Identification of a carbohydrate-based endothelial ligand for a lymphocyte homing receptor

Comparison of L-selectin and E-selectin ligand specificities: the L-selectin can bind the E-selectin ligands sialyl Le(x) and sialyl Le(a)

The L- and E-selectins are leukocyte and endothelial cell surface molecules which mediate leukocyte-endothelial cell adhesion by interacting with carbohydrate ligands. In the present study we find that L-selectin, like E-selectin, can interact with synthetic neoglycoproteins containing Sialyl Le(x) (Neu5Ac alpha 2-3Gal beta 1-4[Fuc alpha 1-3]GlcNAc beta-R), or Sialyl Le(a) (Neu5Ac-alpha 2-3Gal beta 1-3[Fuc alpha 1-4]GlcNAc beta-R). Additionally, both the E-selectin and L-selectin can bind the peripheral lymph node addressin, a high endothelial venule ligand for L-selectin. Despite overlapping interactions, the L- and E-selectins discriminate between their native ligands. The peripheral lymph node addressin is a preferential ligand for L-selectin; and furthermore, L-selectin expressing cells do not interact detectably with the cutaneous lymphocyte antigen, a native glycoprotein ligand for E-selectin found on a subset of lymphocytes associated with the skin.

Recombinant globulins: novel research tools and possible pharmaceuticals

A novel approach to the study of proteins is the construction of chimeras consisting of a target protein fused to an immunoglobulin constant domain. These recombinant globulins have been used in the identification of ligand-receptor pairs, determination of functional consequences of receptor engagement, the elucidation of structural domains necessary for ligand binding, and as potential therapeutic agents.

Selectins and other mammalian sialic acid-binding lectins

Several recently discovered mammalian cell adhesion proteins recognize and bind to sialic acid-containing ligands. Reports concerning the molecular specificities of these interactions have been intriguing but somewhat confusing, partly because of pitfalls in methodology or interpretation. Nevertheless, these protein-carbohydrate recognition phenomena are important in the normal biology of blood cells and in the pathophysiology of many diseases.

Lymphocyte interactions with endothelial cells

Adhesion of lymphocytes to endothelium is vital to lymphocyte migration into lymphoid tissue and into inflammatory sites. In this review, Yoji Shimizu and colleagues identify the molecules that mediate lymphocyte-endothelial cell adhesion, describe the underlying principles of lymphocyte migration, and discuss a model of the sequence of events that allow a lymphocyte to successfully attach to endothelium and migrate into the surrounding tissue.

Adhesive interactions in angiogenesis and metastasis

A variety of adhesive interactions must take place between the tumor cell and the host vasculature in order to potentiate both tumor expansion and metastatic tumor spread. The study of tumor cell and blood vessel adhesive interactions becomes essential for our understanding of the malignant process, especially with regard to organ-specific tumor metastasis. In this article we will review recent progress made in our understanding of the nature of (i) receptor mediated adhesion of endothelial cells to extracellular matrix components and (ii) adhesion of tumor cells to endothelial adhesion molecules and to components of the subendothelial basement membrane.

The ligand recognized by ELAM-1 on HL60 cells is not carried by N-linked oligosaccharides

The sialyl Lewis-x determinant is a ligand for ELAM-1, a major adhesion molecule for HL60 cells and neutrophils. ELAM-1 expression can selectively be induced on human umbilical vein endothelial cells (HUVEC) by tumor necrosis factor, interleukin 1 and lipopolysaccharide. The determinant sialyl Lewis-x is found on both glycolipids as well as on glycoproteins. Using specific inhibitors of the biosynthesis of N-linked glycosylated glycoproteins, we investigated whether N-linked glycans or their modifications are involved in ELAM-1-dependent adhesion of HL60 cells to activated HUVEC. The inhibitors of glycoprotein processing N-methyl-deoxynojirimycin, 1-deoxymannojirimycin and swainsonine did not affect ELAM-1-dependent adhesion. Complex-type N-linked glycans are not required for ELAM-1 mediated adhesion, and therefore the ligand for ELAM-1 is most likely a glycolipid, or a glycoprotein carrying O-linked oligosaccharides.

A lymphocyte homing receptor (L-selectin) mediates the in vitro attachment of lymphocytes to myelinated tracts of the central nervous system

Lymphocytes enter lymph nodes by first adhering to high endothelial venules, an adhesive event mediated by a lectinlike lymphocyte receptor (L-selectin). Previously, it was shown with an in vitro assay that lymphocytes preferentially adhere to myelin-rich regions in brain sections. Here, using a recombinant form of L-selectin as an immunohistochemical reagent, we demonstrate potential ligands for L-selectin in myelinated regions of the central but not the peripheral nervous system. Using several antibodies and phorbol ester downmodulation of the receptor, we establish that L-selectin on human lymphocytes has a primary involvement in lymphocyte adherence to the myelinated regions. On mouse lymphocytes, the contribution of L-selectin appears to be partial. These findings raise the possibility that leukocyte targeting to myelin-rich regions, via a L-selectin dependent mechanism, may be a factor in the pathogenesis of certain central nervous system demyelinating diseases.

The complement binding-like domains of the murine homing receptor facilitate lectin activity

The leukocyte homing receptor (HR), the endothelial leukocyte adhesion molecule, and gmp140/platelet activation-dependent granule membrane protein are members of a family of adhesion molecules, termed the lectin cell adhesion molecules (LEC-CAMS) which are unified by a multi-domain structure containing a lectin motif, an epidermal growth factor-like (egf) motif, and variable numbers of a complement binding-like (CB) motif. Previous data have indicated a predominant role for the lectin motif in cell adhesion directed by the LEC-CAMS, although the egf-like domain of the HR may also play a potential role in cell binding. While the role(s) of the CB domains in the LEC-CAMS is currently not understood, they have been hypothesized to act as rigid spacers or stalks for lectin and perhaps, egf domain presentation. In this paper, we analyze the functional characteristics of murine HR-IgG chimeras containing the lectin, lectin plus egf, and lectin plus egf plus CB domains. The Mel 14 mAb, an adhesion blocking antibody which recognizes a conformational determinant in the N-terminus of the HR lectin domain, shows a significantly decreased affinity for a HR construct which lacks the CB motifs, consistent with the possibility that the CB domains are involved with lectin domain structure. In agreement with this conjecture, HR mutants lacking the CB domains show a profound decrease in lectin-specific interaction with the carbohydrate polyphosphomannan ester, suggesting that the changes in Mel 14 affinity for the lectin domain are reflected in lectin functionality. Various assays investigating the interactions between the HR deletion mutants and the peripheral lymph node high endothelium, including cell blocking, immunohistochemical staining, and radioactively labeled ligand binding, all showed that removal of the CB domains results in a lack of HR adhesive function. These results imply that the CB domains of the HR, and, by analogy, the other members of the LEC-CAM family, may play important structural roles involving induction of lectin domain conformation and resultant functionality.

The neutrophil selectin LECAM-1 presents carbohydrate ligands to the vascular selectins ELAM-1 and GMP-140

LECAM-1 (leukocyte-endothelial cell adhesion molecule 1), the lymphocyte lectin ("selectin") homing receptor for peripheral lymph nodes (PLNs), participates in the earliest interactions of polymorphonuclear neutrophilic leukocytes (PMNs) with inflamed venules. Here, we present evidence that LECAM-1 mediates this function through a novel mechanism--presentation of oligosaccharide ligands to the inducible vascular selectins endothelial-leukocyte adhesion molecule (ELAM-1) and granule membrane protein 140 (GMP-140). PMN, but not lymphocyte, LECAM-1 is modified with the vascular selectin ligand sialyl Lewis x (sLex) and specifically binds ELAM-1-transfected cells. Although only a small fraction of total cell surface sLex, LECAM-1-associated sLex appears to play a prominent role in PMN interactions with cell-associated ELAM-1 and GMP-140, as anti-LECAM-1 monoclonal antibodies or selective removal of cell surface LECAM-1 inhibits PMN binding to vascular selectin transfectants by up to 70%. The enhanced function of LECAM-1-associated sLex may reflect the striking concentration, shown here, of LECAM-1 on PMN surface microvilli, the site of initial cellular contact.