Streptococcus pneumoniae serotype 20 capsular polysaccharide (Spn20 CPS)

The Streptococcus pneumoniae serotype 20 capsular polysaccharide is a high-molecular-weight carbohydrate polymer that encapsulates the bacterium, serving as its primary defense mechanism against the host immune system. By masking surface proteins and inhibiting complement-mediated opsonization, the polysaccharide allows the pathogen to evade phagocytosis and disseminate within the host (Geno et al., 2015). This molecule is a key therapeutic target in the development of vaccines designed to prevent invasive pneumococcal diseases, including pneumonia, meningitis, and sepsis. It is a constituent of the 23-valent polysaccharide vaccine (PPSV23) and the newer 20-valent and 21-valent conjugate vaccines, PCV20 and PCV21 (CDC, 2024; FDA, 2021). In conjugate vaccines, the polysaccharide is covalently linked to a carrier protein (e.g., CRM197) to enhance its immunogenicity by recruiting T-cell help, which is vital for establishing long-term memory and protection in infants and the elderly (Merck, 2024). Upon vaccination, the immune system produces serotype-specific antibodies that recognize the polysaccharide, facilitating the opsonization and subsequent destruction of the bacteria by phagocytic cells. Monitoring the efficacy of drugs targeting this polysaccharide involves measuring serotype-specific IgG levels and opsonophagocytic activity (OPA) titers. A significant therapeutic challenge associated with this target is serotype replacement, where the reduction of vaccine-type strains in the population may lead to an increase in disease caused by non-vaccine serotypes.

Other names

Pneumococcal polysaccharide serotype 20Type 20 pneumococcal polysaccharideCPS20S. pneumoniae serotype 20 capsular polysaccharide

Induction of serotype-specific humoral immunity, specifically the production of opsonizing antibodies that facilitate phagocytosis and clearance of the bacteria.