An Integrin α4β7.IgG Heterodimeric Chimera Binds to MAdCAM-1 on High Endothelial Venules in Gut-Associated Lymphoid Tissue

Lymphocyte homing is regulated by a multistep process mediated by sequential adhesive interactions between circulating lymphocytes and high endothelial venules (HEVs). In gut-associated lymphoid tissue (GALT), the initial interactive step, tethering and rolling, is partly mediated by integrin alpha 4 beta 7 expressed on GALT-homing lymphocytes and its ligand MAdCAM-1, which is exclusively expressed on HEVs in GALT. To probe functional MAdCAM-1 in tissue sections, we developed a soluble integrin alpha 4 beta 7 heterodimeric IgG chimera by joining the extracellular region of mouse integrin alpha 4 and beta 7 subunits to a human IgG Fc domain. Western blot analysis revealed that co-transfection of HEK 293T cells with expression vectors encoding integrin alpha 4.IgG and beta 7.IgG results in the formation of alpha 4 beta 7.IgG heterodimeric chimeras. This complex preferentially binds to CHO cells expressing MAdCAM-1 and, to a lesser extent, to cells expressing VCAM-1, but not to cells expressing ICAM-1. Moreover, alpha 4 beta 7.IgG specifically binds to HEVs in GALT in situ in a divalent cation-dependent fashion and inhibits lymphocyte binding to HEVs in GALT. These findings indicate that alpha 4 beta 7.IgG can be used as a probe for functional MAdCAM-1 expressed on HEVs in GALT and could potentially serve as an anti-inflammatory drug inhibiting GALT-specific lymphocyte migration. (J Histochem Cytochem 59:572-583, 2011)