Streptococcus pneumoniae capsular polysaccharide (Capsule) (CPS)

The Streptococcus pneumoniae capsular polysaccharide (CPS) is the principal surface structure of this Gram-positive bacterium and is essential for its ability to evade host immunity and cause invasive disease[5][7][10]. CPS is composed of repeating oligosaccharide units, whose composition and structure define more than 100 serotypes and determine epidemiology, immunity, and vaccine effectiveness[5][7][10]. It functions as a major antigenic target and virulence factor by shielding underlying bacterial proteins and cell wall from immune recognition, thereby preventing opsonization, complement deposition, and phagocytosis[5][6][10][3]. The diversity of capsule structures poses ongoing challenges for vaccine development and disease control, as immunity and protection are serotype-specific and widespread vaccine use alters serotype prevalence[5][6][10]. Capsule biosynthesis involves multiple enzymes, with the Wzy-dependent pathway predominating; CPS is covalently linked to the cell wall or membrane via specific glycosidic linkages[7]. Current interventions include polysaccharide-based vaccines and monoclonal antibodies that target the capsule, enabling opsonic immune responses for pathogen clearance[5][3][10]. Capsule characteristics, such as thickness and composition, are also used as biomarkers to inform clinical and epidemiological strategies[2][10].

Other names

Pneumococcal capsulePneumococcal capsular polysaccharideS. pneumoniae capsuleS. pneumoniae CPS

Antibodies/vaccine-induced immunity: induce opsonization and phagocytosis by antibodies directed against the capsule, promote complement deposition, block capsule’s protective effects; Direct immune clearance: antibody and complement targeting leads to bacterial killing via enhanced recognition by phagocytes; Serotype-specific immunity: protection is highly specific to the polysaccharide structure of each serotype