Type 3 capsular polysaccharide (Type 3 CPS)

Type 3 capsular polysaccharide is a linear, high-molecular-weight extracellular polysaccharide produced by *Streptococcus pneumoniae* serotype 3. Its repeat unit is a disaccharide composed of glucose (Glc) and glucuronic acid (GlcA), linked via alternating β-(1→4) and β-(1→3) glycosidic bonds, with synthesis catalyzed by the membrane-associated type 3 synthase (Cps3S/Cap3B)[1][5][7][8]. The capsule is critical for bacterial virulence, providing strong resistance to phagocytosis and significantly increasing the organism's ability to cause invasive disease[1][7]. Type 3 CPS is the target for specific pneumococcal vaccines and diagnostic reagents, though it remains a challenging vaccine target due to its poor immunogenicity and the persistence of serotype 3 disease even after vaccine introduction. As an abundant surface polymer, it can also act as a phage receptor in some contexts[6][9].

Other names

Type 3 CPSSerotype 3 capsular polysaccharideS. pneumoniae type 3 capsule

Vaccines: Induce antibodies that opsonize the capsule for immune clearance Monoclonal antibodies: Bind to the capsule, neutralizing its anti-phagocytic effect