Group A Streptococcus Modulates Host Inflammation by Manipulating Polymorphonuclear Leukocyte Cell Death Responses.

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Polymorphonuclear leukocyte (PMN) cell death is critical for managing inflammation during infection.
• Dysregulated PMN cell death can worsen inflammatory conditions and pathologies.
• Group A Streptococcus (GAS) is a significant human pathogen.

Purpose of the Study:

• To investigate the distinct mechanisms of PMN cell death induced by virulent versus avirulent GAS strains.
• To understand how these differing PMN death pathways impact host inflammatory responses.

Main Methods:

• In vitro infection of human PMNs with virulent and avirulent GAS strains.
• Assessment of PMN phagocytosis, reactive oxygen species (ROS) production, and mitochondrial membrane potential.
• In vivo infection model in C57BL/6J mice to evaluate systemic and localized inflammatory responses.

Main Results:

• Virulent GAS exhibited reduced PMN phagocytosis, lower ROS production, and less mitochondrial depolarization compared to avirulent GAS.
• Avirulent GAS induced PMN apoptosis (nuclear fragmentation, caspase-3 activation), while virulent GAS triggered PMN necrosis (vacuolization, membrane permeabilization).
• In vivo, virulent GAS infection led to higher pro-inflammatory cytokine release and PMN infiltration with reduced apoptotic potential, unlike avirulent GAS infection.

Conclusions:

• GAS manipulates PMN cell death pathways; virulent strains induce necrosis, promoting inflammation.
• Avirulent strains induce apoptosis, facilitating inflammation resolution.
• Differential PMN cell death mechanisms are key determinants of the host inflammatory outcome following GAS infection.