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Description

Programmed cell death 1 ligand 1 (UniProt: Q9EP73, also known as PD-L1, PDCD1 ligand 1, Programmed death ligand 1, B7 homolog 1, B7-H1, CD274) is encoded by the Cd274 (also known as B7h1, Pdcd1l1, Pdcd1lg1, Pdl1) gene (Gene ID: 50533) in murine species. PD-L1 is a single-pass type I membrane protein that is highly expressed in the heart, thymus, skeletal muscle, and lung. Its expression is also reported on activated dendritic cells, B-cells, and macrophages. Numerous tumor cell lines of lymphoid origin also express PD-L1. PD-L1 expression can be up-regulated by interferon-gamma treatment in monocytes, B cells, and macrophages. PD-1 and its ligands, PD-L1 and PD-L2 play a key role in the maintenance of peripheral tolerance, a process by which the quiescence of autoreactive mature T cells is maintained. However, tumors and pathogens that cause chronic infections can exploit this pathway to escape T-cell mediated tumor-specific and pathogen-specific immunity. The effector functions of T-cells expressing PD-1 can be downregulated by PD-L1 or PD-L2 expressed by the tumor cells. PD-L1 is initially produced with signal peptide (aa. 1-18) sequence, the removal of which yields the mature protein with a large extracellular (aa. 19-239) domain, a transmembrane domain (aa 240-260), and a cytoplasmic domain (aa 261-290).