NETs promote ALI/ARDS inflammation by regulating alveolar macrophage polarization

Area of Science:

• Immunology
• Pulmonology
• Cell Biology

Background:

• Neutrophil extracellular traps (NETs) are crucial for pathogen capture during acute lung injury (ALI).
• Excessive NETs can exacerbate inflammation, while macrophages (M1/M2) play opposing roles in ALI.
• Alveolar macrophages (AMs) typically polarize to the pro-inflammatory M1 phenotype during ALI.

Purpose of the Study:

• To investigate the hypothesis that NETs aggravate ALI/ARDS inflammation by promoting M1 macrophage polarization.
• To elucidate the role of NETs in neutrophil-macrophage interactions during early ALI.

Main Methods:

• Clinical correlation of NET levels with M1 macrophage polarization in ARDS patients.
• Murine ALI model to assess NET formation, M1/M2 markers in bronchoalveolar lavage fluid (BALF) and lung tissue.
• In vitro experiments using bone marrow-derived macrophages (BMDMs) co-cultured with NETs, with and without LPS pre-stimulation.

Main Results:

• Positive correlation between NET levels and M1-like macrophage polarization in ARDS patients.
• NETs detected in murine ALI lungs, associated with increased M1 and decreased M2 markers.
• NET inhibition downregulated M1 markers and upregulated M2 markers in vivo.
• NETs promoted M1 polarization and pro-inflammatory cytokine secretion in BMDMs, regardless of LPS pre-stimulation.

Conclusions:

• NETs promote ARDS inflammation during the acute phase by driving macrophage polarization to the M1 phenotype.
• NETs are critical mediators in the neutrophil-macrophage crosstalk during the early stages of ALI.