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The contribution of monocytes/macrophages to HTLV-1 infection and persistence

Peripheral blood monocytes can be classified into three main subsets: CD14++CD16 (classical), CD14+CD16++ (non-classical), and CD14++CD16+ (intermediate) which exert important roles in innate and adaptive immunity. Here we investigated whether the different monocyte subsets are potential HTLV-1reserviors that contribute to viral infection and persistence. PBMCs from 17 HTLV-1 infected patients (IP) and 11 normal donors (ND) were phenotypically analyzed by flow cytometry. Classical monocyte frequency was lower in HTLV-1-IPs compared to NDs (p=0.048). Moreover, we found a positive correlation between PVL and intermediate monocyte frequency (r=0.6735, p=0.0042). Focusing on the presence of HTLV-1 provirus DNA in the different monocyte subsets, cell populations were isolated from PBMCs of 16 HTLV-1-IP. When we analyzed by nested PCR genomic DNA isolated from sorted CD4+, CD8+ CD14++CD16, CD14+CD16++, and CD14++CD16+, we found that HTLV-1 patients with high PVL, all monocyte subsets as well as CD4+ and CD8+ cells were positive for HTLV-1. In contrast, the intermediate monocytes were negative or very weakly positive for HTLV-1 in patients with low PVL. To test whether natural STLV-1 infection recapitulates what we find in HTLV-1-IPs, we analyzed the monocyte subsets distribution in 8 STLV-1 infected Rhesus macaques and 16 naïve animals. Consistent with human infection, the frequency of intermediate monocytes was higher in infected macaques compared to naïve animals (p=0.0001) with a positive correlation between PVL and intermediate monocytes frequency (r=0.6530, p=0.03). In conclusion, our results suggest that monocytes play an important role in viral dissemination and persistence and are potential viral reservoirs.

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Correspondence to Maria Fernanda de Castro-Amarante.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

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de Castro-Amarante, M.F., Pise-Masison, C., McKinnon, K. et al. The contribution of monocytes/macrophages to HTLV-1 infection and persistence. Retrovirology 11 (Suppl 1), P123 (2014).

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