Streptococcus pneumoniae serotype 2 capsular polysaccharide (CPS2)

Streptococcus pneumoniae serotype 2 capsular polysaccharide is a complex carbohydrate structure that forms the outermost layer of the serotype 2 pneumococcus. It is a critical virulence factor that enables the bacterium to evade the host's innate immune system by inhibiting opsonophagocytosis and complement-mediated killing [4, 12]. Structurally, it consists of a branched hexasaccharide repeat unit containing glucose, rhamnose, and glucuronic acid [5, 10]. This polysaccharide is a primary target for immunization; it is included in the 23-valent pneumococcal polysaccharide vaccine (PPSV23) to induce protective, serotype-specific antibodies [1, 4]. These antibodies facilitate bacterial clearance by promoting opsonization. While highly effective in adults, the purified polysaccharide is a T-cell-independent antigen, which limits its immunogenicity in infants unless conjugated to a carrier protein [4, 16]. Its presence is considered essential for the pathogenicity of the serotype 2 strain, which is a significant cause of invasive diseases such as pneumonia and meningitis in certain global regions [1, 10].

Other names

Pneumococcal polysaccharide serotype 2 [1, 15]S. pneumoniae type 2 CPS [3, 11]Type 2 capsule [10, 12]SII [5]Streptococcus pneumoniae type 2 polysaccharide antigen [15]

Vaccine antigen that induces the production of serotype-specific antibodies, which promote opsonophagocytosis and bacterial clearance [1, 4, 8].