Tyrosine kinase receptor Tie1 is a single transmembrane type I membrane protein belonging to the protein kinase superfamily, the tyrosine kinase family and the Tie subfamily. Tie1 has three EGF-like domains, three fibronectin type III domains, two immunoglobulin-like type C2 domains, and one protein kinase domain. Tie1 is a cell surface protein specifically expressed in endothelial cells; however, studies have shown that it can also be expressed in immature hematopoietic cells and platelets. Tie1 is essential for the survival and growth of microvascular endothelial cells during the capillary emergence phase of vascular development. Tie1 up-regulates the cell adhesion molecules VCAM-1, E-selectin, and ICAM-1 through a P38-dependent mechanism. The expression of Tie1 enhances the adhesion of monocyte-derived immune cells to endothelial cells. Tie1 has a proinflammatory effect and plays an important role in inflammatory diseases of the endothelium such as atherosclerosis.