Ephrin-A4 belongs to the ephrin family and Contains 1 ephrin RBD (ephrin receptor-binding) domain. The protein is cell surface GPI-bound ligand for Eph receptors, a family of receptor tyrosine kinases which are crucial for migration, repulsion and adhesion during neuronal, vascular and epithelial development. Ephrin-A4 binds promiscuously Eph receptors residing on adjacent cells, leading to contact-dependent bidirectional signaling into neighboring cells. It may play a role in the interaction between activated B-lymphocytes and dendritic cells in tonsils.