Streptococcus pneumoniae capsular polysaccharide serotype 6B (CPS 6B)

The Streptococcus pneumoniae capsular polysaccharide serotype 6B is a key surface structure on this Gram-positive bacterium, forming a protective capsule that shields it from host immune clearance. Composed of repeating units of galactose-glucose-rhamnose-ribitol-phosphate with a characteristic 1→4 rhamnose-ribitol linkage distinguishing it from serotype 6A, this polysaccharide is synthesized via the Wzy-dependent pathway involving glycosyltransferases, flippase (Wzx), and polymerase (Wzy), and anchored to peptidoglycan via a direct 1,6-glycosidic bond at the reducing-end glucose. As the dominant virulence factor, it promotes immune evasion by inhibiting phagocytosis, resisting non-opsonic neutrophil killing, and facilitating nasopharyngeal colonization and invasive disease like pneumonia and sepsis, particularly in children and the elderly. Serotype 6B has historically been prevalent in invasive infections, prompting its inclusion in vaccines such as PPV23 (purified CPS) and conjugate vaccines like PCV13, which elicit protective antibodies for opsonophagocytic activity. These vaccines have reduced 6B-related disease incidence, though challenges include age-dependent efficacy and shifts in serotype epidemiology.

Other names

serotype 6B capsular polysaccharide6B polysaccharide (PS 6B)pneumococcal capsule serotype 6B

Induces serotype-specific antibody production for opsonophagocytic killing of encapsulated S. pneumoniae; conjugation to carrier proteins enhances immunogenicity in infants by promoting T-cell dependent responses