Streptococcus pneumoniae serotype 18C capsular polysaccharide

The Streptococcus pneumoniae serotype 18C capsular polysaccharide is a surface-exposed carbohydrate polymer that encapsulates the bacterium S. pneumoniae of the specific immunological type "serotype 18C." This capsule is composed of repeating oligosaccharide units whose precise structure defines the unique antigenicity and immunogenicity of this serotype. The capsule serves as a major virulence factor by protecting bacteria from phagocytosis by host immune cells, thereby facilitating invasive disease such as pneumonia, meningitis, and sepsis. More than ninety distinct pneumococcal capsules exist; each is distinguished by its chemical structure and corresponding genetic locus. Serotype-specific capsules like that of type 18C are critical targets for both diagnostic typing and vaccine development—purified or conjugated forms are included in multivalent pneumococcal vaccines to induce protective immunity against infection with strains expressing this capsule. The biosynthesis involves multiple glycosyltransferases encoded at the cps locus; regulation can vary between nutrient-rich versus restricted environments, affecting expression levels among different serotypes including 18C[1][3][4]. The presence or absence—and structural features—of these capsules influence epidemiology, carriage prevalence, invasiveness potential, and response to vaccination efforts worldwide[2][4][6].

Other names

Pneumococcal serotype 18C capsular polysaccharideS. pneumoniae type 18C capsuleType 18C pneumococcal CPS

Induction of protective antibodies that promote opsonization and clearance by the immune system when used as a vaccine component[6]