The CD18 (HI18a) antibody recognizes a 95-kDa transmembrane protein, integrin beta-2 subunit, which associates respectively with the integrin α subunits: CD11a, CD11b, CD11c and CD11d forming four heterodimers named CD11a/CD18 (LFA-1), CD11b/CD18 (Mac-1), CD11c/CD18 (p150,95) and CD11d/CD18 (αdβ2). CD18 integrin is expressed exclusively on leukocytes and plays an important role in homotypic and hetorotypic cellular adhesion in immune and inflammatory responses. Patients who have mutated CD18 gene do not express cell membrane CD11/CD18 integrins, a condition known as leucocyte adhesion deficiency (LAD).