Background: High HTLV-1 proviral load (PVL) is mainly found in infected individuals with HTLV-1-associated\nmyelopathy/tropical spastic paraparesis (HAM/TSP). However one third of asymptomatic carriers may have high PVL.\nThis study aimed to evaluate the impact of PVL in the activation of T lymphocytes of asymptomatic individuals\ninfected with HTLV-1.\nMethods: Membrane activation markers (CD25+, CD28+, CD45RO+, CD69+, CD62L+, HLA-DR+), FoxP3+ and intracellular\nIFN-? expression were evaluated on both CD4+ and CD8+ T-lymphocytes from asymptomatic carriers with PVL ?\nand < 1% of infected cells, using flow cytometry. HTLV-1 proviral load was determined using real-time PCR.\nResults: Asymptomatic carriers with PVL ? 1% presented a higher frequency of CD4+CD25+CD45RO+ (13.2% vs. 4%,\np = 0.02), CD4+HLA-DR+ (18% vs. 8.3%, p = 0.01) and CD4+IFN-?+ (4.5%; 1%, p = 0.01) T-cells, than healthy donors.\nHTLV-1 PVL was directly correlated with the proportion of CD4+CD25+CD45RO+ T-cells (R = 0.7, p = 0.003). Moreover, a\nsignificant increase in the proportion of CD4 + FoxP3+ T-cells was observed in HTLV-1-infected individuals, compared\nto healthy donors.\nConclusion: HTLV-1 PVL is associated with activation of both CD4+ and CD8+ T-lymphocytes in asymptomatic\nindividuals. Prospective studies should be conducted to evaluate whether asymptomatic individuals with higher PVL\nand high immune activation are more prone to developing HTLV-1-associated diseases.
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