Carbohydrate-binding proteins lymphocytes

Recently, a carbohydrate-binding protein, L-selectin, has been proposed as an adhesion molecule for human embryo implantation (19). L-Selectin is expressed on the surface of lymphocytes and interacts with sulfated and fucosylated carbohydrates expressed on lymph node endothelial cells (20-26). Carbohydrate ligand for L-selectin in the lymph node is closely related to MECA-79 antigen (Fig. 1). In human endometrium, the expression of MECA-79 antigen is hormonal cycle dependent but the presence of an embryo is not required (27). In the mouse, L-selectin nulls reproduce normally (28). Mutant mice lacking sulfotransferases (22,23,29-32) and glycosyltransferases (21,31,32) required for synthesis of L-selectin ligand exhibited no defects in reproduction. Therefore, it is clear that L-selectin is not required for the mouse embryo implantation. It thus appears that L-selectin is uniquely involved in human embryo implantation. 

In order to determine if lectins affect the reactions of complement mediated hemolysis subsequent to binding of antibody to the lymphocyte we have employed a synthetic particulate antigen. This was accomplished by testing the ability of lectin to inhibit the fixation of complement by the complex of anti-human serum albumin (HSA) and HSA-conjugated aminoethyl Biogel beads. The HSA-conjugated aminoethyl Biogel beads may be considered to be cell-like particles coated with a carbohydrate-free protein. 

The term selectin was introduced to describe three adhesion molecules whose function and expression were highly selective and which possessed a terminal lectin domain. The nomenclature for each molecule relates to the cell on which they were first described E-selectin (endothelium), L-selectin (lymphocyte), and P-selectin (platelet). All three share similar structural features (1) an extracellular amino terminal carbohydrate-binding (i.e., lectin-like) domain that requires Ca2+ for activation (2) an epidermal growth factor-like domain and (3) repeated domains with homologies to complement-regulatoiy proteins. 

---