Human Epidermal Keratinocyte Expression of Sialyl-Lewis X

Cell-surface oligosaccharides can function as ligands for intercellular adhesion receptors, matrix proteins, and growth factors. 9ge report that human neonatal and adult epidermal keratinocytes (KC) express sialyl Lewis X [s-Lex; SAα2-3Galβ-4(Fucα1-3)GlcNAcβ-3R], a ligand for endothelial and platelet selectins. Freshly isolated or cultured KC bind FH6 monoclonal antibody (MoAb), which is specific for s-Lex-containing oligosaccharides. The relevant epitope is bona fide s-Lex, because sialidase treatment of KC suspensions abrogates FH6 binding while generating de novo KC reactivity with anti-Lex KC stained in ice-cold suspension display a knobby membrane distribution of s-Lex detectable by immunofluorescence microscopy. As others have reported, FH6 appeared not to bind KC in perpendicular skin sections However, basal KC in intact epidermal sheets exhibited obvious “honeycomb” reactivity with FH6 when stained and viewed en face, suggesting that s-Lex in intact epidermis may occur in bands that parallel the major tissue axis. FH6 specifically immunoprecipitated proteins of Mr 34 kd, 44 kd, and 56 kd from [35S]-labeled KC, and anti-Lex precipitated similar proteins from sialidase-treated KC The enzymatic basis for KC s-Lex expression was studied by analyzing acceptor specificities and other properties of KC fucosyltransferases. Results indicate that KC express both Lewisand myeloid-type α1-3fucosyltransferases. KC s-Lex could be an important element of the epithelial milieu, because both epithelial cells and immune cells that home to epithelia express s-Lex and related structures, and because KC s-Lex is well positioned for selectin-mediated platelet binding after transcutaneous wounding. The apparent distributions of s-Lex in epidermis and on isolated KC are compatible with a functional role for s-Lex in these intercellular interactions.