Fibrosis is an integral component of the pathogenesis of acute lung injury and is associated with poor outcomes in patients with acute respiratory distress syndrome (ARDS). Fibrocytes are bone ...marrow-derived cells that traffic to injured tissues and contribute to fibrosis; hence their concentration in the peripheral blood has the potential to serve as a biomarker of lung fibrogenesis. We therefore sought to test the hypothesis that the concentration and phenotype of circulating fibrocytes in patients with ARDS predicts clinical outcomes.
For the animal studies, C57Bl/6 mice were infected with experimental Klebsiella pneumoniae in a model of acute lung injury; one-way ANOVA was used to compare multiple groups and two-way ANOVA was used to compare two groups over time. For the human study, 42 subjects with ARDS and 12 subjects with pneumonia (without ARDS) were compared to healthy controls. Chi-squared or Fisher's exact test were used to compare binary outcomes. Survival data was expressed using a Kaplan-Meier curve and compared by log-rank test. Univariable and multivariable logistic regression were used to predict death.
In mice with acute lung injury caused by Klebsiella pneumonia, there was a time-dependent increase in lung soluble collagen that correlated with sequential expansion of fibrocytes in the bone marrow, blood, and then lung compartments. Correspondingly, when compared via cross-sectional analysis, the initial concentration of blood fibrocytes was elevated in human subjects with ARDS or pneumonia as compared to healthy controls. In addition, fibrocytes from subjects with ARDS displayed an activated phenotype and on serial measurements, exhibited intermittent episodes of markedly elevated concentration over a median of 1 week. A peak concentration of circulating fibrocytes above a threshold of > 4.8 × 10
cells/mL cells correlated with mortality that was independent of age, ratio of arterial oxygen concentration to the fraction of inspired oxygen, and vasopressor requirement.
Circulating fibrocytes increase in a murine model of acute lung injury and elevation in the number of these cells above a certain threshold is correlated with mortality in human ARDS. Therefore, these cells may provide a useful and easily measured biomarker to predict outcomes in these patients.
We developed a flow cytometry-based assay to simultaneously quantify multiple leukocyte populations in the marginated vascular, interstitial, and alveolar compartments of the mouse lung. An ...intravenous injection of a fluorescently labeled anti-CD45 antibody was used to label circulating and marginated vascular leukocytes. Following vascular flushing to remove non-adherent cells and collection of broncho-alveolar lavage (BAL) fluid, lungs were digested and a second fluorescent anti-CD45 antibody was added ex vivo to identify cells not located in the vascular space. In the naïve mouse lung, we found about 11million CD45+ leukocytes, of which 87% (9.5million) were in the vascular marginated compartment, consisting of 17% NK cells, 17% neutrophils, 57% mononuclear myeloid cells (monocytes, macrophage precursors and dendritic cells), and 10% T cells (CD4+, CD8+, and invariant NKT cells). Non-vascular compartments including the interstitial compartment contained 7.7×105cells, consisting of 49% NK cells, 25% dendritic cells, and 16% other mononuclear myeloid cells. The alveolar compartment was overwhelmingly populated by macrophages (5.63×105cells, or 93%). We next studied leukocyte margination and extravasation into the lung following acid injury, a model of gastric aspiration. At 1h after injury, neutrophils were markedly elevated in the blood while all other circulating leukocytes declined by an average of 79%. At 4h after injury, there was a peak in the numbers of marginated neutrophils, NK cells, CD4+ and CD8+ T cells and a peak in the number of alveolar NK cells. Most interstitial cells consisted of DCs, neutrophils, and CD4+ T cells, and most alveolar compartment cells consisted of macrophages, neutrophils, and NK cells. At 24h after injury, there was a decline in the number of all marginated and interstitial leukocytes and a peak in alveolar neutrophils. In sum, we have developed a novel assay to study leukocyte margination and trafficking following pulmonary inflammation and show that marginated cells comprise a large fraction of lung leukocytes that increases shortly after lung injury. This assay may be of interest in future studies to determine if leukocytes become activated upon adherence to the endothelium, and have properties that distinguish them from interstitial and circulating cells.
Quantitative computed tomography (QCT) has recently gained an important role in the functional assessment of chronic lung disease. Its capacity in diagnostic, staging, and prognostic evaluation in ...this setting is similar to that of traditional pulmonary function testing. Furthermore, it can demonstrate lung injury before the alteration of pulmonary function test parameters, and it enables the classification of disease phenotypes, contributing to the customization of therapy and performance of comparative studies without the intra- and inter-observer variation that occurs with qualitative analysis. In this review, we address technical issues with QCT analysis and demonstrate the ability of this modality to answer clinical questions encountered in daily practice in the management of patients with chronic lung disease.
Myeloid⁻derived suppressor cells (MDSCs) comprised a heterogeneous subset of bone marrow⁻derived myeloid cells, best studied in cancer research, that are increasingly implicated in the pathogenesis ...of pulmonary vascular remodeling and the development of pulmonary hypertension. Stem cell transplantation represents one extreme interventional strategy for ablating the myeloid compartment but poses a number of translational challenges. There remains an outstanding need for additional therapeutic targets to impact MDSC function, including the potential to alter interactions with innate and adaptive immune subsets, or alternatively, alter trafficking receptors, metabolic pathways, and transcription factor signaling with readily available and safe drugs. In this review, we summarize the current literature on the role of myeloid cells in the development of pulmonary hypertension, first in pulmonary circulation changes associated with myelodysplastic syndromes, and then by examining intrinsic myeloid cell changes that contribute to disease progression in pulmonary hypertension. We then outline several tractable targets and pathways relevant to pulmonary hypertension via MDSC regulation. Identifying these MDSC-regulated effectors is part of an ongoing effort to impact the field of pulmonary hypertension research through identification of myeloid compartment-specific therapeutic applications in the treatment of pulmonary vasculopathies.
Gram-negative bacterial pneumonia is a common and dangerous infection with diminishing treatment options due to increasing antibiotic resistance among causal pathogens. The mononuclear phagocyte ...system is a heterogeneous group of leukocytes composed of tissue-resident macrophages, dendritic cells, and monocyte-derived cells that are critical in defense against pneumonia, but mechanisms that regulate their maintenance and function during infection are poorly defined. M-CSF has myriad effects on mononuclear phagocytes but its role in pneumonia is unknown. We therefore tested the hypothesis that M-CSF is required for mononuclear phagocyte-mediated host defenses during bacterial pneumonia in a murine model of infection. Genetic deletion or immunoneutralization of M-CSF resulted in reduced survival, increased bacterial burden, and greater lung injury. M-CSF was necessary for the expansion of lung mononuclear phagocytes during infection but did not affect the number of bone marrow or blood monocytes, proliferation of precursors, or recruitment of leukocytes to the lungs. In contrast, M-CSF was essential to survival and antimicrobial functions of both lung and liver mononuclear phagocytes during pneumonia, and its absence resulted in bacterial dissemination to the liver and hepatic necrosis. We conclude that M-CSF is critical to host defenses against bacterial pneumonia by mediating survival and antimicrobial functions of mononuclear phagocytes in the lungs and liver.
We sought to compare the occurrence and characteristics of patients with acute myocarditis admitted during the coronavirus disease 2019 pandemic to those admitted prior.
We performed a retrospective ...chart review of patients with the primary discharge diagnosis of acute myocarditis from September 1st 2017 through August 31st 2020.
We identified 67 patients, 45 (67%) admitted pre-pandemic, and 22 (33%) during the pandemic. Rate of admissions for acute myocarditis was 1.5/month 95% CI 1.04–1.95 pre-pandemic, and 3.7/month 95% CI 2.36–4.97 (p < 0.001) during the first 6 months of the pandemic. Of the 22 patients admitted during the pandemic, 10 (45%) tested positive for SARS-CoV-2. Patients who tested positive for SARS-CoV-2 were older and had lower peak troponin levels.
During the pandemic, less than half of the patients admitted with acute myocarditis tested positive for SARS-CoV-2. Patients who tested positive were older and had lower peak troponin levels.
•We found an increase in the occurrence of acute myocarditis during the COVID-19 pandemic•Less than half of acute myocarditis patients tested positive for SARS-CoV-2•SARS-CoV-2 positive patients were older and had lower peak troponin levels
The chemokine ligand CXCL12 is constitutively expressed in the bone marrow and other tissues including the brain endothelium and is responsible for regulating the trafficking of bone marrow ...progenitor cells. CXCL12 has been shown to play a significant role in animal models of ischemic stroke but its role in human stroke is unclear. The aim of this study was to test the hypothesis that elevated circulating baseline CXCL12 levels are associated with subsequent stroke.
We prospectively collected demographic and angiographic data from consecutive patients referred for elective coronary angiography. Before coronary angiography a peripheral blood sample was collected for subsequent measurement of CXCL12. One-year stroke risk was calculated using the Framingham Risk Profile. Clinical follow-up was performed at 6 months and 1 year.
Of 206 subjects enrolled, 10 (4.9%) sustained an ischemic stroke over the 1 year follow-up. There were no significant differences in baseline clinical characteristics or angiographic findings. However, median CXCL12 levels were significantly higher in those who sustained an ischemic stroke compared with those who did not (10 856 pg/mL versus 2241 pg/mL, P=0.007). The time to stroke distribution between subjects with baseline CXCL12 levels≥10 421 pg/mL and those with baseline CXCL12 levels<10 421 pg/mL was significantly different (log rank P<0.001). The weighted Cox proportional hazard model demonstrated that baseline CXCL12 levels≥10 421 pg/mL were significantly associated with ischemic stroke at follow-up (hazard ratio, 15.29; 95% CI, 3.05-76.71).
Plasma CXCL12 levels may represent a novel biomarker of future ischemic stroke.
Iron is essential to the virulence of Aspergillus species, and restricting iron availability is a critical mechanism of antimicrobial host defense. Macrophages recruited to the site of infection are ...at the crux of this process, employing multiple intersecting mechanisms to orchestrate iron sequestration from pathogens. To gain an integrated understanding of how this is achieved in aspergillosis, we generated a transcriptomic time series of the response of human monocyte-derived macrophages to Aspergillus and used this and the available literature to construct a mechanistic computational model of iron handling of macrophages during this infection. We found an overwhelming macrophage response beginning 2 to 4 h after exposure to the fungus, which included upregulated transcription of iron import proteins transferrin receptor-1, divalent metal transporter-1, and ZIP family transporters, and downregulated transcription of the iron exporter ferroportin. The computational model, based on a discrete dynamical systems framework, consisted of 21 3-state nodes, and was validated with additional experimental data that were not used in model generation. The model accurately captures the steady state and the trajectories of most of the quantitatively measured nodes. In the experimental data, we surprisingly found that transferrin receptor-1 upregulation preceded the induction of inflammatory cytokines, a feature that deviated from model predictions. Model simulations suggested that direct induction of transferrin receptor-1 (TfR1) after fungal recognition, independent of the iron regulatory protein-labile iron pool (IRP-LIP) system, explains this finding. We anticipate that this model will contribute to a quantitative understanding of iron regulation as a fundamental host defense mechanism during aspergillosis. IMPORTANCE Invasive pulmonary aspergillosis is a major cause of death among immunosuppressed individuals despite the best available therapy. Depriving the pathogen of iron is an essential component of host defense in this infection, but the mechanisms by which the host achieves this are complex. To understand how recruited macrophages mediate iron deprivation during the infection, we developed and validated a mechanistic computational model that integrates the available information in the field. The insights provided by this approach can help in designing iron modulation therapies as anti-fungal treatments.
The rate of progression of most interstitial lung diseases (ILD) is unpredictable. Fibrocytes are circulating bone marrow-derived cells that have been implicated in the pathogenesis of lung fibrosis. ...Hermansky-Pudlak syndrome (HPS), a genetic cause of ILD in early adulthood, allows for study of biomarkers of ILD in a homogeneous population at near-certain risk of developing fibrotic lung disease.
To test the hypothesis that, in subjects with HPS, the number or phenotype of circulating fibrocytes predicts progression and outcome of ILD.
We measured circulating fibrocyte counts and chemokine levels in a cohort of subjects with HPS and healthy control subjects and correlated the results to disease outcome.
In a cross-sectional analysis, peripheral blood fibrocyte concentrations were markedly elevated in a subset of subjects with HPS who had ILD but not subjects without lung disease or normal control subjects. The blood concentration of fibrocytes expressing the chemokine receptor CXCR4 correlated significantly with the plasma concentration of the CXCR4 ligand, CXCL12. In a longitudinal study, we found marked episodic elevations in circulating fibrocyte counts over a median follow-up period of 614 days. Elevations in both maximal values and final values of peripheral blood CXCR4(+) fibrocyte concentration were strongly associated with death from ILD.
CXCR4(+) fibrocyte concentration may be useful as a biomarker for outcome of ILD in subjects with HPS.
Invasive aspergillosis is a severe pneumonia that is usually fatal despite currently available therapy. The disease disproportionately afflicts immunocompromised patients, indicating the critical ...importance of the immune status of the host in this infection, but the defense mechanisms against this pathogen remain incompletely understood. In the current study, we hypothesized that the chemokine ligand monocyte chemotactic protein-1, also designated CC chemokine ligand-2 (MCP-1/CCL2) is necessary for effective host defense against invasive aspergillosis in immunocompromised hosts. We found a rapid and marked induction of MCP-1/CCL2 in the lungs of neutropenic mice with invasive aspergillosis. Neutralizing MCP-1/CCL2 resulted in twofold greater mortality and greater than threefold increase in pathogen burden in the lungs. Neutralization of MCP-1/CCL2 also resulted in reduced recruitment of NK cells to the lungs at early time points, but did not affect the number of other leukocyte effector cells in the lungs. Ab-mediated depletion of NK cells similarly resulted in impaired defenses against the infection, resulting in a greater than twofold increase in mortality and impaired clearance of the pathogen from the lungs. These data establish MCP-1/CCL2-mediated recruitment of NK cells to the lungs as a critical early host defense mechanism in invasive aspergillosis and demonstrate NK cells to be an important and previously unrecognized effector cell in this infection.
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