Bacterial polysaccharide capsule antigen

Bacterial polysaccharide capsule antigens are high-molecular-weight carbohydrate structures that form a capsule surrounding the surface of many pathogenic bacteria, including both Gram-negative and Gram-positive species. These capsular antigens act as major virulence factors by enabling bacteria to evade phagocytosis and the host immune response, facilitate survival under environmental stress, contribute to adhesion and biofilm formation, and modulate immune responses. Each bacterial species—and even different strains within a species—can produce antigenically distinct capsular polysaccharides (serotypes), which serve as the basis for serological classification and vaccine development. Capsular polysaccharide antigens are the targets of multiple antibacterial vaccines (such as those for Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b), which work by inducing specific antibody responses that facilitate opsonization and clearance of encapsulated bacteria. The high antigenic diversity and ability of bacteria to vary their capsule composition present ongoing challenges for universal vaccine design and efficacy.

Other names

Capsular polysaccharide antigenCapsular antigen (K antigen)CPS antigenBacterial capsule antigen

Induction of protective antibodies (vaccines stimulate anti-capsular/bacterial polysaccharide antibody production); Opsonization and enhanced phagocytosis; Complement activation