Involvement of the LFA-1 ligand JAM-A in inflammatory recruitment of mononuclear cells : identification of the JAM-A binding domain in LFA-1
Junctional adhesion molecule-A (JAM-A) is a ligand of the integrin lymphocyte function-associated antigen-1 (LFA-1). In this study the JAM-A binding site in LFA-1 was identified and the involvement of JAM-A in inflammatory recruitment of mononuclear cells was analyzed. Furthermore, a functional contribution of JAM-A to atherogenesis was investigated. By deletion of the I domain in the aL subunit of LFA-1 and expression of this aL mutant in aL-deficient Jurkat J-ß2.7 T cells, it was here demonstrated that the I domain of LFA-1 is crucial for adhesion to immobilized JAM-A. This was substantiated by blocking the stimulated adhesion of T cells or monocytes to JAM-A using the I domain-directed mAb TS1/22 or the small molecule antagonist BIRT377, which stabilizes the low-affinity conformation of the I domain. The immobilized LFA-1 I domain locked in the open high-affinity conformation was sufficient to support adhesion of transfected Chinese hamster ovary cells expressing human JAM-A. A solid-phase binding assay confirmed a direct interaction of recombinant JAM-A with immobilized LFA 1 I domain locked in the open high-affinity conformation. These data have demonstrated that the I domain of LFA-1 is sufficient and required for the functional interactions of LFA-1 with JAM-A. Using soluble JAM-A.Fc chimeric protein as a competitive inhibitor, the involvement of JAM-A in distinct steps of mononuclear cells recruitment was analyzed. Adhesion assays revealed that LFA-1-mediated binding of T cells or monocytes to immobilized ICAM-1 or cytokine-costimulated endothelium was dose-dependently inhibited by soluble JAM-A.Fc. Similarly, soluble JAM-A.Fc reduced the LFA-1-mediated SDF-1-triggered arrest under flow conditions and transendothelial chemotaxis of T cells. These data have shown that soluble JAM-A can be effectively applied to inhibit distinct steps of inflammatory recruitment of mononuclear cells. Immunofluorescence and real-time RT-PCR analysis showed an upregulation of JAM-A expression on early atherosclerotic endothelium of carotid arteries from apolipoprotein E-deficient (apoE-/-) mice fed a high fat Western-type diet. In ex vivo perfusion assays, soluble JAM-A.Fc inhibited the VLA-4-independent accumulation of mononuclear cells on atherosclerotic endothelium. Together with the upregulation of JAM-A on atherosclerotic endothelium, this suggests a functional contribution of JAM-A to atherogenesis. The role of endothelial JAM-A in atherogenic recruitment was further substantiated by an attenuation of monocyte arrest and transmigration on activated JAM-A-/-apoE-/- versus JAM-A+/+apoE-/- mouse aortal endothelial cells in vitro. The findings from this work may be helpful in designing new stategies for the development of anti-inflammatory therapies.
info:eu-repo/classification/ddc/570, Zell-Adhäsionsmolekül, Tight junction, Chemotaxis, Atherogenese, Biowissenschaften, Biologie, cell adhesion molecule, atherogenesis
Networked Digital Library of Theses and Dissertations
Publikationsserver der RWTH Aachen University