CD49d is a 150 kD α integrin chain, also known as α4 integrin or VLA-4α chain. It forms heterodimers with integrin β1 (α4β1, VLA-4) or β7 (α4β7). CD49d is widely expressed on T lymphocytes, B lymphocytes, monocytes, thymocytes, eosinophils, basophils, mast cells, NK cells, dendritic cells and some non-hematopoietic cells, but is not expressed on normal red blood cells, platelets or neutrophils. VLA-4 binds to VCAM-1 (CD106) and fibronectin. α4β7 is the receptor for VCAM-1 and MAdCAM-1. CD49d is involved in the transport of monocytes to endothelial inflammatory sites and plays a role in cell-cell interactions and cell adhesion to the extracellular matrix. CD49d is involved in lymphocyte migration, T cell activation and hematopoietic stem cell differentiation. CD49d is a marker for the isolation and purification of pure Treg cell populations because it is absent on Foxp3+ cells.
