When a cell or host is defined as permissive in
virology, it refers to the fact that the virusis able to circumvent host defenses and is able to replicate. Usually this occurs when the virus has modulated one or several of the host cellular intrinsic defenses, and the host immune system. 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 [N.J. Dimmock et al. "Introduction to Modern Virology, 6th edition." Blackwell Publishing, 2007.] . Susceptibleversus Permissive
The significance between the difference of the two has now been elucidated with study of the
rabbit-lethal myxoma virus. 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, inoculationof 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). This has been determined to be a result of the myxoma virus's inability to suppress other species' interferonexpression, 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.] .
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