The Notch family of proteins are involved in the regulation of key biological processes such as cell fate determination, proliferation, differentiation, and apoptosis. Jagged-1 (HJ1; CD339), a cell surface glycoprotein, is one of several ligands that activate multiple Notch receptors  and is involved in mediating Notch signalling. Jagged-1 signalling through Notch has been shown to play a role in hematopoiesis. Jagged-1 also seems to be involved in early and late stages of mammalian cardiovascular development. It has been shown to enhance fibroblast growth factor-induced angiogenesis (in vitro). Mutations in the human Jagged-1 gene cause Alagille syndrome.
Jagged-1 binds to Notch 1 receptors and activates Notch 1-dependent signalling pathways. For example, Jagged-1 inhibits T cell activation and is a promising therapeutically beneficial protein for multiple sclerosis or other autoimmune diseases. Additionally Jagged-1 was shown to block osteoclastogenesis in the presence of RANKL and M-CSF.