CD18, also known as integrin β2 subunit, LFA-1 β subunit, and β2 integrin, is a 90 - 95 kD type I glycoprotein. CD18 non-covalently associates with CD11a, CD11b, or CD11c. CD18 is expressed on all leukocytes. CD18 and associated α chains function in the adhesion and signaling in hematopoietic cells.