Ephrin ligands are divided into two subclasses of ephrin-A and ephrin-B based on their structure and linkage to the cell membrane.
Of the eight ephrins that have been identified in humans there are five known ephrin-A ligands (ephrin-A1-5) that interact with nine EphAs (EphA1-8 and EphA10) and three ephrin-B ligands (ephrin-B1-3) that interact with five EphBs (EphB1-4 and EphB6) [REF].