Regulatory T cells modulate monocyte functions in immunocompetent antiretroviral therapy naive HIV-1 infected people

We previously demonstrated that the overall number of regulatory T (Treg) cells decrease proportionately with helper CD4⁺ T cells and their frequencies increase in antiretroviral therapy (ART)-naive human immunodeficiency virus type-1 (HIV-1) infected individuals. The question now is whether the discrepancies in Treg cell numbers and frequencies are synonymous to an impairment of their functions. To address this, we purified Treg cells and assessed their ability to modulate autologous monocytes functions. We observed that Treg cells were able to down modulate autologous monocytes activation as well as interleukin 6 (IL-6) and tumor necrosis factor-alpha (TNF-α) production during stimulation with polyinosinic-polycytidylic acid stabilized with poly-L-lysine and carboxymethylcellulose (poly-ICLC). This activity of Treg cells has been shown to be influenced by immunocompetence including but not limited to helper CD4⁺ T cell counts, in individuals with HIV-1 infection. Compared to immunosuppressed participants (CD4 < 500 cells/µL), immunocompetent participants (CD4 ≥ 500 cells/µL) showed significantly higher levels of transforming growth factor beta (TGF-β) and IL-10 (p < 0.001 and p < 0.05, respectively), key cytokines used by Treg cells to exert their immunosuppressive functions. Our findings suggest the contribution of both TGF-β and IL-10 in the suppressive activity of Treg cells.