Objective Emerging evidence suggests that neuronal guidance cues, typically expressed during development, are involved in both physiological and pathological immune responses. We hypothesized that endothelial expression of such guidance cues may regulate leukocyte trafficking into the vascular wall during atherogenesis. Approach/Results We demonstrate that members of the Netrin, Semaphorin and Ephrin family of guidance molecules are differentially regulated under conditions that promote or protect from atherosclerosis. Netrin-1 and Semaphorin3A are expressed by coronary artery endothelial cells and potently inhibit chemokine-directed migration of human monocytes. Endothelial expression of these negative guidance cues is down-regulated by pro-atherogenic factors, including oscillatory shear stress and pro-inflammatory cytokines associated with monocyte entry into the vessel wall. Furthermore, we show using intravital microscopy that inhibition of Netrin-1 or Semaphorin3A using blocking peptides increases leukocyte adhesion to the endothelium. Unlike Netrin-1 and Semaphorin3A, the guidance cue EphrinB2 is up-regulated under pro-atherosclerotic flow conditions and functions as a chemoattractant, increasing leukocyte migration in the absence of additional chemokines. Conclusions The concurrent regulation of negative and positive guidance cues may facilitate leukocyte infiltration of the endothelium through a balance between chemoattraction and chemorepulsion. These data indicate a previously unappreciated role for axonal guidance cues in maintaining the endothelial barrier and regulating leukocyte trafficking during atherogenesis.

Background & Aims Immune responses in the intestine are controlled by regulatory T cells (Treg cells), which prevent inflammation in response to commensal bacteria. A specific population of intestinal dendritic cells (DCs), marked by expression of CD103, generate Tregs more efficiently than other DC populations, through mechanisms that involve retinoic acid and transforming growth factor (TGF)-β. However, it is not clear how CD103+ DCs are specialized for this function. We investigated the ability of CD103+ DCs to promote Treg generation through activation of TGF-β and the role of integrins with the αv subunit in this process. Methods Naïve T cells were cultured with purified DCs from mesenteric lymph nodes (MLNs) or intestines of wild-type and αv conditional knockout mice, to assess generation of Treg cells. Antigens were administered orally to mice and antigen-specific generation of Treg cells was measured in intestinal tissues. Expression of the integrin αv subunit was measured in purified subpopulations of DCs by quantitative PCR and immunoblot analyses. Results In vitro, CD103+ DCs generated more Treg cells in the presence of latent TGF-β than other MLN DCs. Efficient generation of Treg cells required expression of the integrin αv subunit by DCs; mice that lacked αv in immune cells did not convert naïve T cells to intestinal Treg cells in response to oral antigen. CD103+ DCs derived from the MLNs selectively expressed high levels of integrin αvβ8, compared with other populations of DCs. Conclusions Expression of αvβ8 is required for CD103+ DCs to become specialized and activate latent TGF-β and generate Treg cells during the induction of tolerance to intestinal antigens in mice.