Integrin alpha 4 beta 1, also known as VLA-4, is an Integrin family adhesion receptor that shares the beta 1 subunit with eleven other family members and the alpha 4 subunit with Integrin alpha 4 beta 7. The noncovalent heterodimer of alpha 4/CD49d and beta 1/CD29 subunits mediates cell adhesion to VCAM-1/CD106 on other cells and the CS-1 fragment of Fibronectin in the extracellular matrix. Leukocytes (except for neutrophils), erythroid precursors, and some non-hematopoietic cells such as epicardial, endothelial and smooth muscle precursors, Schwann cells, and chorionic cells express a4b1. In the adult, a4b1 primarily regulates immune cell migration. Circulating leukocyte a4b1 is rapidly activated by inflamed endothelial cells that present VCAM-1 and chemokines such as CXCL12/SDF-1. This activation facilitates rolling, firm adhesion, and extravasation. During immune cell activation, a4b1 can function as a costimulatory molecule.
