Defective interfering particles (DIPs) are virus

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 particles that are missing part or all of their genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

. Because of these deletions in their genome, DIPs cannot sustain an infection

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

 by themselves. Instead, they depend on co-infection with a suitable helper virus. The helper virus provides the gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

 functions that are absent from the DIPs. The DIP interferes with the helper virus by competing for enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s 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

Cell culture

Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...

, if viral titers (minimum infectious dilutions of a virus) can be evaluated, the generation of DIPs is frequently associated with primary high MOI

Multiplicity of infection

The multiplicity of infection or MOI is the ratio of infectious agents to infection targets . For example, when referring to a group of cells inoculated with infectious virus particles, the multiplicity of infection or MOI is the ratio of the number of infectious virus particles to the number of...

infections. The second observed phenomenon is a cyclic alternation of high and low infectious titers produced from passage to passage.