Capsular polysaccharide type 8 (CP8)

Capsular polysaccharide type 8 (CP8) is a complex carbohydrate structure forming the capsule of a subset of pathogenic bacteria such as *Staphylococcus aureus* (where CP8 is the most prevalent capsule type among clinical isolates) and *Streptococcus pneumoniae* (type 8). The capsule is composed of repeating trisaccharide units: *N*-acetyl-d-mannosaminuronic acid (ManNAcA), *N*-acetyl-l-fucosamine (l-FucNAc), and *N*-acetyl-d-fucosamine (d-FucNAc), with specific structural features distinguishing it from other capsule types. The genes required for CP8 biosynthesis are typically organized in the cap8 operon (in *S. aureus*) and the cap8 gene cluster (in *S. pneumoniae*), encoding enzymes for glycopolymer assembly, transport, and regulation. CP8 confers resistance to phagocytosis, enhancing bacterial survival and virulence. Vaccines targeting CP8, particularly conjugate vaccines utilizing synthetic or isolated polysaccharide antigen conjugated to carrier proteins such as CRM197, elicit robust antibody responses and are actively being developed and tested. Detection of anti-CP8 antibodies and the presence of cap8-related genes are clinically useful biomarkers. Safety concerns include the need for conjugation to overcome poor immunogenicity in certain patient groups and the possibility of capsule switching undermining vaccine efficacy.

Other names

CP8Type 8 capsuleType 8 capsular polysaccharideCap8 polysaccharide

Induction of anti-CP8 antibodies (protective humoral immune response by vaccine or mAbs) Opsonization leading to enhanced phagocytosis when antibodies are present