Capsular polysaccharide antigen of Streptococcus pneumoniae (CPS)

The capsular polysaccharide antigen of Streptococcus pneumoniae is a complex, high-molecular-weight carbohydrate polymer forming a discrete capsule surrounding the bacterial cell, and is the dominant surface feature and major virulence factor of the organism. The capsule inhibits innate immune mechanisms such as neutrophil phagocytosis and complement deposition, promoting bacterial survival in the host. There are at least 98 structurally and antigenically distinct capsular serotypes, each encoded by a unique set of genes at the cps locus. These antigens are the immunological basis for current pneumococcal vaccines, which protect by inducing serotype-specific antibodies that opsonize and clear the pathogen. Widespread vaccine use has led to a decrease in diseases caused by vaccine-included serotypes and to an increase in non-vaccine serotypes (serotype replacement). The diversity, complexity, and critical biological functions of the capsular polysaccharide make it a primary target for therapeutic and preventive strategies against Streptococcus pneumoniae infection.

Other names

pneumococcal capsular polysaccharidepneumococcal capsule antigenPPScapsule antigen

Induction of type-specific protective antibodies that opsonize bacteria and promote phagocytosis (vaccine mechanism); Complement-mediated killing via antibody binding to capsule