Growth of new capillaries (angiogenesis) is a complex and highly regulated process which occurs normally during specific physiologic events. Abnormal capillary growth, however, underlies many pathologic states such as diabetic retinopathy, rheumatoid arthritis, and hemangiomas. In addition, the neovascularization of tumors represents an aberrant stimulation of normally quiescent endothelial cells to proliferate, migrate, and form new capillary blood vessels. During this process the endothelial cells align end-to-end, fold over on themselves to form a lumen that is contiguous with adjacent cells,a nd form branches at capillary tips which can then join other branches to form a continuous loop. The biochemical basis of the cell-cell and cell-matrix interactions that occur during capillary formation is not well understood. Our goal is to identify the capillary endothelial cell surface molecules that provide the instructions for the cell adhesion events that occur during the formation of new capillaries. Our preliminary data suggests that lectin-carbohydrate interactions play a critical role in capillary tube formation. To carry out these studies, we have used clonal bovine capillary endothelial (BCE) cells which can be induced to form capillary-like tubes on fibronectin-coated dishes in a reproducible and synchronous manner. This in vitro model for angiogenesis has allowed us to examine the role of BCE oligosaccharides and has led to our hypothesis that at least one type lectin-carbohydrate interaction is required for capillary tube formation. Using a combination of biochemical and molecular techniques, we hope to identify and characterize the endogenous BCE cell lectin and its carbohydrate ligand(s). At least one BCE lectin will be cloned by exploiting its apparent homology to previously cloned lectin known as endothelial cell leukocyte adhesion molecule-1. These studies will contribute to our understanding of capillary morphogenesis and may provide insights for the development of anti- angiogenic therapies.