Proviral loads of human T-lymphotropic virus Type 1 in asymptomatic carriers with different infection routes

High human T-lymphotropic virus Type 1 (HTLV-1) proviral DNA load (PVL) has been reported to be one risk factor for the development of adult T-cell leukemia/lymphoma (ATL). ATL is also believed to develop in HTLV-1 carriers who acquire infection perinatally. ATL cells have been reported to frequently harbor defective provirus. In our study, PVLs for three different regions of HTLV-1 provirus (5′LTR-gag, gag and pX) were measured in 309 asymptomatic carriers with different infection routes. PVLs for the pX region in 21 asymptomatic carriers with maternal infection was significantly higher than in 24 carriers with spousal infection. Among 161 carriers with relatively high pX PVLs (equal to or greater than 1 copy per 100 peripheral blood mononuclear cells), 26 carriers (16%) had low gag PVL/pX PVL (less than 0.5) and four (2%) had low 5′LTR-gag PVL/pX PVL (less than 0.5). Low gag PVL/pX PVL ratio, which reflects deficiency and/or polymorphism of HTLV-1 proviral DNA sequences for the gag region, was also associated with maternal infection. These data suggest that HTLV-1 carriers with maternal infection tend to have high PVLs, which may be related to provirus with deficiency and/or the polymorphism of proviral DNA sequences. In addition, there is a possibility that this ratio may be used as a tool to differentiate the infection routes of asymptomatic HTLV-1 carriers, which supports the need for a large scale study.