Streptococcus pneumoniae surface and capsular antigens (Spn antigens)

Streptococcus pneumoniae surface and capsular antigens are the primary molecular determinants of virulence for the pneumococcus, a major cause of pneumonia, meningitis, and sepsis worldwide (WHO, 2019). The capsular polysaccharide (CPS) is the most critical antigen, forming a protective layer that prevents opsonization by complement and inhibits phagocytosis by host immune cells (NIH, 2022). Beyond the capsule, surface proteins such as Pneumococcal surface protein A (PspA) and Pneumococcal surface protein C (PspC) play essential roles in adhering to host respiratory tissues and evading the innate immune response (Frontiers, 2022). These antigens serve as the basis for current pneumococcal vaccines, which are designed to elicit protective, serotype-specific antibody responses (ASM, 2021). Conjugate vaccines (PCVs) link these polysaccharides to carrier proteins to induce a T-cell dependent immune response, which is particularly effective in infants and young children (NIH, 2021). However, the high diversity of pneumococcal serotypes—with over 100 identified to date—presents a significant challenge for vaccine design and has led to the phenomenon of serotype replacement in vaccinated populations (Frontiers, 2022).

Other names

Pneumococcal antigensCapsular polysaccharides (CPS)Pneumococcal surface proteinsPneumococcal surface protein A (PspA)Pneumococcal surface protein C (PspC)Pneumococcal surface adhesin A (PsaA)Choline-binding proteins

Vaccines targeting these antigens work by stimulating B-lymphocytes to produce serotype-specific antibodies (IgG). These antibodies bind to the capsular polysaccharides or surface proteins, facilitating opsonization and subsequent phagocytosis by neutrophils and macrophages, thereby preventing bacterial invasion and systemic spread (NIH, 2022; Frontiers, 2022).