Gosset Bacterial polysaccharide capsule antigen Overview
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.
Mechanism of Action
Induction of protective antibodies (vaccines stimulate anti-capsular/bacterial polysaccharide antibody production); Opsonization and enhanced phagocytosis; Complement activation
Biological Functions
Disease Associations
Safety Considerations
- Poor immunogenicity in young children when used as plain polysaccharide (not conjugated)
- Potential for serotype replacement
- Antigenic diversity and switching limits universal vaccine efficacy
- Risk of adverse reactions to vaccine components in rare cases
Interacting Drugs
Associated Biomarkers
| Biomarker |
|---|
| Capsular serotyping (basis for vaccine selection and coverage) |
| Anti-capsular antibody titers (for efficacy monitoring) |