In vitro experimental studies of sialyl Lewis x and sialyl Lewis a on endothelial and carcinoma cells: crucial glycans on selectin ligands.

Extravasation from the blood of malignant tumour cells that form metastasis and leukocytes that go into tissues require contact between selectins and their sialyl Lewis x and sialyl Lewis a (sLe(x) and sLe(a) respectively) decorated ligands. Endothelial cells have been shown to express sLe(x) epitopes in lymph nodes and at sites of inflammation, and this is crucial for the selectin-dependent leukocyte traffic. Besides the ability to synthesize sLe(x) on sialylated N-acetyllactosamine via the action of alpha(1,3)fucosyltransferase(s), endothelial cells can also degrade sLe(x) to Lewis x through the action of alpha(2,3)sialidase(s). In addition, several epithelial tumors possess the machinery to synthesize sLe(x), which facilitates their adhesion to endothelial E- and P-selectin.