Recent research of a cohort of HIV exposed sero-negative (HESN) female commercial sex workers in Nairobi has revealed an Immune Quiescent phenotype; characterized by reduced T cell activation and higher regulatory T cells (Tregs) in peripheral blood. HESN women also express lower levels of interferon regulatory factor-1 (IRF-1), a critical regulator known to negatively impact Treg development in mice. In this study, we analyzed the functional capacity of Tregs by an in vitro depletion assay and measured functionality by flow cytometry. Data showed Tregs suppressed CD4+ and CD8+ proliferation responses. We characterized the link between Tregs and IRF-1 in HESN and observed an inverse correlation between IRF-1 expression and Treg proportions. We also established reduced expression of IRF-1 in Tregs of healthy donors by flow cytometry. In a separate study, flow cytometric analysis of high-risk sex-workers revealed that CTLA-4 expression in memory CD4+cells, not Treg frequency, was associated with HIV seroconversion. / February 2017