Pneumolysin activates neutrophil extracellular trap formation.

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Neutrophil extracellular traps (NETs) are crucial in host defense against pathogens.
• Pneumolysin (Ply), a toxin from Streptococcus pneumoniae, is a key virulence factor.
• The role of Ply in inducing NET formation requires further elucidation.

Purpose of the Study:

• To investigate the in vitro potential of pneumolysin (Ply) to activate neutrophil extracellular trap (NET) formation.
• To characterize the dose- and time-dependency of Ply-induced NETosis.
• To explore the mechanisms underlying Ply-induced NETosis, including cell viability and specific signaling pathways.

Main Methods:

• Isolated human neutrophils were exposed to recombinant Ply (5-20 ng/ml).
• NET formation was quantified using flow cytometry (Vybrant® DyeCycle™ Ruby) and spectrofluorimetry (Sytox® Orange).
• Extracellular DNA, citrullinated histone, and myeloperoxidase were visualized via fluorescence microscopy (DAPI staining).

Main Results:

• Ply significantly increased DNA release, citrullinated histone, and myeloperoxidase in a dose- and time-dependent manner.
• NETosis was observed within 30-60 minutes of Ply exposure, affecting a subpopulation of neutrophils.
• Ply-induced NETosis occurred without compromising neutrophil viability and independent of reactive oxygen species and Toll-like receptor 4.

Conclusions:

• Pneumolysin directly induces vital NETosis in human neutrophils.
• Ply-mediated NET formation represents a double-edged sword in pneumococcal infections.
• The outcome of Ply-induced NETosis depends on the inflammatory context, potentially impacting host defense or disease progression.