Distinct macrophage subpopulations characterize acute infection and chronic inflammatory lung disease

Mitigating Viral Impact on the Radiation Response of the Lung

Inflammation is a key factor in both influenza and radiation-induced lung pathophysiology. This implies a commonality of response to pulmonary damage from these insults and suggests exacerbated pathology may occur after combined exposure. We therefore tested the hypothesis that past inflammation from viral infection alters the lung microenvironment and lowers tolerance for radiation injury. Mice were inoculated with influenza A virus (IAV) and three weeks later, after virus clearance, mice received total-body irradiation (TBI). Survival as well as systemic and local lung inflammation were assessed, and strategies to mitigate pulmonary injury were investigated. After IAV infection alone, body condition recovered within 3 weeks, however inflammatory pathways remained active for 15 weeks. IAV infection exacerbated subsequent TBI responses, evident by increased lethality, enhanced histologically evident lung injury and an altered lung macrophage phenotype. To mitigate this enhanced sensitivity, captopril [an angiotensin converting enzyme inhibitor (ACEi)] was administered to limit tissue inflammation, or inflammatory monocyte-derived macrophage recruitment was blocked with a C-C chemokine receptor type 2 (CCR2) inhibitor. Both treatments abrogated the changes in circulating immune cells observed 4 weeks after TBI, and attenuated pro-inflammatory phenotypes in lung alveolar macrophages, appearing to shift immune cell dynamics towards recovery. Histologically apparent lung injury was not improved by either treatment. We show that latent lung injury from viral infection exacerbates radiation morbidity and mortality. Although strategies that attenuate proinflammatory immune cell phenotypes can normalize macrophage dynamics, this does not fully mitigate lung injury. Recognizing that past viral infections can enhance lung radiosensitivity is of critical importance for patients receiving TBI, as it could increase the incidence of adverse outcomes.

Activated eosinophils in early life impair lung development and promote long-term lung damage

Exaggeration of type 2 immune responses promotes lung inflammation and altered lung development; however, eosinophils, despite expansion in the postnatal lung, have not been specifically assessed in the context of neonatal lung disease. Furthermore, early life factors including prematurity and respiratory infection predispose infants to chronic obstructive pulmonary disease later in life. To assess eosinophils in the developing lung and how they may contribute to chronic lung disease, we generated mice harboring eosinophil-specific deletion of the negative regulatory enzyme SH2 domain-containing inositol 5' phosphatase-1. This increased the activity and number of pulmonary eosinophils in the developing lung, which was associated with impaired lung development, expansion of activated alveolar macrophages (AMφ), multinucleated giant cell formation, enlargement of airspaces, and fibrosis. Despite regression of eosinophils following completion of lung development, AMφ-dominated inflammation persisted, alongside lung damage. Bone marrow chimera studies showed that SH2 domain-containing inositol 5' phosphatase-1-deficient eosinophils were not sufficient to drive inflammatory lung disease in adult steady-state mice but once inflammation and damage were present, it could not be resolved. Depletion of eosinophils during alveolarization alleviated pulmonary inflammation and lung pathology, demonstrating an eosinophil-intrinsic effect. These results show that the presence of activated eosinophils during alveolarization aggravates AMφs and promotes sustained inflammation and long-lasting lung pathology.

A novel role for the ROS-ATM-Chk2 axis mediated metabolic and cell cycle reprogramming in the M1 macrophage polarization

Reactive oxygen species (ROS) play a pivotal role in macrophage-mediated acute inflammation. However, the precise molecular mechanism by which ROS regulate macrophage polarization remains unclear. Here, we show that ROS function as signaling molecules that regulate M1 macrophage polarization through ataxia-telangiectasia mutated (ATM) and cell cycle checkpoint kinase 2 (Chk2), vital effector kinases in the DNA damage response (DDR) signaling pathway. We further demonstrate that Chk2 phosphorylates PKM2 at the T95 and T195 sites, promoting glycolysis and facilitating macrophage M1 polarization. In addition, Chk2 activation increases the Chk2-dependent expression of p21, inducing cell cycle arrest for subsequent macrophage M1 polarization. Finally, Chk2-deficient mice infected with lipopolysaccharides (LPS) display a significant decrease in lung inflammation and M1 macrophage counts. Taken together, these results suggest that inhibiting the ROS-Chk2 axis can prevent the excessive inflammatory activation of macrophages, and this pathway can be targeted to develop a novel therapy for inflammation-associated diseases and expand our understanding of the pathophysiological functions of DDR in innate immunity.

Indole-3-carbinol attenuates lipopolysaccharide-induced acute respiratory distress syndrome through activation of AhR: role of CCR2+ monocyte activation and recruitment in the regulation of CXCR2+ neutrophils in the lungs

Introduction

Indole-3-carbinol (I3C) is found in cruciferous vegetables and used as a dietary supplement. It is known to act as a ligand for aryl hydrocarbon receptor (AhR). In the current study, we investigated the role of AhR and the ability of I3C to attenuate LPS-induced Acute Respiratory Distress Syndrome (ARDS).

Methods

To that end, we induced ARDS in wild-type C57BL/6 mice, Ccr2gfp/gfp KI/KO mice (mice deficient in the CCR2 receptor), and LyZcreAhRfl/fl mice (mice deficient in the AhR on myeloid linage cells). Additionally, mice were treated with I3C (65 mg/kg) or vehicle to investigate its efficacy to treat ARDS.

Results

I3C decreased the neutrophils expressing CXCR2, a receptor associated with neutrophil recruitment in the lungs. In addition, LPS-exposed mice treated with I3C revealed downregulation of CCR2+ monocytes in the lungs and lowered CCL2 (MCP-1) protein levels in serum and bronchoalveolar lavage fluid. Loss of CCR2 on monocytes blocked the recruitment of CXCR2+ neutrophils and decreased the total number of immune cells in the lungs during ARDS. In addition, loss of the AhR on myeloid linage cells ablated I3C-mediated attenuation of CXCR2+ neutrophils and CCR2+ monocytes in the lungs from ARDS animals. Interestingly, scRNASeq showed that in macrophage/monocyte cell clusters of LPS-exposed mice, I3C reduced the expression of CXCL2 and CXCL3, which bind to CXCR2 and are involved in neutrophil recruitment to the disease site.

Discussion

These findings suggest that CCR2+ monocytes are involved in the migration and recruitment of CXCR2+ neutrophils during ARDS, and the AhR ligand, I3C, can suppress ARDS through the regulation of immune cell trafficking.

Granulocyte Colony-Stimulating Factor is a Determinant of Severe Bronchopulmonary Dysplasia and Coincident Retinopathy

Bronchopulmonary dysplasia (BPD), also called chronic lung disease of immaturity, afflicts approximately one third of all extremely premature infants, causing lifelong lung damage. There is no effective treatment other than supportive care. Retinopathy of prematurity (ROP), which impairs vision irreversibly, is common in BPD, suggesting a related pathogenesis. However, specific mechanisms of BPD and ROP are not known. Herein, a neonatal mouse hyperoxic model of coincident BPD and retinopathy was used to screen for candidate mediators, which revealed that granulocyte colony-stimulating factor (G-CSF), also known as colony-stimulating factor 3, was up-regulated significantly in mouse lung lavage fluid and plasma at postnatal day 14 in response to hyperoxia. Preterm infants with more severe BPD had increased plasma G-CSF. G-CSF-deficient neonatal pups showed significantly reduced alveolar simplification, normalized alveolar and airway resistance, and normalized weight gain compared with wild-type pups after hyperoxic lung injury. This was associated with a marked reduction in the intensity, and activation state, of neutrophilic and monocytic inflammation and its attendant oxidative stress response, and protection of lung endothelial cells. G-CSF deficiency also provided partial protection against ROP. The findings in this study implicate G-CSF as a pathogenic mediator of BPD and ROP, and suggest the therapeutic utility of targeting G-CSF biology to treat these conditions.

SHIP1 and its role for innate immune regulation-Novel targets for immunotherapy

Phosphoinositide-3-kinase/AKT (PI3K/AKT) signaling plays key roles in the regulation of cellular activity in both health and disease. In immune cells, this PI3K/AKT pathway is critically regulated by the phosphoinositide phosphatase SHIP1, which has been reported to modulate the function of most immune subsets. In this review, we summarize our current knowledge of SHIP1 with a focus on innate immune cells, where we reflect on the most pertinent aspects described in the current literature. We also present several small-molecule agonists and antagonists of SHIP1 developed over the last two decades, which have led to improved outcomes in several preclinical models of disease. We outline these promising findings and put them in relation to human diseases with unmet medical needs, where we discuss the most attractive targets for immune therapies based on SHIP1 modulation.

Enhanced Lyn Activity Causes Severe, Progressive Emphysema and Lung Cancer

The epidemiological patterns of incident chronic obstructive pulmonary disease (COPD) and lung adenocarcinoma are changing, with an increasing fraction of disease occurring in patients who are never-smokers or were not exposed to traditional risk factors. However, causative mechanism(s) are obscure. Overactivity of Src family kinases (SFKs) and myeloid cell-dependent inflammatory lung epithelial and endothelial damage are independent candidate mechanisms, but their pathogenic convergence has not been demonstrated. Here we present a novel preclinical model in which an activating mutation in Lyn, a nonreceptor SFK that is expressed in immune cells, epithelium, and endothelium-all strongly implicated in the pathogenesis of COPD-causes spontaneous inflammation, early-onset progressive emphysema, and lung adenocarcinoma. Surprisingly, even though activated macrophages, elastolytic enzymes, and proinflammatory cytokines were prominent, bone marrow chimeras formally demonstrated that myeloid cells were not disease initiators. Rather, lung disease arose from aberrant epithelial cell proliferation and differentiation, microvascular lesions within an activated endothelial microcirculation, and amplified EGFR (epidermal growth factor receptor) expression. In human bioinformatics analyses, LYN expression was increased in patients with COPD and was correlated with increased EGFR expression, a known lung oncogenic pathway, and LYN was linked to COPD. Our study shows that a singular molecular defect causes a spontaneous COPD-like immunopathology and lung adenocarcinoma. Furthermore, we identify Lyn and, by implication, its associated signaling pathways as new therapeutic targets for COPD and cancer. Moreover, our work may inform the development of molecular risk screening and intervention methods for disease susceptibility, progression, and prevention of these increasingly prevalent conditions.

An Inhalable Hybrid Biomimetic Nanoplatform for Sequential Drug Release and Remodeling Lung Immune Homeostasis in Acute Lung Injury Treatment

Interactions of lung macrophages and recruited neutrophils with the lung microenvironment continuously aggravate the dysregulation of lung inflammation in the pathogenesis of acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Either modulating macrophages or destroying neutrophil counts cannot guarantee a satisfactory outcome in ARDS treatment. Aimed at inhibiting the coordinated action of neutrophils and macrophages and modulating the hyper-inflammatory condition, an inhalable biomimetic sequential drug-releasing nanoplatform was developed for the combinatorial treatment of ALI. The nanoplatform (termed D-SEL) was made by conjugating DNase I, as outer cleavable arms, to a serum exosomal and liposomal hybrid nanocarrier (termed SEL) via a matrix metalloproteinase 9 (MMP-9)-cleavable peptide and then encapsulating methylprednisolone sodium succinate (MPS). In lipopolysaccharide (LPS) induced ALI in mice, the MPS/D-SEL moved through muco-obstructive airways and was retained in the alveoli for over 24 h postinhalation. DNase I was then released from the nanocarrier first after responding to MMP-9, resulting in inner SEL core exposure, which precisely delivered MPS into macrophages for promoting M2 macrophage polarization. Local and sustained DNase I release degraded dysregulated neutrophil extracellular traps (NETs) and suppressed neutrophil activation and the mucus plugging microenvironment, which in turn amplified M2 macrophage polarization efficiency. Such dual-stage drug release behavior facilitated down-regulation of pro-inflammatory cytokines in the lung but anti-inflammatory cytokine production through remodeling lung immune homeostasis, ultimately promoting lung tissue repair. This work presents a versatile hybrid biomimetic nanoplatform for the local pulmonary delivery of dual-drug therapeutics and displays potential in the treatment of acute inflammation.

Influence of the irradiated pulmonary microenvironment on macrophage and T cell dynamics

BACKGROUND

The lung is sensitive to radiation, increasing normal tissue toxicity risks following radiation therapy. Adverse outcomes include pneumonitis and pulmonary fibrosis, which result from dysregulated intercellular communication within the pulmonary microenvironment. Although macrophages are implicated in these pathogenic outcomes, the impact of their microenvironment is not well understood.

MATERIALS AND METHODS

C57BL/6J mice received 6Gyx5 irradiation to the right lung. Macrophage and T cell dynamics were investigated in ipsilateral right lungs, contralateral left lungs and non-irradiated control lungs 4-26wk post exposure. Lungs were evaluated by flow cytometry, histology and proteomics.

RESULTS

Following uni-lung irradiation, focal regions of macrophage accumulation were noted in both lungs by 8wk, however by 26wk fibrotic lesions were observed only in ipsilateral lungs. Infiltrating and alveolar macrophages populations expanded in both lungs, however transitional CD11b + alveolar macrophages persisted only in ipsilateral lungs and expressed lower CD206. Concurrently, arginase-1 + macrophages accumulated in ipsilateral but not contralateral lungs at 8 and 26wk post exposure, while CD206 + macrophages were absent from these accumulations. While radiation expanded CD8 + T cells in both lungs, T regulatory cells only increased in ipsilateral lungs. Unbiased proteomics analysis of immune cells revealed a substantial number of differentially expressed proteins in ipsilateral lungs when compared to contralateral lungs and both differed from non-irradiated controls.

CONCLUSIONS

Pulmonary macrophage and T cell dynamics are impacted by the microenvironmental conditions that develop following radiation exposure, both locally and systemically. While macrophages and T cells infiltrate and expand in both lungs, they diverge phenotypically depending on their environment.

Macrophages: From Simple Phagocyte to an Integrative Regulatory Cell for Inflammation and Tissue Regeneration-A Review of the Literature

The understanding of macrophages and their pathophysiological role has dramatically changed within the last decades. Macrophages represent a very interesting cell type with regard to biomaterial-based tissue engineering and regeneration. In this context, macrophages play a crucial role in the biocompatibility and degradation of implanted biomaterials. Furthermore, a better understanding of the functionality of macrophages opens perspectives for potential guidance and modulation to turn inflammation into regeneration. Such knowledge may help to improve not only the biocompatibility of scaffold materials but also the integration, maturation, and preservation of scaffold-cell constructs or induce regeneration. Nowadays, macrophages are classified into two subpopulations, the classically activated macrophages (M1 macrophages) with pro-inflammatory properties and the alternatively activated macrophages (M2 macrophages) with anti-inflammatory properties. The present narrative review gives an overview of the different functions of macrophages and summarizes the recent state of knowledge regarding different types of macrophages and their functions, with special emphasis on tissue engineering and tissue regeneration.

The Role of Macrophages and Alveolar Epithelial Cells in the Development of ARDS

Acute lung injury (ALI) usually causes acute respiratory distress syndrome (ARDS), or even death in critical ill patients. Immune cell infiltration in inflamed lungs is an important hallmark of ARDS. Macrophages are a type of immune cell that participate in the entire pathogenic trajectory of ARDS and most prominently via their interactions with lung alveolar epithelial cells (AECs). In the early stage of ARDS, classically activated macrophages secrete pro-inflammatory cytokines to clearance of the pathogens which may damage alveolar AECs cell structure and result in cell death. Paradoxically, in late stage of ARDS, anti-inflammatory cytokines secreted by alternatively activated macrophages dampen the inflammation response and promote epithelial regeneration and alveolar structure remodeling. In this review, we discuss the important role of macrophages and AECs in the progression of ARDS.

Unlocking autofluorescence in the era of full spectrum analysis: Implications for immunophenotype discovery projects

Understanding the complex elements affecting signal resolution in cytometry is key for quality experimental design and data. In this study, we incorporate autofluorescence as a contributing factor to our understanding of resolution in cytometry and corroborate its impact in fluorescence signal detection through mathematical predictions supported by empirical evidence. Our findings illustrate the critical importance of autofluorescence extraction via full spectrum unmixing in unmasking dim signals and delineating the expression and subset distribution of low abundance markers in discovery projects. We apply our findings to the precise definition of the tissue and cellular distribution of a weakly expressed fluorescent protein that reports on a low-abundance immunological gene. Exploiting the full spectrum coverage enabled by Aurora 5L, we describe a novel approach to the isolation of pure cell subset-specific autofluorescence profiles based on high dimensionality reduction algorithms. This method can also be used to unveil differences in the autofluorescent fingerprints of tissues in homeostasis and after immunological challenges.

Zanubrutinib ameliorates lipopolysaccharide-induced acute lung injury via regulating macrophage polarization

Acute lung injury (ALI) is a disease characterized by pulmonary diffusion dysfunction and its exacerbation stage is acute respiratory distress syndrome (ARDS), which may develop to multiple organ failure and seriously threatens human health. ALI has high mortality rates and few effective treatments, thus effective protection measures for ALI are becoming increasingly important. Macrophages play a key regulatory role in the pathogenesis of ALI, and the degree of macrophage polarization is closely related to the severity and prognosis of ALI. In this study, we evaluated the effects of Zanubrutinib (ZB), a BTK small molecule inhibitor approved by the FDA for the treatment of cell lymphoma, on macrophage polarization and acute lung injury. In the in vivo study, we constructed a mouse model of Lipopolysaccharide (LPS)-induced acute lung injury and found that ZB could improve the acute injury of mouse lungs by inhibiting the secretion of proinflammatory factors and promoting the secretion of anti-inflammatory factors, reduce the number of inflammatory cells in alveolar lavage fluid, and then alleviate the inflammatory response. In vivo and in vitro studies have shown that ZB could inhibit the M1 macrophage polarization and promote the M2 macrophage polarization. Subsequent mechanistic studies revealed that ZB could inhibit the macrophage M1 polarization via targeting BTK activation and inhibiting JAK2/STAT1 and TLR4/MyD88/NF-κB signaling pathways, and promote the macrophage M2 polarization by promoting the activation of STAT6 and PI3K / Akt signaling pathways. In summary, ZB has shown therapeutic effect in LPS-induced acute lung injury in mice, which provides a potential candidate drug to treat acute lung injury.

Integrins are double-edged swords in pulmonary infectious diseases

Integrins are an important family of adhesion molecules that are widely distributed on immune cells in the lungs. Of note, accumulating evidences have shown that integrins are double-edged swords in pulmonary infectious diseases. On one hand, integrins promote the migration of immune cells to remove the invaded pathogens in the infected lungs. However, on the other hand, integrins also act as the targets for pathogens to escape from host immune system, which is a potential factor leading to further tissue damage. Thus, the innovative therapeutic strategies based on integrins has inspired well-founded hopes to treat pulmonary infectious diseases. In this review, we illustrate the involvement of integrins in pulmonary infectious diseases, and further discuss the innovative therapeutic targets based on integrins.

Cigarette Smoke Exposure Induces Neurocognitive Impairments and Neuropathological Changes in the Hippocampus

Background and Objective

Neurocognitive dysfunction is present in up to ∼61% of people with chronic obstructive pulmonary disease (COPD), with symptoms including learning and memory deficiencies, negatively impacting the quality of life of these individuals. As the mechanisms responsible for neurocognitive deficits in COPD remain unknown, we explored whether chronic cigarette smoke (CS) exposure causes neurocognitive dysfunction in mice and whether this is associated with neuroinflammation and an altered neuropathology.

Methods

Male BALB/c mice were exposed to room air (sham) or CS (9 cigarettes/day, 5 days/week) for 24 weeks. After 23 weeks, mice underwent neurocognitive tests to assess working and spatial memory retention. At 24 weeks, mice were culled and lungs were collected and assessed for hallmark features of COPD. Serum was assessed for systemic inflammation and the hippocampus was collected for neuroinflammatory and structural analysis.

Results

Chronic CS exposure impaired lung function as well as driving pulmonary inflammation, emphysema, and systemic inflammation. CS exposure impaired working memory retention, which was associated with a suppression in hippocampal microglial number, however, these microglia displayed a more activated morphology. CS-exposed mice showed changes in astrocyte density as well as a reduction in synaptophysin and dendritic spines in the hippocampus.

Conclusion

We have developed an experimental model of COPD in mice that recapitulates the hallmark features of the human disease. The altered microglial/astrocytic profiles and alterations in the neuropathology within the hippocampus may explain the neurocognitive dysfunction observed during COPD.

Macrophage NOX2 NADPH oxidase maintains alveolar homeostasis in mice

The leukocyte NADPH oxidase 2 (NOX2) plays a key role in pathogen killing and immunoregulation. Genetic defects in NOX2 result in chronic granulomatous disease (CGD), associated with microbial infections and inflammatory disorders, often involving the lung. Alveolar macrophages (AMs) are the predominant immune cell in the airways at steady state, and limiting their activation is important, given the constant exposure to inhaled materials, yet the importance of NOX2 in this process is not well understood. In this study, we showed a previously undescribed role for NOX2 in maintaining lung homeostasis by suppressing AM activation, in CGD mice or mice with selective loss of NOX2 preferentially in macrophages. AMs lacking NOX2 had increased cytokine responses to Toll-like receptor-2 (TLR2) and TLR4 stimulation ex vivo. Moreover, between 4 and 12 week of age, mice with global NOX2 deletion developed an activated CD11bhigh subset of AMs with epigenetic and transcriptional profiles reflecting immune activation compared with WT AMs. The presence of CD11bhigh AMs in CGD mice correlated with an increased number of alveolar neutrophils and proinflammatory cytokines at steady state and increased lung inflammation after insults. Moreover, deletion of NOX2 preferentially in macrophages was sufficient for mice to develop an activated CD11bhigh AM subset and accompanying proinflammatory sequelae. In addition, we showed that the altered resident macrophage transcriptional profile in the absence of NOX2 is tissue specific, as those changes were not seen in resident peritoneal macrophages. Thus, these data demonstrate that the absence of NOX2 in alveolar macrophages leads to their proinflammatory remodeling and dysregulates alveolar homeostasis.

Investigating the Intercellular Communication Network of Immune Cell in Acute Respiratory Distress Syndrome with Sepsis

Acute respiratory distress syndrome (ARDS) is recognized as a serious public health issue that results in respiratory failure and high mortality rates. The syndrome is characterized by immune cell aggregation, communication, activation, and alveolar epithelial damage. To elucidate the complex dynamic process of the immune system's response in ARDS, we construct the intercellular communication network of immune cells in ARDS based on a single-cell RNA sequencing dataset (including three sepsis-induced ARDS patients and four sepsis-only patients). The results show that macrophages relayed most of the intercellular signals (ligand–receptor pairs) in both groups. Many genes related to immune response (IFI44L, ISG, and HLA-DQB1) and biological functions (response to virus, negative regulation of viral life cycle, and response to interferon-beta) were detected via differentially expressed gene analysis of macrophages between the two groups. Deep analysis of the intercellular signals related to the macrophage found that sepsis-induced ARDS harbored distinctive intercellular signals related to chemokine–chemokine receptors (CCL3/4/5−CCR1), which mainly are involved in the disturbance of the STAT family transcription factors (TFs), such as STAT2 and STAT3. These signals and downstream TFs might play key roles in macrophage M1/M2 polarization in the process of sepsis-induced ARDS. This study provides a comprehensive view of the intercellular communication landscape between sepsis and sepsis-induced ARDS and identifies key intercellular communications and TFs involved in sepsis-induced ARDS. We believe that our study provides valuable clues for understanding the immune response mechanisms of ARDS.

Macrophages as Emerging Key Players in Mitochondrial Transfers

Macrophages are a group of heterogeneous cells widely present throughout the body. Under the influence of their specific environments, via both contact and noncontact signals, macrophages integrate into host tissues and contribute to their development and the functions of their constituent cells. Mitochondria are essential organelles that perform intercellular transfers to regulate cell homeostasis. Our review focuses on newly discovered roles of mitochondrial transfers between macrophages and surrounding cells and summarizes emerging functions of macrophages in transmitophagy, metabolic regulation, and immune defense. We also discuss the negative influence of mitochondrial transfers on macrophages, as well as current therapies targeting mitochondria in macrophages. Regulation of macrophages through mitochondrial transfers between macrophages and their surrounding cells is a promising therapy for various diseases, including cardiovascular diseases, inflammatory diseases, obesity, and cancer.

The Role of Macrophages in the Pathogenesis of SARS-CoV-2-Associated Acute Respiratory Distress Syndrome

Macrophages are cells that mediate both innate and adaptive immunity reactions, playing a major role in both physiological and pathological processes. Systemic SARS-CoV-2-associated complications include acute respiratory distress syndrome (ARDS), disseminated intravascular coagulation syndrome, edema, and pneumonia. These are predominantly effects of massive macrophage activation that collectively can be defined as macrophage activation syndrome. In this review we focus on the role of macrophages in COVID-19, as pathogenesis of the new coronavirus infection, especially in cases complicated by ARDS, largely depends on macrophage phenotypes and functionalities. We describe participation of monocytes, monocyte-derived and resident lung macrophages in SARS-CoV-2-associated ARDS and discuss possible utility of cell therapies for its treatment, notably the use of reprogrammed macrophages with stable pro- or anti-inflammatory phenotypes.

Altered Macrophage Function Associated with Crystalline Lung Inflammation in Acid Sphingomyelinase Deficiency

Deficiency of ASM (acid sphingomyelinase) causes the lysosomal storage Niemann-Pick disease (NPD). Patients with NPD type B may develop progressive interstitial lung disease with frequent respiratory infections. Although several investigations using the ASM-deficient (ASMKO) mouse NPD model revealed inflammation and foamy macrophages, there is little insight into the pathogenesis of NPD-associated lung disease. Using ASMKO mice, we report that ASM deficiency is associated with a complex inflammatory phenotype characterized by marked accumulation of monocyte-derived CD11b+ macrophages and expansion of airspace/alveolar CD11c+ CD11b- macrophages, both with increased size, granularity, and foaminess. Both the alternative and classical pathways were activated, with decreased in situ phagocytosis of opsonized (Fc-coated) targets, preserved clearance of apoptotic cells (efferocytosis), secretion of Th2 cytokines, increased CD11c+/CD11b+ cells, and more than a twofold increase in lung and plasma proinflammatory cytokines. Macrophages, neutrophils, eosinophils, and noninflammatory lung cells of ASMKO lungs also exhibited marked accumulation of chitinase-like protein Ym1/2, which formed large eosinophilic polygonal Charcot-Leyden-like crystals. In addition to providing insight into novel features of lung inflammation that may be associated with NPD, our report provides a novel connection between ASM and the development of crystal-associated lung inflammation with alterations in macrophage biology.

LXA4 Inhibits Lipopolysaccharide-Induced Inflammatory Cell Accumulation by Resident Macrophages in Mice

Introduction

Alveolar macrophages that regulate the inflammatory response in lungs are the main target cell for the treatment of inflammatory pulmonary pathologies, such as acute respiratory distress syndrome (ARDS). Yolk sac derived alveolar resident macrophages play an important role in the pulmonary inflammatory response. With regards to anti-inflammatory actions, lipoxin A4 (LXA4) has been identified as an inflammatory "braking signal".

Methods

In vivo, LXA4 (0.1 µg/mouse) was injected intraperitoneally after intratracheal (1 mg/kg) lipopolysaccharide (LPS) administration; flow cytometry was used to measure peripheral blood monocyte derived recruited macrophage and neutrophil numbers; resident alveolar macrophage was depleted by liposome clodronate; CXCL2, CCL2, MMP9 level was detected by RT-PCR and ELISA. In vitro, sorted resident macrophages (1×10⁶) were cultured with LPS (1 μg/mL) and LXA4 (100 nmol/mL) with or without BOC-2 (10 μM) for 24 h to gain a better understanding of the mechanisms of LXA4.

Results

LXA4 inhibited tumor necrosis factor-a (TNF-a) and interleukin-1β (IL-1β) production induced by LPS. LXA4 also mediated LPS-induced macrophage recruitment and showed that this was dependent on CCL2 secretion and release by resident macrophages. LXA4 protects lung tissue by inhibiting neutrophil recruitment, partly through the CXCL2/MMP-9 signaling pathway. CXCL2 and MMP-9 are mainly expressed by resident macrophages and neutrophils, respectively. Finally, LXA4's beneficial effects were abrogated by BOC-2, an LXA4 receptor inhibitor.

Conclusion

These results suggest that LXA4 may be a promising therapy for preventing and treating ARDS.

SPHK2-Generated S1P in CD11b+ Macrophages Blocks STING to Suppress the Inflammatory Function of Alveolar Macrophages

Acute lung injury (ALI) is a lethal inflammatory lung disorder whose incidence is on the rise. Alveolar macrophages normally act to resolve inflammation, but when dysregulated they can provoke ALI. We demonstrate that monocyte-derived macrophages (CD11b⁺ macrophages) recruited into the airspace upregulate the anti-inflammatory function of alveolar macrophages by suppressing their stimulator of type 1 interferon gene (STING) signaling. Depletion of CD11b⁺ macrophages in mice (macrophage^dep mice) after endotoxin or after Pseudomonas aeruginosa causes expansion of the inflammatory alveolar macrophage population, leading to neutrophil accumulation, irreversible loss of lung vascular barrier function, and lethality. We show that CD11b⁺ macrophages suppress alveolar macrophage-STING signaling via sphingosine kinase-2 (SPHK2) generation of sphingosine-1-phosphate (S1P). Thus, adoptive transfer of wild-type (WT) or STING^−/−, but not SPHK2^−/−, CD11b monocytes from murine bone marrow into injured macrophage^dep mice rescue anti-inflammatory alveolar macrophages and reverse lung vascular injury. SPHK2-induced S1P generation in CD11b⁺ macrophages has the potential to educate alveolar macrophages to resolve ALI.

Joshi et al. demonstrate an essential role of SPHK2⁺ monocyte-derived CD11b⁺ macrophages, which are recruited to the airspace, in promoting anti-inflammatory function of alveolar macrophages during lung injury. They show that S1P generated by recruited SPHK2⁺-CD11b⁺ macrophages suppresses STING signaling in alveolar macrophages to resolve inflammatory injury.

Identification of PD-1 ligands: PD-L1 and PD-L2 on macrophages in lung cancer milieu by flow cytometry

Background

The efficacy of immune checkpoint inhibitors (ICIs) remains unexpected and in some patients the resistance to anti-programmed death-1 (anti-PD-1) and anti-programmed death ligand 1 (anti-PD-L1) agents is observed. One of possible explanation may be PD-L2 activity. PD-1 ligands: PD-L1 and PD-L2 are present on cancer cells but also, not without significance, on alveolar macrophages (AMs) contributing to immune-suppression in the tumor microenvironment. The aim of this study was to analyse PD-L2, PD-L1 expression on AMs in bronchoalveolar lavage fluid (BALF) in relation to PD-1 positive T lymphocytes.

Methods

Seventeen patients with lung cancer were investigated. BALF cells from the lung with cancer (clBALF) and from the opposite “healthy” lung (hlBALF) and peripheral blood (PB) lymphocytes were investigated. Flow cytometry method was used.

Results

We found that 100% of CD68+ AMs from the clBALF were PD-L1 and PD-L2-positive. Unexpectedly, fluorescence minus one (FMO) PD-L1 and PD-L2 stained controls and isotype controls also showed strong autofluorescence. The hlBALF AMs exhibited a similar PD-L1 and PD-L2 autofluorescence. The median proportion of PD-1+ T lymphocytes was higher in the clBALF than the hlBALF and PB (28.9 vs. 23.4% vs. 15.6%, P=0.0281).

Conclusions

We discussed the opportunities of exploring the PD-1-PD-L1/PD-L2 pathway in the lung cancer environment, which may help to find new potential biomarkers for immunotherapy. We concluded that precise identification by flow cytometry of macrophages in the BALF is possible, but our study showed that the autofluorescence of macrophages did not allow to assess a real expression of PD-L2 as well as PD-L1 on AMs.

Cell-Cell Interaction Mechanisms in Acute Lung Injury

ABSTRACT

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are caused by an exaggerated inflammatory response arising from a wide variety of pulmonary and systemic insults. Lung tissue is composed of a variety of cell populations, including parenchymal and immune cells. Emerging evidence has revealed that multiple cell populations in the lung work in concert to regulate lung inflammation in response to both direct and indirect stimulations. To date, the question of how different types of pulmonary cells communicate with each other and subsequently regulate or modulate inflammatory cascades remains to be fully addressed. In this review, we provide an overview of current advancements in understanding the role of cell-cell interaction in the development of ALI and depict molecular mechanisms by which cell-cell interactions regulate lung inflammation, focusing on inter-cellular activities and signaling pathways that point to possible therapeutic opportunities for ALI/ARDS.

IL-17A-Secreting Memory γδ T Cells Play a Pivotal Role in Sensitization and Development of Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) typically presents with interstitial inflammation and granulomas induced by an aberrant immune response to inhaled Ags in sensitized individuals. Although IL-17A is involved in the development of HP, the cellular sources of IL-17A and the mechanisms by which IL-17A contributes to granuloma formation remain unclear. Recent studies report that γδ T cells produce IL-17A and exhibit memory properties in various diseases. Therefore, we focused on IL-17A-secreting memory γδ T cells in the sensitization phase and aimed to elucidate the mechanisms by which IL-17A contributes to granuloma formation in HP. We induced a mouse model of HP using pigeon dropping extract (PDE) in wild-type and IL-17A knockout (IL-17A^-/-) mice. IL-17A^-/- mice exhibited reduced granulomatous areas, attenuated aggregation of CD11b⁺ alveolar macrophages, and reduced levels of CCL2, CCL4, and CCL5 in the bronchoalveolar lavage fluid. Among IL-17A⁺ cells, more γδ T cells than CD4⁺ cells were detected after intranasal PDE administration. Interestingly, the expansion of IL-17A-secreting Vγ4⁺ or Vγ1^-Vγ4^- cells of convalescent mice was enhanced in response to the sensitizing Ag. Additionally, coculture of macrophages with PDE and Vγ4⁺ cells purified from PDE-exposed convalescent mice produced significantly more IL-17A than coculture with Vγ4⁺ cells from naive mice. Our findings demonstrate that in the sensitization phase of HP, IL-17A-secreting memory γδ T cells play a pivotal role. Furthermore, we characterized the IL-17A/CCL2, CCL4, CCL5/CD11b⁺ alveolar macrophage axis, which underlies granuloma formation in HP. These findings may lead to new clinical examinations or therapeutic targets for HP.

Development of improved method to identify and analyze lung fibrocytes with flow cytometry in a reporter mouse strain

Introduction

Fibrocytes are emerging myeloid‐derived circulating cells that can migrate into damaged tissues and usually contribute to their repair. Key features of fibrocytes include the expression myeloid markers, production of extracellular matrix proteins, and secretion of various humoral factors that activate resident fibroblasts; they also have the potential to differentiate into fibroblasts. However, no specific surface markers have been identified to identify fibrocytes in vivo. One reason could be that the method used to detect fibrocytes requires intracellular collagen staining.

Methods

In the present study, to establish an improved method for the detection of lung fibrocytes and to analyze viable fibrocytes, we used collagen I(α)2‐green fluorescent protein (Col‐GFP) reporter mice, which had undergone the intratracheal instillation of bleomycin (BLM).

Results

Using flow cytometry to gate out cells with autofluorescence, we clearly found that CD45⁺ GFP⁺ cells resided in the lungs of Col‐GFP mice at a steady state and these cells increased after BLM injury, peaking at Day 14. These cells expressed not only known cell surface markers of fibrocytes, but also some novel markers, in addition to a low level of collagen I in comparison to CD45⁻ GFP⁺ cells.

Conclusion

Our findings suggest that the improved method can be a useful for the detection of pure lung fibrocytes and allows us to further analyze the characteristics of viable fibrocytes.

Inhibition of the CCL2 receptor, CCR2, enhances tumor response to immune checkpoint therapy

Immunotherapies targeting the PD-1/PD-L1 axis are now a mainstay in the clinical management of multiple cancer types, however, many tumors still fail to respond. CCL2 is highly expressed in various cancer types and has been shown to be associated with poor prognosis. Inhibition or blockade of the CCL2/CCR2 signaling axis has thus been an area of interest for cancer therapy. Here we show across multiple murine tumor and metastasis models that CCR2 antagonism in combination with anti-PD-1 therapy leads to sensitization and enhanced tumor response over anti-PD-1 monotherapy. We show that enhanced treatment response correlates with enhanced CD8+ T cell recruitment and activation and a concomitant decrease in CD4+ regulatory T cell. These results provide strong preclinical rationale for further clinical exploration of combining CCR2 antagonism with PD-1/PD-L1-directed immunotherapies across multiple tumor types especially given the availability of small molecule CCR2 inhibitors and antibodies.

Regulatory role of Gpr84 in the switch of alveolar macrophages from CD11blo to CD11bhi status during lung injury process

Acute respiratory distress syndrome (ARDS) is a kind of comprehensive disease with excessive inflammation and high clinical mortality. Multiple immune cells are involved in the ARDS process. Amongst these populations, lung-resident alveolar macrophages (AMs) are known to participate in the regulation of ARDS. GPR84, a metabolite-sensing GPCR sensing medium-chain fatty acids (MCFAs), is highly expressed in LPS-challenged macrophages and considered as a pro-inflammatory receptor. In this study, it was hypothesized that Gpr84 may be involved in pulmonary homeostasis via its regulatory effect on the switch of AM status. In LPS-induced ALI mouse model, we identified the internal LPS-induced switch of AMs from CD11b^lo to more inflamed CD11b^hi status, which is deeply related to the exacerbated imbalance of homeostasis in the lung injury process. Gpr84 was highly expressed in ALI lung tissues and involved in cytokine release, phagocytosis and status switch of AMs through positive regulatory crosstalk with TLR4-related pathways via CD14 and LBP, which relied on Akt, Erk1/2, and STAT3. If conserved in humans, GPR84 may represent a potential therapeutic target for ARDS.

Soluble PD-L1 improved direct ARDS by reducing monocyte-derived macrophages

Acute respiratory distress syndrome (ARDS) is common in intensive care units (ICUs), although it is associated with high mortality, no effective pharmacological treatments are currently available. Despite being poorly understood, the role of programmed cell death protein 1 (PD-1) and PD-ligand 1 (PD-L1) axis in ARDS may provide significant insights into the immunosuppressive mechanisms that occur after ARDS. In the present study, we observed that the level of soluble PD-L1 (sPD-L1), a potential activator of the PD-1 pathway, was upregulated in survivors of direct ARDS than in non-survivors. Administration of sPD-L1 in mice with direct ARDS relieved inflammatory lung injury and improved the survival rate, indicating the protective role of sPD-L1 in direct ARDS. Using high-throughput mass cytometry, we found a marked decrease in the number of lung monocyte-derived macrophages (MDMs) with proinflammatory markers, and the protective role of sPD-L1 diminished in ARDS mice with monocyte/macrophage depletion. Furthermore, PD-1 expression increased in the MDMs of patients and mice with direct ARDS. Finally, we showed that sPD-L1 induced MDM apoptosis in patients with direct ARDS. Taken together, our results demonstrated that the engagement of sPD-L1 on PD-1 expressing macrophages resulted in a decrease in pro-inflammatory macrophages and eventually improved direct ARDS. Our study identified a prognostic indicator for patients with direct ARDS and a potential target for therapeutic development in direct ARDS.

The Dynamics of the Ferret Immune Response During H7N9 Influenza Virus Infection

As the recent outbreak of SARS-CoV-2 has highlighted, the threat of a pandemic event from zoonotic viruses, such as the deadly influenza A/H7N9 virus subtype, continues to be a major global health concern. H7N9 virus strains appear to exhibit greater disease severity in mammalian hosts compared to natural avian hosts, though the exact mechanisms underlying this are somewhat unclear. Knowledge of the H7N9 host-pathogen interactions have mainly been constrained to natural sporadic human infections. To elucidate the cellular immune mechanisms associated with disease severity and progression, we used a ferret model to closely resemble disease outcomes in humans following influenza virus infection. Intriguingly, we observed variable disease outcomes when ferrets were inoculated with the A/Anhui/1/2013 (H7N9) strain. We observed relatively reduced antigen-presenting cell activation in lymphoid tissues which may be correlative with increased disease severity. Additionally, depletions in CD8⁺ T cells were not apparent in sick animals. This study provides further insight into the ways that lymphocytes maturate and traffic in response to H7N9 infection in the ferret model.

IL-1β prevents ILC2 expansion, type 2 cytokine secretion, and mucus metaplasia in response to early-life rhinovirus infection in mice

BACKGROUND

Early-life wheezing-associated respiratory infection with human rhinovirus (RV) is associated with asthma development. RV infection of 6-day-old immature mice causes mucous metaplasia and airway hyperresponsiveness which is associated with the expansion of IL-13-producing type 2 innate lymphoid cells (ILC2s) and dependent on IL-25 and IL-33. We examined regulation of this asthma-like phenotype by IL-1β.

METHODS

Six-day-old wild-type or NRLP3-/- mice were inoculated with sham or RV-A1B. Selected mice were treated with IL-1 receptor antagonist (IL-1RA), anti-IL-1β, or recombinant IL-1β.

RESULTS

Rhinovirus infection induced Il25, Il33, Il4, Il5, Il13, muc5ac, and gob5 mRNA expression, ILC2 expansion, mucus metaplasia, and airway hyperresponsiveness. RV also induced lung mRNA and protein expression of pro-IL-1β and NLRP3 as well as cleavage of caspase-1 and pro-IL-1β, indicating inflammasome priming and activation. Lung macrophages were a major source of IL-1β. Inhibition of IL-1β signaling with IL-1RA, anti-IL-1β, or NLRP3 KO increased RV-induced type 2 cytokine immune responses, ILC2 number, and mucus metaplasia, while decreasing IL-17 mRNA expression. Treatment with IL-1β had the opposite effect, decreasing IL-25, IL-33, and mucous metaplasia while increasing IL-17 expression. IL-1β and IL-17 each suppressed Il25, Il33, and muc5ac mRNA expression in cultured airway epithelial cells. Finally, RV-infected 6-day-old mice showed reduced IL-1β mRNA and protein expression compared to mature mice.

CONCLUSION

Macrophage IL-1β limits type 2 inflammation and mucous metaplasia following RV infection by suppressing epithelial cell innate cytokine expression. Reduced IL-1β production in immature animals provides a mechanism permitting asthma development after early-life viral infection.

Macrophage polarization and its role in the pathogenesis of acute lung injury/acute respiratory distress syndrome

PURPOSE

Macrophages are highly plastic cells. Under different stimuli, macrophages can be polarized into several different subsets. Two main macrophage subsets have been suggested: classically activated or inflammatory (M1) macrophages and alternatively activated or anti-inflammatory (M2) macrophages. Macrophage polarization is governed by a highly complex set of regulatory networks. Many recent studies have shown that macrophages are key orchestrators in the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) and that regulation of macrophage polarization may improve the prognosis of ALI/ARDS. A further understanding of the mechanisms of macrophage polarization is expected to be helpful in the development of novel therapeutic targets to treat ALI/ARDS. Therefore, we performed a literature review to summarize the regulatory mechanisms of macrophage polarization and its role in the pathogenesis of ALI/ARDS.

METHODS

A computer-based online search was performed using the PubMed database and Web of Science database for published articles concerning macrophages, macrophage polarization, and ALI/ARDS.

RESULTS

In this review, we discuss the origin, polarization, and polarization regulation of macrophages as well as the role of macrophage polarization in various stages of ARDS. According to the current literature, regulating the polarized state of macrophages might be a potential therapeutic strategy against ALI/ARDS.

Lung and Eye Disease Develop Concurrently in Supplemental Oxygen-Exposed Neonatal Mice

Bronchopulmonary dysplasia (BPD) and retinopathy of prematurity (ROP) are two debilitating disorders that develop in preterm infants exposed to supplemental oxygen to prevent respiratory failure. Both can lead to lifelong disabilities, such as chronic obstructive pulmonary disease and vision loss. Due to the lack of a standard experimental model of coincident disease, the underlying associations between BPD and ROP are not well characterized. To address this gap, we used the robust mouse model of oxygen-induced retinopathy exposing C57BL/6 mice to 75% oxygen from postnatal day 7 to 12. The cardinal features of ROP were replicated by this strategy, and the lungs of the same mice were simultaneously examined for evidence of BPD-like lung injury, investigating both the short- and long-term effects of early-life supplemental oxygen exposure. At postnatal days 12 and 18, mild lung disease was evident by histopathologic analysis together with the expected vasculopathy in the inner retina. At later time points, the lung lesion had progressed to severe airspace enlargement and alveolar simplification, with concurrent thinning in the outer layer of the retina. In addition, critical angiogenic oxidative stress and inflammatory factors reported to be dysregulated in ROP were similarly impaired in the lungs. These data shed new light on the interconnectedness of these two neonatal disorders, holding potential for the discovery of novel targets to treat BPD and ROP.

Developmental Immaturity of Siglec Receptor Expression on Neonatal Alveolar Macrophages Predisposes to Severe Group B Streptococcal Infection

Streptococcus agalactiae (Group B Streptococcus, GBS) is the most common neonatal pathogen. However, the cellular and molecular mechanisms for neonatal susceptibility to GBS pneumonia and sepsis are incompletely understood. Here we optimized a mouse model of GBS pneumonia to test the role of alveolar macrophage (ΑΜΦ) maturation in host vulnerability to disease. Compared with juvenile and adult mice, neonatal mice infected with GBS had increased mortality and persistence of lung injury. In addition, neonatal mice were defective in GBS phagocytosis and killing. ΑΜΦ depletion and disruption of ΑΜΦ differentiation in Csf2^−/− mice both impaired GBS clearance. AMΦ engage the heavily sialylated GBS capsule via the cell surface Siglec receptors Sn and Siglec-E. Although both newborn and adult ΑΜΦ expressed Siglec-E, newborn ΑΜΦ expressed significantly lower levels of Sn. We propose that a developmental delay in Sn expression on ΑΜΦ may prevent effective killing and clearing of GBS from the newborn lung.

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Newborn mice fail to kill GBS, developing persistent lung injury

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Mature AMΦ detect the Sialic acid capsule on GBS to mediate bacterial clearance

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Immature newborn AMΦ lack mature Siglec expression required for killing GBS

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GBS engages the inhibitory Siglec-E on newborn AMΦ to suppress innate immunity

Aggravation of asthmatic inflammation by chlorine exposure via innate lymphoid cells and CD11cintermediate macrophages

BACKGROUND

Chlorine is widely used in daily life as disinfectant. However, chronic exposure to chlorine products aggravates allergic T_H 2 inflammation and airway hyperresponsiveness (AHR). Innate lymphoid cells (ILCs) in airways contribute to the inception of asthma in association with virus infection, pollution, and excess of nutrient, but it is not known whether chronic chlorine exposure can activate innate immune cells. The aim of this study was to evaluate the impact of chlorine inhalation on the innate immunity such as ILCs and macrophages in relation with the development of asthma by using murine ovalbumin (OVA) sensitization/challenge model.

METHODS

Six-week-old female BALB/c mice were sensitized and challenged with OVA in the presence and absence of chronic low-dose chlorine exposure by inhalation of naturally vaporized gas of 5% sodium hypochlorite solution. AHR, airway inflammatory cells, from BALF and the population of ILCs and macrophages in the lung were evaluated.

RESULTS

The mice exposed to chlorine with OVA (Cl + OVA group) showed enhanced AHR and eosinophilic inflammation compared to OVA-treated mice (OVA group). The population of T_H 2 cells, ILC2s, and ILC3s increased in Cl + OVA group compared with OVA group. CD11c^int macrophages also remarkably increased in Cl + OVA group compared with OVA group. The deletion of macrophages by clodronate resulted in reduction of ILC2s and ILC3s population which was restored by adoptive transfer of CD11c^int macrophages.

CONCLUSIONS

Chronic chlorine inhalation contributes to the exacerbation of airway inflammation in asthmatic airway by mobilizing pro-inflammatory macrophage into the lung as well as stimulating group 2 and 3 ILCs.

SHIP-1, a target of miR-155, regulates endothelial cell responses in lung fibrosis

Src Homology 2-containing Inositol Phosphatase-1 (SHIP-1) is a target of miR-155, a pro-inflammatory factor. Deletion of the SHIP-1 gene in mice caused spontaneous lung inflammation and fibrosis. However, the role and function of endothelial miR-155 and SHIP-1 in lung fibrosis remain unknown. Using whole-body miR-155 knockout mice and endothelial cell-specific conditional miR-155 (VEC-Cre-miR-155 or VEC-miR-155) or SHIP-1 (VEC-SHIP-1) knockout mice, we assessed endothelial-mesenchymal transition (EndoMT) and fibrotic responses in bleomycin (BLM) induced lung fibrosis models. Primary mouse lung endothelial cells (MLEC) and human umbilical vein endothelial cells (HUVEC) with SHIP-1 knockdown were analyzed in TGF-β1 or BLM, respectively, induced fibrotic responses. Fibrosis and EndoMT were significantly reduced in miR-155KO mice and changes in EndoMT markers in MLEC after TGF-β1 stimulation confirmed the in vivo findings. Furthermore, lung fibrosis and EndoMT responses were reduced in VEC-miR-155 mice but significantly enhanced in VEC-SHIP-1 mice after BLM challenge. SHIP-1 knockdown in HUVEC cells resulted in enhanced EndoMT induced by BLM. Meanwhile, these changes involved the PI3K/AKT, JAK/STAT3, and SMAD/STAT signaling pathways. These studies demonstrate that endothelial miR-155 plays an important role in fibrotic responses in the lung through EndoMT. Endothelial SHIP-1 is essential in controlling fibrotic responses and SHIP-1 is a target of miR-155. Endothelial cells are an integral part in lung fibrosis.

Heterogeneity and plasticity of porcine alveolar macrophage and pulmonary interstitial macrophage isolated from healthy pigs in vitro

This study investigated the heterogeneity and plasticity of porcine alveolar macrophages (PAM) and pulmonary interstitial macrophages (IM) isolated from healthy pigs, including phenotype, function and gene expression. Dynamic changes of nitric oxide (NO) levels secreted by PAM and IM with stimulation of different doses of lipopolysaccharide (LPS) were investigated by Griess method, and the viability of the PAM and IM cells was investigated by MTT assay. Flow cytometry, fluorescence quantitative PCR and ELISA techniques were used to measure cell phenotype, gene expression and cytokine secretion, respectively. The PAM and IM cells in normal healthy pigs showed heterogeneity with 95.42±1.51% and 31.99±5.84% of CD163+ macrophage, respectively. The NO level in IM was significantly higher versus PAM after LPS treatment. Consistently, the ratio of Arg I/iNOS in IM was much lower than that in PAM, suggesting that the PAM belong to M2 macrophages and the IM belong to M1 macrophages. The PAM and IM cells in normal healthy pigs also showed plasticity. The Arg I/iNOS ratio and TIMP1/MMP12 ratio were significantly decreased in LPS- or LPS+IFNγ-treated PAM and IM, suggesting that cells were polarized towards M1 macrophages under LPS or LPS+IFNγ stimulation. On the contrary, IL-4 and IL-13 stimulation on PAM and IM lead to M2 polarization. A similar result was found in IL-1β gene expression and TNFα secretion. In conclusion, porcine macrophages have shown heterogeneity and plasticity on polarization under the stimulation of LPS, IFNγ, IL-4 and IL-13.

Immunotherapeutic Challenges for Pediatric Cancers

Solid tumors contain a mixture of malignant cells and non-malignant infiltrating cells that often create a chronic inflammatory and immunosuppressive microenvironment that restricts immunotherapeutic approaches. Although childhood and adult cancers share some similarities related to microenvironmental changes, pediatric cancers are unique, and adult cancer practices may not be wholly applicable to our pediatric patients. This review highlights the differences in tumorigenesis, viral infection, and immunologic response between children and adults that need to be considered when trying to apply experiences from experimental therapies in adult cancer patients to pediatric cancers.

Improving the Quality and Reproducibility of Flow Cytometry in the Lung. An Official American Thoracic Society Workshop Report

Defining responses of the structural and immune cells in biologic systems is critically important to understanding disease states and responses to injury. This requires accurate and sensitive methods to define cell types in organ systems. The principal method to delineate the cell populations involved in these processes is flow cytometry. Although researchers increasingly use flow cytometry, technical challenges can affect its accuracy and reproducibility, thus significantly limiting scientific advancements. This challenge is particularly critical to lung immunology, as the lung is readily accessible and therefore used in preclinical and clinical studies to define potential therapeutics. Given the importance of flow cytometry in pulmonary research, the American Thoracic Society convened a working group to highlight issues and technical challenges to the performance of high-quality pulmonary flow cytometry, with a goal of improving its quality and reproducibility.

A Flow Cytometric Method for Isolating Cystic Fibrosis Airway Macrophages from Expectorated Sputum

Research to understand the contribution of macrophages to nonresolving airway inflammation in cystic fibrosis (CF) and other chronic suppurative airways diseases has been hindered by a lack of methods for isolating and studying these cells. With the development of technologies that can characterize small numbers of cells or individual cells, there is an even greater need for methodologies to isolate rare cells in heterogeneous specimens. Here, we describe a method that overcomes the technical obstacles imposed by sputum debris and apoptotic cells, and allows isolation of pure populations of macrophages from CF sputum. In addition to enhancing our ability to study human CF airway macrophages, this protocol can be adapted to study cells in sputum from other chronic suppurative lung diseases (e.g., chronic obstructive pulmonary disease) and used for isolation of individual cells for single cell analyses.

Rhinovirus-induces progression of lung disease in a mouse model of COPD via IL-33/ST2 signaling axis

Rhinovirus (RV), which is associated with acute exacerbations, also causes persistent lung inflammation in patients with chronic obstructive pulmonary disease (COPD), but the underlying mechanisms are not well-known. Recently, we demonstrated that RV causes persistent lung inflammation with accumulation of a subset of macrophages (CD11b⁺/CD11c⁺), and CD8⁺ T cells, and progression of emphysema. In the present study, we examined the mechanisms underlying the RV-induced persistent inflammation and progression of emphysema in mice with COPD phenotype. Our results demonstrate that at 14 days post-RV infection, in addition to sustained increase in CCL3, CXCL-10 and IFN-γ expression as previously observed, levels of interleukin-33 (IL-33), a ligand for ST2 receptor, and matrix metalloproteinase (MMP)12 are also elevated in mice with COPD phenotype, but not in normal mice. Further, MMP12 was primarily expressed in CD11b⁺/CD11c⁺ macrophages. Neutralization of ST2, reduced the expression of CXCL-10 and IFN-γ and attenuated accumulation of CD11b⁺/CD11c⁺ macrophages, neutrophils and CD8⁺ T cells in COPD mice. Neutralization of IFN-γ, or ST2 attenuated MMP12 expression and prevented progression of emphysema in these mice. Taken together, our results indicate that RV may stimulate expression of CXCL-10 and IFN-γ via activation of ST2/IL-33 signaling axis, which in turn promote accumulation of CD11b+/CD11c+ macrophages and CD8⁺ T cells. Furthermore, RV-induced IFN-γ stimulates MMP12 expression particularly in CD11b⁺/CD11c⁺ macrophages, which may degrade alveolar walls thus leading to progression of emphysema in these mice. In conclusion, our data suggest an important role for ST2/IL-33 signaling axis in RV-induced pathological changes in COPD mice.

Gr1int/high Cells Dominate the Early Phagocyte Response to Mycobacterial Lung Infection in Mice

Lung infection by Mycobacterium tuberculosis is characterized by chronic infection of lung-resident macrophages, long considered to be the primary hosts and determinants of the outcome of the early immune response. Although alveolar macrophages are well-known to host intracellular mycobacteria at later stages of disease, little is known about the earliest events of the innate immune response. The phagocytes that take up mycobacteria immediately following infection, and how the early lung phagocyte response is altered by vaccination with M. bovis bacille Calmette-Guérin (BCG) were unknown. Using BCG expressing the bright red fluorescent protein tdTomato and flow cytometry, we modeled early infection in C57BL/6 mice and tracked phagocyte population kinetics and uptake of mycobacteria, to better understand the involvement of specific phagocyte subsets. By 1 day post-infection, dose-dependent accumulation of neutrophils was observed and surprisingly, granulocytes comprised a greater proportion of infected phagocytes than alveolar macrophages. By 7 days post-infection alveolar macrophages had become the dominant BCG-associated phagocytes. Prior mucosal BCG exposure provided immunized mice with greater frequencies and numbers of lung macrophage subsets, and a significantly greater proportion of alveolar macrophages expressed CD11b prior to and following challenge infection. These data provide the first evidence of granulocytes as the dominant infected phagocyte subset early after mycobacterial infection, and highlight enhanced recruitment of lung macrophages as a factor associated with protection in BCG-immunized mice.

Intranasal and epicutaneous administration of Toll-like receptor 7 (TLR7) agonists provides protection against influenza A virus-induced morbidity in mice

Toll-like receptor 7 (TLR7) is a pattern recognition receptor that recognizes viral RNA following endocytosis of the virus and initiates a powerful immune response characterized by Type I IFN production and pro-inflammatory cytokine production. Despite this immune response, the virus causes very significant pathology, which may be inflammation-dependent. In the present study, we examined the effect of intranasal delivery of the TLR7 agonist, imiquimod or its topical formulation Aldara, on the inflammation and pathogenesis caused by IAV infection. In mice, daily intranasal delivery of imiquimod prevented peak viral replication, bodyweight loss, airway and pulmonary inflammation, and lung neutrophils. Imiquimod treatment also resulted in a significant reduction in pro-inflammatory neutrophil chemotactic cytokines and prevented the increase in viral-induced lung dysfunction. Various antibody isotypes (IgG1, IgG2a, total IgG, IgE and IgM), which were increased in the BALF following influenza A virus infection, were further increased with imiquimod. While epicutaneous application of Aldara had a significant effect on body weight, it did not reduce neutrophil and eosinophil airway infiltration; indicating less effective drug delivery for this formulation. We concluded that intranasal imiquimod facilitates a more effective immune response, which can limit the pathology associated with influenza A virus infection.

Regulation of hematopoietic cell signaling by SHIP-1 inositol phosphatase: growth factors and beyond

SHIP-1 is a hematopoietic-specific inositol phosphatase activated downstream of a multitude of receptors including those for growth factors, cytokines, antigen, immunoglobulin and toll-like receptor agonists where it exerts inhibitory control. While it is constitutively expressed in all immune cells, SHIP-1 expression is negatively regulated by the inflammatory and oncogenic micro-RNA miR-155. Knockout mouse studies have shown the importance of SHIP-1 in various immune cell subsets and have revealed a range of immune-mediated pathologies that are engendered due to loss of SHIP-1's regulatory activity, impelling investigations into the role of SHIP-1 in human disease. In this review, we provide an overview of the literature relating to the role of SHIP-1 in hematopoietic cell signaling and function, we summarize recent reports that highlight the dysregulation of the SHIP-1 pathway in cancers, autoimmune disorders and inflammatory diseases, and lastly we discuss the importance of SHIP-1 in restraining myeloid growth factor signaling.

NAMPT: A pleiotropic modulator of monocytes and macrophages

Nicotinamide phosphoribosyltransferase (NAMPT) is the bottleneck enzyme of the NAD salvage pathway and thereby is a controller of intracellular NAD concentrations. It has been long known that the same enzyme can be secreted by a number of cell types and acts as a cytokine, although its receptor is at present unknown. Investigational compounds have been developed that target the enzymatic activity as well as the extracellular action (i.e. neutralizing antibodies). The present contribution reviews the evidence that links intracellular and extracellular NAMPT to myeloid biology, for example governing monocyte/macrophage differentiation, polarization and migration. Furthermore, it reviews the evidence that links this protein to some disorders in which myeloid cells have a prominent role (acute infarct, inflammatory bowel disease, acute lung injury and rheumatoid arthritis) and the data showing that inhibition of the enzymatic activity or the neutralization of the cytokine is beneficial in preclinical animal models.

Effects of Influenza on Alveolar Macrophage Viability Are Dependent on Mouse Genetic Strain

Secondary bacterial coinfections following influenza virus pose a serious threat to human health. Therefore, it is of significant clinical relevance to understand the immunological causes of this increased susceptibility. Influenza-induced alterations in alveolar macrophages (AMs) have been shown to be a major underlying cause of the increased susceptibility to bacterial superinfection. However, the mechanisms responsible for this remain under debate, specifically in terms of whether AMs are depleted in response to influenza infection or are maintained postinfection, but with disrupted phagocytic activity. The data presented in this article resolves this issue by showing that either mechanism can differentially occur in individual mouse strains. BALB/c mice exhibited a dramatic IFN-γ-dependent reduction in levels of AMs following infection with influenza A, whereas AM levels in C57BL/6 mice were maintained throughout the course of influenza infection, although the cells displayed an altered phenotype, namely an upregulation in CD11b expression. These strain differences were observed regardless of whether infection was performed with low or high doses of influenza virus. Furthermore, infection with either the H1N1 A/California/04/2009 (CA04) or H1N1 A/PR8/1934 (PR8) virus strain yielded similar results. Regardless of AM viability, both BALB/c and C57BL/6 mice showed a high level of susceptibility to postinfluenza bacterial infection. These findings resolve the apparent inconsistencies in the literature, identify mouse strain-dependent differences in the AM response to influenza infection, and ultimately may facilitate translation of the mouse model to clinical application.

The Role of Macrophages in the Pathogenesis of ALI/ARDS

Despite development in the understanding of the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), the underlying mechanism still needs to be elucidated. Apart from leukocytes and endothelial cells, macrophages are also essential for the process of the inflammatory response in ALI/ARDS. Notably, macrophages play a dual role of proinflammation and anti-inflammation based on the microenvironment in different pathological stages. In the acute phase of ALI/ARDS, resident alveolar macrophages, typically expressing the alternatively activated phenotype (M2), shift into the classically activated phenotype (M1) and release various potent proinflammatory mediators. In the later phase, the M1 phenotype of activated resident and recruited macrophages shifts back to the M2 phenotype for eliminating apoptotic cells and participating in fibrosis. In this review, we summarize the main subsets of macrophages and the associated signaling pathways in three different pathological phases of ALI/ARDS. According to the current literature, regulating the function of macrophages and monocytes might be a promising therapeutic strategy against ALI/ARDS.