Human T-lymphotropic virus
| Human T-lymphotropic virus | |
|---|---|
| Virus classification | |
| Group: | Group VI (ssRNA-RT) |
| Family: | Retroviridae |
| Subfamily: | Orthoretrovirinae |
| Genus: | Deltaretrovirus |
| Species: | Simian T-lymphotropic virus |
| Serotypes | |
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Human T-lymphotropic virus |
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Human T-lymphotropic virus
The human T-lymphotropic virus, human T-cell lymphotropic virus, or human T-cell leukemia-lymphoma virus (HTLV) family of viruses are a group of human retroviruses that are known to cause a type of cancer called adult T-cell leukemia/lymphoma and a demyelinating disease called HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP). The HTLVs belong to a larger group of primate T-lymphotropic viruses (PTLVs). Members of this family that infect humans are called HTLVs, and the ones that infect Old World monkeys are called Simian T-lymphotropic viruses (STLVs). To date, four types of HTLVs (human T-lymphotropic virus 1 [HTLV-I], human T-lymphotropic virus 2 [HTLV-II], HTLV-III, and HTLV-IV) and four types of STLVs (STLV-I, STLV-II, STLV-III, and STLV-V) have been identified. HTLV types HTLV-1 and HTLV-2 viruses are the first retroviruses which were discovered. Both belong to the oncovirus subfamily of retroviruses and can transform human lymphocytes so that they are self-sustaining in vitro. The HTLVs are believed to originate from intraspecies transmission of STLVs. The original name for HIV, the virus that causes AIDS, was HTLV-III. The HTLV-1 genome is diploid, composed of two copies of a single-stranded RNA virus whose genome is copied into a double-stranded DNA form that integrates into the host cell genome, at which point the virus is referred to as a provirus. A closely related virus is bovine leukemia virus BLV.
HTLV-I is an abbreviation for human T-cell lymphotropic virus type 1, also called human T-cell leukemia type 1, a virus that has been seriously implicated in several kinds of diseases, including HTLV-I-associated myelopathy, and as a virus cancer link for leukemia (see adult T-cell leukemia/lymphoma).HTLV-1 has six reported subtypes (subtypes A to F). The great majority of infections are caused by the cosmopolitan subtype A. HTLV was discovered by Robert Gallo and colleagues in 1980. Between 1 in 20 and 1 in 25 infected persons are thought to develop cancer as a result of the virus. HTLV-1 infection is thought to spread only through dividing cells since, reverse transcriptase generates proviral DNA from genomic viral RNA, and the provirus is integrated into the host genome by viral integrase after transmission. Therefore, the quantification of provirus reflects the number of HTLV-1-infected cells. So, an increase in numbers of HTLV-1-infected cells using cell division, by actions of accessory viral genes, especially tax, may provide an enhancement of infectivity tax expression induces proliferation, inhibits the apoptosis of HTLV-1-infected cells and, conversely, evokes the host immune response, including cytotoxic T cells, to kill virus-infected cells.
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