Carbohydrate-carbohydrate interaction provides adhesion force and specificity for cellular recognition

The adhesion force and specificity in the first experimental evidence for cell-cell recognition in the animal kingdom were assigned to marine sponge cell surface proteoglycans. However, the question whether the specificity resided in a protein or carbohydrate moiety could not yet be resolved. Here, the strength and species specificity of cell-cell recognition could be assigned to a direct carbohydrate-carbohydrate interaction. Atomic force microscopy measurements revealed equally strong adhesion forces between glycan molecules (190-310 piconewtons) as between proteins in antibody-antigen interactions (244 piconewtons). Quantitative measurements of adhesion forces between glycans from identical species versus glycans from different species confirmed the species specificity of the interaction. Glycan-coated beads aggregated according to their species of origin, i.e., the same way as live sponge cells did. Live cells also demonstrated species selective binding to glycans coated on surfaces. These findings confirm for the first time the existence of relatively strong and species-specific recognition between surface glycans, a process that may have significant implications in cellular recognition.