Background
PD-1, also named CD279, is a receptor belonging to immunoglobulin superfamily which is expressed primarily on activated T cells. NK cells, B cells, and monocytes. PD-1 interaction with its ligands, PD-L1 and PD-L2, leads to downregulation of T cell responses, including T cell proliferation and cytokine production, and limits immune-destruction of tissues. The interaction between PD-1 and its ligands, thus plays a role in maintaining the balance between immune activation and tolerance, potentially including tumor tolerance.
