Ephrin-A4 (EFNA4) is also known as EPH-related receptor tyrosine kinase ligand 4 (LERK4), EPLG4, which belongs to the ephrin family. EFNA4 contains one ephrin RBD (ephrin receptor-binding) domain. EFNA4 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. EFNA4 binds promiscuously Eph receptors residing on adjacent cells, leading to contact-dependent bidirectional signaling into neighboring cells. EFNA4 may play a role in the interaction between activated B-lymphocytes and dendritic cells in tonsils.