L-Selectin (CD62L) and Its Ligands

Cell adhesion molecules are glycoproteins expressed on the cell surface and play an important role in inflammatory as well as neoplastic diseases. There are four main groups: the integrin family, the immunoglobulin superfamily, selectins, and cadherins. The integrin family has eight subfamilies, designated as β1 through β8. The most widely studied subfamilies are β1 (CD29, very late activation [VLA] members), β2 (leukocyte integrins such as CD11a/CD18, CD11b/CD18, CD11c/CD18, and αd β2), β3 (CD61, cytoadhesions), and β7 (α4 β7 and αE β7). The immunoglobulin superfamily includes leukocyte function antigen-2 (LFA-2 or CD2), leukocyte function antigen-3 (LFA-3 or CD58), intercellular adhesion molecules (ICAMs), vascular adhesion molecule-1 (VCAM-1), platelet-endothelial cell adhesion molecule-1 (PE-CAM-1), and mucosal addressin cell adhesion molecule-1 (MAdCAM-1). The selectin family includes L-selectin (CD62L), P-selectin (CD62P), and E-selectin (CD62E). Cadherins are major cell-cell adhesion molecules and include epithelial (E), placental (P), and neural (N) subclasses. The binding sites (ligands/receptors) are different for each of these cell adhesion molecules (e.g., ICAM binds to CD11/CD18; VCAM-1 binds to VLA-4). The specific cell adhesion molecules and their ligands that may be involved in pathologic conditions and potential therapeutic strategies by modulating the expression of these molecules have been discussed (Elangbam et al. 1997). The main classes of adhesion molecule involved in lymphocyte interactions are the selectins, the integrins, members of the Ig superfamily, and some mucinlike molecules. Most adhesion molecules play fairly broad roles in the generation of immune responses. The three selectins act in concert with other cell adhesion molecules (e.g., intracellular adhesion molecule (ICAM-1), vascular cell adhesion molecule- 1 (VCAM-1), and leukocyte integrins (Springer 1990; Shimizu et al. 1992) to effect adhesive interactions of leukocytes, platelets, and endothelial cells. Hence selectins which belong to C-type lectins family are reviewed in Chaps. 21–23.