TIE is a new receptor-type tyrosine kinase that was cloned from K562, a chronic myelocytic leukemia cell line. Its molecular weight is 117 kDa and its structure begins with an immunoglobulin-like domain from the extracellular N terminal, continues to 3 EGF-like domains, another immunoglobulin-like domain, 3 fibronectin III-like domains, a membrane-penetrating domain, 2 tyrosine kinase domains and a C-terminal domain. It has been reported that Tek molecules with a high homology (about 80%) have been cloned from the kinase domains. These molecules are believed to make up a Tie family. Tie-2 and a receptor type tyrosine kinase Tie-1 that is expressed specifically in endothelial cells are included in this Tie family. Among the Tie-1 gene knockout mice, a vasculature is formed in a homozygote (-/-) but the mouse is likely to succumb to pulmonary edema. Thus it has been reported that the signal via Tie-1 is important in maintaining the vascular structure. This monoclonal antibody recognizes Tie-1 by W.B. and I.P. applications and it enables FACS analysis of Tie-1-expressing cells.