The 6D3 monoclonal antibody specifically binds to mouse B lymphocyte-induced maturation protein 1 (Blimp-1) and crossreacts with human BLIMP-1. Blimp-1 is a 98 kDa zinc finger-containing protein that is encoded by the Prdm1 gene. Blimp-1 was first discovered as a transcriptional repressor of the IFN-β promoter. Blimp-1 is critical for primordial germ cells specification in the early embryo and induction of terminal cell differentiation in multiple somatic cell types. It is largely known as a master regulator of antibody-secreting plasma cells due to its function in the repression of PAX5, CIITA and cMYC genes. Blimp-1 also controls T cell homeostasis and effector differentiation through different mechanisms, including repression of IL-17 producing cells. Blimp-1 also plays roles in the maturation and activity of dendritic cells and natural killer cells.