CD18 Integrin beta-2 is a receptor for ICAM1, ICAM2, ICAM3 and ICAM4. CD18 Integrin beta-2 is a receptor for the iC3b fragment of the third complement component and for fibrinogen. CD18 Integrin beta-2 recognizes the sequence G-P-R in fibrinogen alpha-chain, binds P1 and P2 peptides of fibrinogen gamma chain, and is also a receptor for factor , Xenopus/Amphibian,. Defects in CD18 Integrin beta-2 are the cause of leukocyte adhesion deficiency type 1 (LAD1). LAD1 patients have recurrent bacterial infections and their leukocytes are deficient in a wide range of adhesion-dependent functions.