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  • Title: [Natural history of human T-lymphotropic virus type 1 (HTLV-1) infection].
    Author: Okayama A.
    Journal: Rinsho Byori; 2005 Sep; 53(9):837-44. PubMed ID: 16235837.
    Abstract:
    The natural history of human T-lymphotropic virus type-1 (HTLV-1) infection has been difficult to be clarified, because only a small proportion of HTLV-1 carriers develop adult T-cell leukemia(ATL) after a long incubation period. We have performed a long-term follow-up study of HTLV-1 carriers for 17 years. Based on the findings of this study and other studies, the natural history of HTLV-1 carriers is hypothesized as follows. The major routes of infection of this virus are from mother to child, between spouses, and through blood products. The target of HTLV-1 infection is CD4 positive peripheral blood mononuclear cells (PBMCs). The number of infected cells is supposed to be increased just after the infection, then decreased in a year. The number of infected cells does not change thereafter during more than 10 years. In 90% of newly infected people, this level is low or medium ranging from less than 0.05% to 5% of PBMCs infected; however, approximately 10% of newly infected people develop into carriers with many number of infected cells as more than 5% of PBMCs infected. Clonal expansion of infected cells is likely to be contributing to the maintenance of the HTLV-1 infection. Replication of certain clones among many infected cells may be accelerated by the expression of Tax protein and some of them develop to have a phenotype to avoid immune surveillance. Finally, some of these clones, which acquired the accumulation of genomic abnormality, develop the pre-leukemic state. The increased number of certain T-cells due to HTLV-1 infection may also cause imbalance of the immune system, resulting in immune dysfunction or inflammatory diseases like myelopathy and uveitis. Therefore, it seems to be important to find ways to prevent HTLV-1 associated diseases among the carriers especially those with many infected cells.
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