Pneumococcal Neuraminidases Increase Platelet Killing by Pneumolysin

Area of Science:

• Microbiology
• Immunology
• Hematology

Background:

• Platelets seal gaps in inflamed endothelium to prevent fluid extravasation, reducing pneumonia-associated respiratory distress.
• Streptococcus pneumoniae, a leading cause of pneumonia, produces pneumolysin (PLY) and neuraminidases.
• Neuraminidases cleave sialic acid residues from platelet glycoproteins, potentially affecting PLY interactions.

Purpose of the Study:

• To investigate the impact of pneumococcal neuraminidase-induced desialylation on platelet binding and pore formation by pneumolysin (PLY).
• To evaluate the efficacy of therapeutic immunoglobulin G preparations in mitigating these effects.

Main Methods:

• Human platelets were incubated with purified neuraminidases and PLY, or S. pneumoniae strains and mutants.
• Platelet desialylation, PLY binding, and pore formation were quantified using flow cytometry.
• The inhibitory effects of intravenous immunoglobulin (IVIG) were assessed.

Main Results:

• Pneumococcal neuraminidases effectively desialylated platelet glycoproteins, enhancing PLY binding and pore formation.
• Desialylation significantly increased PLY-induced platelet pore formation.
• Polyvalent IVIG demonstrated significant inhibition of platelet desialylation and reduced PLY-mediated pore formation.

Conclusions:

• Pneumococcal neuraminidases are critical virulence factors that promote platelet damage by facilitating PLY binding and pore formation.
• Neuraminidases and PLY act synergistically to compromise platelet integrity.
• Therapeutic interventions using human polyvalent immunoglobulin G show promise for treating severe pneumococcal pneumonia.