Rheostat regulation of integrin-mediated leukocyte adhesion
J. Clin. Invest. Ivor S. Douglas, et al. 117:2391 doi:10.1172/JCI33376 [Go to this article.]

Figure 2
Gut-targeted homing of α₄β₇⁺ naive and effector T cells. The gut-associated lymphoid tissues consist of (A) inductive sites, including secondary lymphoid organs, organized lymphoid tissues such as Peyer’s patches, and mesenteric lymph nodes that are responsible for the inductive phase of the immune response; and (B) effector sites, including epithelium and lamina propria (LP) of the intestinal mucosa. Endothelial cells of HEVs secrete chemokines that attract naive T cells. Endothelial chemokines trigger the activation of α₄β₇ integrin, which binds MAdCAM-1 on HEVs with high affinity, leading to the firm adhesion of rolling lymphocytes. The T cells then transmigrate across the endothelium into the T cell zone of the secondary lymphoid organs, where dendritic cells present antigen to the T cells. Antigen sampling in Peyer’s patches is controlled by a layer of specialized epithelial cells known as the follicular-associated epithelium. Peyer’s patch dendritic cells imprint gut-homing specificity on T cells (34), which become activated and upregulate integrin α₄β₇ expression. These activated T cells then migrate to the epithelium and lamina propria of the gut (B).