L-selectin, also known as CD62L, is a cell adhesion molecule found on leukocytes and the preimplantation embryo. It belongs to the selectin family of proteins, which recognize sialylated carbohydrate groups. It is cleaved by ADAM17.
CD62L is a cell surface component that is a member of a family of adhesion/homing receptors that play important roles in lymphocyte-endothelial cell interactions. The molecule is composed of multiple domains: one homologous to lectins, one to epidermal growth factor, and two to the consensus repeat units found in C3/C4-binding proteins.
L-selectin acts as a "homing receptor" for lymphocytes to enter secondary lymphoid tissues via high endothelial venules. Ligands present on endothelial cells will bind to lymphocytes expressing L-selectin, slowing lymphocyte trafficking through the blood, and facilitating entry into a secondary lymphoid organ at that point. The receptor is commonly found on the cell surfaces of T cells. Naive T-lymphocytes, which have not yet encountered their specific antigen, need to enter secondary lymph nodes to encounter their antigen. Central memory T-lymphocytes, which have encountered antigen, express L-selectin to localize in secondary lymphoid organs. Here they reside ready to proliferate upon re-encountering antigen. Effector memory T-lymphocytes do not express L-selectin, as they circulate in the periphery and have immediate effector functions upon encountering antigen.
High expression of L-selectin on human bone marrow progenitor cells is an early sign of cells becoming committed to lymphoid differentiation.
L-selectin is also present on the surface of human embryo trophoblasts prior to implantation into the uterus. Similar to its function in lymphocytes, L-selectin acts as a receptor to facilitate adhesion of the embryo to the site of invasion on the surface epithelium of the uterine endometrium. The embryo secretes human chorionic gonadotropin (hCG), which downregulates anti-adhesion factor, MUC-1, located on the uterine epithelium at the site of invasion. Removal of MUC-1 exposes the oligosaccharide ligands of the uterine epithelium, thus allowing binding by the L-selectin receptor of the trophopblast cell, followed by embryo adhesion and invasion.
^James JL, Carter AM, Chamley LW (May 2012). "Human placentation from nidation to 5 weeks of gestation. Part I: What do we know about formative placental development following implantation?". Placenta. 33 (5): 327–34. doi:10.1016/j.placenta.2012.01.020. PMID22374510.
Ord DC, Ernst TJ, Zhou LJ, et al. (1990). "Structure of the gene encoding the human leukocyte adhesion molecule-1 (TQ1, Leu-8) of lymphocytes and neutrophils". J. Biol. Chem. 265 (14): 7760–7. PMID1692315.
Bajorath J, Aruffo A (1995). "A template for generation and comparison of three-dimensional selectin models". Biochem. Biophys. Res. Commun. 216 (3): 1018–23. doi:10.1006/bbrc.1995.2722. PMID7488174.
Dianzani U, Bragardo M, Buonfiglio D, et al. (1995). "Modulation of CD4 lateral interaction with lymphocyte surface molecules induced by HIV-1 gp120". Eur. J. Immunol. 25 (5): 1306–11. doi:10.1002/eji.1830250526. PMID7539755.
Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, et al. (1997). "Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library". Gene. 200 (1–2): 149–56. doi:10.1016/S0378-1119(97)00411-3. PMID9373149.
Prakobphol A, Thomsson KA, Hansson GC, et al. (1998). "Human low-molecular-weight salivary mucin expresses the sialyl lewisx determinant and has L-selectin ligand activity". Biochemistry. 37 (14): 4916–27. doi:10.1021/bi972612a. PMID9538010.