Highlight
1. Single-cell RNA sequencing of bronchoalveolar lavage (BAL) cells from COPD patients reveals marked alterations in immune cell composition compared to healthy controls.
2. There is an increased abundance of proinflammatory and profibrotic macrophages, classical monocytes, and neutrophils in COPD airways, contributing to disease pathology.
3. Changes in regulatory T cells and double-negative T lymphocyte populations correlate with disease severity and functional measures of gas exchange and airway structure.
Study Background
Chronic obstructive pulmonary disease (COPD) is a progressive respiratory disorder characterized by airflow limitation, airway remodeling, and chronic inflammation. Immune dysregulation, particularly involving innate and adaptive immune cells within the distal airways and alveoli, is a well-recognized but poorly defined component of its pathogenesis. Macrophages and lymphocytes predominate in these regions and exhibit extensive plasticity, with heterogeneous phenotypes that may orchestrate inflammation and fibrosis. However, comprehensive characterization of these cell populations at the single-cell level in human COPD lung compartments has been lacking. This knowledge gap limits understanding of how specific immune cell subtypes contribute to COPD progression and severity. Advances in single-cell RNA sequencing (scRNA-seq) now permit unbiased profiling of airway immune cells, enabling identification of altered cellular states and underlying transcriptomic changes in COPD.
Study Design
The study recruited 17 individuals, including 10 patients with clinically diagnosed COPD and 7 healthy controls. All participants underwent bronchoscopy with retrieval of bronchoalveolar lavage samples. Single-cell suspensions were generated from BAL fluid and subsequently processed for single-cell RNA sequencing analysis to enable high-resolution transcriptomic profiling of individual immune cells. Comprehensive pulmonary phenotyping included full pulmonary function testing, thoracic computed tomography (CT) for airway and parenchymal assessment, and xenon-129 hyperpolarized gas magnetic resonance imaging (MRI) to evaluate regional ventilation and gas exchange. These multimodal assessments allowed correlation of immune cell composition with airway structure and functional impairment.
Key Findings
Analysis of 97,254 cells yielded distinct immune landscape signatures separating COPD patients from controls. Among the COPD group, 52,840 cells were profiled.
Immune Cell Composition and Changes in COPD:
- Macrophages: COPD BAL samples showed a significant expansion of a population described as non-typable macrophages, identified by transcriptomic signatures suggesting a profibrotic and proinflammatory phenotype. These cells likely contribute to airway remodeling and fibrotic changes observed in COPD.
- Monocytes and Neutrophils: Classical monocytes and neutrophils were increased in frequency in COPD airways, reflecting active recruitment and inflammatory processes. The infiltrating monocyte pool may serve as precursors for profibrotic macrophages, thus perpetuating local immune dysregulation.
- Lymphocytes: Regulatory T cells (Tregs), known for their immunomodulatory role, were decreased in COPD BAL and inversely correlated with MRI measures of regional gas transfer and diffusing capacity (DLCO), suggesting their potential role in maintaining alveolar function. Conversely, double-negative T cells (lacking CD4 and CD8 markers) were increased and directly associated with airway luminal narrowing on CT, implicating their involvement in structural airway changes.
Relation to Disease Severity:
The proportions of these altered immune subsets showed progressive changes according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) severity classification, indicating that these immune alterations correlate with the degree of airflow limitation and disease progression.
Functional Imaging Correlations:
- Double-negative T cell proportions correlated positively with reduced airway luminal area, an imaging biomarker of airway remodeling.
- Regulatory T cell frequencies inversely correlated with impaired ventilation and gas exchange on hyperpolarized gas MRI and DLCO, linking immunoregulatory deficits to impaired alveolar function.
Expert Commentary
This study provides valuable mechanistic insights by integrating cutting-edge single-cell transcriptomics with advanced pulmonary imaging and functional testing. The identification of profibrotic macrophages and an expanded infiltrating monocyte niche underscores the importance of innate immune cell plasticity in COPD pathobiology. These findings align with emerging paradigms implicating myeloid cell-driven fibrosis and inflammation as key drivers of remodeling. The novel associations between regulatory T cell depletion and gas exchange abnormalities highlight an immunoregulatory component potentially targetable to preserve lung function.
However, the relatively small sample size and cross-sectional design necessitate cautious interpretation. Longitudinal validation in larger cohorts and functional interrogation of identified cell subsets are needed. Furthermore, sampling from BAL may not fully capture compartmental heterogeneity, especially within lung tissue. Despite these limitations, this study advances understanding of immune dysregulation in COPD, providing a foundation for future biomarker development and therapeutic targeting.
Conclusion
The single-cell transcriptomic profiling of bronchoalveolar immune cells reveals a complex immune landscape in COPD characterized by expansion of profibrotic macrophages, monocytes, and neutrophils, alongside dysregulated T lymphocyte populations. These alterations correlate with disease severity and functional impairments in ventilation and gas exchange, underscoring their relevance to COPD pathogenesis. Targeting specific immune subpopulations may represent a promising strategy to modulate airway remodeling and improve clinical outcomes in COPD.
Funding and ClinicalTrials.gov
The original study’s funding sources and clinical trial registration were not specified in the available abstract.
References
Gerayeli FV, Yang CX, Wang CJ, et al. Single-cell sequencing unveils a profibrotic macrophage and infiltrating monocyte niche in the bronchoalveolar lavage of patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2026 Aug 1;212(8):1710-1720. PMID: 42153326.
Additional references for background and context drawn from established literature on COPD immunopathogenesis and single-cell technologies include:
- Wang X, Proudfoot JA, et al. The role of macrophages in COPD: shaping disease progression. Immunol Rev. 2021;302(1):67-78.
- Agusti A, Hogg JC. Update on the Pathogenesis of Chronic Obstructive Pulmonary Disease. N Engl J Med. 2019;381(13):1248-1256.
- Villani AC, Satija R, Reynolds G, et al. Single-cell RNA-seq reveals new types of human blood dendritic cells, monocytes, and progenitors. Science. 2017 Apr 21;356(6335):eaah4573.
