Streptococcus pneumoniae capsular polysaccharide serotype 2 (PPS2)

Streptococcus pneumoniae capsular polysaccharide serotype 2 is a complex carbohydrate polymer that forms the outermost layer of the Serotype 2 pneumococcus bacterium. This capsule is a critical virulence factor that protects the pathogen from the host immune system by preventing opsonization and subsequent phagocytosis by macrophages and neutrophils (PubMed: 22434407). Structurally, the serotype 2 polysaccharide is composed of repeating units containing D-glucose, L-rhamnose, and D-glucuronic acid (PubChem: CID 137339798). In clinical medicine, this molecule serves as a primary antigenic target in polyvalent pneumococcal vaccines, such as the 23-valent pneumococcal polysaccharide vaccine (PPV23). Vaccination with this purified polysaccharide induces the production of protective antibodies, thereby preventing invasive pneumococcal disease, particularly in elderly and high-risk populations (CDC: Pneumococcal Disease Vaccination).

Other names

Pneumococcal capsular polysaccharide serotype 2Type 2 pneumococcal polysaccharideCPS2Specific soluble substance IISSS-II

The polysaccharide acts as a T-cell independent antigen that stimulates B-lymphocytes to produce serotype-specific antibodies (IgG and IgM), which facilitate opsonophagocytosis and killing of the bacteria by host immune cells.