Tetra- and Hexavalent Siglec-8 Ligands Modulate Immune Cell Activation.

Area of Science:

• Carbohydrate-protein interactions
• Immunology
• Glycobiology

Background:

• Carbohydrate-binding proteins often exhibit low affinity due to shallow, solvent-exposed binding sites.
• Nature utilizes multivalency to enhance binding interactions through simultaneous engagement of multiple epitopes.

Purpose of the Study:

• To synthesize and thermodynamically characterize oligovalent ligands for Siglec-8 (sialic acid-binding immunoglobulin-like lectin 8).
• To investigate the potential of these ligands to modulate immune cell activation.

Main Methods:

• Synthesis of various oligovalent ligands targeting Siglec-8.
• Thermodynamic analysis of ligand-protein binding.
• Assessment of Siglec-8 binding and immune cell activation modulation on eosinophils and mast cells.

Main Results:

• Binding affinity was enhanced with increasing ligand valency, with an increasing entropic penalty.
• Tetravalent, hexavalent, and multivalent ligands showed agonistic binding to Siglec-8 on immune cells.
• Low oligovalent ligands induced biological effects, while monovalent ligands exhibited an antagonistic effect despite similar binding affinity.

Conclusions:

• Oligovalency is a successful strategy to enhance Siglec-8 binding and function.
• Ligand valency influences both binding thermodynamics and biological activity (agonism vs. antagonism).
• Low oligovalent ligands can trigger Siglec-8-mediated immune cell responses.