Addressin is an extracellular protein of the endothelium of venules. Addressins are the ligands to the homing receptors of lymphocytes.The task of these ligands and their receptors is to determine which tissue the lymphocyte will enter next. The carry carbohydrates in order to be recognized by L-selectin. The predicted amino acid sequence defines the mucosal addressin as a novel immunoglobulin family member with 2 N-terminal domains that display strong homology to previously described vascular adhesion receptors for leukocytes: ICAM1 and VCAM1. The membrane proximal domain is homologous to the third domain of another mucosa-associated member of the immunoglobulin family, namely, IgA0 .