Group B Streptococcus serotype III capsular polysaccharide (GBS type III CPS)

Group B Streptococcus serotype III capsular polysaccharide is a complex carbohydrate antigen found on the surface of *Streptococcus agalactiae* (Group B Streptococcus) strains classified as serotype III[1][2][3][4]. Its repeating unit consists of a backbone of glucose, N-acetylglucosamine, and galactose, with a sialic acid–galactose disaccharide side chain linked to the backbone N-acetylglucosamine[3][4]. The sialic acid residues confer a negative charge and play a key role in epitope conformation and immune evasion[1][2]. This capsular polysaccharide is a critical virulence factor that protects the bacterium from host complement and phagocyte-mediated killing, and it is the major antigenic component targeted by candidate glycoconjugate vaccines to prevent GBS disease, especially in neonates where serotype III is a predominant cause of meningitis and sepsis[1][2][3][4][5]. Mapping of protective epitopes and understanding of its structure have led to the design of vaccine immunogens capable of eliciting opsonic and protective antibodies in humans, confirming its role as a validated vaccine target[1][2][5].

Other names

GBS type III capsular polysaccharideGroup B Streptococcus type III CPSGBS CPS IIIType III polysaccharide (in GBS context)GBS PSIII

Induction of specific antibody responses (vaccine mechanism: polysaccharide, often conjugated to carrier protein, elicits anti-capsular antibodies facilitating opsonophagocytic clearance of GBS)[1][2][5]. Antibodies bind sialic acid-dependent epitopes on the polysaccharide, promoting phagocytosis and killing of GBS[1][2].