Streptococcus pneumoniae (S. pneumoniae) employs several strategies to avoid destruction by phagocytes:
Capsule formation: S. pneumoniae produces a polysaccharide capsule, which inhibits phagocytosis by preventing the activation of complement proteins and blocking the binding of phagocytic receptors.
Immunoglobulin A1 (IgA1) protease production: S. pneumoniae secretes an enzyme that cleaves IgA1, an antibody that plays a key role in mucosal immunity, reducing its effectiveness.
Complement evasion: S. pneumoniae can bind to complement regulatory proteins, such as factor H, to prevent the activation of the complement cascade.
Phagocyte membrane disruption: S. pneumoniae can insert its cholesterol-binding toxin, pneumolysin, into the phagocyte membrane, causing membrane disruption and inhibiting phagocytosis.
Inhibition of phagolysosome fusion: S. pneumoniae can prevent the fusion of phagosomes with lysosomes, which contain digestive enzymes, thereby avoiding degradation.
Modulation of cytokine responses: S. pneumoniae can influence cytokine production, suppressing the activation of immune cells and reducing the effectiveness of the immune response.