Vimentin function in lymphocyte adhesion and transcellular migration.

Although the adhesive interactions of leukocytes with endothelial cells are well understood, little is known about the detailed mechanisms underlying the actual migration of leukocytes across the endothelium (diapedesis). Leukocytes have been shown to use both paracellular and transcellular routes for transendothelial migration. Here we show that peripheral blood mononuclear cells (PBMCs; T- and B-lymphocytes) preferentially use the transcellular route. The intermediate filaments of both endothelial cells and lymphocytes formed a highly dynamic anchoring structure at the site of contact between these two cell types. The initiation of this process was markedly reduced in vimentin-deficient (vim(-/-)) PBMCs and endothelial cells. When compared with wild-type PBMCs, vim(-/-) PBMCs showed a markedly reduced capacity to home to mesenteric lymph nodes and spleen. Furthermore, endothelial integrity was compromised in vim(-/-) mice, demonstrating that intermediate filaments also regulate the barrier that governs leukocyte extravasation. Absence of vimentin resulted in highly aberrant expression and distribution of surface molecules critical for homing (ICAM-1 and VCAM-1 on endothelial cells and integrin-beta1 on PBMCs). These data show that intermediate filaments are active in lymphocyte adhesion and transmigration.

Vascular adhesion protein-1 is involved in both acute and chronic inflammation in the mouse.

Vascular adhesion protein-1 (VAP-1) is an endothelial molecule that possesses both adhesive and enzymatic properties in vitro. So far, however, elucidation of its in vivo function has suffered from the lack of function-blocking reagents that are suitable for use in animal models. In this work we produced monoclonal antibodies against murine VAP-1 and characterized them using in vitro binding assays. We then examined whether the antibodies could prevent leukocyte migration in in vivo inflammation models, including two acute models (peritonitis induced with proteose peptone and interleukin-1 and air pouch inflammation enhanced by CCL21) and one chronic model (autoimmune diabetes in nonobese diabetic mice). Antibodies 7-88 and 7-106 inhibited migration of granulocytes and monocytes in both acute models of inflammation. Strikingly, antibody 7-88 significantly prevented diabetes in a subset of nonobese diabetic mice. The results show for the first time that in mouse models of inflammation, VAP-1 mediates leukocyte trafficking to sites of inflammation and thus is a potential target for anti-inflammatory therapies.

Function-blocking antibodies to human vascular adhesion protein-1: a potential anti-inflammatory therapy.

Human vascular adhesion protein-1 (VAP-1) is a homodimeric 170-kDa sialoglycoprotein that is expressed on the surface of endothelial cells and functions as a semicarbazide-sensitive amine oxidase and as an adhesion molecule. Blockade of VAP-1 has been shown to reduce leukocyte adhesion and transmigration in in vivo and in vitro models, suggesting that VAP-1 is a potential target for anti-inflammatory therapy. In this study we have constructed mouse-human chimeric antibodies by genetic engineering in order to circumvent the potential problems involved in using murine antibodies in man. Our chimeric anti-VAP-1 antibodies, which were designed to lack Fc-dependent effector functions, bound specifically to cell surface-expressed recombinant human VAP-1 and recognized VAP-1 in different cell types in tonsil. Furthermore, the chimeric antibodies prevented leukocyte adhesion and transmigration in vitro and in vivo. Hence, these chimeric antibodies have the potential to be used as a new anti-inflammatory therapy.

Ly6C induces clustering of LFA-1 (CD11a/CD18) and is involved in subtype-specific adhesion of CD8 T cells.

Ly6C is a hemopoietic cell differentiation Ag found on a subset of CD8 T cells in the periphery. It is involved in target cell killing by CTLs, augments TCR-mediated activation of IL-2 and IFN-gamma production in CD8 T cells, and regulates CD8 T cell homing in vivo. In this study, we show that cross-linking of Ly6C causes clustering of LFA-1 (CD11a/CD18) on the surface of CD8 T cells via a mechanism dependent on reorganization of actin cytoskeleton and intracellular protease, calpain, but not the phosphatidylinositol 3-kinase pathway. In the capillary flow-adhesion assay, Ly6C cross-linking significantly augments lymphocyte adhesion to endothelium, and this is inhibited by an Ab that blocks LFA-1 function. Furthermore, upon in vitro cross-linking and during in vivo homing into lymph nodes, Ly6C is transiently lost from cell surface but becomes re-expressed on lymph node-resident CD8 T cells. The abilities of Ly6C to induce LFA-1 clustering and to be re-expressed after signaling-associated down-regulation may be important in regulating the homing of CD8 T cells into lymph nodes and in subsequent steps of CD8 T cell activation and effector function that again involve LFA-1.

The same endothelial receptor controls lymphocyte traffic both in vascular and lymphatic vessels.

The mechanisms controlling the exit of lymphocytes from tissues via lymphatics are practically unknown. We have now identified a 270-300-kDa molecule designated common lymphatic endothelial and vascular endothelial receptor-1 (CLEVER-1) on human lymphatic endothelium and high endothelial venules. We show that it mediates binding of lymphocytes both to high endothelial venules and to lymphatic vessels. Moreover, blocking of the function of CLEVER-1 results in significant reduction of lymphocyte traffic in vivo. Notably, CLEVER-1 is also an inducible vascular adhesion molecule for other classes of leukocytes at sites of inflammation in peripheral tissues. These findings suggest that CLEVER-1 is involved in regulation of lymphocyte recirculation and migration of leukocytes to sites of inflammation and is a potential new target to control inflammation.