CD6 recognizes the neural adhesion molecule BEN

CD6 and its ligand activated leukocyte cell adhesion molecule (ALCAM, CD166) have been detected on various immune cells and in the brain. CD6-ligand interactions have been implicated in the regulation of T cell function. ALCAM shares the same extracellular domain organization and significant sequence homology with the chicken neural adhesion molecule BEN. Although ALCAM's CD6 binding site is only partially conserved in BEN, CD6 specifically binds BEN, albeit with approximately 10-fold lower avidity than ALCAM. Differences in binding avidity are not detected when ALCAM and BEN fusion proteins containing the full-length extracellular regions are tested. Homotypic interactions between full-length forms are likely to account for these observations. The identified cross-species interaction between CD6 and BEN suggests that CD6-ligand interactions are highly conserved.