S. pneumoniae Cell Wall Polysaccharide Antigen

Streptococcus pneumoniae can cause pneumonia, otitis media and meningitis. It is transmitted through close contact and aerosols, with attachment to nasopharyngeal mucosal epithelial cells being an important step in the pathogenesis. Surface proteins such as pneumococcal surface adhesin A (PsaA) are involved in the process of bacterial attachment to host cells. The next pathogenic step is infection in the lungs, bloodstream, or other sites, and this mode of establishment depends on host susceptibility, regulation of bacterial gene expression, and opportunities for interaction between Streptococcus pneumoniae and host components. Streptococcus pneumoniae utilizes a variety of strategies to evade host immune defenses, pneumolysin promotes bacterial uptake and escape from lysosomes when the bacterium binds to mannose receptor C-type 1 on dendritic cells, and pneumococcal surface protein A (PspA) and outer polysaccharide capsule in the bloodstream help the bacterium survive. PspA shortens pneumococcal lysis by inhibiting complement C3 deposition, and outer polysaccharide capsules help prevent bacterial phagocytosis by shielding pneumococcal surface antigens from C3 and reducing adhesion in neutrophil extracellular traps.

A key feature of pneumococci is their complex cell wall structure, which plays a key role in bacterial pathogenicity and interaction with the host immune system. The outermost layer of this bacterium is the capsular polysaccharides, which consists of more than 90 chemically distinct molecules. Underneath the capsular polysaccharide is the cell wall, the main structural component of which is peptidoglycan, a reticulated polymer formed by cross-linking alternating N-acetylmuramic acid and N-acetylglucosamine residues through short peptide chains, which provides structural integrity of the cell and protection against osmotic lysis. Covalently attached to the peptidoglycan is alginate, another key component of the pneumococcal cell wall, and the phosphorylcholine (PCho) residue modification of alginate in pneumococci serves as a binding site for the host proteins C-reactive protein and platelet-activating factor receptors.

Figure 1. Diagram of the cell wall complex of pneumococci
(Source: Vollmer W, et al. 2019)

At the same time, cell wall polysaccharides of Streptococcus pneumoniae can act as an attachment factor to help S. pneumoniae attach to host cells and trigger infection. In conclusion, the cell wall of Streptococcus pneumoniae is a complex and multifunctional structure that is critical to the survival and pathogenicity of the bacterium, and understanding the detailed composition and biology of the pneumococcal cell wall is important for the development of novel antimicrobial and vaccine strategies against this important human pathogen.

S. pneumoniae CWPS Antigen
Streptococcus pneumoniae CWPS Antigen