Macrophages regulate lung ILC2 activation via Pla2g5-dependent mechanisms.

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Group V phospholipase A2 (Pla2g5) is essential for macrophage functions in pulmonary inflammation.
• The specific lipid mediators and cellular targets regulated by Pla2g5 remain unidentified.

Purpose of the Study:

• To elucidate the role of Pla2g5 in pulmonary inflammation and type-2 immunity.
• To identify the lipid mediators and cellular targets involved in Pla2g5-mediated immune responses.

Main Methods:

• Mice lacking Pla2g5 were used to study lung inflammation following Alternaria alternata inhalation.
• Adoptive transfer of bone marrow-derived macrophages and administration of IL-33, free fatty acids (linoleic acid and oleic acid) were performed.
• Mass spectrometry was used to analyze free fatty acid levels. ILC2 activation and expression of FFA-receptor-1 were assessed.

Main Results:

• Pla2g5-null mice exhibited reduced ILC2 activation and eosinophilia.
• Pla2g5 deficiency impaired IL-33 upregulation in macrophages upon repeated allergen exposure.
• Reduced levels of free fatty acids, including linoleic acid and oleic acid, were observed in Pla2g5-deficient macrophages.
• Exogenous administration of oleic acid, but not linoleic acid, restored inflammation and ILC2 expansion in Pla2g5-null mice, suggesting differential roles.

Conclusions:

• Macrophage-associated Pla2g5 is critical for type-2 immunity.
• Pla2g5 regulates IL-33 induction and free fatty acid-driven activation of ILC2s.
• These findings highlight a novel mechanism linking lipid metabolism to allergic airway inflammation.