Tyrosine-protein kinase receptor Tie1, is a single-pass type I membrane protein which belongs to the protein kinase superfamily, Tyr protein kinase family and Tie subfamily. Tie1 contains three EGF-like domains, three fibronectin type-III domains, two immunoglobulin-like C2-type domains and one protein kinase domain. Tie1 is a cell surface protein expressed exclusively in endothelial cells, however, it has also been shown to be expressed in immature hematopoietic cells and platelets. It is required for the survival and growth of microvascular endothelial cells during the capillary sprouting phase of vascular development. Tie1 upregulates the cell adhesion molecules VCAM-1, E-selectin, and ICAM-1 through a p38-dependent mechanism. Attachment of monocyte derived immune cells to endothelial cells is also enhanced by Tie1 expression. Tie1 has a proinflammatory effect and may play a role in the endothelial inflammatory diseases such as atherosclerosis.