CD49d (Anti–VLA-α4), clone L25, is derived from the fusion of mouse Sp2/0 cells with popliteal lymph node cells from a BALB/c mouse immunized with a CD8+ T-cell line.
CD49d (Anti–VLA-α4) recognizes the 150-kilodalton (kd) α chain of very-late antigen (VLA)-4, a member of the integrin family of cell adhesion molecules. VLA-4, like other integrins, is a noncovalently associated heterodimeric glycoprotein composed of α and β subunits and is involved in cell–cell and cell–extracellular matrix interactions. The β chain of the VLA-4 complex is the CD29 antigen, a 130-kd glycoprotein. The CD29 antigen, also known as the β1 subunit, is common to the VLA family of integrins. When acting as a matrix receptor, the CD49d antigen binds to CS-1, an alternatively spliced domain of fibronectin. When functioning as a cell receptor, the CD49d antigen binds to the vascular cell-adhesion molecule-1 (VCAM-1). The interaction between the CD49d antigen and VCAM-1 is known to play an important role in stabilizing the adhesion of lymphocytes to endothelial cells and in mediating B-lymphocyte precursor/bone marrow stromal cell adhesion. The CD49d antigen, when associated with the β7 integrin, forms a lymphocyte homing receptor for Peyer's patch, binding to the mucosal vascular addressin MAdCAM-1. The CD49d antigen is also involved in CD3-dependent CD4+T-lymphocyte activation via its interaction with fibronectin.