Two distinct lymphocyte homing systems involved in the pathogenesis of chronic inflammatory gastrointestinal diseases.

Under normal and pathological conditions, lymphocyte migration into the gastrointestinal mucosa to form gut-associated lymphoid tissue is mediated by the L-selectin ligand peripheral lymph node addressin and the integrin α4β7 ligand mucosal addressin cell adhesion molecule 1 (MAdCAM-1) expressed on high endothelial venules (HEVs) and HEV-like vessels. In this review, we discuss these two distinct lymphocyte homing systems involved in the pathogenesis of chronic inflammatory gastrointestinal diseases with reference to our and others' previously published works. We also describe a recently developed recombinant integrin α4β7 heterodimeric IgG chimera that can be used as an immunohistochemical reagent to stain functional MAdCAM-1.