CD18 Antigen

The beta2 integrins (CD11/CD18) are the major adhesion molecule family of leukocytes. Most leukocytes express one or more members of this family. CD18 is the 95 kDa integrin β2-chain which forms non-covalently-bound heterodimers with one of four α subunits. The four alpha subunits are: CD11a (αL) (all leukocytes), CD11b (αM) (granulocytes, monocytes, some macrophages), CD11c (αX) (granulocytes, monocytes, dendritic antigen presenting cells), CD11d  (αD) (CD8 T-cell subpopulation including large granular lymphocytes, macrophages and gamma-delta T cells in splenic red pulp). CD18 is expressed by all leukocytes (including histiocytes - macrophages, Langerhan's cells and dendritic cells) but no platelets. Macrophages and granulocytes express 10-fold more CD18 than do lymphocytes.