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JC Virus (JCV) Facts
JCV is a polyomavirus which infects humans. Most people are infected, developing JCV antibodies by the time they reach adolescence. JCV primarily infects kidney cells and cells in the central nervous system (CNS) such as oligodendrocytes and astrocytes.
A healthy immune system will prevent JCV replication and keep the virus in a latent state. Viral proteins are undetectable and generally no clinical symptoms are seen. In immunocompromised individuals JCV can cause a lytic infection in the CNS and lead to development of the fatal, demyelinating disease - progressive multifocal leukoencephalopathy (PML). In PML, replication of the virus causes destruction of oligodendrocytes.
Polyomaviruses can cause mutagenic change in cells, therefore JCV may be involved in human cancer. However, the exact role of JCV and human tumors is not clear. Some researchers have reported an association of JC virus and medulloblastoma, colorectal cancers and gastrointestinal tract cancers, while other research shows no link.
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Research on JCV and Cancer
Numerous studies provide evidence for an association of JCV with various tumors of the central nervous system and other tumors such as colon cancer and lymphoma of the CNS.The first indication of a relationship between JCV and cancer came from reports of brain tumors in patients with PML, but JCV has also been associated with brain tumors in the absence of PML. For example, JCV DNA was detected in tumor tissue from a non PML patient with oligoastrocytoma in 1996.
Medulloblastoma is a malignant primary brain tumor which is more common in children than in adults. In a study on JC virus and medulloblastoma, JCV DNA was detected in over half of medulloblastoma samples tested. However, there is evidence that JCV does not replicate in brain tumors; as shown by a lack of expression of the viral capsid proteins. This suggests that tumor tissue does not provides a favorable environment for JCV growth.
When laboratory animals are inoculated intracranially with JCV they develop brain tumors. Furthermore, laboratory mice which have been genetically engineered to contain the JCV early region, develop brain tumors.
The currently available evidence for an association between JCV and cancer is not conclusive. If there is a true association between JCV infection and brain tumors, it could be due to an increased ability of JC virus to enter diseased brain tissue. The virus may contribute to initiation of malignant change or aid in tumor progression. Further research is required in order to clarify the possible mechanisms involved.
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Human Polyomaviruses and Brain Tumors by M.White, J.Gordon, K.Reiss, L.Del Valle, S.Croul, A.Giordano, A.Darbinyan & K.Khalili. Brain Research Reviews, 2005, Vol 50, P69-85
JCV: An Oncogenic Virus in Animals and Humans? M.Maginnis & W.Atwood. Seminars in Cancer Biology. 2009, Vol 19, P261–269.