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Blood, 15 January 2007, Vol. 109, No. 2, pp. 661-669. Prepublished online as a Blood First Edition Paper on September 26, 2006; DOI 10.1182/blood-2005-12-023044.
IMMUNOBIOLOGY Active MAC-1 (CD11b/CD18) on DCs inhibits full T-cell activation1 Cell Biology, Department of Dermatology, University of Münster, Germany; 2 Center for Molecular Biology of Inflammation, University of Münster, Germany; 3 Max-Planck-Institute for Molecular Biomedicine, Münster, Germany; 4 Max-Delbrück-Center for Molecular Medicine, Berlin-Buch, Germany; 5 Department of Dermatology, University of Ulm, Germany; 6 Department of Dermatology, University of Essen, Germany
The ß2 integrins are important for transendothelial migration of leukocytes as well as for T-cell activation during antigen presentation. Despite abundant expression of ß2 integrins on antigen-presenting cells (APCs), their functional relevance for antigen presentation is completely unclear. We show here that dendritic cells (DCs) from CD18-deficient mice, which lack all functional ß2 integrins, have no defect in antigen presentation. Moreover, DCs from normal mice express inactive ß2 integrins that do not become activated on contact with T cells, at least in vitro. Pharmacologic activation of ß2 integrins on DCs results in a significant reduction of their T cellactivating capacity. This effect is mediated by Mac-1 (CD11b/CD18) on DCs because it could be reversed via blocking antibodies against CD18 and CD11b. Furthermore, the antigen-presenting capacity of macrophages, which express constitutively active ß2 integrins, is significantly enhanced on Mac-1 blockade. We therefore conclude that active CD11b/CD18 (Mac-1) on APCs directly inhibits T-cell activation.
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