Streptococcus pneumoniae capsular polysaccharide (13 serotypes) (CPS)

The capsular polysaccharide (CPS) of Streptococcus pneumoniae is a complex carbohydrate layer that encapsulates the bacterial cell, serving as its most critical virulence factor. Its primary biological function is to inhibit the host's immune response by preventing opsonization and phagocytosis, thereby allowing the bacteria to survive and disseminate within the host (StatPearls, 2023). There are more than 100 known serotypes of S. pneumoniae, each defined by a unique polysaccharide structure. The 13 serotypes targeted by the PCV13 vaccine (1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F) were historically responsible for the majority of invasive pneumococcal diseases, such as meningitis and bacteremia, as well as community-acquired pneumonia (CDC, 2022). In the context of pharmacology, these polysaccharides are used as vaccine antigens; when conjugated to a carrier protein, they stimulate a T-cell dependent immune response that produces high-affinity antibodies and immunological memory (PubMed, PMID: 25883065). These antibodies bind to the CPS on the surface of live bacteria, facilitating their clearance via the complement system and phagocytic cells.

Other names

Pneumococcal capsular polysaccharideS. pneumoniae CPSPCV13 antigensPneumococcal surface polysaccharidePneumococcal capsule

Induction of serotype-specific opsonophagocytic antibodies through T-cell dependent (conjugate) or T-cell independent (polysaccharide) immune pathways, leading to bacterial clearance.