Effects of Defective Interfering Viruses on Virus Replication and Pathogenesis In Vitro and In Vivo

Defective interfering (DI) particles are subgenomic deletion mutants generated from the infectious virus genomes, generally by replicase errors. DI particles and related satellite genomes of the plant RNA viruses are generated by a wide variety of animal, plant, and fungal viruses. The ubiquity of DI viruses was first clearly recognized by Huang and Baltimore. They proposed and defined the term “DI particle” to include defective viruses containing only some portion of the infectious virus genome, requiring homologous parental virus as a helper for the replication, containing virus structural proteins and antigens, and exhibiting the capacity to replicate preferentially at the expense of infectious helper virus in cells infected by both. Satellite RNAs of plants are small RNAs that usually share little or no homology with their helper viruses, although some do exhibit some sequence homology with their helper viruses, and thus resemble DI particles in at least a portion of their genomes. Depending on the leaving sites and resumption sites, DI particles can be produced that are simple internal deletions of the virus genome, simple deletions with a new terminus, or complex or bizarre genomes with multiple rearrangements of the virus segments. DI viruses and defective viruses generally are widespread in nature. Laboratory studies show that they can sometimes exert powerful disease-modulating effects (either attenuation or intensification of symptoms). Their role in nature remains largely unexplored, despite the recent suggestive evidence for their importance in a number of systems.