The JES5-2A5 monoclonal antibody reacts with mouse IL-10. IL-10 is a 17-21 kDa cytokine which is primarily produced by monocytes and, to a lesser extent, Th2 cells, mast cells, T regulatory cells, and certain subsets of activated T and B cells. IL-10 has pleiotropic effects in immunoregulation and inflammation. It down-regulates the expression of Th1 cytokines, MHC class II antigens, and costimulatory molecules on macrophages. It also enhances B cell survival, proliferation, and antibody production. This cytokine can block NF-κB activity, and is involved in the regulation of the JAK-STAT signaling pathway. Knockout studies in mice suggest that this cytokine is an essential immunoregulator in the intestinal tract. The JES5-2A5 antibody has been shown to neutralize the bioactivity of natural or recombinant IL-10.