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Background. Semen is the main vector for human immunodeficiency virus (HIV) transmission from men to women. We investigated the influence of cytokines in semen on local HIV burden and activated T cells.Methods. Blood and semen were collected from 42 HIV-negative and 38 HIV-positive men. Concentrations of 20 cytokines were measured by Luminex, and frequencies of activated T cells were measured by flow cytometry.Results. Semen contained higher concentrations of proinflammatory (monocyte chemotactic protein-1, interleukin [IL]-8, IL-6, Fractalkine, macrophage inflammatory protein (MIP)-1β, granulocyte macrophage colony-stimulating factor) and adaptive cytokines (IL-7 and IL-15) and higher frequencies of activated T cells compared to blood. Plasma IL-2, eotaxin, MIP-1β, and IL-15 and semen eotaxin and granulocyte colony-stimulating factor (G-CSF) concentrations were associated with T-cell activation. Cytokines in semen were highly coregulated in HIV-negative men; however, this network was disrupted during HIV infection. Several cytokines in semen correlated with HIV shedding (G-CSF, tumor necrosis factor-alpha [TNF-α], interferon-gamma [IFN-γ], IL-10).Conclusion. Higher levels of inflammation and T-cell activation were observed in semen compared with blood. Seminal G-CSF, which influences neutrophil survival, T-cell function, and dendritic cell activation, was associated with T-cell activation and HIV shedding and may be an important target for reducing HIV shedding or risk. [ABSTRACT FROM AUTHOR]