Referee 3's Review:

**********
N.B. These are the comments made by the referee when reviewing an earlier version of this paper. Prior to publication the manuscript has been revised in light of these comments and to address other editorial requirements.
**********

The study has been well designed and the manuscript is well organized with
addressing a clear scientific question that increased Sn expression on monocytes in HIV-1 subjects enhances the infectivity to HIV-1. This manuscript needs to be further modified before final acceptation for publication to PLoS ONE. It is necessary for authors to address or answer the following issues in the discussion section of the manuscript.

1. Whether the study has got the approval from the authors’ institutions as well as from each participant, it was not claimed in the manuscript.
2. The findings in this study showed that the increased Sn expression on human monocytes in HIV-1 patients were correlated with the levels of circulating HIV-1 loads, but it is still unclear the cause-and-effect relationship between the viral load and high Sn expression on monocytes? Have authors conducted the in vitro experiments that is Sn highly expressed on monocytes when they are incubated with HIV-1 in vitro?
3. Whether and how the increased Sn expression affects the monocyte functionality in HIV-1 patients?
4. Whether authors found there was decreased Sn expression in AIDS patients undergoing a successful antiviral treatment.