Activated leukocyte cell adhesion molecule
The CD166 antigen is coded by the ALCAM gene at 3q13.11. It has several isoforms activated by various regulatory mechanisms and some of these interfere with its prime functions so the common name activated leukocyte cell adhesion molecule for this cell adhesion molecule that mediates both heterotypic cell-cell contacts via its interaction with CD6, as well as homotypic cell-cell contacts implies less than it seems. However it is clearly an end stage regulatory effector protein coded by default as a 583 amino acid chain if not otherwise regulated during transcription and translation. It causes T-cell activation and proliferation via its interactions with CD6 and can facilite T-cell migration into the CNS. It is required for normal hematopoietic stem cell engraftment in the bone marrow. With its homotypic interactions it allows the attachment of dendritic cells onto endothelial cells and can inhibit endothelial cell migration and promote endothelial tube formation. Thus its function is required for normal organization of the lymph vessel network and normal haemophoiesis. It is likely to promote osteoblast proliferation and differentiation in man as it does this in other mammals. It promotes neurite extension, axon growth and axon guidance; in particular axons grow preferentially on surfaces that express CD166. It is likely to have a similar role with outgrowth and pathfinding for retinal ganglion cell axons. The soluble isoform 3 is known to inhibit activities of the membrane-bound isoforms by competing for the same interaction partners preventing cell attachment, promoting endothelial cell migration and inhibiting endothelial cell tube formation.