Bacterial polysaccharide antigen

Bacterial polysaccharide antigens are complex, high-molecular-weight carbohydrate structures found on the surface of many pathogenic bacteria, appearing primarily as capsules or as the O-antigen component of lipopolysaccharides. These molecules serve as critical virulence factors by enabling bacteria to evade the host's innate immune system through the inhibition of phagocytosis and the prevention of complement-mediated killing. Additionally, they facilitate bacterial adhesion to host tissues and contribute to the formation of protective biofilms. Because they are highly exposed and often unique to specific bacterial strains or serotypes, these polysaccharides are primary targets for immunization. Vaccines targeting these antigens work by inducing the production of protective antibodies that facilitate opsonization and clearance of the encapsulated bacteria. While plain polysaccharide vaccines are available, they are often poorly immunogenic in young children due to their T-cell-independent nature; consequently, many modern therapies utilize glycoconjugate vaccines, which link the polysaccharide to a carrier protein to elicit a robust and long-lasting T-cell-dependent immune response.

Other names

Bacterial polysaccharideCapsular polysaccharideCPSO-antigenExopolysaccharideBacterial surface carbohydrate

Vaccines targeting these antigens induce the production of serotype-specific antibodies (IgG and IgM) that bind to the bacterial surface, facilitating opsonization, enhanced phagocytosis, and complement-mediated bactericidal activity.