Two-step model of leukocyte-endothelial cell interaction in inflammation: distinct roles for LECAM-1 and the leukocyte beta 2 integrins in vivo.

Abstract

The lectin homing receptor LECAM-1 (LAM-1, Leu8) and the P2 integrins, particularly Mac-i (CD11b/CD18), participate in leukocyte-endothelial cell interactions in inflammation. LECAM-1 is rapidly shed whileMac-i expression is dramatically increased upon neutrophil activation, suggesting functionally distinct roles for these molecules. Using intravital video microscopy, we have compared the effect of antibodies against LECAM-1 and CD18 on leukocyte interactions with rabbit mesenteric venules. Anti-LECAM-i monoclonal antibody and its Fab fragments inhibited initial reversible leukocyte rolling along the vascular wall.Anti-CD18 monoclonal antibody had no effect on rolling but prevented subsequent firm attachment of leukocytes to venular endothelium. Antibodies to CD18, the leukocyte integrin P2 chain, block firm attachment and diapedesis of neutrophils but have no effect on leukocyte rolling at normal venular shear rates (1). The surface molecules on leukocytes and endothelial cells that mediate rolling have not been defined. Rolling is attenuated by superoxide dismutase and action of oxygen-derived free radicals on endothelial cells may play a role in its induction (2,3). This unique event is calcium dependent (4) and can be inhibited by intravenous injection of neuraminidase but not sialic acid (5) and by some (but not all) polyanionic polysaccharides, such as dextran sulfate or heparin (6-9). These findings suggest a possible role for cell-surface adhesion receptors with affinity for charged carbohydrates.The leukocyte surface selectin/LEC-CAM LECAM-1 (LAM-1, Leu8), the peripheral lymph node homing receptor (10, 11), has been implicated in leukocyte interactions with activated endothelium in inflammation. The lectin domain in the extracellular portion of LECAM-1 contains many positively charged amino acids (12)(13)(14) and can interact with certain anionic carbohydrates (15). Anti-LECAM-1 monoclonal antibodies (mAbs) block neutrophil binding to cytokine-activated endothelial cells in vitro, inhibiting an adhesion pathway that is independent of (2 integrin function (16, 17). Administration of anti-LECAM-1 mAbs or a soluble homing receptor-IgG chimeric molecule as well as removal of LECAM-1 from the cell surface dramatically reduces leukocyte extravasation into sites of acute inflammation in various inflammatory models (18-21). The finding that LECAM-1 is rapidly shed from the neutrophil surface in response to several cytokines in vivo (20, 21) and in vitro (22, 23) in conjunction with observations of a parallel increase in (2 integrin expression has led to the hypothesis that LECAM-1 might mediate early neutrophil adhesive events, preceding the role of activation-triggered (32 integrins (20)(21)(22)(23). Such early events might be involved in leukocyte rolling. The present studies were undertaken to examine the role of LECAM-1 in in situ leukocyte interactions with venular endothelium in the rabbit mesentery.MATERIALS AND METHODS Antibodies. mAb DREG-200, which reacts with a surface molecule on rabbit...

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