Streptococcus pneumoniae capsular polysaccharide serotype 15A (CPS 15A)

Streptococcus pneumoniae capsular polysaccharide serotype 15A is a complex carbohydrate structure located on the outermost surface of the bacterium. It serves as a critical virulence factor by protecting the pathogen from host immune defenses, particularly by inhibiting opsonophagocytosis and complement deposition. Serotype 15A is part of serogroup 15, which also includes serotypes 15B, 15C, and 15F; however, 15A is chemically distinct, characterized by a flexible linear pentasaccharide repeating unit composed of D-galactose, D-glucose, 2-acetamido-2-deoxy-D-glucose, phosphate, and glycerol. This polysaccharide is a primary target for next-generation pneumococcal conjugate vaccines, such as the 21-valent vaccine (PCV21/Capvaxive), which was specifically designed to address serotypes like 15A that have become more prevalent due to serotype replacement following the widespread use of earlier vaccines (like PCV13 and PCV20). Immunization with 15A-containing vaccines induces serotype-specific antibodies that facilitate bacterial clearance and provide protection against invasive pneumococcal diseases, including pneumonia, meningitis, and bacteremia. The inclusion of serotype 15A in newer formulations significantly expands the coverage of vaccines against the strains currently responsible for a high burden of disease in adults.

Other names

Pneumococcal serotype 15A polysaccharideS. pneumoniae type 15A capsular polysaccharideAmerican type 30 pneumococcal polysaccharideSerotype 15A CPS

Active immunization; induction of serotype-specific antibodies (measured by opsonophagocytic activity) that facilitate bacterial clearance by the host immune system.