Group B Streptococcus serotype Ib capsular polysaccharide antigen (GBS serotype Ib CPS)

The Group B Streptococcus (GBS) serotype Ib capsular polysaccharide (CPS) is a primary virulence factor of Streptococcus agalactiae, a leading cause of neonatal sepsis and meningitis. This polysaccharide forms a protective layer that inhibits host complement deposition and prevents opsonophagocytosis, allowing the bacteria to evade the innate immune system. A key structural feature of the Ib CPS is the presence of terminal sialic acid residues, which mimic human cell surface glycans and further facilitate immune evasion. Serotype Ib is one of the most prevalent serotypes responsible for invasive GBS disease worldwide, including neonatal infections and maternal complications. In clinical development, this antigen is a central component of multivalent conjugate vaccines, such as the hexavalent GBS6 vaccine, where it is conjugated to a carrier protein to induce a T-cell dependent immune response. Vaccination of pregnant women with these conjugates aims to generate high titers of serotype-specific IgG antibodies that are transferred transplacentally to the fetus, providing passive immunity to the neonate during the period of highest vulnerability.

Other names

Streptococcus agalactiae serotype Ib capsular polysaccharideGBS Ib CPSType Ib capsular polysaccharideGroup B Streptococcus type Ib antigen

Induction of serotype-specific opsonophagocytic IgG antibodies that facilitate bacterial clearance and provide passive immunity to neonates via transplacental transfer.