出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2014/11/17 17:34:05」(JST)
ヒトTリンパ好性ウイルス | |||||||||||||||
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ヒトTリンパ球向性ウイルス |
ヒトTリンパ好性ウイルス(ヒトティーリンパこうせいウイルス、Human T-lymphotropic Virus、HTLV)は、レトロウイルスの一種。HTLV-I, II, III, IVがある。
特にHTLV-Iは最初に発見された疾患を起こすヒトレトロウイルス。類縁ウイルスにsimian T-lymphotropic virus (= STLV) がある。
宿主であるヒトのT細胞内では核内に移行し、RNAからcDNAを逆転写により生成し、cDNAは宿主ゲノムDNAへインテグレーション (integration) する。integration siteは決まってはいない。messenger mRNA (gag mRNA) を生成した後、スプライシング (splicing) を受け、env mRNAとなる。env RNAはさらにスプライシング (secondary splicing) を受けpX mRNAとなる。px mRNAは複製制御を担うp40tax/p27rex 蛋白をコードする。 これらのmRNAはopen reading frame(ORF)が異なるため、もとのウイルスゲノムRNAが一本であっても、それぞれのmRNAは異なった蛋白をコードする。感染T細胞は必ずしも死滅するわけではない。そのため、T細胞からT細胞へ感染するほかに、感染したT細胞の増殖によるウイルス増殖もみられる。
HTLVはフリーのウイルス粒子による感染は効率が非常に悪いので[1]、ウイルスの感染には、感染細胞と非感染細胞の細胞間接触が必要である。
HTLV-1は腫瘍ウイルスのひとつで、ウイルス保持者(キャリアと呼ぶ)は生涯の何れかの時点でATL(=adult T-cell leukemia, 成人T細胞白血病)を発症する可能性がある。
1977年に、京都大学の内山卓、高月清らによって、日本の九州出身の白血病患者には特有のT細胞性白血病が多いことから成人T細胞性白血病 (adult T-cell leukemia; ATL) という疾患概念を提唱した。その後、1981年に、京都大学の日沼頼夫らによってレトロウイルスが分離され「ATL virus (ATLV)」とした。これは1980年にアメリカ国立衛生研究所のロバート・ギャロらが菌状息肉症患者から分離した、ヒトから初めて発見されたレトロウイルスと同一のウイルスとのちに判明し、名称はHuman T-cell leukemia virus type 1 (HTLV-1) と改められた。
このウイルスは、自然には性行為または哺乳により感染することが多いが、出産時、母体内での感染もある。母乳感染は、母親がHTLV-Iキャリアであることが判明した場合、母乳哺育を行わずに人工乳を用いることによって回避できる。人工的には、血液曝露(感染リンパ球を含んだ輸血)により感染するが、血漿成分輸血、血液製剤ではあまり感染しない。これはcell-to-cell infection(細胞から細胞へ感染)のためだといわれている。日本では現在、献血に際して抗体スクリーニングが行われており、輸血での感染のリスクは低い。また発症率は3~5%と低いため、HTLV-1キャリアであっても生涯発症しない場合もある。
文化人類学的に、HTLV-Iの塩基配列を検討することによって、人類の移動を推測する研究もなされている。夫婦・親子と感染するため、ヒト・ゲノムと同様に、一群のヒト集団(血族)の移動を示唆すると考えられる。ティワナクの項に詳しい。 tax遺伝子をT細胞および胸腺細胞で発現させたトランスジェニックマウスではT細胞性白血病 / リンパ腫を発症する[2]。
Adult T-cell leukemia (ATL) ともいう。
HTLV-I感染を原因とする白血病/悪性リンパ腫であり、日本、特に九州、沖縄に非常に多いという特徴がある。ATLは初回から薬剤耐性を示すことが少なくなく、標準的な治療法が未だに確立していない。
HAM/TSP(HTLV-I associated myelopathy, HTLV-I関連脊髄症/tropical spastic paraparesis, 熱帯性痙性対麻痺)、HAB (HTLV-I associated bronchitis), HAU (HTLV-I associated uveitis) などがある。
アフリカを中心にみられる。
カメルーンで2005年に発見された。
出典は列挙するだけでなく、脚注などを用いてどの記述の情報源であるかを明示してください。記事の信頼性向上にご協力をお願いいたします。(2011年12月) |
ウィキメディア・コモンズには、ヒトTリンパ好性ウイルスに関連するカテゴリがあります。 |
Human T-lymphotropic virus | |
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HTLV-1 and HIV | |
Virus classification | |
Group: | Group VI (ssRNA-RT) |
Family: | Retroviridae' |
Subfamily: | Orthoretrovirinae |
Genus: | Deltaretrovirus |
Species: | Simian T-lymphotropic virus |
Serotypes | |
Human T-lymphotropic virus |
Human T-cell lymphotropic virus type 1 or human T-lymphotropic virus type 1 (HTLV-I), also called the adult T-cell lymphoma virus type 1, is a retrovirus of the human T-lymphotropic virus (HTLV) family that has been implicated in several kinds of diseases including very aggressive adult T-cell lymphoma (ATL), HTLV-I-associated myelopathy, uveitis, strongyloides stercoralis hyper-infection and some other diseases. However, only about 1–5% of infected persons are thought to develop cancer as a result of the infection with HTLV-I over their lifetimes.[1]
HTLV was discovered in 1977 in Japan. The virus was first isolated by Bernard Poiesz and Francis Ruscetti and their co-workers in the laboratory of Robert C. Gallo at the National Cancer Institute.[2] It was the first identified human retrovirus. Infection with HTLV-I, like infection with other retroviruses, probably occurs for life. A patient infected with HTLV can be diagnosed when antibodies against HTLV-1 are detected in the serum.[1]
HTLV-1 is a retrovirus belonging to the family retroviridae and the genus deltaretrovirus. It has a positive-sense RNA genome that is reverse transcribed into DNA and then integrated into the cellular DNA. Once integrated, HTLV-1 continues to exist only as a provirus which can spread from cell to cell through a viral synapse. Few, if any, free virions are produced and there is usually no detectable virus in the blood plasma though the virus is present in genital secretions. Like HIV, HTLV-1 predominately infects CD4+ T cells.[1]
The viral RNA is packed into the icosahedral capsid which is contained inside the protein inner envelope. The lipid outer envelope is of host cell origin but contains viral transmembrane and surface proteins. The virion is spherical in shape with a diameter of about 100 nm.[1]
Seven HTLV-1 genotypes are recognised—HTLV-1a through HTLV-1g.[1] It is estimated that from 10 to 20 million people worldwide are infected; 3–8 million of them are in Africa.[3] The most widespread genotype is type A. Types B, D, E, F and G have only been isolated from Central Africa. Type C is only present in Asia. Simian HTLV-1 genotypes are interspersed in between the human genotypes indicating frequent animal-human and human-animal transmission.[1] The only human genotype that does not have a simian relative is A. It is thought that genotypes B, D, E, F and G originated in Africa from closely related STLV about 30,000 years ago, while the Asian genotype C is thought to have originated independently in Indonesia from the simians present there.[1] Two subtypes are found in Japan: a transcontinental subgroup and a Japanese subgroup.[4]
The knowledge about HTLV-1 epidemiology is limited.
The high prevalence is detected in Japan where more than 10% of the population are infected. The reasons for this extremely high prevalence are not known. In Taiwan, in Iran, and in Fujian, a Chinese province near Taiwan the prevalence is 0.1–1%. The infection rate is about 1% in Papua New Guinea, the Solomon Islands, and Vanuatu, where the genotype C predominates. In Europe HTLV-1 is still uncommon, although it is present in some high risk populations including immigrants and intravenous drug uses. In Americas the virus is found in indigenous populations and descendants of African slaves from where it is thought to have originated. The general prevalence is from 0.1 to 1%. In Africa the prevalence is well not known but it is about 1% in some countries.[1]
HTLV-I infection in the United States appears to be about half as prevalent among IV drug users and about one-tenth as prevalent in the population at large as HIV infection. Although little serologic data exist, the prevalence of infection is thought to be highest among blacks living in the Southeast. A prevalence rate of 30% has been found among black intravenous drug users in New Jersey, and a rate of 49% has been found in a similar group in New Orleans.[5]
HTLV-I infection in Australia is very high among the indigenous peoples of central and northern Australia, with a prevalence rate of 10–30%. It is also high among the Inuit of Northern Canada, in Japan, northeastern Iran,[6] Peru, the Pacific coast of Colombia and Ecuador, the Caribbean, and in Africa.
Transmission of HTLV-I is believed to occur by sexual contact, from mother to child via breastfeeding, and through exposure to contaminated blood, either through blood transfusion or sharing of contaminated needles. The importance of the various routes of transmission is believed to vary geographically. The research in discordant couples showed that probability of sexual transmission is about 0.9 per 100 person-years.[1]
The term viral tropism refers to which cell types HTLV-I infects. Although HTLV-1 is primarily found in CD4+ T cells, other cell types in the peripheral blood of infected individuals have been found to contain HTLV-1, including CD8+ T cells, dendritic cells and B cells. HTLV-I entry is mediated through interaction of the surface unit of the virion envelope glycoprotein (SU) with its cellular receptor GLUT1, a glucose transporter, on target cells.[9]
HTLV-1 is also associated with adult T-cell leukemia/lymphoma and has been quite well studied in Japan. The time between infection and onset of cancer also varies geographically. It is believed to be about sixty years in Japan and less than forty years in the Caribbean. The cancer is thought to be due to the pro-oncogenic effect of viral DNA incorporated into host lymphocyte DNA. Chronic stimulation of the lymphocytes at the cytokine level may play a role in the development of the malignancy. The lymphoma ranges from a very indolent and slowly progressive type to a very aggressive and nearly uniformly lethal proliferative type.
There is some evidence that HTLV-1 is a causative agent of cutaneous T-cell lymphoma.[1]
HTLV-1 is also associated with a progressive demyelinating upper motor neuron disease known as HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP), an characterized by sensory and motor deficits, particularly of the lower extremities, incontinence and impotence.[10] Only 0.3 to 4% of infected individuals develop HAM/TSP, but this will vary from one geographic location to another.[1]
Signs and symptoms of HTLV myelopathy include:
Other neurologic findings that may be found in HTLV include:
HTLV-1 is associated with a rheumatoid-like arthropathy, although the evidence is contradictory. In these cases patients have a negative rheumatoid factor.[1]
Studies from Japan demonstrated that HTLV-1 infection may be associated with an intermediate uveitis. At onset the patients present with blurred vision and floaters. The prognosis is favorable—the condition usually resolves within weeks.[1]
Individuals infected with HTLV-1 are at risk for opportunistic infections—diseases not caused by the virus itself, but by alterations in the host's immune functions.[1]
HTLV-1, unlike the distantly related retrovirus HIV, has an immunostimulating effect which actually becomes immunosuppressive. The virus activates a subset of T-helper cells called Th1 cells. The result is a proliferation of Th1 cells and overproduction of Th1 related cytokines (mainly IFN-γ and TNF-α). Feedback mechanisms of these cytokines cause a suppression of the Th2 lymphocytes and a reduction of Th2 cytokine production (mainly IL-4, IL-5, IL-10 and IL-13). The end result is a reduction in the ability of the infected host to mount an adequate immune response to invading organisms that require a predominantly Th2 dependent response (these include parasitic infections and production of mucosal and humoral antibodies).[citation needed]
In the central Australian Aboriginal population, HTLV-1 is thought to be related to their extremely high rate of death from sepsis. It is also particularly associated with bronchiectasis, a chronic lung condition predisposing to recurrent pneumonia. It is also associated with chronic infected dermatitis, often superinfected with Staphylococcus aureus and a severe form of Strongyloides stercoralis infection called hyper-infestation which may lead to death from polymicrobial sepsis. HTLV-1 infection has also been associated with tuberculosis.[1]
This section requires expansion. (January 2010) |
Treatment of opportunistic infections varies depending on the type of disease and ranges from careful observation to aggressive chemotherapy and antiretroviral agents.[citation needed] Adult T cell lymphoma is a common complication of HLTV infection and requires aggressive chemotherapy, typically R-CHOP. Other treatments for ATL in HLTV infected patients include interferon alpha, zidovudine with interferon alpha and CHOP with arsenic trioxide. Treatments for HLTV myelopathy are even more limited and focus mainly on symptomatic therapy. Therapies studied include corticosteroids, plasmapheresis, cyclophosphamide, and interferon, which may produce a temporary symptomatic improvement in myelopathy symptoms.[12]
Valproic acid has been studied to determine if it might slow the progression of HLTV disease by reducing viral load. Although in one human study it was effective in reducing viral load, there did not appear to be a clinical benefit. Recently however, a study of valproic acid combined with zidovudine showed a major decrease in the viral load of baboons infected with HLTV-1. It is important to monitor HLTV patients for opportunistic infections such as cytomegalovirus, histoplasmosis, scabies, pneumocystis pneumonia, and staphylococcal infections. HIV testing should also be performed, as some patients may be co-infected with both viruses.[13]
Allogenic bone marrow transplantation has been investigated in the treatment of HLTV-1 disease with varied results. One case report describes an HLTV-1 infected woman who developed chronic refractory eczema, corneal injury and adult T cell leukemia. She was subsequently treated with allogenic stem cell transplantation and had complete resolution of symptoms. One year post-transplant, she has had no recurrence of any symptoms, and furthermore has had a decrease in her proviral load.[14]
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国試過去問 | 「114E046」「104E005」 |
リンク元 | 「成人T細胞白血病」「ヒトT細胞白血病ウイルス」「ヒトT細胞白血病ウイルス1型」「HTLV-I」「human T lymphotropic virus type 1」 |
拡張検索 | 「HTLV-1関連脊髄症」「HTLV-1抗体」「HTLV-1関連ぶどう膜」「HTLV-1 associated uveitis」 |
関連記事 | 「HT」「HTLV」 |
- 血中抗体価報告書氏名◯◯◯◯
測定方法 検査結果 病院実習の基準を満たす陽性 単位 麻疹 (IgG-EIA法) 20.4 (≧ 16.0) 風疹 (IgG-EIA法) 10 (≧ 8.0) 水痘 (IgG-EIA法) 6.4 (≧ 4.0) 流行性耳下腺炎 (IgG-EIA法) 陽性 陽性 B型肝炎 (CLIA法) 4.8 (≧ 10.0) mIU/mL 結核 (IGRA)* 陰性 陰性
- *結核菌特異的全血インターフェロン γ遊離測定法
A
※国試ナビ4※ [114E045]←[国試_114]→[114E047]
A
※国試ナビ4※ [104E004]←[国試_104]→[104E006]
急性型 | リンパ腫型 | 慢性型 | くすぶり型 | |
典型的な症状 | 腫瘍随伴症状(腫瘍熱、高カルシウム血症(意識障害・脱水・腎機能障害) (50%で認められる))が初発症状であることが多い。 臓器浸潤による症状(消化管浸潤(下痢・腹痛)、肝臓浸潤(黄疸)、 肺浸潤(呼吸困難)、中枢神経浸潤(脳神経症状)) |
リンパ節腫大は全例で認められる。 腫瘍熱、高カルシウム血症を初発症状とする場合もある。 末梢血中の形態的異常細胞は1%以下 |
多くの場合、自覚症状を欠き、健康診断などで偶然診断される。 日和見感染症や腫瘍の浸潤に伴う皮膚症状(皮疹、皮膚腫瘤)、 肺病変(労作時息切れ、咳嗽)が診断の発端となる場合もある。 |
リンパ球増多を伴わないため、血液検査では診断に至らない。 無症候キャリアーと同様、多くの患者では症状を欠く。 |
PS>1 | 67.6% | 45.4% | 27.2% | 22.7% |
感染性併発症 | 26.9% | 10.9% | 35.5% | 35.6% |
皮膚病変 | 40.2% | 25% | 46.1% | 48.9% |
肺病変 | 20.2% | 10.9% | 15.1% | 15.6% |
肝腫大 | 35.9% | 16% | 13.8% | 0% |
脾腫大 | 29.9% | 15.4% | 11.2% | 0% |
4個以上の腫大リンパ節 | 80.7% | 62.2% | 54% | 6.7% |
高カルシウム血症 | 50.3% | 16.7% | 0% | 0% |
貧血(Hb<10g/dl) | 10.1% | 4.5% | 4% | 0% |
血小板減少(10万/ul) | 19.4% | 4.5% | 2% | 6.7% |
ヒトTリンパ好性ウイルス : 約 29,900 件 ヒトTリンパ球向性ウイルス : 約 74,200 件 ヒトT細胞白血球ウイルス : 15 件 ヒトT細胞白血病ウイルス : 約 171,000 件
ヒトTリンパ好性ウイルス : 約 29,900 件 ヒトTリンパ球向性ウイルス : 約 74,200 件 ヒトT細胞白血球ウイルス : 15 件 ヒトT細胞白血病ウイルス : 約 171,000 件
HTLV-1型関連ミエロパシー : nothing HTLV-1型関連ミエロパチー : nothing HTLV-1脊髄症 : 30 件 HTLV-I型関連ミエロパシー : 9 件 HTLV-I型関連ミエロパチー : nothing HTLV-I脊髄症 : 70 件 ヒトT細胞白血病ウイルス関連脊髄症 : 4 件 ヒトTリンパ球向性ウイルス脊髄症 : 49 件 ヒトT細胞白血病ウイルスI型関連ミエロパシー : 2 件 ヒトTリンパ好性ウイルスI型関連脊髄症 : 10 件 ヒトTリンパ球関連ウイルス脊髄症 : nothing
[★] HTLV-1関連ぶどう膜 HAU
.