High endothelial cells synthesize and degrade sLex. Putative implications for L-selectin-dependent recognition

L-selectin guides lymphocytes into peripheral lymphoid tissues by recognizing glycoprotein ligands decorated with 6-sulfated sialyl Lewis x (sulfo sLex). Here we have used a rat peripheral lymph node high endothelial cell line (Ax) to study in detail the synthesis, expression and degradation of sLex epitope. We show here that Ax cells possess active α(1,3)fucosyltransferase Fuc-TVII, the enzyme responsible for the final fucosylation of sialyl- N-acetyllactosamine during sLex synthesis, and express sLex on the cell surface. Furthermore, these cells degrade sLex, primarily by desialylating it to neutral Lex epitopes by α(2,3)sialidase(s).