Comparative susceptibilities of twelve insect cell lines to infection by three baculoviruses.

Insect cell lines are commonly used to study insect viruses (Blissard, 1996) and have often been considered for production of certain virus species as biopesticides or for recombinant proteins. In the case of proteins, the Spodoptera frugiperda line IPLB-Sf21AE and the Sf-9 clone derived from it have been most frequently used with the baculovirus expression vector derived from Autographa californica nucleopolyhedrovirus (AcMNPV). However, many other lepidopteran cell lines are permissive to infection by this virus. In the present study, twelve insect cell lines (Table 1) were tested for susceptibility to baculovirus infection by use of a typical endpoint assay procedure (Lynn, 2002) using extracellular virus (ecv) suspensions of three nucleopolyhedroviruses (NPVs), including A. californica NPV (AcMNPV), Anagrapha falcifera NPV (AfMNPV), and Anticarsia gemmatalis NPV (AgMNPV). Each of these viruses was originally isolated from a noctuid moth species and infect many species from this family as well as some other Lepidoptera. By using the same virus dilutions on each line and scoring for infection, the relative susceptibility of the cells can be determined for each virus. Cultures were maintained in 25cm Greiner Cellstar tissue culture flasks (Frickenhausen, Germany) at 26 C on a weekly subculture interval. The specific media used for maintenance was the one that provided the best growth for each line and was used in the assays since this provides the most consistent results (Lynn, 2000). Cell identity was confirmed by isozyme analysis. The resulting titers obtained with the various cell/virus combinations are presented in Fig. 1. Because of its wide use in baculovirus research, the Sf21 cell line was used as a benchmark in Fig. 1 by dividing the TCID50/ ml (titer) obtained on each line by the value obtained with this line for each virus. This method eliminates the differences in actual titers for each virus suspension, making comparisons between viruses easier. Sensitivity to infection is one aspect of virus replication that can vary between cell lines. I have previously shown the TN-R line was more than 100-fold more susceptible to AcMNPV than the more commonly used Sf21 cell line (Lynn, 1992a). This was confirmed in the present study. The TN-R line was also most susceptible to AfMNPV which is not surprising since the AfMNPV virus has a great deal of genetic homology to AcMNPV (Harrison and Bonning, 1999). Ag286 from the velvetbean caterpillar also was considerably more susceptible to these viruses than Sf21 and was most susceptible to its homologous virus, AgMNPV, by 600-fold over Sf21. Journal of Invertebrate Pathology 82 (2003) 129–131 Journal of INVERTEBRATE PATHOLOGY