Fig. 2: The four possible glycan activation categories.

The basic structures of resultant glycoconjugates are shown. Glycan chains are depicted as strings of red squares, where each square indicates an epitope (see Fig. 1). Random activation of glycans results in cross-linked medium-sized oligosaccharide (OS) glycoconjugates (a) or cross-linked long-chain polysaccharide (PS) conjugates (b). Activation of glycan termini yields end-linked medium-sized OS glycoconjugates (c) or end-linked long-chain PS conjugates (d). Rarely performed activation of both ends of glycan chains may yield vaccines with a low-to-intermediate level of cross-linking. In current practice, b and c result in better-optimized glycoconjugate vaccines (see text for details).