Polymers Containing 6'-sulfated Sialyl Lewis X (6'-su-sLex) Selectively Engage Siglec-8 on Human Eosinophils.

RATIONALE: Siglec-8 is a cell-surface protein with lectin activity that is selectively expressed by eosinophils and mast cells. It preferentially binds the glycan 6'-su-sLeX. Engagement of Siglec-8 with specific antibodies results in eosinophil apoptosis and inhibition of FcɛRI-dependent mast cell mediator release. We determined whether a soluble, synthetic polyacrylamide polymer decorated with 6'-su-sLeX glycan selectively binds to Siglec-8. METHODS: Eosinophils were purified from blood using density gradient centrifugation and negative selection. HEK cells were stably transfected with wild type Siglec-8. Attachment to low (≈40 kDa) and high molecular weight (≈2000 kDa) biotinylated multivalent polyacrylamide polymers decorated with 6'-su-sLeX or structurally related control glycans (e.g., sLeX) was examined in static adhesion assays and by flow cytometry. RESULTS: HEK cell transfectants, but not eosinophils, bound the 40 kDa polymer. Both cell types bound the 2000 kDa polymer. Polymer binding was inhibited by polyclonal Siglec-8 antibody and neither cell type bound any of the control glycan polymers. In whole blood, eosinophils were the only cells to detectably bind the 2000 kDa polymer. HEK cell transfectants bound to plates coated with 6'-su-sLeX polymers but not to control glycan polymers. CONCLUSIONS: Antibodies as well as a large multivalent form of 6'-su-sLeX can be used to selectively engage Siglec-8. Additional studies will be needed to determine whether 6'-su-sLeX polymer or a related glycomimetic can reproduce the biology seen with Siglec-8 antibodies. If so, such agents might be useful for in vitro or in vivo manipulation of eosinophil and mast cell function.