In molecular biology, CD18 (Integrin beta chain-2) is an integrin beta chain protein that is encoded by the ITGB2 gene in humans.[5] Upon binding with one of a number of alpha chains, CD18 is capable of forming multiple heterodimers, which play significant roles in cellular adhesion and cell surface signaling, as well as important roles in immune responses.[5][6] CD18 also exists in soluble, ligand binding forms. Deficiencies in CD18 expression can lead to adhesion defects in circulating white blood cells in humans, reducing the immune system's ability to fight off foreign invaders.