Bacterial pore-forming toxin pneumolysin drives pathogenicity through host extracellular vesicles released during...

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Streptococcus pneumoniae is a major cause of respiratory illness and death worldwide.
• Pneumolysin (PLY), a pore-forming cytotoxin, is a key virulence factor in pneumococcal infections.

Purpose of the Study:

• To investigate the role of pneumolysin (PLY) in the release and function of extracellular vesicles (EVs) during Streptococcus pneumoniae infection.
• To determine the pathogenic mechanisms mediated by PLY-induced EVs.

Main Methods:

• Utilized human THP-1 monocytes and pneumococcal strains (wild-type and PLY mutant).
• Analyzed EV shedding, cytotoxicity, hemolysis, and protein content (proteomics).
• Assessed dendritic cell maturation and immune priming.
• Employed zebrafish and mouse models for in vivo validation.

Main Results:

• PLY upregulated the shedding of extracellular vesicles (EVs) containing membrane-bound toxin from monocytes.
• PLY-EVs induced dose-dependent cytotoxicity and hemolysis in dendritic cells.
• Proteomics revealed enrichment of inflammatory host proteins (IFI16, NLRC4, PTX3, MMP9) in PLY-EVs.
• EVs from PLY-challenged cells promoted dendritic cell maturation and primed them for infection.
• In vivo studies showed PLY-EVs caused mortality and edema in zebrafish, and lung damage in mice.

Conclusions:

• Host EVs released during pneumococcal infection, particularly PLY-EVs, are critical mediators of pathogenesis.
• PLY-EVs contribute to cytotoxicity, inflammation, and immune cell modulation.
• These findings reveal a novel mechanism by which bacteria exploit host cell processes to cause disease.