When a cell or host is defined as permissive in virology, it refers to the fact that the virus is 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.
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