Enzymatic synthesis of alpha 3 ' sialylated and multiply alpha 3fucosylated biantennary polylactosamines - A bivalent [sialyl diLe(x)]-saccharide inhibited lymphocyte-endothelium adhesion organ-selectively

Multifucosylated sialo-polylactosamines are known to be high affinity ligan ds for E-selectin. PSGL-1, the physiological ligand of P-selectin, is decor ated in HL-60 cells by a sialylated and triply fucosylated polylactosamine that is believed to be of functional importance. Mimicking some of these sa ccharide structures, we have synthesized enzymatically a bivalent [sialyl d iLe(x)]-glycan, Neu5Ac alpha 2-3'Le(x)beta 1-3'Le(x)beta 1-3'(Neu5Ac alpha 2-3 'Le(x)beta 1-3'Le(x)beta 1-6')LN [where Neu5Ac is N-acetylneuraminic ac id, Le(x) is the trisaccharide Gal beta 1-4(Fuc alpha 1-3)GlcNAc and LN is the disaccharide Gal beta 1-4GlcNAc]. Several structurally related, novel p olylactosamine glycans were also constructed. The inhibitory effects of the se glycans on two L-selectin-dependent, lymphocyte-to-endothelium adhesion processes of rats were analysed in ex-vivo Stamper-Woodruff binding assays. The IC50 value of the bivalent [sialyl diLe(x)]-glycan at lymph node high endothelium was 50 nM, but at the capillaries of rejecting cardiac allograf ts it was only 5 nM. At both adhesion sites, the inhibition was completely dependent on the presence of fucose units on the sialylated LN units of the inhibitor saccharide. These data show that the bivalent [sialyl diLe(x)]-g lycan is a high affinity ligand for L-selectin, and may reduce extravasatio n of lymphocytes at sites of inflammation in vivo without severely endanger ing the normal recirculation of lymphocytes via lymph nodes.