Capsular polysaccharide of Streptococcus pneumoniae serotype 3 (CPS3)

The capsular polysaccharide of Streptococcus pneumoniae serotype 3 (CPS3) is a critical virulence factor and a primary target for pneumococcal vaccines (1.1.1, 1.4.5). Unlike most other pneumococcal serotypes that use a Wzy-dependent assembly pathway, serotype 3 utilizes a synthase-dependent mechanism, resulting in a thick, mucoid capsule that is not covalently linked to the cell wall and can be shed into the surrounding environment (1.2.2, 1.4.3). This abundant polysaccharide layer protects the bacterium from host immune defenses by inhibiting complement-mediated opsonization and preventing phagocytosis by neutrophils and macrophages (1.1.1, 1.4.2). In clinical settings, serotype 3 is associated with severe manifestations of pneumococcal disease, including invasive pneumonia, meningitis, and bacteremia, often carrying a higher mortality rate compared to other serotypes (1.3.2, 1.5.3). Therapeutic intervention primarily involves the use of conjugate vaccines (e.g., PCV13, PCV15, PCV20) and polysaccharide vaccines (PPSV23), which aim to induce serotype-specific antibodies that facilitate bacterial clearance (1.3.1, 1.5.1). However, serotype 3 remains a significant challenge due to its ability to escape vaccine-induced immunity, likely through the shedding of its capsule which can neutralize antibodies before they reach the bacterial surface (1.3.4, 1.5.4).

Other names

Serotype 3 capsular polysaccharidePneumococcal polysaccharide serotype 3SSS-IIIType 3 capsular polysaccharidePn3P

Induction of serotype-specific humoral immunity, where vaccine-elicited antibodies bind to the capsular polysaccharide to facilitate opsonophagocytosis and complement-mediated killing of the bacteria.