The RMP1-30 antibody is specific for mouse CD279, also known as programmed death-1 (PD-1), a 55 kDa glycoprotein member of the Ig superfamily of molecules. PD-1 exists in a monomeric form that is expressed by CD4- CD8- thymocytes, where it participates in the processes of clonal selection, elimination of autoreactive lymphocytes, and development of tolerance. PD-1 expression is also inducible upon activation of mature T cells, where it has been proposed to interact with the co-stimulatory receptor CD80 to limit T cell activation. Two ligands for PD-1, known as PD-L1 (B7-H1) and PD-L2 (B7-DC) are differentially expressed on T and B cells, monocytes, macrophages, NK cells or dendritic cells.