The MECA-367 monoclonal antibody specifically recognizes mucosal vascular addressin MAdCAM-1. In the fetus and neonate, MAdCAM-1 is the predominant vascular addressin on the high endothelial venules (HEV) of peripheral lymph nodes. In adult mice, MAdCAM-1 is preferentially expressed in mucosal lymphoid tissues and lamina propria; it is also expressed on sinus-lining cells in the spleen. MAdCAM-1 expression is upregulated on the HEV of peripheral lymph nodes in adult NOD mice4 and is involved in the development of diabetes and insulitis. Furthermore, there is evidence that IFN-γ can induce MAdCAM-1 expression in non-mucosal sites in adult mice. MAdCAM-1 is a predominant ligand for integrin α4β7, a lymphocyte mucosal homing receptor, and a facultative ligand for CD62L (L-selectin). MECA-367 mAb binds to the first domain of MAdCAM-1 and blocks MAdCAM-1-dependent binding in vitro and lymphocyte homing to Peyer's patch HEV in vivo. Source of the immunogen was endothelial cells from BALB/c mouse mesenteric and peripheral lymph nodes.