Leukocyte adhesion has biological importance in numerous processes involving host defense. The CD11/CD18 integrins are differentiated antigens which play a critical role in this mechanism. CD11a/CD18 are apparent on early progenitors of all myeloid and erythroid cells. CD11b/CD18 and CD11c/CD18 are more restricted antigens normally expressed on monocytes, macrophages, PMN and natural killer cells.[1]