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

Abstract

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.

Figure 1

Activation profile of CD4+ (A) and CD8+ (B) T-lymphocytes from asymptomatic HTLV-1-infected individuals. Flow cytometry was performed using fresh whole blood samples. Data represents median and interquartile range of 20 asymptomatic HTLV-1infected individuals grouped according to HTLV-1 PVL expressed as ≥1% (10 individuals) and <1% of infected cells (10 individuals) and 10 healthy donors (HD). Kruskal–Wallis test with the Bonferroni-Dunn multiple comparisons. The level of significance was set at P < 0.05.

Figure 2

Intercellular detection of IFN-γ from asymptomatic HTLV-1 infected individuals. PBMCs (2 × 10⁵ cells/well) were cultured for 18 hours. Data are presented as median (interquartile range). P-value: Kruskal–Wallis test with the Bonferroni-Dunn multiple comparisons.to compare HTLV-1 PVL ≥1% (n = 10) and <1% infected cells (n = 10) groups and healthy donors (HD, n = 10). The level of significance was set at P < 0.05. *p = 0.02.

Figure 3

CD4 + FoxP3+ T-cell frequency in both HTLV-1-infected and healthy donors. Data are presented as median (interquartile range). The Mann–Whitney U-test was used to compare healthy donors (HD; n = 5) and asymptomatic HTLV-1-infected individuals (ASS n = 15). ASS individuals had PVL < 1% infected cells, except one 26% of infected cells. *p = 0.02.