Innate type 2 lymphocytes trigger an inflammatory switch in alveolar macrophages

Area of Science:

• Immunology
• Pulmonology
• Cell Biology

Background:

• Tissue-resident alveolar macrophages (trAMs) are crucial for lung homeostasis and immune regulation.
• They are generally considered more resistant to inflammatory reprogramming than recruited macrophages.
• Their role in type 2 immunity and allergic lung diseases is not fully understood.

Purpose of the Study:

• To investigate the role of trAMs in type 2 immunity and allergic lung inflammation.
• To elucidate the molecular mechanisms underlying trAM reprogramming during allergen exposure.
• To understand how trAMs contribute to allergen-induced lung pathology.

Main Methods:

• Utilized a novel mouse model for selective depletion and replacement of trAMs.
• Analyzed cellular and molecular changes in the lung following allergen challenge.
• Investigated the role of transcription factors IRF4 and PPARγ in trAM function.

Main Results:

• Allergen exposure induced interleukin-13 production by innate type 2 lymphoid cells (ILC2s), reprogramming trAMs.
• This reprogramming involved the induction of transcription factor IRF4, suppressing PPARγ and altering trAM identity.
• Reprogrammed trAMs promoted chemokine production, cell fusion, and the recruitment of inflammatory cells, leading to lung pathology.

Conclusions:

• Contrary to previous assumptions, trAMs can adopt a pro-inflammatory phenotype during type 2 immunity.
• A critical switch from PPARγ to IRF4 reconfigures trAMs into effector cells driving allergic lung inflammation.
• These findings reveal a novel mechanism of macrophage plasticity in the context of allergic lung disease.