Streptococcus pneumoniae capsular polysaccharide (CPS) (CPS)

Streptococcus pneumoniae capsular polysaccharides (CPS) are complex carbohydrates that form the outermost layer of the bacterium, serving as its primary virulence factor by inhibiting opsonophagocytosis by host immune cells (Geno et al., 2015, Clin Microbiol Rev). There are more than 100 distinct serotypes of S. pneumoniae, each characterized by a unique polysaccharide structure that determines its antigenicity and invasiveness (Geno et al., 2015; WHO, 2022). These polysaccharides are the target antigens for all current pneumococcal vaccines, including pneumococcal polysaccharide vaccines (PPSV) and pneumococcal conjugate vaccines (PCV) (CDC, 2023). PPSVs, such as PPSV23, contain purified polysaccharides that induce a T-cell independent B-cell response, whereas PCVs, such as PCV13 or PCV20, chemically link the polysaccharides to a carrier protein to induce a T-cell dependent response, providing better protection in infants and establishing immunological memory (Pollard et al., 2009, Nat Rev Immunol). While highly effective at reducing invasive pneumococcal disease, the use of these antigens in vaccines has led to serotype replacement, where non-vaccine serotypes increase in prevalence within the population (CDC, 2023; WHO, 2022).

Other names

Pneumococcal capsular polysaccharidePnCPS. pneumoniae CPSCapsular antigen

Induction of serotype-specific opsonophagocytic antibodies that facilitate bacterial clearance; conjugate vaccines additionally recruit T-cell help via carrier proteins to induce high-affinity antibodies and memory B cells (Pollard et al., 2009, Nat Rev Immunol).