Summary: TNF, also known as tumor necrosis factor isoform 1, is the prototypic ligand of the TNF superfamily. It is a pleiotropic molecule that plays a central role in inflammation, apoptosis, and immune system development. This protein is produced by a wide variety of immune and epithelial cell types. It is assembled intracellularly to form a noncovalently linked homotrimer which is expressed on the cell surface. Cell surface TNF can induce the lysis of neighboring tumor cells and virus infected cells, and it can generate its own downstream cell signaling following ligation by soluble TNFR I. It also promotes inflammatory responses by inducing the activation of vascular endothelial cells and macrophages.