CHARACTERIZATION OF THE E-SELECTIN LIGAND ON NK CELLS

In this study we demonstrate that human CD56(+)CD16(+)/CD3(-) NK cells adhere to the E-selectin expressed by stimulated HUVEC in a sialidase - and Ca2+-dependent manner, and express a sialylated Le(x) adhesion s tructure. We have characterized this sLe(x) epitope on NK cell in deta il and show here that the sLe(x) on NK cells was not recognized by the CSLEX1 Ab, but was readily identified by two anti-di-sle(x) Abs, KM-9 3 and FH-6. Furthermore, cleaving sialic acid with a sialidase treatme nt revealed a pool of Le(x) epitopes on the NK cell surface, providing further proof that NK cells express sLe(x) epitopes. Extensive protea se treatments did not cleave the sLe(x) epitope from NK cells, which s uggests that it could be linked to a lipid backbone. This di-sle(x) wa s able to mediate adhesion to E-selectin, suggesting that it represent s an essential part or is closely related to a selection ligand on NK cells. We were also able to show that NK cells possess several alpha 2 ,3 sialyltransferases and alpha 1,3 or alpha 1,3/4 fucosyltransferases . These enzymes are crucial in the synthesis of sLe(x) epitopes on cel l surfaces. Taken together, we provide evidence that NK cells have a d i-sLe(x) oligosaccharide capable of adhesion to E-selectin, and NK cel ls have the machinery (i.e., relevant transferases) to generate these sialylated Lewis oligosaccharides.