Thrombospondin type-1 domain-containing protein 1 (THSD1) is also known as Transmembrane molecule with thrombospondin module (TMTSP), which is a single-pass type I membrane protein and contains a type 1 thrombospondin domain that is found in thrombospondin, a number of proteins involved in the complement pathway, as well as extracellular matrix proteins. In addition, THSD1 is widely expressed on endothelial cells, with highest expression in the lung. THSD1's ligand and function are unknown, but it is postulated that THSD1 may be involved in the regulation of vasculogenesis and/or angiogenesis through its interaction with its specific ligand.