The specificity of Helicoverpa armigera stunt virus infectivity

Helicoverpa armigera stunt virus (HaSV) is a member of the Tetraviridae fam ily of RNA viruses whose replication and expression strategies are not well understood due to the absence of an in vitro cell culture system. We set o ut to find such a system for HaSV by screening an array of 13 insect and 1 mammalian cell culture lines with both virus particle infection and genomic RNA transfection. No cell line was found to be permissive for replication, although entry of genomic RNA was verified. The apparent specificity of th is virus for its in vivo mid-gut target site was strongly corroborated by s tudies involving Northern blots of RNA extracted from infected insects. Onl y larval midgut RNA showed the presence of virus after hosts were infected per os or by injection which exposed other host cell types to the virus. Th e absence of replication in cell culture was due to a lack, or presence, of host factors important to replicase activity and also the likely absence o f virus particle binding and entry. We thus provide both in vitro- and in v ivo-based evidence demonstrating that this virus is extremely specific in t he type of cells in which it will initiate an infection. (C) 1999 Academic Press.