{{about, , the 1970 British film, Permissive (film), the grammatical mode, Permissive mood, the flavor of software license, permissive free software licence
A permissive cell or host is one that allows a
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsk ...
to circumvent its defenses and replicate. Usually this occurs when the virus has modulated one or several of the host cellular intrinsic defenses and the host
immune system
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
. The permissive state of a host has now been determined to be the primary factor in determining whether a virus will cause pathological symptoms in a host.
Susceptible ''versus'' permissive
A virus can enter a
susceptible
Susceptibility may refer to:
Physics and engineering
In physics the susceptibility is a quantification for the change of an extensive property under variation of an intensive property. The word may refer to:
* In physics, the susceptibility of ...
cell, but it cannot replicate. A virus can replicate in a permissive cell. Viral replication will therefore only occur in a cell that 1) facilitates entry (susceptible cell) and 2) supports intracellular replication (permissive cell). The significance between the difference of the two has now been elucidated with study of the
rabbit
Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit sp ...
-lethal
myxoma virus
''Myxoma virus'' is a poxvirus in the genus ''Leporipoxvirus''. The two broad geographic types of ''myxoma virus'' are Californian and South American. Californian ''myxoma virus'' is found on the West Coast of the United States, the Baja Penins ...
. Many species of rabbit cells in culture (without the presence of any antiviral defenses that would normally be in a host) can be infected by the myxoma virus, causing infection and cell death. However,
inoculation
Inoculation is the act of implanting a pathogen or other microorganism. It may refer to methods of artificially inducing immunity against various infectious diseases, or it may be used to describe the spreading of disease, as in "self-inoculati ...
of the myxoma virus in many species of rabbit shows that only one species of rabbit is affected, the rest being completely unharmed by the virus (lack of even
viral shedding
Viral shedding is the expulsion and release of virus progeny following successful reproduction during a host cell infection. Once replication has been completed and the host cell is exhausted of all resources in making viral progeny, the viruse ...
). This has been determined to be a result of the myxoma virus's inability to suppress other species'
interferon
Interferons (IFNs, ) are a group of signaling proteins made and released by host cells in response to the presence of several viruses. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten th ...
expression, and hence resulting in the interferon in turn suppressing the myxoma virus.
This is a result of the positive susceptibility of many species of rabbit's cells, but negative permissibility of all but one of the rabbit species' cells.Nash P. et al. "Immunomodulation by viruses: the myxoma virus story." Immunol Rev. 1999 Apr;168:103-20.