Tie1 is a cell surface protein expressed exclusively in endothelial cells. 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. the combinatorial function of angiopoietin-1 and the orphan receptor TIE1 is critical for the development of the right-hand side venous system but is dispensable for the left-hand side venous system. This finding revealed the existence of a distinct genetic program for the establishment of the right-hand side and left-hand side vascular networks well before the network asymmetry becomes morphologically discernible.