A ROLE FOR LECTIN INTERACTIONS DURING HUMAN NEUTROPHIL AGGREGATION

We have recently reported that neutrophil aggregation is dependent on both L-selectin and the beta2-integrin Mac-1, raising the possibility that carbohydrate interactions play a role in aggregation. We used mon o- and polysaccharides known to inhibit L-selectin-dependent adhesion of lymphocytes to high endothelial venules to test whether these carbo hydrates could inhibit neutrophil aggregation. Similar types and conce ntrations of carbohydrates found by others to inhibit lymphocyte adhes ion were effective in blocking neutrophil aggregation. Thus, nanomolar concentrations of the polysaccharides dextran sulfate (m.w. 500,000) and fucoidan inhibited aggregation, whereas dermatan sulfate, alpha-ca rrageenan, and dextran sulfate (m.w. 5,000) showed no inhibition. All of the phosphorylated monosaccharides tested inhibited aggregation wit h ED50 values between 8 and 17 mM, the most potent being mannose-6-pho sphate and fucose-1-phosphate. The nonphosphorylated monosaccharides g lucose and fucose were noninhibitory. The inhibitory effects of fucoid an or dextran sulfate (m.w. 500,000) did not appear to be due to alter ed regulation of L-selectin after stimulation because fucoidan reduced the rate of L-selectin shedding, whereas dextran sulfate had no effec t compared with control. Neither carbohydrate inhibited the binding of formyl peptide to its receptor. However, carbohydrates were able to c ompete with mAb binding to a number of known leukocyte adhesion protei ns. We used endotoxin pretreatment to create L-selectin-deficient neut rophils to study the minimum adhesive requirements for aggregation usi ng two-color fluorescence flow cytometry. Our results implicate a lect inlike contribution to neutrophil aggregation, and suggest that L-sele ctin is the molecule that mediates the carbohydrate-dependent adhesive -event.