Defective interfering particles (DIPs) are virus particles that are missing part or all of their genome. Because of these deletions in their genome, DIPs cannot sustain an infection by themselves. Instead, they depend on co-infection with a suitable helper virus. The helper virus provides the gene functions that are absent from the DIPs. The DIP interferes with the helper virus by competing for enzymes that the helper virus requires to multiply. Unfortunately, the interference is not sufficient to eliminate the viral infection, and DIPs are not used clinically. Usually, the small genomes of the DIPs are more efficiently replicated than the full length viral genome, generating a very large number of non-infectious particles. In cell culture, if viral titers (minimum infectious dilutions of a virus) can be evaluated, the generation of DIPs is frequently associated with primary high MOI infections. The second observed phenomenon is a cyclic alternation of high and low infectious titers produced from passage to passage.
1. Philip I. Marcus,John M. Ngunjiri, and Margaret J. Sekellick. 2009. Dynamics of Biologically Active Subpopulations of Influenza Virus: Plaque-Forming, Noninfectious Cell-Killing, and Defective Interfering Particles. Journal of Virology 83:8122-8130