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J Clin Invest ; 131(4)2021 02 15.
Article in English | MEDLINE | ID: covidwho-1172781


Alveolar macrophages orchestrate the response to viral infections. Age-related changes in these cells may underlie the differential severity of pneumonia in older patients. We performed an integrated analysis of single-cell RNA-Seq data that revealed homogenous age-related changes in the alveolar macrophage transcriptome in humans and mice. Using genetic lineage tracing with sequential injury, heterochronic adoptive transfer, and parabiosis, we found that the lung microenvironment drove an age-related resistance of alveolar macrophages to proliferation that persisted during influenza A viral infection. Ligand-receptor pair analysis localized these changes to the extracellular matrix, where hyaluronan was increased in aged animals and altered the proliferative response of bone marrow-derived macrophages to granulocyte macrophage colony-stimulating factor (GM-CSF). Our findings suggest that strategies targeting the aging lung microenvironment will be necessary to restore alveolar macrophage function in aging.

Aging/immunology , Cellular Microenvironment/immunology , Lung/immunology , Macrophages, Alveolar/immunology , Aging/pathology , Animals , Humans , Lung/pathology , Macrophages, Alveolar/pathology , Mice , Mice, Transgenic , RNA-Seq
Nature ; 590(7847): 635-641, 2021 02.
Article in English | MEDLINE | ID: covidwho-1019856


Some patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) develop severe pneumonia and acute respiratory distress syndrome1 (ARDS). Distinct clinical features in these patients have led to speculation that the immune response to virus in the SARS-CoV-2-infected alveolus differs from that in other types of pneumonia2. Here we investigate SARS-CoV-2 pathobiology by characterizing the immune response in the alveoli of patients infected with the virus. We collected bronchoalveolar lavage fluid samples from 88 patients with SARS-CoV-2-induced respiratory failure and 211 patients with known or suspected pneumonia from other pathogens, and analysed them using flow cytometry and bulk transcriptomic profiling. We performed single-cell RNA sequencing on 10 bronchoalveolar lavage fluid samples collected from patients with severe coronavirus disease 2019 (COVID-19) within 48 h of intubation. In the majority of patients with SARS-CoV-2 infection, the alveolar space was persistently enriched in T cells and monocytes. Bulk and single-cell transcriptomic profiling suggested that SARS-CoV-2 infects alveolar macrophages, which in turn respond by producing T cell chemoattractants. These T cells produce interferon-γ to induce inflammatory cytokine release from alveolar macrophages and further promote T cell activation. Collectively, our results suggest that SARS-CoV-2 causes a slowly unfolding, spatially limited alveolitis in which alveolar macrophages containing SARS-CoV-2 and T cells form a positive feedback loop that drives persistent alveolar inflammation.

COVID-19/immunology , COVID-19/virology , Macrophages, Alveolar/immunology , Pneumonia, Viral/immunology , Pneumonia, Viral/virology , SARS-CoV-2/pathogenicity , T-Lymphocytes/immunology , Bronchoalveolar Lavage Fluid/chemistry , Bronchoalveolar Lavage Fluid/immunology , COVID-19/genetics , Cohort Studies , Humans , Interferon-gamma/immunology , Interferons/immunology , Interferons/metabolism , Macrophages, Alveolar/metabolism , Macrophages, Alveolar/virology , Pneumonia, Viral/genetics , RNA-Seq , SARS-CoV-2/immunology , Signal Transduction/immunology , Single-Cell Analysis , T-Lymphocytes/metabolism , Time Factors