The JES3-19F1 monoclonal antibody specifically recognizes human Interleukin-10 (IL-10) that is encoded by IL10. IL-10 is also known as Cytokine Synthesis Inhibitory Factor (CSIF), B cell-derived T cell growth factor (B-TCGF), and T-cell growth inhibitory factor (TGIF). The JES3-19F1 antibody crossreacts with ebvIL-10 protein, the Epstein-Barr viral IL-10 homolog (viral IL-10 or vIL-10) encoded by the BCRF1 gene. IL-10 is produced by a variety of cells such as some activated T cells and B cells including regulatory T cells (Treg) and B cells (Breg), monocytes and macrophages, dendritic cells (DC), keratinocytes, and mast cells. IL-10 is a multifunctional cytokine that can downregulate immune and proinflammatory responses. IL-10 can act to reduce expression of major histocompatibility complex class II antigens, costimulatory molecules, or proinflammatory cytokines including IL-1β, IL-2, IL-3, IL-12, IFN-γ, TNF or GM-CSF expressed by activated monocytes, macrophages, dendritic cells (DC), natural killer (NK) cells, or T cells. IL-10 has been shown to play a role in chronic viral infections. IL-10 can also enhance B cell survival, proliferation, and differentiation to become antibody-producing cells. The JES3-19F1 antibody reportedly neutralizes the biological activity of human IL-10 and ebvIL-10. IL-10 mediates its biological activities by signaling through a heterotetrameric receptor complex composed of the type II cytokine receptor subunits CD210a (IL-10 Rα) and CD210b (IL-10 Rβ).