Integrin alpha-4 (CD49d) is a receptor for fibronectin. Integrin alpha-4 recognizes one or more domains within the alternatively spliced CS-1 and CS-5 regions of fibronectin. Integrin alpha-4 is also a receptor for VCAM1, recognizing the sequence Q-I-D-S in VCAM1, and a receptor for MADCAM1, recognizing the sequence L-D-T in MADCAM1. On activated endothelial cells, integrin alpha-4 triggers homotypic aggregation for most VLA-4-positive leukocyte cell lines, and also participates in cytolytic T-cell interactions with target cells.