Human T lymphotropic virus type 1 (HTLV-1) proviral load induces activation of T-lymphocytes in asymptomatic carriers

BACKGROUND: High HTLV-1 proviral load (PVL) is mainly found in infected individuals with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). However one third of asymptomatic carriers may have high PVL. This study aimed to evaluate the impact of PVL in the activation of T lymphocytes of asymptomatic individuals infected with HTLV-1. METHODS: Membrane activation markers (CD25(+), CD28(+), CD45RO(+), CD69(+), CD62L(+), HLA-DR(+)), FoxP3(+) and intracellular IFN-γ expression were evaluated on both CD4(+) and CD8+ T-lymphocytes from asymptomatic carriers with PVL ≥ and < 1% of infected cells, using flow cytometry. HTLV-1 proviral load was determined using real-time PCR. RESULTS: Asymptomatic carriers with PVL ≥ 1% presented a higher frequency of CD4(+)CD25(+)CD45RO(+) (13.2% vs. 4%, p = 0.02), CD4(+)HLA-DR(+) (18% vs. 8.3%, p = 0.01) and CD4(+)IFN-γ(+) (4.5%; 1%, p = 0.01) T-cells, than healthy donors. HTLV-1 PVL was directly correlated with the proportion of CD4(+)CD25(+)CD45RO(+) T-cells (R = 0.7, p = 0.003). Moreover, a significant increase in the proportion of CD4 + FoxP3+ T-cells was observed in HTLV-1-infected individuals, compared to healthy donors. CONCLUSION: HTLV-1 PVL is associated with activation of both CD4(+) and CD8(+) T-lymphocytes in asymptomatic individuals. Prospective studies should be conducted to evaluate whether asymptomatic individuals with higher PVL and high immune activation are more prone to developing HTLV-1-associated diseases. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/1471-2334-14-453) contains supplementary material, which is available to authorized users.