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Published on: October 26, 2018
Cytometry TOF identifies alveolar macrophage subtypes in acute respiratory distress syndrome
Eric D Morrell1, Alice Wiedeman2, S Alice Long2
1Division of Pulmonary, Critical Care, and Sleep Medicine, Department of Medicine, University of Washington, Seattle, Washington, USA.
Abstract:
Studies in human peripheral blood monocyte-derived macrophages in vitro have shown clear evidence that multiple macrophage polarization states exist. The extent to which different alveolar macrophage (AM) polarization states exist in homeostasis or in the setting of severe injury such as acute respiratory distress syndrome (ARDS) is largely unknown. We applied single-cell cytometry TOF (CyTOF) to simultaneously measure 36 cell-surface markers on CD45+ cells present in bronchoalveolar lavage from healthy volunteers, as well as mechanically ventilated subjects with and without ARDS. Visualization of the high-dimensional data with the t-distributed stochastic neighbor embedding algorithm demonstrated wide diversity of cell-surface marker profiles among CD33+CD71+CD163+ AMs. We then used a κ-nearest neighbor density estimation algorithm to statistically identify distinct alveolar myeloid subtypes, and we discerned 3 AM subtypes defined by CD169 and PD-L1 surface expression. The percentage of AMs that were classified into one of the 3 AM subtypes was significantly different between healthy and mechanically ventilated subjects. In an independent cohort of subjects with ARDS, PD-L1 gene expression and PD-L1/PD-1 pathway-associated gene sets were significantly decreased in AMs from patients who experienced prolonged mechanical ventilation or death. Unsupervised CyTOF analysis of alveolar leukocytes from human subjects has potential to identify expected and potentially novel myeloid populations that may be linked with clinical outcomes.
Insights
This study identifies distinct alveolar macrophage (AM) subtypes in lung injury patients using single-cell cytometry. Specific AM populations and PD-L1 expression levels correlate with acute respiratory distress syndrome (ARDS) severity and outcomes.
Area of Science:
- Immunology
- Cell Biology
- Pulmonary Medicine
Background:
- Macrophage polarization is crucial in immune responses, but alveolar macrophage (AM) states in lung injury remain unclear.
- Acute Respiratory Distress Syndrome (ARDS) involves complex pulmonary inflammation, where AMs play a key role.
Purpose of the Study:
- To investigate the diversity of alveolar macrophage (AM) polarization states in healthy individuals and patients with ARDS.
- To identify distinct AM subtypes and their association with clinical outcomes in ARDS.
Main Methods:
- Utilized single-cell cytometry time-of-flight (CyTOF) to analyze 36 cell-surface markers on bronchoalveolar lavage leukocytes.
- Applied t-distributed stochastic neighbor embedding (t-SNE) for data visualization and κ-nearest neighbor density estimation to identify AM subtypes.
- Correlated AM subtype frequencies and PD-L1 expression with clinical data, including mechanical ventilation duration and mortality in ARDS patients.
Main Results:
- Discovered three distinct AM subtypes defined by CD169 and PD-L1 surface expression.
- Observed significant differences in the distribution of these AM subtypes between healthy subjects and mechanically ventilated patients.
- Found decreased PD-L1 gene expression and pathway activity in AMs from ARDS patients with prolonged ventilation or death.
Conclusions:
- Unsupervised CyTOF analysis reveals diverse alveolar myeloid populations in humans.
- Specific AM subtypes and PD-L1 expression patterns are associated with ARDS severity and patient outcomes.
- This approach can identify known and novel myeloid populations linked to clinical conditions.
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