Integrin αE(CD103)β7 Mediates Adhesion to Intestinal Microvascular Endothelial Cell Lines Via an E-Cadherin-Independent Interaction

Abstract

Integrins are important for T cell interactions with endothelial cells. Because the integrin αEβ7 is expressed on some circulating gut-homing T cells and as T cell numbers are reduced in the intestinal lamina propria of αE-deficient mice, we evaluated whether αEβ7 mediates binding to intestinal endothelial cells. We found that anti-αEβ7 mAbs partially blocked the binding of cultured intraepithelial T cells to human intestinal microvascular endothelial cells (HIMEC). Furthermore, αEβ7-transfected K562 cells bound more efficiently than vector-transfected K562 cells to HIMEC. Finally, HIMEC bound directly to an αEβ7-Fc fusion protein. These interactions were partially blocked by anti-αEβ7 mAbs, and endothelial cell binding to the αEβ7-Fc was dependent upon the metal ion-dependent adhesion site within the αE A domain. Of note, the HIMEC lacked expression of E-cadherin, the only known αEβ7 counterreceptor as assessed by functional studies, flow cytometry, and RT-PCR. Thus, HIMEC/αEβ7 binding was independent of E-cadherin. In addition, this interaction appeared to be tissue selective, as HIMEC bound to the αEβ7-Fc, whereas microvascular endothelial cells from the skin did not. Finally, there was evidence for an αEβ7 ligand on intestinal endothelial cells in vivo, as αEβ7 expression enhanced lymphocyte binding around vessels in the lamina propria in tissue sections. Thus, we have defined a novel interaction for αEβ7 at a nonepithelial location. These studies suggest a role for αEβ7 in interactions with the intestinal endothelium that may have implications for intestinal T cell homing or functional responses.