SummaryA skin-associated population of memory T lymphocytes, defined by expression of the cutaneous lymphocyte antigen (CLA), binds selectively and avidly to the vascular lectin endothelial cellleukocyte adhesion molecule 1 (ELAM-1), an interaction that may be involved in targeting of CLA + T cells to cutaneous sites of chronic inflammation. Here we present evidence that CLA itself is the (or a) lymphocyte homing receptor for ELAM-1. Antigen isolated with anti-CLA monoclonal antibody HECA-452 from human tonsillar lysates avidly binds ELAM-1 transfected mouse cells. Anti-CLA antibody blocks T lymphocyte binding to ELAM-1 transfectants. HECA-452 and ELAM-1 binding to lymphocytes or to isolated tonsillar HECA-452 antigen is abrogated by neuraminidase treatment implying a prominent role for sialic acid in CLA structure and function. The dominant form of CLA on T cells is immunologically distinct from the major neutrophil ELAM-1 ligand, the sialyl Lewis x (sLe ~) antigen (NeuAcc~2-3GalB1-4[Fuccxl-3]GlcNAc), which is absent, weakly expressed, or masked on T ceUs. However, neuraminidase treatment of CLA + T cells, but not of CLA-T cells, reveals Lewis x (CD15) structures. In combination with the known requirement for terminal NeuAcoe2-3Gal and fucose residues attached to N-acetylglucosamine for ELAM-1 and HECA-452 binding, this finding suggests that CLA may comprise an additionally sialylated or otherwise modified form of sLe x. The identification of a lymphocyte homing receptor for skin may permit novel approaches to the diagnosis and therapy of cutaneous and inflammatory disorders.

Monoclonal antibodies recognizing CD18, CD1la, CD1lb, and neutrophil lectin adhesion molecule 1 (LECAM-1), i.e., the human homologue of the murine MEL-14 antigen, were used to assess the relative contribution of these glycoproteins to neutrophil-endothelial adhesion. Under static conditions, the adhesion of neutrophils to IL-l-stimulated human umbilical vein endothelial cell (HUVEC) monolayers was inhibited by antibodies to CD18, CD1 la, and the neutrophil LECAM-1, and the effect of combining anti-LECAM-1 and anti-CD1 la was almost additive. Under flow at a wall shear stress of 1.85 dyn/ cm2, a condition where CD18-dependent adhesion is minimal, anti-LECAM-1 inhibited adhesion by > 50%. Chemotactic stimulation of neutrophils induced a rapid loss of LECAM-1 from the neutrophil surface, and the level of neutrophil surface LECAM-1 was closely correlated with adhesion under flow. Neutrophils contacting the activated endothelial cells for 30 min lost much of their surface LECAM-1, a phenomenon induced by a soluble factor or factors released into the medium by the stimulated monolayers, and a high percentage migrated through the HUVEC monolayer. This migration was almost completely inhibited by anti-CD18, but was unaffected by antibodies to neutrophil LECAM-1. These results support the concept that LECAM-1 is a neutrophil adhesion molecule that participates in the adherence of unstimulated neutrophils to cytokine-stimulated endothelial cells under conditions of flow, and is then lost from the neutrophil surface coincident with the engagement of CD18-dependent mechanisms leading to transendothelial migration. (J. Clin. Invest. 1991. 87:609-618.)

Neutrophil adhesion to interleukin-1 (IL-1)-stimulated human umbilical vein endothelial cells (HUVEC) involves the CD18 family of leukocyte integrins (lymphocyte function-associated antigen-1 [LFA-1], Mac-1, and p150,95) and LECAM-1 (DREG-56/LEU-8/LAM-1 antigen) on neutrophils and intercellular adhesion molecule-1 (ICAM-1) and endothelial leukocyte adhesion molecule-1 (ELAM-1) on the endothelium. In this study, we compare CD18-independent adhesion pathways mediated by neutrophil LECAM- 1 and endothelial ELAM-1 and find that these two pathways overlap in a variety of assays: (1) anti-LECAM-1 and anti-ELAM-1 monoclonal antibody (MoAb) inhibit neutrophil binding to HUVEC, and the inhibitory effect is not additive; (2) anti-LECAM-1 MoAb, like anti-ELAM-1 MoAb, inhibits neutrophil binding to HUVEC stimulated for 3 hours with IL-1, but not to HUVEC stimulated for 8 hours, by which time ELAM-1 expression is downregulated; (3) anti-ELAM-1 MoAb has no effect on transendothelial migration, a CD18-dependent, LECAM-1-independent neutrophil function. Interestingly, anti-ELAM MoAb has a reduced but significant inhibitory effect on the adhesion of activated neutrophils that have shed their cell-surface LECAM-1. We also show that neutrophil binding to ELAM-1- transfected L cells is inhibited not only by anti-ELAM-1 but also by anti-LECAM-1 MoAb. These results suggest that LECAM-1 and ELAM-1 can operate in the same adhesion pathway, possibly as a receptor- counterreceptor pair. LECAM-1 and ELAM-1 are likely to interact with other ligands as well, perhaps through carbohydrate determinants that modify more than one glycoprotein.

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