Macrophage-epithelial interactions in pulmonary alveoli

Cancer treatments as paradoxical catalysts of tumor awakening in the lung

Much of the fatality of tumors is linked to the growth of metastases, which can emerge months to years after apparently successful treatment of primary tumors. Metastases arise from disseminated tumor cells (DTCs), which disperse through the body in a dormant state to seed distant sites. While some DTCs lodge in pre-metastatic niches (PMNs) and rapidly develop into metastases, other DTCs settle in distinct microenvironments that maintain them in a dormant state. Subsequent awakening, induced by changes in the microenvironment of the DTC, causes outgrowth of metastases. Hence, there has been extensive investigation of the factors causing survival and subsequent awakening of DTCs, with the goal of disrupting these processes to decrease cancer lethality. We here provide a detailed overview of recent developments in understanding of the factors controlling dormancy and awakening in the lung, a common site of metastasis for many solid tumors. These factors include dynamic interactions between DTCs and diverse epithelial, mesenchymal, and immune cell populations resident in the lung. Paradoxically, among key triggers for metastatic outgrowth, lung tissue remodeling arising from damage induced by the treatment of primary tumors play a significant role. In addition, growing evidence emphasizes roles for inflammation and aging in opposing the factors that maintain dormancy. Finally, we discuss strategies being developed or employed to reduce the risk of metastatic recurrence.

The breathtaking world of human respiratory in vitro models: Investigating lung diseases and infections in 3D models, organoids, and lung-on-chip

The COVID-19 pandemic illustrated an urgent need for sophisticated, human tissue models to rapidly test and develop effective treatment options against this newly emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Thus, in particular, the last 3 years faced an extensive boost in respiratory and pulmonary model development. Nowadays, 3D models, organoids and lung-on-chip, respiratory models in perfusion, or precision-cut lung slices are used to study complex research questions in human primary cells. These models provide physiologically relevant systems for studying SARS-CoV-2 and, of course, other respiratory pathogens, but they are, too, suited for studying lung pathologies, such as CF, chronic obstructive pulmonary disease, or asthma, in more detail in terms of viral infection. With these models, the cornerstone has been laid for further advancing the organs by, for example, inclusion of several immune cell types or humoral immune components, combination with other organs in microfluidic organ-on-chip devices, standardization and harmonization of the devices for reliable and reproducible drug and vaccine testing in high throughput.

Biomass-related PM2.5 induced inflammatory microenvironment via IL-17F/IL-17RC axis

Biomass exposure is a significant environmental risk factor for COPD, but the underlying mechanisms have not yet been fully elucidated. Inflammatory microenvironment has been shown to drive the development of many chronic diseases. Pollution exposure can cause increased levels of inflammatory factors in the lungs, leading to an inflammatory microenvironment which is prevalent in COPD. Our findings revealed that IL-17F was elevated in COPD, while exposure to biomass led to increased expression of IL-17F in both alveolar epithelial and macrophage cells in mice. Blocking IL-17F could alleviate the lung inflammation induced by seven days of biomass exposure in mice. We employed a transwell co-culture system to simulate the microenvironment and investigate the interactions between MLE-12 and MH-S cells. We demonstrated that anti-IL-17F antibody attenuated the inflammatory responses induced by BRPM2.5 in MLE-12 and MH-S co-cultured with BRPM2.5-MLE-12, which reduced inflammatory changes in microenvironment. We found that IL-17RC, an important receptor for IL-17F, played a key role in the interactions. Knockout of IL-17RC in MH-S resulted in inhibited IL-17F signaling and attenuated inflammatory response after MH-S co-culture with BRPM2.5-MLE-12. Our investigation suggests that BRPM2.5 induces lung epithelial-macrophage interactions via IL-17F/IL-17RC axis regulating the inflammatory response. These results may provide a novel strategy for effective prevention and treatment of biomass-related COPD.

Global Trends in Research Regarding Macrophages Associated with Chronic Obstructive Pulmonary Disease: A Bibliometric Analysis from 2011 to 2022

Purpose

Chronic obstructive pulmonary disease (COPD) is a prevalent respiratory condition characterized by chronic airway inflammation, where macrophages from the innate immune system may exert a pivotal influence. Our study aimed to summarize the present state of knowledge and to identify the focal points and emerging developments regarding macrophages associated with COPD through bibliometrics.

Methods

Publications regarding research on macrophages associated with COPD from January 1, 2011, to January 1, 2022, were retrieved from the Science Citation Index-Expanded (SCI-E) which is part of the Web of Science database. In total, 1521 publications were analyzed using bibliometric methodology. VOSviewer was used to analyze the annual publications, countries, institutions, authors, journals, and research hotspots.

Results

Based on the bibliometric analysis, publications relating to macrophages associated with COPD tended to increase from 2011 to 2022. The United States was the largest producer and most influential country in this field. Research during the past decade has focused on inflammation in the lungs. Most previous studies have mainly focused on the mechanisms that promote the initiation and progression of COPD. Macrophage-related oxidative stress and immunity, communication between macrophages and epithelial cells, and interventions for acute exacerbations have become the focus of more recent studies and will become a hot topic in the future.

Conclusion

Global research on macrophage-associated COPD has been growing rapidly in the past decade. The hot topics in this field gradually tended to shift focus from "inflammation" to "oxidative stress", "epithelial-cells", and "exacerbations". The significance of macrophages in coordinating immune responses, interacting with other cells, and exhibiting dysregulated capacities has attracted increasing attention to COPD pathogenesis. The adoption of new technologies may provide a more promising and comprehensive understanding of the specific role of macrophages in COPD in the future.

Alveolar macrophages in tissue homeostasis, inflammation, and infection: evolving concepts of therapeutic targeting

Alveolar macrophages (AMs) are the sentinel cells of the alveolar space, maintaining homeostasis, fending off pathogens, and controlling lung inflammation. During acute lung injury, AMs orchestrate the initiation and resolution of inflammation in order to ultimately restore homeostasis. This central role in acute lung inflammation makes AMs attractive targets for therapeutic interventions. Single-cell RNA-Seq and spatial omics approaches, together with methodological advances such as the generation of human macrophages from pluripotent stem cells, have increased understanding of the ontogeny, function, and plasticity of AMs during infectious and sterile lung inflammation, which could move the field closer to clinical application. However, proresolution phenotypes might conflict with proinflammatory and antibacterial responses. Therefore, therapeutic targeting of AMs at vulnerable time points over the course of infectious lung injury might harbor the risk of serious side effects, such as loss of antibacterial host defense capacity. Thus, the identification of key signaling hubs that determine functional fate decisions in AMs is of the utmost importance to harness their therapeutic potential.

Acyloxyacyl hydrolase promotes pulmonary defense by preventing alveolar macrophage tolerance

Although alveolar macrophages (AMs) play important roles in preventing and eliminating pulmonary infections, little is known about their regulation in healthy animals. Since exposure to LPS often renders cells hyporesponsive to subsequent LPS exposures ("tolerant"), we tested the hypothesis that LPS produced in the intestine reaches the lungs and stimulates AMs, rendering them tolerant. We found that resting AMs were more likely to be tolerant in mice lacking acyloxyacyl hydrolase (AOAH), the host lipase that degrades and inactivates LPS; isolated Aoah-/- AMs were less responsive to LPS stimulation and less phagocytic than were Aoah+/+ AMs. Upon innate stimulation in the airways, Aoah-/- mice had reduced epithelium- and macrophage-derived chemokine/cytokine production. Aoah-/- mice also developed greater and more prolonged loss of body weight and higher bacterial burdens after pulmonary challenge with Pseudomonas aeruginosa than did wildtype mice. We also found that bloodborne or intrarectally-administered LPS desensitized ("tolerized") AMs while antimicrobial drug treatment that reduced intestinal commensal Gram-negative bacterial abundance largely restored the innate responsiveness of Aoah-/- AMs. Confirming the role of LPS stimulation, the absence of TLR4 prevented Aoah-/- AM tolerance. We conclude that commensal LPSs may stimulate and desensitize (tolerize) alveolar macrophages in a TLR4-dependent manner and compromise pulmonary immunity. By inactivating LPS in the intestine, AOAH promotes antibacterial host defenses in the lung.

Effects of LRRK2 Inhibitors in Nonhuman Primates

Toxicology studies in nonhuman primates were conducted to evaluate selective, brain penetrant inhibitors of LRRK2. GNE 7915 was limited to 7-day administration in cynomolgus monkeys at 65 mg/kg/day or limited to 14 days in rhesus at 22.5 mg/kg b.i.d. due to physical signs. Compound 25 demonstrated acceptable tolerability at 50 and 225 mg/kg b.i.d. for 7 days in rhesus monkeys. MK-1468 was tolerated during 7-day administration at 100, 200 or 800 mg/kg/day or for 30-day administration at 30, 100, or 500 mg/kg b.i.d. in rhesus monkeys. The lungs revealed hypertrophy of type 2 pneumocytes, with accumulation of intra-alveolar macrophages. Transmission electron microscopy confirmed increased lamellar structures within hypertrophic type 2 pneumocytes. Hypertrophy and hyperplasia of type 2 pneumocytes with accumulation of intra-alveolar macrophages admixed with neutrophils were prominent at peripheral lungs of animals receiving compound 25 or MK-1468. Affected type 2 pneumocytes were immuno-positive for pro-surfactant C, but negative for CD11c, a marker for intra-alveolar macrophages. Accumulation of collagen within alveolar walls, confirmed by histochemical trichrome stain, accompanied changes described for compound 25 and MK-1468. Following a 12-week treatment-free interval, animals previously receiving MK-1468 for 30 days exhibited remodeling of alveolar structure and interstitial components that did not demonstrate reversibility.

Exosomal Non-Coding RNAs: Novel Regulators of Macrophage-Linked Intercellular Communication in Lung Cancer and Inflammatory Lung Diseases

Macrophages are innate immune cells and often classified as M1 macrophages (pro-inflammatory states) and M2 macrophages (anti-inflammatory states). Exosomes are cell-derived nanovesicles that range in diameter from 30 to 150 nm. Non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), are abundant in exosomes and exosomal ncRNAs influence immune responses. Exosomal ncRNAs control macrophage-linked intercellular communication via their targets or signaling pathways, which can play positive or negative roles in lung cancer and inflammatory lung disorders, including acute lung injury (ALI), asthma, and pulmonary fibrosis. In lung cancer, exosomal ncRNAs mediated intercellular communication between lung tumor cells and tumor-associated macrophages (TAMs), coordinating cancer proliferation, migration, invasion, metastasis, immune evasion, and therapy resistance. In inflammatory lung illnesses, exosomal ncRNAs mediate macrophage activation and inflammation to promote or inhibit lung damage. Furthermore, we also discussed the possible applications of exosomal ncRNA-based therapies for lung disorders.

Mechanisms by Which Liposomes Improve Inhaled Drug Delivery for Alveolar Diseases

Diseases of the pulmonary alveolus, such as pulmonary fibrosis, are leading causes of morbidity and mortality, but exceedingly few drugs are developed for them. A major reason for this gap is that after inhalation, drugs are quickly whisked away from alveoli due to their high perfusion. To solve this problem, the mechanisms by which nano-scale drug carriers dramatically improve lung pharmacokinetics using an inhalable liposome formulation containing nintedanib, an antifibrotic for pulmonary fibrosis, are studied. Direct instillation of liposomes in murine lung increases nintedanib's total lung delivery over time by 8000-fold and lung half life by tenfold, compared to oral nintedanib. Counterintuitively, it is shown that pulmonary surfactant neither lyses nor aggregates the liposomes. Instead, each lung compartment (alveolar fluid, alveolar leukocytes, and parenchyma) elutes liposomes over 24 h, likely serving as "drug depots." After deposition in the surfactant layer, liposomes are transferred over 3-6 h to alveolar leukocytes (which take up a surprisingly minor 1-5% of total lung dose instilled) in a nonsaturable fashion. Further, all cell layers of the lung parenchyma take up liposomes. These and other mechanisms elucidated here should guide engineering of future inhaled nanomedicine for alveolar diseases.

Innate immune responses in pneumonia

The lungs are an immunologically unique environment; they are exposed to innumerable pathogens and particulate matter daily. Appropriate clearance of pathogens and response to pollutants is required to prevent overwhelming infection, while preventing tissue damage and maintaining efficient gas exchange. Broadly, the innate immune system is the collection of immediate, intrinsic immune responses to pathogen or tissue injury. In this review, we will examine the innate immune responses of the lung, with a particular focus on their role in pneumonia. We will discuss the anatomic barriers and antimicrobial proteins of the lung, pathogen and injury recognition, and the role of leukocytes (macrophages, neutrophils, and innate lymphocytes) and lung stromal cells in innate immunity. Throughout the review, we will focus on new findings in innate immunity as well as features that are unique to the lung.

microRNA-33 deficiency in macrophages enhances autophagy, improves mitochondrial homeostasis, and protects against lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and ultimately fatal disease. Recent findings have shown a marked metabolic reprogramming associated with changes in mitochondrial homeostasis and autophagy during pulmonary fibrosis. The microRNA-33 (miR-33) family of microRNAs (miRNAs) encoded within the introns of sterol regulatory element binding protein (SREBP) genes are master regulators of sterol and fatty acid (FA) metabolism. miR-33 controls macrophage immunometabolic response and enhances mitochondrial biogenesis, FA oxidation, and cholesterol efflux. Here, we show that miR-33 levels are increased in bronchoalveolar lavage (BAL) cells isolated from patients with IPF compared with healthy controls. We demonstrate that specific genetic ablation of miR-33 in macrophages protects against bleomycin-induced pulmonary fibrosis. The absence of miR-33 in macrophages improves mitochondrial homeostasis and increases autophagy while decreasing inflammatory response after bleomycin injury. Notably, pharmacological inhibition of miR-33 in macrophages via administration of anti-miR-33 peptide nucleic acids (PNA-33) attenuates fibrosis in different in vivo and ex vivo mice and human models of pulmonary fibrosis. These studies elucidate a major role of miR-33 in macrophages in the regulation of pulmonary fibrosis and uncover a potentially novel therapeutic approach to treat this disease.

Intravital microscopy for real-time monitoring of drug delivery and nanobiological processes

Intravital microscopy (IVM) expands our understanding of cellular and molecular processes, with applications ranging from fundamental biology to (patho)physiology and immunology, as well as from drug delivery to drug processing and drug efficacy testing. In this review, we highlight modalities, methods and model organisms that make up today's IVM landscape, and we present how IVM - via its high spatiotemporal resolution - enables analysis of metabolites, small molecules, nanoparticles, immune cells, and the (tumor) tissue microenvironment. We furthermore present examples of how IVM facilitates the elucidation of nanomedicine kinetics and targeting mechanisms, as well as of biological processes such as immune cell death, host-pathogen interactions, metabolic states, and disease progression. We conclude by discussing the prospects of IVM clinical translation and examining the integration of machine learning in future IVM practice.

Frontline workers: Mediators of mucosal immunity in community acquired pneumonia and COVID-19

The current COVID-19 pandemic has highlighted a need to further understand lung mucosal immunity to reduce the burden of community acquired pneumonia, including that caused by the SARS-CoV-2 virus. Local mucosal immunity provides the first line of defence against respiratory pathogens, however very little is known about the mechanisms involved, with a majority of literature on respiratory infections based on the examination of peripheral blood. The mortality for severe community acquired pneumonia has been rising annually, even prior to the current pandemic, highlighting a significant need to increase knowledge, understanding and research in this field. In this review we profile key mediators of lung mucosal immunity, the dysfunction that occurs in the diseased lung microenvironment including the imbalance of inflammatory mediators and dysbiosis of the local microbiome. A greater understanding of lung tissue-based immunity may lead to improved diagnostic and prognostic procedures and novel treatment strategies aimed at reducing the disease burden of community acquired pneumonia, avoiding the systemic manifestations of infection and excess morbidity and mortality.

CLEC5A is critical in Pseudomonas aeruginosa-induced acute lung injury

Pseudomonas aeruginosa is one of the most common nosocomial infections worldwide, and it frequently causes ventilator-associated acute pneumonia in immunocompromised patients. Abundant neutrophil extracellular traps (NETs) contribute to acute lung injury, thereby aggravating ventilator-induced lung damage. While pattern recognition receptors (PRRs) TLR4 and TLR5 are required for host defense against P. aeruginosa invasion, the PRR responsible for P. aeruginosa–induced NET formation, proinflammatory cytokine release, and acute lung injury remains unclear. We found that myeloid C-type lectin domain family 5 member A (CLEC5A) interacts with LPS of P. aeruginosa and is responsible for P. aeruginosa–induced NET formation and lung inflammation. P. aeruginosa activates CLEC5A to induce caspase-1–dependent NET formation, but it neither causes gasdermin D (GSDMD) cleavage nor contributes to P. aeruginosa–induced neutrophil death. Blockade of CLEC5A attenuates P. aeruginosa–induced NETosis and lung injury, and simultaneous administration of anti-CLEC5A mAb with ciprofloxacin increases survival rate and decreases collagen deposition in the lungs of mice challenged with a lethal dose of P. aeruginosa. Thus, CLEC5A is a promising therapeutic target to reduce ventilator-associated lung injury and fibrosis in P. aeruginosa–induced pneumonia.

A Barrier to Defend - Models of Pulmonary Barrier to Study Acute Inflammatory Diseases

Pulmonary diseases represent four out of ten most common causes for worldwide mortality. Thus, pulmonary infections with subsequent inflammatory responses represent a major public health concern. The pulmonary barrier is a vulnerable entry site for several stress factors, including pathogens such as viruses, and bacteria, but also environmental factors e.g. toxins, air pollutants, as well as allergens. These pathogens or pathogen-associated molecular pattern and inflammatory agents e.g. damage-associated molecular pattern cause significant disturbances in the pulmonary barrier. The physiological and biological functions, as well as the architecture and homeostatic maintenance of the pulmonary barrier are highly complex. The airway epithelium, denoting the first pulmonary barrier, encompasses cells releasing a plethora of chemokines and cytokines, and is further covered with a mucus layer containing antimicrobial peptides, which are responsible for the pathogen clearance. Submucosal antigen-presenting cells and neutrophilic granulocytes are also involved in the defense mechanisms and counterregulation of pulmonary infections, and thus may directly affect the pulmonary barrier function. The detailed understanding of the pulmonary barrier including its architecture and functions is crucial for the diagnosis, prognosis, and therapeutic treatment strategies of pulmonary diseases. Thus, considering multiple side effects and limited efficacy of current therapeutic treatment strategies in patients with inflammatory diseases make experimental in vitro and in vivo models necessary to improving clinical therapy options. This review describes existing models for studyying the pulmonary barrier function under acute inflammatory conditions, which are meant to improve the translational approaches for outcome predictions, patient monitoring, and treatment decision-making.

Epithelial‑derived exosomes promote M2 macrophage polarization via Notch2/SOCS1 during mechanical ventilation

Alveolar macrophages (AMs) play an essential role in ventilator-induced lung injury (VILI). Exosomes and their cargo, including microRNAs (miRNAs/miRs) serve as regulators of the intercellular communications between macrophages and epithelial cells (ECs), and are involved in maintaining homeostasis in lung tissue. The present study found that exosomes released by ECs subjected to cyclic stretching promoted M2 macrophage polarization. It was demonstrated that miR-21a-5p, upregulated in epithelial-derived exosomes, increased the percentage of M2 macrophages by suppressing the expression of Notch2 and the suppressor of cytokine signaling 1 (SOCS1). The overexpression of Notch2 decreased the percentage of M2 macrophages. However, these effects were reversed by the downregulation of SOCS1. The percentage of M2 macrophages was increased in both short-term high- and low-tidal-volume mechanical ventilation, and the administration of exosomes-derived from cyclically stretched ECs had the same function. However, the administration of miR-21a-5p antagomir decreased M2 macrophage activation induced by cyclically stretched ECs or ventilation. Thus, the present study demonstrates that the intercellular transferring of exosomes from ECs to AMs promotes M2 macrophage polarization. Exosomes may prove to be a novel treatment for VILI.

ISM1 protects lung homeostasis via cell-surface GRP78-mediated alveolar macrophage apoptosis

Alveolar macrophages (AMs) are critical for lung immune defense and homeostasis. They are orchestrators of chronic obstructive pulmonary disease (COPD), with their number significantly increased and functions altered in COPD. However, it is unclear how AM number and function are controlled in a healthy lung and if changes in AMs without environmental assault are sufficient to trigger lung inflammation and COPD. We report here that absence of isthmin 1 (ISM1) in mice (Ism1-/- ) leads to increase in both AM number and functional heterogeneity, with enduring lung inflammation, progressive emphysema, and significant lung function decline, phenotypes similar to human COPD. We reveal that ISM1 is a lung resident anti-inflammatory protein that selectively triggers the apoptosis of AMs that harbor high levels of its receptor cell-surface GRP78 (csGRP78). csGRP78 is present at a heterogeneous level in the AMs of a healthy lung, but csGRP78high AMs are expanded in Ism1-/- mice, cigarette smoke (CS)-induced COPD mice, and human COPD lung, making these cells the prime targets of ISM1-mediated apoptosis. We show that csGRP78high AMs mostly express MMP-12, hence proinflammatory. Intratracheal delivery of recombinant ISM1 (rISM1) depleted csGRP78high AMs in both Ism1-/- and CS-induced COPD mice, blocked emphysema development, and preserved lung function. Consistently, ISM1 expression in human lungs positively correlates with AM apoptosis, suggesting similar function of ISM1-csGRP78 in human lungs. Our findings reveal that AM apoptosis regulation is an important physiological mechanism for maintaining lung homeostasis and demonstrate the potential of pulmonary-delivered rISM1 to target csGRP78 as a therapeutic strategy for COPD.

Lung epithelial cells interact with immune cells and bacteria to shape the microenvironment in tuberculosis

The lung epithelium has long been overlooked as a key player in tuberculosis disease. In addition to acting as a direct barrier to Mycobacterium tuberculosis (Mtb), epithelial cells (EC) of the airways and alveoli act as first responders during Mtb infections; they directly sense and respond to Mtb by producing mediators such as cytokines, chemokines and antimicrobials. Interactions of EC with innate and adaptive immune cells further shape the immune response against Mtb. These three essential components, epithelium, immune cells and Mtb, are rarely studied in conjunction, owing in part to difficulties in coculturing them. Recent advances in cell culture technologies offer the opportunity to model the lung microenvironment more closely. Herein, we discuss the interplay between lung EC, immune cells and Mtb and argue that modelling these interactions is of key importance to unravel early events during Mtb infection.

Autocrine, Paracrine, and Endocrine Signals That Can Alter Alveolar Macrophages Function

Alveolar macrophages (AMs) are extremely versatile cells with complex functions involved in health or diseases such as pneumonia, asthma, and pulmonary alveolar proteinosis. In recent years, it has been widely identified that the different functions and states of macrophages are the results from the complex interplay between microenvironmental signals and macrophage lineage. Diverse and complicated signals to which AMs respond are mentioned when they are described individually or in a particular state of AMs. In this review, the microenvironmental signals are divided into autocrine, paracrine, and endocrine signals based on their secreting characteristics. This new perspective on classification provides a more comprehensive and systematic introduction to the complex signals around AMs and is helpful for understanding the roles of AMs affected by physiological environment. The existing possible treatments of AMs are also mentioned in it. The thorough understanding of AMs signals modulation may be contributed to the development of more effective therapies for AMs-related lung diseases.

Imaging reveals novel innate immune responses in lung, liver, and beyond

Highly dynamic immune responses are generated toward pathogens or injuries, in vivo. Multiple immune cell types participate in various facets of the response which leads to a concerted effort in the removal and clearance of pathogens or injured tissue and a return to homeostasis. Intravital microscopy (IVM) has been extensively utilized to unravel the dynamics of immune responses, visualizing immune cell behavior in intact living tissues, within a living organism. For instance, the phenomenon of leukocyte recruitment cascade. Importantly, IVM has led to a deep appreciation that immune cell behavior and responses in individual organs are distinct, but also can influence one another. In this review, we discuss how IVM as a tool has been used to study the innate immune responses in various tissues during homeostasis, injury, and infection.

ProLung™-budesonide Inhibits SARS-CoV-2 Replication and Reduces Lung Inflammation

Background:

Inhaled budesonide benefits patients with COVID-19. ProLung™-budesonide enables the sustained, low dose administration of budesonide within a delivery vehicle similar to lung surfactant. ProLung™-budesonide may offer anti-inflammatory and protective effects to the lung in COVID-19, yet it’s effect on SARS-CoV-2 replication is unknown.

Objective:

To determine the efficacy of ProLung™-budesonide against SARS-CoV-2-infection in vitro, evaluate its ability to decrease inflammation, and airway hyperresponsiveness in an animal model of lung inflammation.

Methods:

SARS-CoV-2-infected Vero 76 cells were treated with ProLung™-budesonide ([0.03–100 µg/ml]) for 3 days, and virus yield in the supernatant was measured. Ovalbumin-sensitized C57BL/6 mice received aerosolized (a) ProLung™-budesonide weekly, (b) only budesonide, either daily or weekly, or (c) weekly empty ProLung™ carrier (without budesonide). All treatment groups were compared to sensitized untreated, or normal mice using histopathologic examination, electron microscopy (EM), airway hyperresponsiveness (AHR) to Methacholine (Mch) challenge, and eosinophil peroxidase activity (EPO) measurements in bronchioalveolar lavage (BAL).

Results:

ProLung™-budesonide showed significant inhibition of viral replication of SARS-CoV-2-infected cells with the selectivity index (SI) value >24. Weekly ProLung™-budesonide and daily budesonide therapy significantly decreased lung inflammation and EPO in BAL. ProLung™-budesonide localized in type II pneumocytes, and was the only group to significantly decrease AHR, and EPO in BAL with Mch challenge

Conclusions:

ProLung™-budesonide significantly inhibited viral replication in SARS-CoV-2-infected cells. It localized into type II pneumocytes, decreased lung inflammation, AHR and EPO activity with Mch challenge. This novel drug formulation may offer a potential inhalational treatment for COVID-19.

Cytokine Cocktail Promotes Alveolar Macrophage Reconstitution and Functional Maturation in a Murine Model of Haploidentical Bone Marrow Transplantation

Infectious pneumonia is one of the most common complications after bone marrow transplantation (BMT), which is considered to be associated with poor reconstitution and functional maturation of alveolar macrophages (AMs) post-transplantation. Here, we present evidence showing that lack of IL-13-secreting group 2 innate lymphoid cells (ILC2s) in the lungs may underlay poor AM reconstitution in a mouse model of haploidentical BMT (haplo-BMT). Recombinant murine IL-13 was able to potentiate monocyte-derived AM differentiation in vitro. When intranasally administered, a cocktail of granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-13, and CCL2 not only promoted donor monocyte-derived AM reconstitution in haplo-BMT-recipient mice but also enhanced the innate immunity of the recipient animals against pulmonary bacterial infection. These results provide a useful clue for a clinical strategy to prevent pulmonary bacterial infection at the early stage of recipients post-BMT.

In vitro and ex vivo models in inhalation biopharmaceutical research - advances, challenges and future perspectives

Oral inhalation results in pulmonary drug targeting and thereby reduces systemic side effects, making it the preferred means of drug delivery for the treatment of respiratory disorders such as asthma, chronic obstructive pulmonary disease or cystic fibrosis. In addition, the high alveolar surface area, relatively low enzymatic activity and rich blood supply of the distal airspaces offer a promising pathway to the systemic circulation. This is particularly advantageous when a rapid onset of pharmacological action is desired or when the drug is suffering from stability issues or poor biopharmaceutical performance following oral administration. Several cell and tissue-based in vitro and ex vivo models have been developed over the years, with the intention to realistically mimic pulmonary biological barriers. It is the aim of this review to critically discuss the available models regarding their advantages and limitations and to elaborate further which biopharmaceutical questions can and cannot be answered using the existing models.

Physiological and Disease Models of Respiratory System Based on Organ-on-a-Chip Technology

The pathogenesis of respiratory diseases is complex, and its occurrence and development also involve a series of pathological processes. The present research methods are have difficulty simulating the natural developing state of the disease in the body, and the results cannot reflect the real growth state and function in vivo. The development of microfluidic chip technology provides a technical platform for better research on respiratory diseases. The size of its microchannel can be similar to the space for cell growth in vivo. In addition, organ-on-a-chip can achieve long-term co-cultivation of multiple cells and produce precisely controllable fluid shear force, periodically changing mechanical force, and perfusate with varying solute concentration gradient. To sum up, the chip can be used to analyze the specific pathophysiological changes of organs meticulously, and it is widely used in scientific research on respiratory diseases. The focus of this review is to describe and discuss current studies of artificial respiratory systems based on organ-on-a-chip technology and to summarize their applications in the real world.

Cellular and molecular mechanisms of allergic asthma

Asthma is a chronic disease of the airways, which affects more than 350 million people worldwide. It is the most common chronic disease in children, affecting at least 30 million children and young adults in Europe. Asthma is a complex, partially heritable disease with a marked heterogeneity. Its development is influenced both by genetic and environmental factors. The most common, as well as the most well characterized subtype of asthma is allergic eosinophilic asthma, which is characterized by a type 2 airway inflammation. The prevalence of asthma has substantially increased in industrialized countries during the last 60 years. The mechanisms underpinning this phenomenon are incompletely understood, however increased exposure to various environmental pollutants probably plays a role. Disease inception is thought to be enabled by a disadvantageous shift in the balance between protective and harmful lifestyle and environmental factors, including exposure to protective commensal microbes versus infection with pathogens, collectively leading to airway epithelial cell damage and disrupted barrier integrity. Epithelial cell-derived cytokines are one of the main drivers of the type 2 immune response against innocuous allergens, ultimately leading to infiltration of lung tissue with type 2 T helper (T_H2) cells, type 2 innate lymphoid cells (ILC2s), M2 macrophages and eosinophils. This review outlines the mechanisms responsible for the orchestration of type 2 inflammation and summarizes the novel findings, including but not limited to dysregulated epithelial barrier integrity, alarmin release and innate lymphoid cell stimulation.

Characterization of low-dose ozone-induced murine acute lung injury

Ozone is a toxic and highly reactive gaseous oxidizing chemical with well‐documented adverse health effects in humans. On the basis of animal and human data, environmental guidelines and air quality standards recommend a threshold for exposure of no more than 0.063 ppm of ozone (daily concentrations). This research describes a standardized sensitive model of sterile murine lung inflammation induced by exposing mice to acute (0, 4 or 24 hr), yet low, levels of ozone (0.005, 0.05 or 0.5 ppm), one that are below the current recommendations for what is considered a safe or “ambient” ozone concentration for humans. Ozone led to concentration and time‐dependent phlogistic cell death in the bronchoalveolar lavage, lung epithelial damage and hemorrhage. Interestingly, we observed distinct large bright CD11b positive cells in the bronchoalveolar lavage, upregulation of lung vascular and alveolar ATP synthase as well as plasminogen and bronchiolar angiostatin expression in ozone‐exposed mice, platelet and neutrophil accumulation in the lung vasculature and an eotaxin‐2, IL‐16, CXCL5, CXCL12, and CXCL13 dominant inflammatory response leading to lung injury. Using a fluorescent intravital microscopy set up, we quantified ozone‐induced extensive alveolar cellular damage. We observed ozone‐induced actin filament disorganization, perturbed respiratory mechanics, acute suppression of the alveolar reactive oxygen species (ROS) production and mitochondrial potential in ventilated lungs. We present evidence of systemic, as well as pulmonary toxicity, at 40‐fold lower ozone concentrations than previously reported in mice. The findings are important in establishing a sensitive means of quantifying structural and functional lung disorganization following exposure to an aerosolized pollutant, even at levels of ozone exposure previously thought to be safe in humans.

In Vitro Models for Studying Respiratory Host-Pathogen Interactions

Respiratory diseases and lower respiratory tract infections are among the leading cause of death worldwide and, especially given the recent severe acute respiratory syndrome coronavirus-2 pandemic, are of high and prevalent socio-economic importance. In vitro models, which accurately represent the lung microenvironment, are of increasing significance given the ethical concerns around animal work and the lack of translation to human disease, as well as the lengthy time to market and the attrition rates associated with clinical trials. This review gives an overview of the biological and immunological components involved in regulating the respiratory epithelium system in health, disease, and infection. The evolution from 2D to 3D cell biology and to more advanced technological integrated models for studying respiratory host-pathogen interactions are reviewed and provide a reference point for understanding the in vitro modeling requirements. Finally, the current limitations and future perspectives for advancing this field are presented.

Seeing and Touching the Mycomembrane at the Nanoscale

Mycobacteria have unique cell envelopes, surface properties, and growth dynamics, which all play a part in the ability of these important pathogens to infect, evade host immunity, disseminate, and resist antibiotic challenges. Recent atomic force microscopy (AFM) studies have brought new insights into the nanometer-scale ultrastructural, adhesive, and mechanical properties of mycobacteria. The molecular forces with which mycobacterial adhesins bind to host factors, like heparin and fibronectin, and the hydrophobic properties of the mycomembrane have been unraveled by AFM force spectroscopy studies. Real-time correlative AFM and fluorescence imaging have delineated a complex interplay between surface ultrastructure, tensile stresses within the cell envelope, and cellular processes leading to division. The unique capabilities of AFM, which include subdiffraction-limit topographic imaging and piconewton force sensitivity, have great potential to resolve important questions that remain unanswered on the molecular interactions, surface properties, and growth dynamics of this important class of pathogens.

Novel Mechanisms of Ozone-Induced Pulmonary Inflammation and Resolution, and the Potential Protective Role of Scavenger Receptor BI

INTRODUCTION

Increases in ambient levels of ozone (O3), a criteria air pollutant, have been associated with increased susceptibility and exacerbations of chronic pulmonary diseases through lung injury and inflammation. O3 induces pulmonary inflammation, in part by generating damage-associated molecular patterns (DAMPs), which are recognized by pattern recognition receptors (PRRs), such as toll-like receptors (TLRs) and scavenger receptors (SRs). This inflammatory response is mediated in part by alveolar macrophages (AMs), which highly express PRRs, including scavenger receptor BI (SR-BI). Once pulmonary inflammation has been induced, an active process of resolution occurs in order to prevent secondary necrosis and to restore tissue homeostasis. The processes known to promote the resolution of inflammation include the clearance by macrophages of apoptotic cells, known as efferocytosis, and the production of specialized pro-resolving mediators (SPMs). Impaired efferocytosis and production of SPMs have been associated with the pathogenesis of chronic lung diseases; however, these impairments have yet to be linked with exposure to air pollutants.

SPECIFIC AIMS

The primary goals of this study were: Aim 1 - to define the role of SR-BI in O3-derived pulmonary inflammation and resolution of injury; and Aim 2 - to determine if O3 exposure alters pulmonary production of SPMs and processes known to promote the resolution of pulmonary inflammation and injury.

METHODS

To address Aim 1, female wild-type (WT) and SR-BI-deficient, or knock-out (SR-BI KO), mice were exposed to either O3 or filtered air. In one set of experiments mice were instilled with an oxidized phospholipid (oxPL). Bronchoalveolar lavage fluid (BALF) and lung tissue were collected for the analyses of inflammatory and injury markers and oxPL. To estimate efferocytosis, mice were administered apoptotic cells (derived from the Jurkat T cell line) after O3 or filtered air exposure.

To address Aim 2, male WT mice were exposed to either O3 or filtered air, and levels of SPMs were assessed in the lung, as well as markers of inflammation and injury in BALF. In some experiments SPMs were administered before exposure to O3or filtered air, to determine whether SPMs could mitigate inflammatory or resolution responses. Efferocytosis was measured as in Aim 1.

RESULTS

For Aim 1, SR-BI protein levels increased in the lung tissue of mice exposed to O3, compared with mice exposed to filtered air. Compared with WT controls, SR-BI KO mice had a significant increase in the number of neutrophils in their airspace 24 hours post O3 exposure. The oxPL levels increased in the airspace of both WT and SR-BI KO mice after O3 exposure, compared with filtered air controls. Four hours after instillation of an oxPL, SR-BI KO mice had an increase in BALF neutrophils and total protein, and a nonsignificant increase in macrophages compared with WT controls. O3 exposure decreased efferocytosis in both WT and SR-BI KO female mice.

For Aim 2, mice given SPM supplementation before O3 exposure showed significantly increased AM efferocytosis when compared with the O3exposure control mice and also showed some mitigation of the effects of O3 on inflammation and injury. Several SPMs and their precursors were measured in lung tissue using reverse-phase high performance liquid chromatography (HPLC) with tandem mass spectrometry (MS/MS). At 24 hours after O3 exposure 14R-hydroxydocosahexaenoic acid (HDHA) and 10,17-dihydroxydocosahexaenoic acid (diHDoHE) were significantly decreased in lung tissue, but at 6 hours after exposure, levels of these SPMs increased.

CONCLUSIONS

Our findings identify novel mechanisms by which O3 may induce pulmonary inflammation and also increase susceptibility to and exacerbations of chronic lung diseases.

Macrophages: Checking Toxicity of Fungal Metabolites in the Colon

It is well known that the intestine absorbs nutrients, electrolytes, and water. Chikina et al. recently demonstrated that it is also able to sense, recognize, and block the absorption of toxins through a very sophisticated interactive cellular cooperation between novel subpopulations of macrophages and epithelial cells.

Modulating the Barrier Function of Human Alveolar Epithelial (hAELVi) Cell Monolayers as a Model of Inflammation

The incidence of inflammatory lung diseases such as acute respiratory distress syndrome (ARDS) remains an important problem, particularly in the present time with the Covid-19 pandemic. However, an adequate in vitro test system to monitor the barrier function of the alveolar epithelium during inflammation and for assessing anti-inflammatory drugs is urgently needed. Therefore, we treated human Alveolar Epithelial Lentivirus-immortalised cells (hAELVi cells) with the pro-inflammatory cytokines TNF-α (25 ng/ml) and IFN-γ (30 ng/ml), in the presence or absence of hydrocortisone (HC). While TNF-α and IFN-γ are known to reduce epithelial barrier properties, HC could be expected to protect the barrier function and result in an anti-inflammatory effect. We investigated the impact of anti-inflammatory/inflammatory treatment on transepithelial electrical resistance (TEER) and the apparent permeability coefficient (P app) of the low permeability marker sodium fluorescein (NaFlu). After incubating hAELVi cells for 48 hours with a combination of TNF-α and IFN-γ, there was a significant decrease in TEER and a significant increase in the P app. The presence of HC maintained the TEER values and barrier properties, so that no significant P app change was observed. By using hAELVi cells to study anti-inflammatory drugs in vitro, the need for animal experiments could be reduced and pulmonary drug development accelerated.

Urban air PM modifies differently immune defense responses against bacterial and viral infections in vitro

Epidemiological evidence has shown the association between exposure to ambient fine particulate matter (PM) and increased susceptibility to bacterial and viral respiratory infections. However, to date, the underlying mechanisms of immunomodulatory effects of PM remain unclear. Our objective was to explore how exposure to relatively low doses of urban air PM alters innate responses to bacterial and viral stimuli in vitro. We used secondary alveolar epithelial cell line along with monocyte-derived macrophages to replicate innate lung barrier in vitro. Co-cultured cells were first exposed for 24 h to PM_2.5-1 (particle aerodynamic diameter between 1 and 2.5 μm) and subsequently for an additional 24 h to lipopolysaccharide (TLR4), polyinosinic-polycytidylic acid (TLR3), and synthetic single-stranded RNA oligoribonucleotides (TLR7/8) to mimic bacterial or viral stimulation. Toxicological endpoints included pro-inflammatory cytokines (IL-8, IL-6, and TNF-α), cellular metabolic activity, and cell cycle phase distribution. We show that cells exposed to PM_2.5-1 produced higher levels of pro-inflammatory cytokines following stimulation with bacterial TLR4 ligand than cells exposed to PM_2.5-1 or bacterial ligand alone. On the contrary, PM_2.5-1 exposure reduced pro-inflammatory responses to viral ligands TLR3 and TLR7/8. Cell cycle analysis indicated that viral ligands induced cell cycle arrest at the G2-M phase. In PM-primed co-cultures, however, they failed to induce the G2-M phase arrest. Contrarily, bacterial stimulation caused a slight increase in cells in the sub-G1 phase but in PM_2.5-1 primed co-cultures the effect of bacterial stimulation was masked by PM_2.5-1. These findings indicate that PM_2.5-1 may alter responses of immune defense differently against bacterial and viral infections. Further studies are required to explain the mechanism of immune modulation caused by PM in altering the susceptibility to respiratory infections.

Alveolar epithelial cell-derived Sonic hedgehog promotes pulmonary fibrosis through OPN-dependent alternative macrophage activation

The alternative activation of macrophages in the lungs has been considered as a major factor promoting pulmonary fibrogenesis; however, the mechanisms underlying this phenomenon are still elusive. In this study, we investigated the interaction between macrophages and fibrosis-associated alveolar epithelial cells using a bleomycin-induced mouse pulmonary fibrosis model and a coculture system. We demonstrated that fibrosis-promoting macrophages are spatially proximate to alveolar type II (ATII) cells, permissive for paracrine-induced macrophage polarization. Importantly, we revealed that fibrosis-associated ATII cells secrete Sonic hedgehog (Shh), a hedgehog pathway ligand, and that ATII cell-derived Shh promotes the development of pulmonary fibrosis by osteopontin (OPN)-mediated macrophage alternative activation. Mechanistically, Shh promotes the secretion of OPN in macrophages via Shh/Gli signaling cascade. The secreted OPN acts on the surrounding macrophages in an autocrine or paracrine manner and induces macrophage alternative activation through activating the JAK2/STAT3 signaling pathway. Tissue samples from idiopathic pulmonary fibrosis patients confirmed the increased expression of Shh and OPN in ATII cells and macrophages, respectively. Together, our study illustrated an alveolar epithelium-dependent mechanism for macrophage M2 polarization and pulmonary fibrogenesis and suggested that targeting Shh may offer a selective and efficient therapeutic strategy for the development and progression of pulmonary fibrosis.

The role of lncRNAs in innate immunity and inflammation

The innate immune system relies on a germ-line-encoded repertoire of pattern recognition receptors (PRRs), activated by deeply conserved pathogen signatures, such as bacterial cell wall components or foreign nucleic acids. To enable effective defence against invading pathogens and prevent from deleterious inflammation, PRR-driven immune responses are tightly controlled by a dense network of nuclear and cytoplasmic regulators. Long non-coding RNAs (lncRNAs) are increasingly recognized as important components of these regulatory circuitries, providing positive and negative control of PRR-induced innate immune responses. The present review provides an overview of the presently known roles of lncRNAs in human and murine innate antiviral and antibacterial immunity. The emerging roles in host defence and inflammation suggest that further mechanistic insights into the cellular functions of lncRNAs will decisively advance our molecular understanding of immune-associated diseases and open new avenues for therapeutic intervention.

Patrolling Alveolar Macrophages Conceal Bacteria from the Immune System to Maintain Homeostasis

During respiration, humans breathe in more than 10,000 liters of non-sterile air daily, allowing some pathogens access to alveoli. Interestingly, alveoli outnumber alveolar macrophages (AMs), which favors alveoli devoid of AMs. If AMs, like most tissue macrophages, are sessile, then this numerical advantage would be exploited by pathogens unless neutrophils from the blood stream intervened. However, this would translate to omnipresent persistent inflammation. Developing in vivo real-time intravital imaging of alveoli revealed AMs crawling in and between alveoli using the pores of Kohn. Importantly, these macrophages sensed, chemotaxed, and, with high efficiency, phagocytosed inhaled bacterial pathogens such as P. aeruginosa and S. aureus, cloaking the bacteria from neutrophils. Impairing AM chemotaxis toward bacteria induced superfluous neutrophil recruitment, leading to inappropriate inflammation and injury. In a disease context, influenza A virus infection impaired AM crawling via the type II interferon signaling pathway, and this greatly increased secondary bacterial co-infection.

Legionella-Infected Macrophages Engage the Alveolar Epithelium to Metabolically Reprogram Myeloid Cells and Promote Antibacterial Inflammation

Alveolar macrophages are among the first immune cells that respond to inhaled pathogens. However, numerous pathogens block macrophage-intrinsic immune responses, making it unclear how robust antimicrobial responses are generated. The intracellular bacterium Legionella pneumophila inhibits host translation, thereby impairing cytokine production by infected macrophages. Nevertheless, Legionella-infected macrophages induce an interleukin-1 (IL-1)-dependent inflammatory cytokine response by recruited monocytes and other cells that controls infection. How IL-1 directs these cells to produce inflammatory cytokines is unknown. Here, we show that collaboration with the alveolar epithelium is critical for controlling infection. IL-1 induces the alveolar epithelium to produce granulocyte-macrophage colony-stimulating factor (GM-CSF). Intriguingly, GM-CSF signaling amplifies inflammatory cytokine production in recruited monocytes by enhancing Toll-like receptor (TLR)-induced glycolysis. Our findings reveal that alveolar macrophages engage alveolar epithelial signals to metabolically reprogram monocytes for antibacterial inflammation.

Multi-walled carbon nanotubes induce IL-1β secretion by activating hemichannels-mediated ATP release in THP-1 macrophages

Multi-walled carbon nanotubes (MWCNTs) are known to induce pulmonary inflammatory effects through stimulating pro-inflammatory cytokine secretion from alveolar macrophages. Despite extensive studies on MWCNTs' pro-inflammatory reactivity, the understanding of molecular mechanisms involved is still incomplete. In this study, we investigated hemichannel's involvement in MWCNTs-induced macrophage IL-1β release. Our results showed that the unmodified and COOH MWCNTs could induce ATP release and ATP-P2X₇R axis-dependent IL-1β secretion from THP-1 macrophages. By using various inhibitors, we confirmed that the MWCNTs-induced ATP release was primarily through hemichannels. EtBr dye uptake assay detected significant hemichannels opening in MWCNTs exposed THP-1 macrophages. Inhibition of hemichannels by CBX, ⁴³Gap27, or ¹⁰Panx1 pretreatment results in decreased ATP and IL-1β release. The addition of ATP restored the reduced IL-1β secretion level from hemichannel inhibition. We also confirmed with five other types of MWCNTs that the induction of hemichannels by MWCNTs strongly correlates with their capacity to induce IL-1β secretion. Taken together, we conclude that hemichannels-mediated ATP release and subsequent NLRP3 inflammasome activation through P2X₇R may be one mechanism by which MWCNTs induce macrophage IL-1β secretion. Our findings may provide a novel molecular mechanism for MWCNTs induced IL-1β secretion.

Lung macrophages: current understanding of their roles in Ozone-induced lung diseases

Through the National Ambient Air Quality Standards (NAAQS), the Clean Air Act of the United States outlines acceptable levels of six different air pollutants considered harmful to humans and the environment. Included in this list is ozone (O₃), a highly reactive oxidant gas, respiratory health hazard, and common environmental air pollutant at ground level. The respiratory health effects due to O₃ exposure are often associated with molecular and cellular perturbations in the respiratory tract. Periodic review of NAAQS requires comprehensive scientific evaluation of the public health effects of these pollutants, which is formulated through integrated science assessment (ISA) of the most policy-relevant scientific literature. This review focuses on the protective and pathogenic effects of macrophages in the O₃-exposed respiratory tract, with emphasis on mouse model-based toxicological studies. Critical findings from 39 studies containing the words O₃, macrophage, mice, and lung within the full text were assessed. While some of these studies highlight the presence of disease-relevant pathogenic macrophages in the airspaces, others emphasize a protective role for macrophages in O₃-induced lung diseases. Moreover, a comprehensive list of currently known macrophage-specific roles in O₃-induced lung diseases is included in this review and the significant knowledge gaps that still exist in the field are outlined. In conclusion, there is a vital need in this field for additional policy-relevant scientific information, including mechanistic studies to further define the role of macrophages in response to O₃.

Tim‑3 regulates the ability of macrophages to counter lipopolysaccharide‑induced pulmonary epithelial barrier dysfunction via the PI3K/Akt pathway in epithelial cells

Pulmonary epithelial barrier dysfunction is a critical pathological component of lung injury, caused primarily by impaired epithelial cell migration. Moreover, macrophage-epithelial interactions in pulmonary alveoli may either protect or damage epithelial barrier function. To investigate the effects of different macrophage subtypes, M1 and M2, on lipopolysaccharide (LPS)-induced epithelial barrier dysfunction, M1 and M2 macrophages were used to treat LPS-injured musculus lung epithelial cells (MLE-12). Barrier function was evaluated by monitoring cell monolayer permeability, T-cell immunoglobulin mucin 3 (Tim-3) small interfering RNA and anti-mouse Tim-3 antibody were used to knockdown or block endogenous Tim-3, to verify the role of the Tim-3 in macrophage-mediated barrier protection in LPS-injured MLE-12 cells. LY294002 was used to inhibit the activity of PI3K to verify the role of the PI3K/Akt signaling pathway in the restoration of epithelial cell. The present results revealed that co-culture of LPS-treated epithelial MLE-12 cells with M1 macrophages decreased cell migration and promoted permeability, whereas co-culture with M2 macrophages caused the opposite effects. It was determined that blocking T-cell immunoglobulin mucin 3 (Tim-3) signaling in macrophages and PI3K/Akt signaling in epithelial cells eliminated the barrier protection supplied by M2 macrophages. Tim-3, which maintains macrophage M2 polarization, is a key component of the macrophage-mediated barrier-repair process, while M2 macrophages regulate PI3K/Akt signaling in epithelial cells, which in turn enhances pulmonary epithelial barrier function by restoring cell migration.

In Vivo Assessment of Alveolar Macrophage Efferocytosis Following Ozone Exposure

Ozone (O3) is a criteria air pollutant that exacerbates and increases the incidence of chronic pulmonary diseases. O3 exposure is known to induce pulmonary inflammation, but little is known regarding how exposure alters processes important to the resolution of inflammation. Efferocytosis is a resolution process, whereby macrophages phagocytize apoptotic cells. The purpose of this protocol is to measure alveolar macrophage efferocytosis following O3-induced lung injury and inflammation. Several methods have been described for measuring efferocytosis; however, most require ex vivo manipulations. Described in detail here is a protocol to measure in vivo alveolar macrophage efferocytosis 24 h after O3 exposure, which avoids ex vivo manipulation of macrophages and serves as a simple technique that can be used to accurately represent perturbations in this resolution process. The protocol is a technically non-intensive and relatively inexpensive method that involves whole-body O3 inhalation followed by oropharyngeal aspiration of apoptotic cells (i.e., Jurkat T cells) while under general anesthesia. Alveolar macrophage efferocytosis is then measured by light microscopy evaluation of macrophages collected from bronchoalveolar (BAL) lavage. Efferocytosis is finally measured by calculating an efferocytic index. Collectively, the outlined methods quantify efferocytic activity in the lung in vivo while also serving to analyze the negative health effects of O3 or other inhaled insults.

Intercellular communication between alveolar epithelial cells and macrophages

BACKGROUND

The alveolus in the lung tissue is an extremely vulnerable site. Alveolar macrophages control this micro-environment both in states of health and illnesssuch as acute lung injury and infection. It has been reported in mice in vivo that intercellular communication between alveolar macrophages and alveolar epithelial cells is mediated by gap junctions. However, little is known about thismicro-environment in human cells.

METHODS

Since this gap junctional intercellular communication is hard to investigate in human tissues, a co-culture model of two human cell lines, one of epithelial and one of macrophage origin, was used. Immunoblot analysis, freeze fracture replica immunolabeling and electron microscopy were performed.

RESULTS

Connexin (Cx) 43 protein expression as well as ultrastructurally defined Cx43 gap junctions were detected in co-cultures, yielding evidence of intercellular gap junctions between human alveolar cells of two distinct entities.

CONCLUSION

Alveolar macrophages possibly have direct access to the alveolar epithelium via gap junctions in humans, enabling the orchestration of the microenvironment in physiology and disease states.

A pathologic two-way street: how innate immunity impacts lung fibrosis and fibrosis impacts lung immunity

Lung fibrosis is characterised by the accumulation of extracellular matrix within the lung and is secondary to both known and unknown aetiologies. This accumulation of scar tissue limits gas exchange causing respiratory insufficiency. The pathogenesis of lung fibrosis is poorly understood, but immunologic‐based treatments have been largely ineffective. Despite this, accumulating evidence suggests that innate immune cells and receptors play important modulatory roles in the initiation and propagation of the disease. Paradoxically, while innate immune signalling may be important for the pathogenesis of fibrosis, there is also evidence to suggest that innate immune function against pathogens may be impaired, leading to dysregulated and/or impaired host defence. This review summarises the evidence for this pathologic two‐way street, highlights new concepts of pathogenesis and recommends future directions for research emphasis.

Respiratory epithelial cells as master communicators during viral infections

PURPOSE OF REVIEW

Communication by epithelial cells during respiratory viral infections is critical in orchestrating effective anti-viral responses but also can lead to excessive inflammation. This review will evaluate studies that investigate how respiratory epithelial cells influence the behavior of immune cells and how epithelial cell/immune cell interactions contribute to antiviral responses and immunopathology outcomes.

RECENT FINDINGS

Previous studies have characterized cytokine responses of virus-infected epithelial cells. More recent studies have carefully demonstrated the effects of these cytokines on cellular behaviors within the infected lung. Infected epithelial cells release exosomes that specifically regulate responses of monocytes and neighboring epithelial cells without promoting spread of virus. In contrast, rhinovirus-infected cells induce monocytes to upregulate expression of the viral receptor, promoting spread of the virus to alternate cell types. The precise alteration of PDL expression on infected epithelial cells has been shown to switch between inhibition and activation of antiviral responses.

SUMMARY

These studies have more precisely defined the interactions between epithelial and immune cells during viral infections. This level of understanding is critical for the development of novel therapeutic strategies that promote effective antiviral responses or epithelial repair, or inhibit damaging inflammatory responses during severe respiratory viral infections.

Building and Regenerating the Lung Cell by Cell

The unique architecture of the mammalian lung is required for adaptation to air breathing at birth and thereafter. Understanding the cellular and molecular mechanisms controlling its morphogenesis provides the framework for understanding the pathogenesis of acute and chronic lung diseases. Recent single-cell RNA sequencing data and high-resolution imaging identify the remarkable heterogeneity of pulmonary cell types and provides cell selective gene expression underlying lung development. We will address fundamental issues related to the diversity of pulmonary cells, to the formation and function of the mammalian lung, and will review recent advances regarding the cellular and molecular pathways involved in lung organogenesis. What cells form the lung in the early embryo? How are cell proliferation, migration, and differentiation regulated during lung morphogenesis? How do cells interact during lung formation and repair? How do signaling and transcriptional programs determine cell-cell interactions necessary for lung morphogenesis and function?

Integrative Physiology of Pneumonia

Pneumonia is a type of acute lower respiratory infection that is common and severe. The outcome of lower respiratory infection is determined by the degrees to which immunity is protective and inflammation is damaging. Intercellular and interorgan signaling networks coordinate these actions to fight infection and protect the tissue. Cells residing in the lung initiate and steer these responses, with additional immunity effectors recruited from the bloodstream. Responses of extrapulmonary tissues, including the liver, bone marrow, and others, are essential to resistance and resilience. Responses in the lung and extrapulmonary organs can also be counterproductive and drive acute and chronic comorbidities after respiratory infection. This review discusses cell-specific and organ-specific roles in the integrated physiological response to acute lung infection, and the mechanisms by which intercellular and interorgan signaling contribute to host defense and healthy respiratory physiology or to acute lung injury, chronic pulmonary disease, and adverse extrapulmonary sequelae. Pneumonia should no longer be perceived as simply an acute infection of the lung. Pneumonia susceptibility reflects ongoing and poorly understood chronic conditions, and pneumonia results in diverse and often persistent deleterious consequences for multiple physiological systems.

Eicosanoid Control Over Antigen Presenting Cells in Asthma

Asthma is a common lung disease affecting 300 million people worldwide. Allergic asthma is recognized as a prototypical Th2 disorder, orchestrated by an aberrant adaptive CD4+ T helper (Th2/Th17) cell immune response against airborne allergens, that leads to eosinophilic inflammation, reversible bronchoconstriction, and mucus overproduction. Other forms of asthma are controlled by an eosinophil-rich innate ILC2 response driven by epithelial damage, whereas in some patients with more neutrophilia, the disease is driven by Th17 cells. Dendritic cells (DCs) and macrophages are crucial regulators of type 2 immunity in asthma. Numerous lipid mediators including the eicosanoids prostaglandins and leukotrienes influence key functions of these cells, leading to either pro- or anti-inflammatory effects on disease outcome. In this review, we will discuss how eicosanoids affect the functions of DCs and macrophages in the asthmatic lung and how this leads to aberrant T cell differentiation that causes disease.

Human lung development: recent progress and new challenges

Recent studies have revealed biologically significant differences between human and mouse lung development, and have reported new in vitro systems that allow experimental manipulation of human lung models. At the same time, emerging clinical data suggest that the origins of some adult lung diseases are found in embryonic development and childhood. The convergence of these research themes has fuelled a resurgence of interest in human lung developmental biology. In this Review, we discuss our current understanding of human lung development, which has been profoundly influenced by studies in mice and, more recently, by experiments using in vitro human lung developmental models and RNA sequencing of human foetal lung tissue. Together, these approaches are helping to shed light on the mechanisms underlying human lung development and disease, and may help pave the way for new therapies.

Summary: This Review describes how recent technological advances have shed light on the mechanisms underlying human lung development and disease, and outlines the future challenges in this field.

Alpha-1 Antitrypsin Inhibits ATP-Mediated Release of Interleukin-1β via CD36 and Nicotinic Acetylcholine Receptors

While interleukin (IL)-1β is a potent pro-inflammatory cytokine involved in host defense, high levels can cause life-threatening sterile inflammation including systemic inflammatory response syndrome. Hence, the control of IL-1β secretion is of outstanding biomedical importance. In response to a first inflammatory stimulus such as lipopolysaccharide, pro-IL-1β is synthesized as a cytoplasmic inactive pro-form. Extracellular ATP originating from injured cells is a prototypical second signal for inflammasome-dependent maturation and release of IL-1β. The human anti-protease alpha-1 antitrypsin (AAT) and IL-1β regulate each other via mechanisms that are only partially understood. Here, we demonstrate that physiological concentrations of AAT efficiently inhibit ATP-induced release of IL-1β from primary human blood mononuclear cells, monocytic U937 cells, and rat lung tissue, whereas ATP-independent IL-1β release is not impaired. Both, native and oxidized AAT are active, suggesting that the inhibition of IL-1β release is independent of the anti-elastase activity of AAT. Signaling of AAT in monocytic cells involves the lipid scavenger receptor CD36, calcium-independent phospholipase A2β, and the release of a small soluble mediator. This mediator leads to the activation of nicotinic acetylcholine receptors, which efficiently inhibit ATP-induced P2X7 receptor activation and inflammasome assembly. We suggest that AAT controls ATP-induced IL-1β release from human mononuclear blood cells by a novel triple-membrane-passing signaling pathway. This pathway may have clinical implications for the prevention of sterile pulmonary and systemic inflammation.

Neuropilin-2 regulates airway inflammatory responses to inhaled lipopolysaccharide

Neuropilins are multifunctional receptors that play important roles in immune regulation. Neuropilin-2 (NRP2) is expressed in the lungs, but whether it regulates airway immune responses is unknown. Here, we report that Nrp2 is weakly expressed by alveolar macrophages (AMs) in the steady state but is dramatically upregulated following in vivo lipopolysaccharide (LPS) inhalation. Ex vivo treatment of human AMs with LPS also increased NRP2 mRNA expression and cell-surface display of NRP2 protein. LPS-induced Nrp2 expression in AMs was dependent upon the myeloid differentiation primary response 88 signaling pathway and the transcription factor NF-κB. In addition to upregulating display of NRP2 on the cell membrane, inhaled LPS also triggered AMs to release soluble NRP2 into the airways. Finally, myeloid-specific ablation of NRP2 resulted in increased expression of the chemokine (C-C motif) ligand 2 ( Ccl2) in the lungs and prolonged leukocyte infiltration in the airways following LPS inhalation. These findings suggest that NRP2 expression by AMs regulates LPS-induced inflammatory cell recruitment to the airways and reveal a novel role for NRP2 during innate immune responses in the lungs.

Downregulation of SLC7A7 Triggers an Inflammatory Phenotype in Human Macrophages and Airway Epithelial Cells

Lysinuric protein intolerance (LPI) is a recessively inherited aminoaciduria caused by mutations of SLC7A7, the gene encoding y+LAT1 light chain of system y⁺L for cationic amino acid transport. The pathogenesis of LPI is still unknown. In this study, we have utilized a gene silencing approach in macrophages and airway epithelial cells to investigate whether complications affecting lung and immune system are directly ascribable to the lack of SLC7A7 or, rather, mediated by an abnormal accumulation of arginine in mutated cells. When SLC7A7/y+LAT1 was silenced in human THP-1 macrophages and A549 airway epithelial cells by means of short interference RNA (siRNA), a significant induction of the expression and release of the inflammatory mediators IL1β and TNFα was observed, no matter the intracellular arginine availability. This effect was mainly regulated at transcriptional level through the activation of NFκB signaling pathway. Moreover, since respiratory epithelial cells are the important sources of chemokines in response to pro-inflammatory stimuli, the effect of IL1β has been addressed on SLC7A7 silenced A549 cells. Results obtained indicated that the downregulation of SLC7A7/y+LAT1 markedly strengthened the stimulatory effect of the cytokine on CCL5/RANTES expression and release without affecting the levels of CXCL8/IL8. Consistently, also the conditioned medium of silenced THP-1 macrophages activated airway epithelial cells in terms of CCL5/RANTES expression due to the presence of elevated amount of proinflammatory cytokines. In conclusion, our results point to a novel thus far unknown function of SLC7A7/y+LAT1, that, under physiological conditions, besides transporting arginine, may act as a brake to restrain inflammation.