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Programmed cell death protein 1
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<p>Programmed cell death protein 1 (PD-1), (CD279 <a href="/facts/Cluster_of_differentiation/cLEuDQId">cluster of differentiation</a> 279). PD-1 is a <a href="/facts/Protein/Jxmagu3E">protein</a> encoded in humans by the <i>PDCD1</i> <a href="/facts/Gene/e1swwPY6">gene</a>. PD-1 is a <a href="/facts/Cell_surface_receptor/0YGSjDdL">cell surface receptor</a> on <a href="/facts/T_cell/5z6PQ9UN">T cells</a> and <a href="/facts/B_cell/6Y1tgwwp">B cells</a> that has a role in regulating the <a href="/facts/Immune_system/HRCTf1pb">immune system</a>'s response to the cells of the human body by down-regulating the immune system and promoting self-tolerance by suppressing <a href="/facts/T_cell/5z6PQ9UN">T cell</a> inflammatory activity. This prevents <a href="/facts/Autoimmune_diseases/sojBeQ7t">autoimmune diseases</a>, but it can also prevent the immune system from killing cancer cells. </p><p>PD-1 is an <a href="/facts/Immune_checkpoint/ElM22IqY">immune checkpoint</a> and guards against autoimmunity through two mechanisms. First, it promotes <a href="/facts/Apoptosis/8dVzSm4y">apoptosis</a> (programmed cell death) of <a href="/facts/Antigen/9JlAernG">antigen</a>-specific T-cells in <a href="/facts/Lymph_node/vkwfcQjH">lymph nodes</a>. Second, it reduces apoptosis in <a href="/facts/Regulatory_T_cell/1ECRAGMg">regulatory T cells</a> (anti-inflammatory, suppressive T cells). </p><p><a href="/facts/PD-1_inhibitor/0QKPeh5x">PD-1 inhibitors</a>, a new class of drugs that block PD-1, activate the immune system to attack tumors and are used to treat certain types of cancer. </p><p>PD-1 is a cell surface receptor that belongs to the <a href="/facts/Immunoglobulin_superfamily/Wveu4BIL">immunoglobulin superfamily</a> and is expressed on T cells and <a href="/facts/Pro-B_cell/6Y1tgwwp">pro-B cells</a>. PD-1 binds two <a href="/facts/Ligand_(biochemistry)/44QLL4eU">ligands</a>, <a href="/facts/PD-L1/0jyfJ2nE">PD-L1</a> and <a href="/facts/CD273/HCspqje6">PD-L2</a>. </p>