VCAM-1 (CD106), a member of the immunoglobulin superfamily, is a cell surface protein expressed by activated endothelial cells and certain leukocytes (such as macrophages). VCAM-1 expression is induced by IL-1 beta, IL-4, TNF-alpha and IFN-gamma. VCAM-1 binds to leukocyte integrins VLA-4 and alpha ₄ beta ₇. The human and mouse VCAM-1 proteins share approximately 76% amino acid similarity. During the inflammatory adhesion mechanism, activated integrins halt rolling leukocytes and attach them firmly to the vascular endothelium. They do this by binding to their ligands, for example VCAM-1, on endothelium. The VCAM-1: VLA-4/ alpha ₄ beta ₇ interaction is also thought to be involved in the extravasation of white blood cells through the blood vessel wall to sites of inflammation. ELISA techniques have shown that detectable levels of soluble VCAM-1 are present in the biological fluids of apparently normal individuals. Furthermore, a number of studies have reported that levels of VCAM-1 may be elevated or lowered in subjects with a variety of pathological conditions.