JC Virus (JCV)

JC virus is a type of human polyomavirus and is genetically similar to BK virus and SV40. JCV can cross the blood–brain barrier into the central nervous system, where it infects oligodendrocytes and astrocytes, possibly through the 5-HT2A serotonin receptor. JC viral DNA can be detected in both non-PML affected and PML-affected (see below) brain tissue. JCV found in the central nervous system of PML patients almost invariably have differences in promoter sequence to the JCV found in healthy individuals. It is thought that these differences in promoter sequence contribute to the fitness of the virus in the CNS and thus to the development of PML. Certain transcription factors present in the early promoter sequences of the JC virus can induce trophism and viral proliferation that leads to PML. The Spi-B factor was shown to be crucial in initiating viral replication in certain strains of transgenic mice.