Entyvio is an integrin receptor antagonist. Integrin receptors are proteins expressed on the surface of certain cells. Integrin receptors function as bridges for cell-cell interactions. Entyvio blocks the interaction of a specific integrin receptor (expressed on circulating inflammatory cells) with a specific protein (expressed on cells in the interior wall of blood vessels), and thereby blocks the migration of those circulating inflammatory cells across those blood vessels and into areas of inflammation in the gastrointestinal tract.