CD18 is a 95 kD protein, also known as integrin β2 subunit. It is expressed on all leukocytes. CD18, in association with integrin α chain CD11a, CD11b, and CD11c forms LFA-1, Mac-1, and αXβ2, respectively, and plays an important role in leukocytes adhesion. The CD18 integrin complexes bind ICAM-1 (CD54), ICAM-2 (CD102), ICAM-3 (CD50), iC3b, and fibrinogen.