Streptococcus pneumoniae capsular polysaccharide of serotypes 1, 4, 5, 6B, 7F, 9V, 14, 18C, 19F, and 23F

The *Streptococcus pneumoniae* capsular polysaccharides from serotypes **1**, **4**, **5**, **6B**, **7F**, **9V**, **14**, **18C**, **19F**, and **23F** are complex carbohydrate structures forming the outermost layer ("capsule") on the bacterial cell wall. These capsules are major virulence factors that protect pneumococcus from host immune responses by inhibiting phagocytosis. Each serotype's capsule has a unique chemical structure that determines its immunologic identity; more than one hundred such types exist overall. These ten specific serotypes are among those most frequently associated with invasive pneumococcal diseases—including pneumonia, meningitis, bacteremia—and have been prioritized for inclusion in widely used pneumococcal vaccines due to their prevalence and clinical impact across different age groups and regions.[3][5] Vaccines containing purified or conjugated forms of these capsular antigens stimulate protective antibody responses that reduce disease incidence.[1][3] Measurement of antibodies against these specific capsules is also used diagnostically to assess immune competence or vaccine efficacy. While not a "receptor" or "enzyme," the *capsular polysaccharide* is an established therapeutic target because it is directly targeted by both natural immunity and all current pneumococcal vaccines.[6]

Other names

Pneumococcal capsular polysaccharides (serotypes as listed)S. pneumoniae capsule (serotype-specific)Pneumococcal vaccine antigens (for these serotypes)

Vaccines induce production of anti-capsular IgG antibodies that promote opsonization and clearance by phagocytes[1][3]