Streptococcus pneumoniae capsular polysaccharide serotype 3 (CPS3) (CPS3)

Streptococcus pneumoniae capsular polysaccharide serotype 3 (CPS3) is a complex carbohydrate polymer that serves as a primary virulence factor for the S. pneumoniae bacterium. It is chemically defined as a linear polymer of repeating cellobiuronic acid units, specifically [→4)-β-D-GlcpA-(1→3)-β-D-Glcp-(1→] (PubChem CID 441350). This polysaccharide forms a thick, mucoid capsule that provides a physical barrier against host immune defenses, particularly by inhibiting opsonophagocytosis and complement deposition (PubMed ID 15134104). Serotype 3 is a major cause of invasive pneumococcal disease (IPD), including pneumonia, bacteremia, and meningitis, and is associated with higher mortality rates compared to many other serotypes (CDC, 2023). In the context of pharmacology, CPS3 is the target of several multi-valent pneumococcal vaccines, such as PCV13, PCV15, and PCV20, which utilize the polysaccharide (often conjugated to a carrier protein like CRM197) to stimulate the production of protective antibodies (FDA, 2021). However, CPS3 remains a challenging target because it can be shed during infection and may require higher antibody thresholds for protection than other serotypes (PubMed ID 29439065).

Other names

Pn3PType 3 pneumococcal polysaccharideSSS-IIISerotype 3 capsular polysaccharideStreptococcus pneumoniae type 3 carbohydrate

Induction of serotype-specific opsonophagocytic antibodies (IgG) that bind to the bacterial capsule, facilitating recognition and ingestion by phagocytes and subsequent bacterial clearance.