell level was performed using fluorescence-activated cell sorting (FACS) technology. Cell cultures were infected with recombinant viruses containing CAT reporter genes under the transcriptional control of viral early, late or very late promoters. Cells were immunostained to detect the CAT gene product and the relative CAT content of infected cells on a per cell basis was determined by FACS analysis. Productive infection of IPLB-SF21 cells involved essentially 100% of the cells while analysis of less productive lines (IPRL-CF-1 and SES-MaBr-3) suggests that the virus initiates and completes the replication process only in a subpopulation of cells. Analysis of non-productive infections (in BmN-4, IPLB-Ld652Y, Hz1b3, Drosophila Schneider) revealed different patterns of viral DNA replication and promoter use in each cell line suggesting a variety of obstacles to productive infection.