Integrin alpha4beta1 (Very Late Antigen-4) is an integrindimer. It is composed of CD49d (alpha) and CD29 (beta).
VCAM-1 (integrin receptor) binds to the integrin VLA-4 which are normally expressed on leukocyte plasma membranes, but they do not adhere to their appropriate ligands until the leukocytes are activated by chemotactic agents or other stimuli (often produced by the endothelium or other cells at the site of injury). Only then do the integrins undergo the conformational change necessary to confer high binding affinity for the endothelial adhesion molecules.
