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In Vivo Assessment of Alveolar Macrophage Efferocytosis Following Ozone Exposure
Published on: October 22, 2019
Assessment of Alveolar Macrophage Dysfunction Using an in vitro Model of Acute Respiratory Distress Syndrome
Rahul Y Mahida1, Aaron Scott1, Dhruv Parekh1
1Birmingham Acute Care Research Group, Institute of Inflammation and Ageing, University of Birmingham, Birmingham, United Kingdom.
Abstract:
Background: Impaired alveolar macrophage (AM) efferocytosis may contribute to acute respiratory distress syndrome (ARDS) pathogenesis; however, studies are limited by the difficulty in obtaining primary AMs from patients with ARDS. Our objective was to determine whether an in vitro model of ARDS can recapitulate the same AM functional defect observed in vivo and be used to further investigate pathophysiological mechanisms. Methods: AMs were isolated from the lung tissue of patients undergoing lobectomy and then treated with pooled bronchoalveolar lavage (BAL) fluid previously collected from patients with ARDS. AM phenotype and effector functions (efferocytosis and phagocytosis) were assessed by flow cytometry. Rac1 gene expression was assessed using quantitative real-time PCR. Results: ARDS BAL treatment of AMs decreased efferocytosis (p = 0.0006) and Rac1 gene expression (p = 0.016); however, bacterial phagocytosis was preserved. Expression of AM efferocytosis receptors MerTK (p = 0.015) and CD206 (p = 0.006) increased, whereas expression of the antiefferocytosis receptor SIRPα decreased following ARDS BAL treatment (p = 0.036). Rho-associated kinase (ROCK) inhibition partially restored AM efferocytosis in an in vitro model of ARDS (p = 0.009). Conclusions: Treatment of lung resection tissue AMs with ARDS BAL fluid induces impairment in efferocytosis similar to that observed in patients with ARDS. However, AM phagocytosis is preserved following ARDS BAL treatment. This specific impairment in AM efferocytosis can be partially restored by inhibition of ROCK. This in vitro model of ARDS is a useful tool to investigate the mechanisms by which the inflammatory alveolar microenvironment of ARDS induces AM dysfunction.
Insights
Impaired efferocytosis in alveolar macrophages (AMs) is linked to acute respiratory distress syndrome (ARDS). An in vitro ARDS model using AMs and bronchoalveolar lavage (BAL) fluid confirmed this defect, which ROCK inhibition partially restored.
Area of Science:
- Pulmonary Medicine
- Immunology
- Cell Biology
Background:
- Alveolar macrophage (AM) efferocytosis is crucial for lung homeostasis.
- Impaired AM efferocytosis is implicated in acute respiratory distress syndrome (ARDS) pathogenesis.
- Current research is limited by challenges in obtaining primary AMs from ARDS patients.
Purpose of the Study:
- To establish and validate an in vitro model of ARDS using AMs.
- To investigate if this model recapitulates AM functional defects observed in vivo.
- To explore the mechanisms underlying ARDS-induced AM dysfunction.
Main Methods:
- AMs isolated from lung resection tissue.
- AMs treated with pooled bronchoalveolar lavage (BAL) fluid from ARDS patients.
- Assessment of AM phenotype, efferocytosis, phagocytosis, and gene expression (Rac1) via flow cytometry and qPCR.
- Evaluation of receptor expression (MerTK, CD206, SIRPα) and effect of Rho-associated kinase (ROCK) inhibition.
Main Results:
- ARDS BAL fluid treatment impaired AM efferocytosis and reduced Rac1 gene expression.
- Bacterial phagocytosis by AMs remained preserved.
- Expression of efferocytosis receptors (MerTK, CD206) increased, while the antiefferocytosis receptor (SIRPα) decreased.
- ROCK inhibition partially restored efferocytosis in the ARDS model.
Conclusions:
- The in vitro ARDS model effectively replicates impaired AM efferocytosis seen in ARDS patients.
- AM phagocytic capacity is maintained despite efferocytosis deficits.
- ROCK pathway inhibition offers a potential therapeutic strategy for restoring AM function in ARDS.
