Sialyl Lewis X binding lectins on natural killer cells and their functions

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Natural killer (NK) cells mediate cytotoxicity through cell-surface receptors including lectin-like receptors. We have investigated whether sialyl Lewis X (sLeX) antigen, Neu5Acα2,3Galβ1,4 (Fucα1,3)GlcNAc-R, can bind to the lectin-like receptor on human NK-derived KHYG cells, using transferrin secreted by human hepatoma-derived HepG2 cells (Hep-TF), whose N-glycans are rich in α1,3-fucosylated bi-, tri-, and tetra-antennary complex types of N-glycans, and commercially available human transferrin (Nor-TF), which is comprised of bi-antennary N-glycans without α1,3-fucosylation.High sLeX-expressing erythroleukemia-derived K562 cells isolated from fucosyltransferase 3-transfected cells were 2.5 fold more susceptible than wild-type K562 cells to KHYG cells. Fluorescein isothiocyanate (FITC)-labeled Hep-TF bound 1.8 fold more strongly to KHYG cells than did FITC-labeled Nor-TF. The binding was suppressed by treatment with anti-NKG2D, anti-NKG2C, anti-CD94, and anti-CD 161 antibodies. FITC-labeled Hep-TF bound more strongly to human monocyte-derived U937 cells transfected with NKG2D and CD94 than to wild-type U937 cells. Moreover, tyrosine phosphorylation of a 17 kDa protein in the KHYG cells was enhanced by incubation on a Hep-TF coated plate and treatment with an anti-NKG2D antibody, but not by a Nor-TF coated plate and an anti-CD94 antibody.These results indicated that the interaction of sLeX antigen with the lectin-like receptors on NK cells induces cytotoxicity, which is mediated through a tyrosine-phosphorylated 17 kDa protein.