Mucosal addressin cell adhesion molecule-1 (MadCAM-1) is a cell-surface immunogloblin (Ig) superfamily member composed of two extracellular Ig domains, followed by a mucin-like domain, a transmembrane domain, and a short cutoplasmic domain. The molecule is similar to ICAM1 and VCAM1. It interacts via its N-terminal Ig domain with the lymphocyte homing receptor alpha4 beta73, which plays a critical role in forming the gut-associated lymphoid system. MAdCAM-1 promotes the adhesion of T and B cells, monocytes/macrophages, and potentially eosinophils, basophils, and differentiated mast cells to the vascular endothelium. At least seven alternatively spliced transcripts encoding different protein isoforms have been found for this gene. The molecular weight is about 43kD, and it is highly expressed on high endothelial venules(VEC) and lamina propia venules found in the small intestine.