Pneumococcal capsular polysaccharide serotype 3 (CPS3)

Pneumococcal capsular polysaccharide serotype 3 (CPS3) is a complex carbohydrate polymer composed of repeating [→3)-β-D-GlcA-(1→4)-β-D-Glc-(1→] units that constitutes the protective capsule of Streptococcus pneumoniae serotype 3 (PubMed: 26251961). It serves as a critical virulence factor by providing an antiphagocytic barrier and inhibiting the deposition of complement C3b on the bacterial surface (PubMed: 29030928). Serotype 3 is characterized by a unique mucoid phenotype and the ability to shed its capsule, which may contribute to its persistence and high mortality rates in invasive diseases like pneumonia and meningitis (CDC: Pneumococcal Disease). CPS3 is a primary target for several vaccines, including the 13-valent, 15-valent, and 20-valent conjugate vaccines (PCV13, PCV15, PCV20) and the 23-valent polysaccharide vaccine (PPSV23) (FDA: Prevnar 20). Despite its inclusion in these vaccines, serotype 3 continues to be a leading cause of disease, often showing lower vaccine-induced protection compared to other serotypes (PubMed: 32163543).

Other names

Streptococcus pneumoniae serotype 3 capsular polysaccharideType 3 pneumococcal polysaccharideSSS-IIISpecific Soluble Substance IIIPneumococcal polysaccharide serotype 3

Induction of serotype-specific opsonophagocytic antibodies (IgG) that bind to the polysaccharide capsule, facilitating bacterial recognition and clearance by host phagocytes (StatPearls: Pneumococcal Vaccine).