Streptococcus pneumoniae Capsular Polysaccharide Antigen (Type 18C) (CPS 18C)

The Streptococcus pneumoniae capsular polysaccharide antigen, specifically type 18C, is a serotype-specific carbohydrate structure that forms the outermost layer (capsule) of the bacterium. This capsule is a major virulence factor and plays a critical role in protecting the bacterium from host immune responses, particularly by inhibiting phagocytosis and interfering with complement-mediated clearance mechanisms. Type 18C is included among vaccine-targeted serotypes due to its role in invasive pneumococcal diseases such as pneumonia, meningitis, bacteremia, otitis media, and sinusitis. Purified type-specific polysaccharides like 18C are used for vaccine development/evaluation as well as diagnostic assays tracking epidemiology. Each capsular type has a unique repeating oligosaccharide unit structure determined by genes within the cps locus; structural diversity arises from genetic variation within these loci.

Other names

S. pneumoniae Type 18C Capsular PolysaccharidePneumococcal Capsular Polysaccharide Type 18CType 18C Capsular Polysaccharide Antigen

Vaccines stimulate the production of serotype-specific antibodies that opsonize bacteria and promote phagocytosis and complement-mediated killing.