Small saccharides are not normally immunogenic, unless they are conjugated to a carrier protein. Hence, they are usually linked to a protein in ways that the structural integrity of the saccharide is maintained.
Structural Integrity
Carbohydrates are normally found in aqueous solutions as cyclic structures, i.e. pyranoside or furanoside types of rings. However, under certain conditions, these rings can open to yield linear chains; forms that are not found naturally. Also, chemical modifications such as oxidation can open the rings to deliver new derivatives and allow high degree of conjugation. These changes would impact recognition of the sugars by antibodies and cellular receptors, i.e. lectins, making them physiologically and/or immunologically ineffective.
What protein carriers can be used?
In principle any protein that is non-glycosylated is fine as a carrier. Proteins that are glycosylated as KLH and ovalbumin are not recommended, as their oligosaccharides may also induce the formation of antibodies, which would interfere with the screening process, in the case of looking for a specific monoclonal. Proteins as tetanus toxoids, edestin and serum albumin are recommended as carriers.
What density of the ligand is desirable?
While normally we would like to have 20 to 30 sugar residues per mole of protein, the binding is usually in the order of 4 to 10 residues per mole of protein which is sufficient to induce an effective immune response.
How Bio-Synthesis perform the conjugation?
In principle we try to avoid procedures that alter the cyclic nature of the sugars. While somewhat more complicated, these methods deliver conjugates where the sugars are present as they are found normally in the body and not as a derivative that maybe physiologically non-functional.
Types of chemistry used by Bio-Synthesis
The selected chemical approach depends on the sugar in question. We look for groups that allow chemical modifications without altering the overall sugar structure, while avoiding procedures that will destroy their native characteristics.