ABSTRACT
The appearance of defective interfering (DI) particles is a well-recognized consequence of passaging virus at high multiplicity of infection. Those properties that define DI particles and distinguish them from other interfering phenomena, first delineated by Huang and Baltimore, 1 include the following: (1) they contain only a part of the viral genome; (2) helper virus is required for replication and encapsidation of the defective genome; (3) they replicate at the expense of the nondefective virus and interfere with the intracellular replication of the latter; and (4) interference is specific; it is most severe for the homologous virus, can occur with related viruses, but is not observed with unrelated viruses. In addition, the defective particles are encapsidated by the same constellation of viral proteins as the helper virus. In some instances, the accumulation of DI particles decreases the cytopathic effects of the virus infection and may be essential in the establishment of persistent infections.
