Airway Macrophages Encompass Transcriptionally and Functionally Distinct Subsets Altered by Smoking

Alveolar macrophages (AMs) are functionally important innate cells involved in lung homeostasis and immunity and whose diversity in health and disease is a subject of intense investigations. Yet, it remains unclear to what extent conditions like smoking or chronic obstructive pulmonary disease (COPD) trigger changes in the AM compartment. Here, we aimed to explore heterogeneity of human AMs isolated from healthy nonsmokers, smokers without COPD, and smokers with COPD by analyzing BAL fluid cells by flow cytometry and bulk and single-cell RNA sequencing. We found that subpopulations of BAL fluid CD2061 macrophages could be distinguished based on their degree of autofluorescence in each subject analyzed. CD2061 autofluorescenthigh AMs were identified as classical, self-proliferative AM, whereas autofluorescentlow AMs were expressing both monocyte and classical AM-related genes, supportive of a monocytic origin. Of note, monocyte-derived autofluorescentlow AMs exhibited a functionally distinct immunoregulatory profile, including the ability to secrete the immunosuppressive cytokine IL-10. Interestingly, single-cell RNA-sequencing analyses showed that transcriptionally distinct clusters of classical and monocyte-derived AM were uniquely enriched in smokers with and without COPD as compared with healthy nonsmokers. Of note, such smoking-associated clusters exhibited gene signatures enriched in detoxification, oxidative stress, and proinflammatory responses. Our study independently confirms previous reports supporting that monocyte-derived macrophages coexist with classical AM in the airways of healthy subjects and patients with COPD and identifies smoking-associated changes in the AM compartment that may favor COPD initiation or progression.

Automated summary

This study explores the heterogeneity of human alveolar macrophages (AMs) isolated from different groups, finding distinct subpopulations of AMs in BAL fluid based on autofluorescence levels. Single-cell RNA sequencing analyses reveal transcriptionally distinct clusters of classical and monocyte-derived AM enriched in smokers with and without COPD. Signs of gene signatures related to detoxification, oxidative stress, and proinflammatory responses are observed in smoking-associated clusters, indicating potential implications for COPD initiation or progression.