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Project description:Recent studies suggest that training of innate immune cells such as tissue-resident macrophages by repeated noxious stimuli can heighten host defense responses. However, it remains unclear whether trained immunity of tissue-resident macrophages also enhances injury resolution to counterbalance the heightened inflammatory responses. Here, we studied lung-resident alveolar macrophages (AMs) prechallenged with either the bacterial endotoxin or with Pseudomonas aeruginosa and observed that these trained AMs showed greater resilience to pathogen-induced cell death. Transcriptomic analysis and functional assays showed greater capacity of trained AMs for efferocytosis of cellular debris and injury resolution. Single-cell high-dimensional mass cytometry analysis and lineage tracing demonstrated that training induces an expansion of a MERTKhiMarcohiCD163+F4/80low lung-resident AM subset with a proresolving phenotype. Reprogrammed AMs upregulated expression of the efferocytosis receptor MERTK mediated by the transcription factor KLF4. Adoptive transfer of these trained AMs restricted inflammatory lung injury in recipient mice exposed to lethal P. aeruginosa. Thus, our study has identified a subset of tissue-resident trained macrophages that prevent hyperinflammation and restore tissue homeostasis following repeated pathogen challenges.
| S-EPMC10450795 | biostudies-literature
Project description:Recent studies suggest that training of innate immune cells such as tissue-resident macrophages by repeated noxious stimuli can heighten host defense responses. However, it remains unclear whether trained immunity of tissue-resident macrophages also comprises enhanced injury resolution capacity to counterbalance the heightened inflammatory responses. Here, we studied lung-resident alveolar macrophages (AMs) pre-challenged with either the bacterial endotoxin or with Pseudomonas aeruginosa and observed that these trained AMs showed greater resilience to pathogen-induced cell death. Transcriptomic analysis, and functional assays showed greater capacity of trained AMs to efferocytosis of cellular- debris, and facilitate injury resolution. Single-cell high-dimensional mass-cytometry analysis and lineage tracing demonstrated that training induces an expansion of a MERTKhiMarcohiCD163+F4/80low lung-resident AMs subset with pro-resolving phenotypes. Training epigenetically reprogrammed AMs to express a higher level of the transcription factor KLF4 which in turn upregulates the efferocytosis receptor MERTK. Adoptive transfer of these trained AMs restricted inflammatory lung injury in recipient mice exposed to lethal Pseudomonas aeruginosa. Thus, our study has identified a unique subset of tissue-resident trained macrophages which prevent hyper-inflammation and restore tissue homeostasis following pathogen challenge.
2023-08-16 | GSE231217 | GEO
Project description:Recent studies suggest that training of innate immune cells such as tissue-resident macrophages by repeated noxious stimuli can heighten host defense responses. However, it remains unclear whether trained immunity of tissue-resident macrophages also comprises enhanced injury resolution capacity to counterbalance the heightened inflammatory responses. Here, we studied lung-resident alveolar macrophages (AMs) pre-challenged with either the bacterial endotoxin or with Pseudomonas aeruginosa and observed that these trained AMs showed greater resilience to pathogen-induced cell death. Transcriptomic analysis, and functional assays showed greater capacity of trained AMs to efferocytosis of cellular- debris, and facilitate injury resolution. Single-cell high-dimensional mass-cytometry analysis and lineage tracing demonstrated that training induces an expansion of a MERTKhiMarcohiCD163+F4/80low lung-resident AMs subset with pro-resolving phenotypes. Training epigenetically reprogrammed AMs to express a higher level of the transcription factor KLF4 which in turn upregulates the efferocytosis receptor MERTK. Adoptive transfer of these trained AMs restricted inflammatory lung injury in recipient mice exposed to lethal Pseudomonas aeruginosa. Thus, our study has identified a unique subset of tissue-resident trained macrophages which prevent hyper-inflammation and restore tissue homeostasis following pathogen challenge.
2023-08-16 | GSE231218 | GEO
Project description:Trained immunity of alveolar macrophages promotes injury resolution by enhancing KLF4-MERTK-mediated efferocytosis
| PRJNA963001 | ENA
Project description:Trained immunity of alveolar macrophages promotes injury resolution by enhancing KLF4-MERTK-mediated efferocytosis.
| PRJNA962998 | ENA
Project description:Trained immunity of alveolar macrophages promotes injury resolution by enhancing KLF4-MERTK-mediated efferocytosis [RNA-seq]
| PRJNA963000 | ENA
Project description:Lung inflammation, caused by acute exposure to ozone (O3) - one of the six criteria air pollutants - is a significant source of morbidity in susceptible individuals. Alveolar macrophages (AMØs) are the most abundant immune cells in the normal lung and their number increases following O3 exposure. However, the role of AMØs in promoting or limiting O3-induced lung inflammation has not been clearly defined. Here, we used a mouse model of acute O3 exposure, lineage tracing, genetic knockouts, and data from O3-exposed human volunteers to define the role and ontogeny of AMØs during acute O3 exposure. Lineage tracing experiments showed that 12, 24, and 72 h after exposure to O3 (2 ppm) for 3h all AMØs were tissue-resident origin. Similarly, in humans exposed to FA and O3 (200 ppb) for 135 minutes, we did not observe ~21h post-exposure an increase in monocyte-derived AMØs by flow cytometry. Highlighting a role for tissue-resident AMØs, we demonstrate that depletion of tissue-resident AMØs with clodronate-loaded liposomes led to persistence of neutrophils in the alveolar space after O3 exposure, suggesting that impaired neutrophil clearance (i.e., efferocytosis) leads to prolonged lung inflammation. Moreover, depletion of tissue-resident AMØ demonstrated reduced clearance of intratracheally instilled apoptotic Jurkat cells, consistent with reduced efferocytosis. Genetic ablation of MerTK - a key receptor involved in efferocytosis - also resulted in impaired clearance of apoptotic neutrophils followed O3 exposure. Overall, these findings underscore the pivotal role of tissue-resident AMØs in resolving O3-induced inflammation via MerTK-mediated efferocytosis.
| S-EPMC10659406 | biostudies-literature
Project description:Microparticles are a newly recognized class of mediators in the pathophysiology of lung inflammation and injury, but little is known about the factors that regulate their accumulation and clearance. The primary objective of our study was to determine whether alveolar macrophages engulf microparticles and to elucidate the mechanisms by which this occurs. Alveolar microparticles were quantified in bronchoalveolar fluid of mice with lung injury induced by LPS and hydrochloric acid. Microparticle numbers were greatest at the peak of inflammation and declined as inflammation resolved. Isolated, fluorescently labeled particles were placed in culture with macrophages to evaluate ingestion in the presence of endocytosis inhibitors. Ingestion was blocked with cytochalasin D and wortmannin, consistent with a phagocytic process. In separate experiments, mice were treated intratracheally with labeled microparticles, and their uptake was assessed though microscopy and flow cytometry. Resident alveolar macrophages, not recruited macrophages, were the primary cell-ingesting microparticles in the alveolus during lung injury. In vitro, microparticles promoted inflammatory signaling in LPS primed epithelial cells, signifying the importance of microparticle clearance in resolving lung injury. Microparticles were found to have phosphatidylserine exposed on their surfaces. Accordingly, we measured expression of phosphatidylserine receptors on macrophages and found high expression of MerTK and Axl in the resident macrophage population. Endocytosis of microparticles was markedly reduced in MerTK-deficient macrophages in vitro and in vivo. In conclusion, microparticles are released during acute lung injury and peak in number at the height of inflammation. Resident alveolar macrophages efficiently clear these microparticles through MerTK-mediated phagocytosis.
| S-EPMC6335009 | biostudies-literature
Project description:Environmental microbial triggers shape the development and functionality of the immune system. Alveolar macrophages (AMs), tissue-resident macrophages of the lungs, are in constant and direct contact with inhaled particles and microbes. Such exposures likely impact AM reactivity to subsequent challenges by immunological imprinting mechanisms referred to as trained immunity. Here, we investigated whether a ubiquitous microbial compound has the potential to induce AM training in vivo. We discovered that intranasal exposure to ambient amounts of lipopolysaccharide (LPS) induced a pronounced AM memory response, characterized by enhanced reactivity upon pneumococcal challenge. Exploring the mechanistic basis of AM training, we identified a critical role of type 1 interferon signaling and found that inhibition of fatty acid oxidation and glutaminolysis significantly attenuated the training effect. Notably, adoptive transfer of trained AMs resulted in increased bacterial loads and tissue damage upon subsequent pneumococcal infection. In contrast, intranasal pre-exposure to LPS promoted bacterial clearance, highlighting the complexity of stimulus-induced immune responses, which likely involve multiple cell types and may depend on the local immunological and metabolic environment. Collectively, our findings demonstrate the profound impact of ambient microbial exposure on pulmonary immune memory and reveal tissue-specific features of trained immunity.
| S-EPMC9385480 | biostudies-literature
Project description:Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive fibrosing interstitial pneumonia. The pathogenicity of IPF has been widely investigated but still remains to be clarified. Efferocytosis, the specialized recognition and ingestion of apoptotic cells by phagocytes, is essential for the resolution of inflammation in the lungs and repair of injured tissues. Impaired efferocytosis contributes to the pathogenesis of chronic lung diseases such as emphysema and cystic fibrosis. We hypothesized that efferocytosis would also be reduced in alveolar macrophages isolated from subjects with IPF.Efferocytosis, was evaluated using Wright-Giemsa stained cell preparations isolated from the bronchoalveolar lavage (BAL) fluid of patients with IPF (n = 5), nonspecific interstitial pneumonitis (n = 6), cryptogenic organizing pneumonia (n = 4) and eosinophilic pneumonia (EP) (n = 5).Uningested apoptotic cells were significantly higher in BAL fluid from patients with IPF compared to other forms of interstitial lung disease. Macrophages isolated from patients with eosinophilic pneumonia had significantly fewer phagocytic ingestions than macrophages from the other three groups.Efferocytosis by alveolar macrophages was significantly lower in subjects with IPF compared to subjects with other interstitial pneumonia. Dysregulated efferocytosis may contribute to the pathogenesis of IPF.
| S-EPMC4030720 | biostudies-literature