Sessile alveolar macrophages communicate with alveolar epithelium to modulate immunity. Nature. 2014;506:503-506. [PMID: 24463523 DOI: 10.1038/nature12902]

Myeloid Cells in Asthma

Asthma is a heterogeneous chronic inflammatory disorder of the airways, and not surprisingly, many myeloid cells play a crucial role in pathogenesis. Antigen-presenting dendritic cells are the first to recognize the allergens, pollutants, and viruses that are implicated in asthma pathogenesis, and subsequently initiate the adaptive immune response by migrating to lymph nodes. Eosinophils are the hallmark of type 2 inflammation, releasing toxic compounds in the airways and contributing to airway remodeling. Mast cells and basophils control both the early- and late-phase allergic response and contribute to alterations in smooth muscle reactivity. Finally, relatively little is known about neutrophils and macrophages in this disease. Although many of these myeloid cells respond well to treatment with inhaled steroids, there is now an increasing armamentarium of targeted biologicals that can specifically eliminate only one myeloid cell population, like eosinophils. It is only with those new tools that we will be able to fully understand the role of myeloid cells in chronic asthma in humans.

Differential regulation of C5a receptor 1 in innate immune cells during the allergic asthma effector phase

C5a drives airway constriction and inflammation during the effector phase of allergic asthma, mainly through the activation of C5a receptor 1 (C5aR1). Yet, C5aR1 expression on myeloid and lymphoid cells during the allergic effector phase is ill-defined. Recently, we generated and characterized a floxed green fluorescent protein (GFP)-C5aR1 knock-in mouse. Here, we used this reporter strain to monitor C5aR1 expression in airway, pulmonary and lymph node cells during the effector phase of OVA-driven allergic asthma. C5aR1 reporter and wildtype mice developed a similar allergic phenotype with comparable airway resistance, mucus production, eosinophilic/neutrophilic airway inflammation and Th2/Th17 cytokine production. During the allergic effector phase, C5aR1 expression increased in lung tissue eosinophils but decreased in airway and pulmonary macrophages as well as in pulmonary CD11b⁺ conventional dendritic cells (cDCs) and monocyte-derived DCs (moDCs). Surprisingly, expression in neutrophils was not affected. Of note, moDCs but not CD11b⁺ cDCs from mediastinal lymph nodes (mLN) expressed less C5aR1 than DCs residing in the lung after OVA challenge. Finally, neither CD103⁺ cDCs nor cells of the lymphoid lineage such as Th2 or Th17-differentiated CD4⁺ T cells, B cells or type 2 innate lymphoid cells (ILC2) expressed C5aR1 under allergic conditions. Our findings demonstrate a complex regulation pattern of C5aR1 in the airways, lung tissue and mLN of mice, suggesting that the C5a/C5aR1 axis controls airway constriction and inflammation through activation of myeloid cells in all three compartments in an experimental model of allergic asthma.

Cellular Innate Immunity: An Old Game with New Players

Innate immunity is a rapidly evolving field with novel cell types and molecular pathways being discovered and paradigms changing continuously. Innate and adaptive immune responses are traditionally viewed as separate from each other, but emerging evidence suggests that they overlap and mutually interact. Recently discovered cell types, particularly innate lymphoid cells and myeloid-derived suppressor cells, are gaining increasing attention. Here, we summarize and highlight current concepts in the field, focusing on innate immune cells as well as the inflammasome and DNA sensing which appear to be critical for the activation and orchestration of innate immunity, and may provide novel therapeutic opportunities for treating autoimmune, autoinflammatory, and infectious diseases.

Human lung ex vivo infection models

Pneumonia is counted among the leading causes of death worldwide. Viruses, bacteria and pathogen-related molecules interact with cells present in the human alveolus by numerous, yet poorly understood ways. Traditional cell culture models little reflect the cellular composition, matrix complexity and three-dimensional architecture of the human lung. Integrative animal models suffer from species differences, which are of particular importance for the investigation of zoonotic lung diseases. The use of cultured ex vivo infected human lung tissue may overcome some of these limitations and complement traditional models. The present review gives an overview of common bacterial lung infections, such as pneumococcal infection and of widely neglected pathogens modeled in ex vivo infected lung tissue. The role of ex vivo infected lung tissue for the investigation of emerging viral zoonosis including influenza A virus and Middle East respiratory syndrome coronavirus is discussed. Finally, further directions for the elaboration of such models are revealed. Overall, the introduced models represent meaningful and robust methods to investigate principles of pathogen-host interaction in original human lung tissue.

Staphylococcus aureus α toxin potentiates opportunistic bacterial lung infections

Broad-spectrum antibiotic use may adversely affect a patient's beneficial microbiome and fuel cross-species spread of drug resistance. Although alternative pathogen-specific approaches are rationally justified, a major concern for this precision medicine strategy is that co-colonizing or co-infecting opportunistic bacteria may still cause serious disease. In a mixed-pathogen lung infection model, we find that the Staphylococcus aureus virulence factor α toxin potentiates Gram-negative bacterial proliferation, systemic spread, and lethality by preventing acidification of bacteria-containing macrophage phagosomes, thereby reducing effective killing of both S. aureus and Gram-negative bacteria. Prophylaxis or early treatment with a single α toxin neutralizing monoclonal antibody prevented proliferation of co-infecting Gram-negative pathogens and lethality while also promoting S. aureus clearance. These studies suggest that some pathogen-specific, antibody-based approaches may also work to reduce infection risk in patients colonized or co-infected with S. aureus and disparate drug-resistant Gram-negative bacterial opportunists.

Mechanisms of Organ Injury and Repair by Macrophages

Macrophages regulate tissue regeneration following injury. They can worsen tissue injury by producing reactive oxygen species and other toxic mediators that disrupt cell metabolism, induce apoptosis, and exacerbate ischemic injury. However, they also produce a variety of growth factors, such as IGF-1, VEGF-α, TGF-β, and Wnt proteins that regulate epithelial and endothelial cell proliferation, myofibroblast activation, stem and tissue progenitor cell differentiation, and angiogenesis. Proresolving macrophages in turn restore tissue homeostasis by functioning as anti-inflammatory cells, and macrophage-derived matrix metalloproteinases regulate fibrin and collagen turnover. However, dysregulated macrophage function impairs wound healing and contributes to the development of fibrosis. Consequently, the mechanisms that regulate these different macrophage activation states have become active areas of research. In this review, we discuss the common and unique mechanisms by which macrophages instruct tissue repair in the liver, nervous system, heart, lung, skeletal muscle, and intestine and illustrate how macrophages might be exploited therapeutically.

Identification of a role for TRIM29 in the control of innate immunity in the respiratory tract

The respiratory tract is heavily populated with innate immune cells, but the mechanisms that control such cells are poorly defined. Here we found that the E3 ubiquitin ligase TRIM29 was a selective regulator of the activation of alveolar macrophages, the expression of type I interferons and the production of proinflammatory cytokines in the lungs. We found that deletion of TRIM29 enhanced macrophage production of type I interferons and protected mice from infection with influenza virus, while challenge of Trim29-/- mice with Haemophilus influenzae resulted in lethal lung inflammation due to massive production of proinflammatory cytokines by macrophages. Mechanistically, we demonstrated that TRIM29 inhibited interferon-regulatory factors and signaling via the transcription factor NF-κB by degrading the adaptor NEMO and that TRIM29 directly bound NEMO and subsequently induced its ubiquitination and proteolytic degradation. These data identify TRIM29 as a key negative regulator of alveolar macrophages and might have important clinical implications for local immunity and immunopathology.

Early local immune defences in the respiratory tract

The respiratory immune response consists of multiple tiers of cellular responses that are engaged in a sequential manner in order to control infections. The stepwise engagement of effector functions with progressively increasing host fitness costs limits tissue damage. In addition, specific mechanisms are in place to promote disease tolerance in response to respiratory infections. Environmental factors, obesity and the ageing process can alter the efficiency and regulation of this tiered response, increasing pathology and mortality as a result. In this Review, we describe the cell types that coordinate pathogen clearance and tissue repair through the serial secretion of cytokines, and discuss how the environment and comorbidity influence this response.

Essential Role of mTORC1 in Self-Renewal of Murine Alveolar Macrophages

Alveolar macrophages (AMϕ) have the capacity of local self-renewal through adult life; however, mechanisms that regulate AMϕ self-renewal remain poorly understood. We found that myeloid-specific deletion of Raptor, an essential component of the mammalian/mechanistic target of rapamycin complex (mTORC)1, resulted in a marked decrease of this population of cells accompanying altered phenotypic features and impaired phagocytosis activity. We demonstrated further that Raptor/mTORC1 deficiency did not affect AMϕ development, but compromised its proliferative activity at cell cycle entry in the steady-state as well as in the context of repopulation in irradiation chimeras. Mechanically, mTORC1 confers AMϕ optimal responsiveness to GM-CSF-induced proliferation. Thus, our results demonstrate an essential role of mTORC1 for AMϕ homeostasis by regulating proliferative renewal.

Exogenous remodeling of lung resident macrophages protects against infectious consequences of bone marrow-suppressive chemotherapy

Infection is the single greatest threat to survival during cancer chemotherapy because of depletion of bone marrow-derived immune cells. Phagocytes, especially neutrophils, are key effectors in immunity to extracellular pathogens, which has limited the development of new approaches to protect patients with cancer and chemotherapy-induced neutropenia. Using a model of vaccine-induced protection against lethal Pseudomonas aeruginosa pneumonia in the setting of chemotherapy-induced neutropenia, we found a population of resident lung macrophages in the immunized lung that mediated protection in the absence of neutrophils, bone marrow-derived monocytes, or antibodies. These vaccine-induced macrophages (ViMs) expanded after immunization, locally proliferated, and were closely related to alveolar macrophages (AMs) by surface phenotype and gene expression profiles. By contrast to AMs, numbers of ViMs were stable through chemotherapy, showed enhanced phagocytic activity, and prolonged survival of neutropenic mice from lethal P. aeruginosa pneumonia upon intratracheal adoptive transfer. Thus, induction of ViMs by tissue macrophage remodeling may become a framework for new strategies to activate immune-mediated reserves against infection in immunocompromised hosts.

Alveolar macrophage development in mice requires L-plastin for cellular localization in alveoli

Alveolar macrophages are lung-resident sentinel cells that develop perinatally and protect against pulmonary infection. Molecular mechanisms controlling alveolar macrophage generation have not been fully defined. Here, we show that the actin-bundling protein L-plastin (LPL) is required for the perinatal development of alveolar macrophages. Mice expressing a conditional allele of LPL (CD11c.Cre^pos-LPL^fl/fl) exhibited significant reductions in alveolar macrophages and failed to effectively clear pulmonary pneumococcal infection, showing that immunodeficiency results from reduced alveolar macrophage numbers. We next identified the phase of alveolar macrophage development requiring LPL. In mice, fetal monocytes arrive in the lungs during a late fetal stage, maturing to alveolar macrophages through a prealveolar macrophage intermediate. LPL was required for the transition from prealveolar macrophages to mature alveolar macrophages. The transition from prealveolar macrophage to alveolar macrophage requires the upregulation of the transcription factor peroxisome proliferator-activated receptor-γ (PPAR-γ), which is induced by exposure to granulocyte-macrophage colony-stimulating factor (GM-CSF). Despite abundant lung GM-CSF and intact GM-CSF receptor signaling, PPAR-γ was not sufficiently upregulated in developing alveolar macrophages in LPL^-/- pups, suggesting that precursor cells were not correctly localized to the alveoli, where GM-CSF is produced. We found that LPL supports 2 actin-based processes essential for correct localization of alveolar macrophage precursors: (1) transmigration into the alveoli, and (2) engraftment in the alveoli. We thus identify a molecular pathway governing neonatal alveolar macrophage development and show that genetic disruption of alveolar macrophage development results in immunodeficiency.

NK cells regulate CXCR2+ neutrophil recruitment during acute lung injury

A critical step in the pathogenesis of acute lung injury (ALI) is excessive recruitment of polymorphonuclear neutrophils (PMNs) into the lungs, causing significant collateral tissue damage. Defining the molecular and cellular steps that control neutrophil infiltration and activation during ALI is therefore of important therapeutic relevance. Based on previous findings implicating the transcription factor Tbet in mucosal Th1-inflammation, we hypothesized a detrimental role for Tbet during ALI. In line with our hypothesis, initial studies of endotoxin-induced lung injury revealed a marked protection of Tbet^-/- mice, including attenuated neutrophilia compared to WT counterparts. Surprisingly, subsequent studies identified natural killer (NK) cells as the major source of pulmonary Tbet during ALI. In addition, a chemokine screen suggested that mature Tbet⁺ NK-cells are critical for the production of pulmonary CXCL1 and -2, thereby contributing to pulmonary PMN recruitment. Indeed, both NK-cell Ab depletion and adoptive transfer studies provide evidence for NK cells in the orchestration of neutrophil recruitment during endotoxin-induced ALI. Taken together, these findings identify a novel role for Tbet⁺ NK-cells in initiating the early events of noninfectious pulmonary inflammation.

Control of lung defence by mucins and macrophages: ancient defence mechanisms with modern functions

Owing to the need to balance the requirement for efficient respiration in the face of tremendous levels of exposure to endogenous and environmental challenges, it is crucial for the lungs to maintain a sustainable defence that minimises damage caused by this exposure and the detrimental effects of inflammation to delicate gas exchange surfaces. Accordingly, epithelial and macrophage defences constitute essential first and second lines of protection that prevent the accumulation of potentially harmful agents in the lungs, and under homeostatic conditions do so effectively without inducing inflammation. Though epithelial and macrophage-mediated defences are seemingly distinct, recent data show that they are linked through their shared reliance on airway mucins, in particular the polymeric mucin MUC5B. This review highlights our understanding of novel mechanisms that link mucus and macrophage defences. We discuss the roles of phagocytosis and the effects of factors contained within mucus on phagocytosis, as well as newly identified roles for mucin glycoproteins in the direct regulation of leukocyte functions. The emergence of this nascent field of glycoimmunobiology sets forth a new paradigm for considering how homeostasis is maintained under healthy conditions and how it is restored in disease.

Classically Activated Macrophages Protect against Lipopolysaccharide-induced Acute Lung Injury by Expressing Amphiregulin in Mice

BACKGROUND

Alveolar macrophages (AMs) activated into M1 phenotype are involved in the development of lipopolysaccharide-induced acute lung injury (ALI). However, whether AMs express amphiregulin and what roles amphiregulin plays in lipopolysaccharide-induced ALI remain poorly understood.

METHODS

Acute lung injury was induced by intratracheal instillation of lipopolysaccharide in male C57BL/6 mice. Lung injury scores, level of protein, and level of neutrophils in bronchial alveolar lavage fluid of lipopolysaccharide-induced ALI mice were compared with those in mice challenged with recombinant exogenous amphiregulin and antiamphiregulin antibody. Amphiregulin expression in macrophages and neutrophils in bronchial alveolar lavage fluid of lipopolysaccharide-induced ALI mice was determined by using immunofluorescence technique and further detected in M0, M1, and M2 phenotypes of both peritoneal macrophages and AMs. The effect of amphiregulin on apoptosis of MLE12 cells and activation of epithelial growth factor receptor-AKT pathway were, respectively, examined by using flow cytometry and western blotting.

RESULTS

Alveolar macrophages were found to highly express amphiregulin in ALI mice. Amphiregulin neutralization aggravated, whereas recombinant exogenous amphiregulin attenuated lipopolysaccharide-induced ALI in mice (n = 6). In cultured AMs and peritoneal macrophages, amphiregulin was mainly generated by M1, rather than M0 or M2 phenotype (n = 5). Apoptosis ratio of lipopolysaccharide-challenged MLE12 cells was significantly reduced by recombinant exogenous amphiregulin from 16.60 ± 1.82 to 9.47 ± 1.67% (n = 5) but significantly increased from 17.45 ± 1.13 to 21.67 ± 1.10% (n = 5) after stimulation with supernatant of M1-polarized AM media conditioned with amphiregulin-neutrolizing antibody. Western blotting revealed that amphiregulin activated epithelial growth factor receptor and AKT in the lung tissues and MLE12 cells (n = 5).

CONCLUSIONS

Different from the common notion that classically activated AMs have just a detrimental effect on the lung tissues, the results of this study showed that classically activated AMs also exerted a protective effect on the lung tissues by producing high-level amphiregulin in lipopolysaccharide-induced ALI.

Innate cell communication kick-starts pathogen-specific immunity

Innate cells are responsible for the rapid recognition of infection and mediate essential mechanisms of pathogen elimination, and also facilitate adaptive immune responses. We review here the numerous intricate interactions among innate cells that initiate protective immunity. The efficient eradication of pathogens depends on the coordinated actions of multiple cells, including innate cells and epithelial cells. Rather than acting as isolated effector cells, innate cells are in constant communication with other responding cells of the immune system, locally and distally. These interactions are critically important for the efficient control of primary infections as well for the development of 'trained' innate cells that facilitate the rapid elimination of homologous or heterologous infections.

Connexins in endothelial barrier function - novel therapeutic targets countering vascular hyperpermeability

Prolonged vascular hyperpermeability is a common feature of many diseases. Vascular hyperpermeability is typically associated with changes in the expression patterns of adherens and tight junction proteins. Here, we focus on the less-appreciated contribution of gap junction proteins (connexins) to basal vascular permeability and endothelial dysfunction. First, we assess the association of connexins with endothelial barrier integrity by introducing tools used in connexin biology and relating the findings to customary readouts in vascular biology. Second, we explore potential mechanistic ties between connexins and junction regulation. Third, we review the role of connexins in microvascular organisation and development, focusing on interactions of the endothelium with mural cells and tissue-specific perivascular cells. Last, we see how connexins contribute to the interactions between the endothelium and components of the immune system, by using neutrophils as an example. Mounting evidence of crosstalk between connexins and other junction proteins suggests that we rethink the way in which different junction components contribute to endothelial barrier function. Given the multiple points of connexin-mediated communication arising from the endothelium, there is great potential for synergism between connexin-targeted inhibitors and existing immune-targeted therapeutics. As more drugs targeting connexins progress through clinical trials, it is hoped that some might prove effective at countering vascular hyperpermeability.

Long-Term Persistence of Donor Alveolar Macrophages in Human Lung Transplant Recipients That Influences Donor-Specific Immune Responses

Steady-state alveolar macrophages (AMs) are long-lived lung-resident macrophages with sentinel function. Evidence suggests that AM precursors originate during embryogenesis and populate lungs without replenishment by circulating leukocytes. However, their presence and persistence are unclear following human lung transplantation (LTx). Our goal was to examine donor AM longevity and evaluate whether AMs of recipient origin seed the transplanted lungs. Origin of AMs was accessed using donor-recipient HLA mismatches. We demonstrate that 94-100% of AMs present in bronchoalveolar lavage (BAL) were donor derived and, importantly, AMs of recipient origin were not detected. Further, analysis of BAL cells up to 3.5 years post-LTx revealed that the majority of AMs (>87%) was donor derived. Elicitation of de novo donor-specific antibody (DSA) is a major post-LTx complication and a risk factor for development of chronic rejection. The donor AMs responded to anti-HLA framework antibody (Ab) with secretion of inflammatory cytokines. Further, in an experimental murine model, we demonstrate that adoptive transfer of allogeneic AMs stimulated humoral and cellular immune responses to alloantigen and lung-associated self-antigens and led to bronchiolar obstruction. Therefore, donor-derived AMs play an essential role in the DSA-induced inflammatory cascade leading to obliterative airway disease of the transplanted lungs.

The Dynamics of Apoptotic Cell Clearance

The phagocytic clearance of dying cells in a tissue is a highly orchestrated series of intercellular events coordinated by a complex signaling network. Recent data from genetic, biochemical, and live-imaging approaches have greatly enhanced our understanding of the dynamics of cell clearance and how the process is orchestrated at the cellular and tissue levels. We discuss how networks regulating apoptotic cell clearance are integrated to enable a rapid, efficient, and high-capacity clearance system within tissues.

Selective and inducible targeting of CD11b+ mononuclear phagocytes in the murine lung with hCD68-rtTA transgenic systems

During homeostasis two distinct macrophage (Mø) populations inhabit the lungs: tissue Mø (often called interstitial Mø) and resident alveolar Mø (resAMø). During acute lung inflammation, monocytes from the circulation migrate to areas of injury where they mature into a third Mø population: recruited Mø. Resident AMø uniquely express low levels of CD11b and high levels of CD11c. In comparison, recruited Mø and tissue Mø express high levels of CD11b and low levels of CD11c. It is likely that these three Mø subpopulations play distinct roles in injury and disease states; however, tools with which to individually target or track these populations are lacking. Here we demonstrate the utility of an hCD68-rtTA transgenic system for specific, robust, and inducible targeting of CD11b(+) recruited Mø and tissue Mø in the murine lung with negligible activation in resAMø. Using hCD68rtTA-GFP reporter mice, we show both during homeostasis and inflammation that administration of doxycycline induces tet-On reporter expression in recruited Mø and tissue Mø but not in resident AMø. We further demonstrate how hCD68-rtTA can be effectively combined with tet-On Cre to target these same recMø and tissue Mø. Accordingly, the hCD68-rtTA system is a powerful new tool that can be used for lineage tracing, fate mapping, and gene deletion in a variety of murine models, thereby enabling sophisticated investigation of the unique role of these CD11b(+) Mø during lung heath and disease.

Alveolar Epithelial Cell-Derived Prostaglandin E2 Serves as a Request Signal for Macrophage Secretion of Suppressor of Cytokine Signaling 3 during Innate Inflammation

Preservation of gas exchange mandates that the pulmonary alveolar surface restrain unnecessarily harmful inflammatory responses to the many challenges to which it is exposed. These responses reflect the cross-talk between alveolar epithelial cells (AECs) and resident alveolar macrophages (AMs). We recently determined that AMs can secrete suppressor of cytokine signaling (SOCS) proteins within microparticles. Uptake of these SOCS-containing vesicles by epithelial cells inhibits cytokine-induced STAT activation. However, the ability of epithelial cells to direct AM release of SOCS-containing vesicles in response to inflammatory insults has not been studied. In this study, we report that SOCS3 protein was elevated in bronchoalveolar lavage fluid of both virus- and bacteria-infected mice, as well as in an in vivo LPS model of acute inflammation. In vitro studies revealed that AEC-conditioned medium (AEC-CM) enhanced AM SOCS3 secretion above basal levels. Increased amounts of PGE2 were present in AEC-CM after LPS challenge, and both pharmacologic inhibition of PGE2 synthesis in AECs and neutralization of PGE2 in AEC-CM implicated this prostanoid as the major AEC-derived factor mediating enhanced AM SOCS3 secretion. Moreover, pharmacologic blockade of PGE2 synthesis or genetic deletion of a PGE2 synthase similarly attenuated the increase in bronchoalveolar lavage fluid SOCS3 noted in lungs of mice challenged with LPS in vivo. These results demonstrate a novel tunable form of cross-talk in which AECs use PGE2 as a signal to request SOCS3 from AMs to dampen their endogenous inflammatory responses during infection.

Macrophage-epithelial interactions in pulmonary alveoli

Alveolar macrophages have been investigated for years by approaches involving macrophage extraction from the lung by bronchoalveolar lavage, or by cell removal from lung tissue. Since extracted macrophages are studied outside their natural milieu, there is little understanding of the extent to which alveolar macrophages interact with the epithelium, or with one another to generate the lung's innate immune response to pathogen challenge. Here, we review new evidence of macrophage-epithelial interactions in the lung, and we address the emerging understanding that the alveolar epithelium plays an important role in orchestrating the macrophage-driven immune response.

Flow Cytometric Analysis of Myeloid Cells in Human Blood, Bronchoalveolar Lavage, and Lung Tissues

Clear identification of specific cell populations by flow cytometry is important to understand functional roles. A well-defined flow cytometry panel for myeloid cells in human bronchoalveolar lavage (BAL) and lung tissue is currently lacking. The objective of this study was to develop a flow cytometry-based panel for human BAL and lung tissue. We obtained and performed flow cytometry/sorting on human BAL cells and lung tissue. Confocal images were obtained from lung tissue using antibodies for cluster of differentiation (CD)206, CD169, and E cadherin. We defined a multicolor flow panel for human BAL and lung tissue that identifies major leukocyte populations. These include macrophage (CD206(+)) subsets and other CD206(-) leukocytes. The CD206(-) cells include: (1) three monocyte (CD14(+)) subsets, (2) CD11c(+) dendritic cells (CD14(-), CD11c(+), HLA-DR(+)), (3) plasmacytoid dendritic cells (CD14(-), CD11c(-), HLA-DR(+), CD123(+)), and (4) other granulocytes (neutrophils, mast cells, eosinophils, and basophils). Using this panel on human lung tissue, we defined two populations of pulmonary macrophages: CD169(+) and CD169(-) macrophages. In lung tissue, CD169(-) macrophages were a prominent cell type. Using confocal microscopy, CD169(+) macrophages were located in the alveolar space/airway, defining them as alveolar macrophages. In contrast, CD169(-) macrophages were associated with airway/alveolar epithelium, consistent with interstitial-associated macrophages. We defined a flow cytometry panel in human BAL and lung tissue that allows identification of multiple immune cell types and delineates alveolar from interstitial-associated macrophages. This study has important implications for defining myeloid cells in human lung samples.

Molecular and epigenetic basis of macrophage polarized activation

Macrophages are unique cells for origin, heterogeneity and plasticity. At steady state most of macrophages are derived from fetal sources and maintained in adulthood through self-renewing. Despite sharing common progenitors, a remarkable heterogeneity characterized tissue-resident macrophages indicating that local signals educate them to express organ-specific functions. Macrophages are extremely plastic: chromatin landscape and transcriptional programs can be dynamically re-shaped in response to microenvironmental changes. Owing to their ductility, macrophages are crucial orchestrators of both initiation and resolution of immune responses and key supporters of tissue development and functions in homeostatic and pathological conditions. Herein, we describe current understanding of heterogeneity and plasticity of macrophages using the M1-M2 dichotomy as operationally useful simplification of polarized activation. We focused on the complex network of signaling cascades, metabolic pathways, transcription factors, and epigenetic changes that control macrophage activation. In particular, this network was addressed in sepsis, as a paradigm of a pathological condition determining dynamic macrophage reprogramming.

Origin, Localization, and Immunoregulatory Properties of Pulmonary Phagocytes in Allergic Asthma

Allergic asthma is a chronic inflammatory disease of the airways that is driven by maladaptive T helper 2 (Th2) and Th17 immune responses against harmless, airborne substances. Pulmonary phagocytes represent the first line of defense in the lung where they constantly sense the local environment for potential threats. They comprise two distinct cell types, i.e., macrophages and dendritic cells (DC) that differ in their origins and functions. Alveolar macrophages quickly take up most of the inhaled allergens, yet do not deliver their cargo to naive T cells sampling in draining lymph nodes. In contrast, pulmonary DCs instruct CD4(+) T cells develop into Th2 and Th17 effectors, initiating the maladaptive immune responses toward harmless environmental substances observed in allergic individuals. Unraveling the mechanisms underlying this mistaken identity of harmless, airborne substances by innate immune cells is one of the great challenges in asthma research. The identification of different pulmonary DC subsets, their role in antigen uptake, migration to the draining lymph nodes, and their potential to instruct distinct T cell responses has set the stage to unravel this mystery. However, at this point, a detailed understanding of the spatiotemporal resolution of DC subset localization, allergen uptake, processing, autocrine and paracrine cellular crosstalk, and the humoral factors that define the activation status of DCs is still lacking. In addition to DCs, at least two distinct macrophage populations have been identified in the lung that are either located in the airway/alveolar lumen or in the interstitium. Recent data suggest that such populations can exert either pro- or anti-inflammatory functions. Similar to the DC subsets, detailed insights into the individual roles of alveolar and interstitial macrophages during the different phases of asthma development are still missing. Here, we will provide an update on the current understanding of the origin, localization, and function of the diverse pulmonary antigen-presenting cell subsets, in particular with regard to the development and regulation of allergic asthma. While most data are from mouse models of experimental asthma, we have also included available human data to judge the translational value of the findings obtained in experimental asthma models.

Macrophages in Tissue Repair, Regeneration, and Fibrosis

Inflammatory monocytes and tissue-resident macrophages are key regulators of tissue repair, regeneration, and fibrosis. After tissue injury, monocytes and macrophages undergo marked phenotypic and functional changes to play critical roles during the initiation, maintenance, and resolution phases of tissue repair. Disturbances in macrophage function can lead to aberrant repair, such that uncontrolled production of inflammatory mediators and growth factors, deficient generation of anti-inflammatory macrophages, or failed communication between macrophages and epithelial cells, endothelial cells, fibroblasts, and stem or tissue progenitor cells all contribute to a state of persistent injury, and this could lead to the development of pathological fibrosis. In this review, we discuss the mechanisms that instruct macrophages to adopt pro-inflammatory, pro-wound-healing, pro-fibrotic, anti-inflammatory, anti-fibrotic, pro-resolving, and tissue-regenerating phenotypes after injury, and we highlight how some of these mechanisms and macrophage activation states could be exploited therapeutically.

Innate Immune Signaling Activated by MDR Bacteria in the Airway

Health care-associated bacterial pneumonias due to multiple-drug resistant (MDR) pathogens are an important public health problem and are major causes of morbidity and mortality worldwide. In addition to antimicrobial resistance, these organisms have adapted to the milieu of the human airway and have acquired resistance to the innate immune clearance mechanisms that normally prevent pneumonia. Given the limited efficacy of antibiotics, bacterial clearance from the airway requires an effective immune response. Understanding how specific airway pathogens initiate and regulate innate immune signaling, and whether this response is excessive, leading to host-induced pathology may guide future immunomodulatory therapy. We will focus on three of the most important causes of health care-associated pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and review the mechanisms through which an inappropriate or damaging innate immune response is stimulated, as well as describe how airway pathogens cause persistent infection by evading immune activation.

Simple in vitro models can predict pulmonary toxicity of silver nanoparticles

To study the effects of nanomaterials after inhalation, a large number of in vitro lung models have been reported in literature. Although the in vitro models contribute to the reduction of animal studies, insufficient data exists to determine the predictive value of these in vitro models for the in vivo situation. The aim of this study was to determine the correlation between in vitro and in vivo data by comparing the dose metrics of silver nanoparticles in an in vitro lung model of increasing complexity to our previously published in vivo inhalation study. In vivo, the previously published study showed that the alveolar dose expressed as particle surface area is the most suitable dose metric to describe the toxicity of silver nanoparticles after inhalation. The results of the present study show that particle surface area is a suitable dose metric to describe the effects of silver nanoparticles when using a simple monolayer of lung epithelial cells. The dose metric shifted from particle surface area to particle mass when adding an increasing number of macrophages. In addition, a co-culture of endothelial cells, epithelial cells and macrophages on a Transwell® insert correlated less well to the in vivo results compared to the epithelial monolayer. We conclude that for studying the acute pulmonary toxicity of nanoparticles simple in vitro models using an epithelial monolayer better predict the in vivo response compared to complex co-culture models.

TLR-Activated Gap Junction Channels Protect Mice against Bacterial Infection through Extracellular UDP Release

Extracellular UDP (eUDP), released as a danger signal by stressed or apoptotic cells, plays an important role in a series of physiological processes. Although the mechanism of eUDP release in apoptotic cells has been well defined, how the eUDP is released in innate immune responses remains unknown. In this study, we demonstrated that UDP was released in both Escherichia coli-infected mice and LPS- or Pam3CSK4-treated macrophages. Also, LPS-induced UDP release could be significantly blocked by selective TLR4 inhibitor Atractylenolide I and selective gap junction inhibitors carbenoxolone and flufenamic acid (FFA), suggesting the key role of TLR signaling and gap junction channels in this process. Meanwhile, eUDP protected mice from peritonitis by reducing invaded bacteria that could be rescued by MRS2578 (selective P2Y6 receptor inhibitor) and FFA. Then, connexin 43, as one of the gap junction proteins, was found to be clearly increased by LPS in a dose- and time-dependent manner. Furthermore, if we blocked LPS-induced ERK signaling by U0126, the expression of connexin 43 and UDP release was also inhibited dramatically. In addition, UDP-induced MCP-1 secretion was significantly reduced by MRS2578, FFA, and P2Y6 mutation. Accordingly, pretreating mice with U0126 and Gap26 increased invaded bacteria and aggravated mice death. Taken together, our study reveals an internal relationship between danger signals and TLR signaling in innate immune responses, which suggests a potential therapeutic significance of gap junction channel-mediated UDP release in infectious diseases.

Targeting of the pulmonary capillary vascular niche promotes lung alveolar repair and ameliorates fibrosis

Although the lung can undergo self-repair after injury, fibrosis in chronically injured or diseased lungs can occur at the expense of regeneration. Here we study how a hematopoietic-vascular niche regulates alveolar repair and lung fibrosis. Using intratracheal injection of bleomycin or hydrochloric acid in mice, we show that repetitive lung injury activates pulmonary capillary endothelial cells (PCECs) and perivascular macrophages, impeding alveolar repair and promoting fibrosis. Whereas the chemokine receptor CXCR7, expressed on PCECs, acts to prevent epithelial damage and ameliorate fibrosis after a single round of treatment with bleomycin or hydrochloric acid, repeated injury leads to suppression of CXCR7 expression and recruitment of vascular endothelial growth factor receptor 1 (VEGFR1)-expressing perivascular macrophages. This recruitment stimulates Wnt/β-catenin-dependent persistent upregulation of the Notch ligand Jagged1 (encoded by Jag1) in PCECs, which in turn stimulates exuberant Notch signaling in perivascular fibroblasts and enhances fibrosis. Administration of a CXCR7 agonist or PCEC-targeted Jag1 shRNA after lung injury promotes alveolar repair and reduces fibrosis. Thus, targeting of a maladapted hematopoietic-vascular niche, in which macrophages, PCECs and perivascular fibroblasts interact, may help to develop therapy to spur lung regeneration and alleviate fibrosis.

Conceptual approaches to lung injury and repair

Lung injury and repair is a broad topic that includes many cell types and is relevant to the pathogenesis of most lung diseases. Here, we focus on injury and repair of the alveolus, the principal function of which is to achieve gas exchange. The many cell types and structures present in the alveolus are discussed, with emphasis on their interactions in both health and disease. We define injury as damage resulting in impaired gas exchange; physiologic repair, then, requires restoration of normal alveolar architecture and function. The role of inflammation in both injury and repair of structural alveolar cells, particularly epithelial cells, as well as mechanisms of resolution of inflammation will be addressed. Finally, emphasis is placed on the importance of addressing quantitatively the dynamic and complex multidirectional interactions between the many alveolar cell types and structures in three dimensions over time and in relating such mechanistic studies to physiologic outcomes and human disease.

Targeting vascular and leukocyte communication in angiogenesis, inflammation and fibrosis

Regulation of vascular permeability, recruitment of leukocytes from blood to tissue and angiogenesis are all processes that occur at the level of the microvasculature during both physiological and pathological conditions. The interplay between microvascular cells and leukocytes during inflammation, together with the emerging roles of leukocytes in the modulation of the angiogenic process, make leukocyte-vascular interactions prime targets for therapeutics to potentially treat a wide range of diseases, including pathological and dysfunctional vessel growth, chronic inflammation and fibrosis. In this Review, we discuss how the different cell types that are present in and around microvessels interact, cooperate and instruct each other, and in this context we highlight drug targets as well as emerging druggable processes that can be exploited to restore tissue homeostasis.

The Renal Connexome and Possible Roles of Connexins in Kidney Diseases

Connexins are membrane-spanning proteins that allow for the formation of cell-to-cell channels and cell-to-extracellular space hemichannels. Many connexin subtypes are expressed in kidney cells. Some mutations in connexin genes have been linked to various human pathologies, including cardiovascular, neurodegenerative, lung, and skin diseases, but the exact role of connexins in kidney disease remains unclear. Some hypotheses about a connection between genetic mutations, endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) in kidney pathology have been explored. The potential relationship of kidney disease to abnormal production of connexin proteins, mutations in their genes together with ER stress, or the UPR is still a matter of debate. In this scenario, it is tantalizing to speculate about a possible role of connexins in the setting of kidney pathologies that are thought to be caused by a deregulated podocyte protein expression, the so-called podocytopathies. In this article, we give examples of the roles of connexins in kidney (patho)physiology and propose avenues for further research concerning connexins, ER stress, and UPR in podocytopathies that may ultimately help refine drug treatment.

Diverse profiles of ricin-cell interactions in the lung following intranasal exposure to ricin

Ricin, a plant-derived exotoxin, inhibits protein synthesis by ribosomal inactivation. Due to its wide availability and ease of preparation, ricin is considered a biothreat, foremost by respiratory exposure. We examined the in vivo interactions between ricin and cells of the lungs in mice intranasally exposed to the toxin and revealed multi-phasic cell-type-dependent binding profiles. While macrophages (MΦs) and dendritic cells (DCs) displayed biphasic binding to ricin, monophasic binding patterns were observed for other cell types; epithelial cells displayed early binding, while B cells and endothelial cells bound toxin late after intoxication. Neutrophils, which were massively recruited to the intoxicated lung, were refractive to toxin binding. Although epithelial cells bound ricin as early as MΦs and DCs, their rates of elimination differed considerably; a reduction in epithelial cell counts occurred late after intoxication and was restricted to alveolar type II cells only. The differential binding and cell-elimination patterns observed may stem from dissimilar accessibility of the toxin to different cells in the lung and may also reflect unequal interactions of the toxin with different cell-surface receptors. The multifaceted interactions observed in this study between ricin and the various cells of the target organ should be considered in the future development of efficient post-exposure countermeasures against ricin intoxication.

The heterogeneity of lung macrophages in the susceptibility to disease

Alveolar macrophages are specialised resident phagocytes in the alveolus, constituting the first line of immune cellular defence in the lung. As the lung microenvironment is challenged and remodelled by inhaled pathogens and air particles, so is the alveolar macrophage pool altered by signals that maintain and/or replace its composition. The signals that induce the recruitment of circulating monocytes to the injured lung, as well as their distinct gene expression profile and susceptibility to epigenetic reprogramming by the local environment remain unclear. In this review, we summarise the unique characteristics of the alveolar macrophage pool ontogeny, phenotypic heterogeneity and plasticity during homeostasis, tissue injury and normal ageing. We also discuss new evidence arising from recent studies where investigators described how the epigenetic landscape drives the specific gene expression profile of alveolar macrophages. Altogether, new analysis of macrophages by means of “omic” technologies will allow us to identify key pathways by which these cells contribute to the development and resolution of lung disease in both mice and humans.

Alveolar macrophages: the influence of ontogeny and microenvironment on epigenetically programmed responses to stresshttp://ow.ly/Owei1

Resolvins Decrease Oxidative Stress Mediated Macrophage and Epithelial Cell Interaction through Decreased Cytokine Secretion

Background

Inflammation is a key hallmark of ALI and is mediated through ungoverned cytokine signaling. One such cytokine, interleukin-1beta (IL-1β) has been demonstrated to be the most bioactive cytokine in ALI patients. Macrophages are the key players responsible for IL-1β secretion into the alveolar space. Following the binding of IL-1β to its receptor, “activated” alveolar epithelial cells show enhanced barrier dysfunction, adhesion molecule expression, cytokine secretion, and leukocyte attachment. More importantly, it is an important communication molecule between the macrophage and alveolar epithelium. While the molecular determinants of this inflammatory event have been well documented, endogenous resolution processes that decrease IL-1β secretion and resolve alveolar epithelial cell activation and tissue inflammation have not been well characterized. Lipid mediator Aspirin-Triggered Resolvin D1 (AT-RvD1) has demonstrated potent pro-resolutionary effects in vivo models of lung injury; however, the contribution of the alveoli to the protective benefits of this molecule has not been well documented. In this study, we demonstrate that AT-RvD1 treatment lead to a significant decrease in oxidant induced macrophage IL-1β secretion and production, IL-1β-mediated cytokine secretion, adhesion molecule expression, leukocyte adhesion and inflammatory signaling.

Methods

THP-1 macrophages were treated with hydrogen peroxide and extracellular ATP in the presence or absence of AT-RvD1 (1000–0.1 nM). A549 alveolar-like epithelial cells were treated with IL-1β (10 ng/mL) in the presence or absence of AT-RvD1 (0.1 μM). Following treatment, cell lysate and cell culture supernatants were collected for Western blot, qPCR and ELISA analysis of pro-inflammatory molecules. Functional consequences of IL-1β induced alveolar epithelial cell and macrophage activation were also measured following treatment with IL-1β ± AT-RvD1.

Results

Results demonstrate that macrophages exposed to H₂O₂ and ATP in the presence of resolvins show decreased IL-1β production and activity. A549 cells treated with IL-1β in the presence of AT-RvD1 show a reduced level of proinflammatory cytokines IL-6 and IL-8. Further, IL-1β-mediated adhesion molecule expression was also reduced with AT-RvD1 treatment, which was correlated with decreased leukocyte adhesion. AT-RvD1 treatment demonstrated reduced MAP-Kinase signaling. Taken together, our results demonstrate AT-RvD1 treatment reduced IL-1β-mediated alveolar epithelial cell activation. This is a key step in unraveling the protective effects of resolvins, especially AT-RvD1, during injury.

13th ERS Lung Science Conference. The most important take home messages: News from the Underground

The 13th ERS Lung Science Conference (LSC) was organised to bring academics together from all over the world to present and discuss the latest developments regarding lung infection and immunity. The conference took place in breathtaking Estoril, Portugal; however, it wasn't the beautiful surroundings that were our main motivation to attend, but instead the scientific merit of the conference and the chance to create new scientific collaborations. The scientific programme [1] was packed with the most up-to-date content in the field of lung infection and immunity and included some of the top researchers within this exciting area. Moreover, the convenient size of the LSC offered the opportunity to renew and intensify friendships and collaborations. In particular, for researchers at the start of their career, this is a great feature and we therefore warmly recommend the LSC to ERS Juniors Members!

The role of tissue resident cells in neutrophil recruitment

Neutrophils are first responders of the immune system, rapidly migrating into affected tissues in response to injury or infection. To effectively call in this first line of defense, strategically placed cells within the vasculature and tissue respond to noxious stimuli by sending out coordinated signals that recruit neutrophils. Regulation of organ-specific neutrophil entry occurs at two levels. First, the vasculature supplying the organ provides cues for neutrophil egress out of the bloodstream in a manner dependent upon its unique cellular composition and architectural features. Second, resident immune cells and stromal cells within the organ send coordinated signals that guide neutrophils to their final destination. Here, we review recent findings that highlight the importance of these tissue-specific responses in the regulation of neutrophil recruitment and the initiation and resolution of inflammation.

The Immune Fulcrum: Regulatory T Cells Tip the Balance Between Pro- and Anti-inflammatory Outcomes upon Infection

Regulatory T cells (Tregs) are indispensable for immune homeostasis and the prevention of autoimmunity. In the context of infectious diseases, Tregs are multidimensional. Here, we describe how they may potentiate effector responses by assisting in recruitment of T cells into the infection site to resolve infection, facilitate accelerated antigen-specific memory responses, limit pathology, and contribute to disease resolution and healing, to the great benefit of the host. We also explore the villainous functions of Tregs during infection by reviewing several diseases in which the depletion or reduction in Treg frequency allows for better generation of effector memory, and results in acute resolution of infection, as opposed to chronicity or severe long-term outcomes. We describe findings generated using mouse models of infection as well as experiments performed using human cells and tissues. We propose that Tregs represent an immunologic fulcrum, promoting both pathogen clearance and damage control by preventing excessive destruction of infected tissues though unchecked immune responses.

Recruited alveolar macrophages, in response to airway epithelial-derived monocyte chemoattractant protein 1/CCl2, regulate airway inflammation and remodeling in allergic asthma

Although alveolar macrophages (AMs) from patients with asthma are known to be functionally different from those of healthy individuals, the mechanism by which this transformation occurs has not been fully elucidated in asthma. The goal of this study was to define the mechanisms that control AM phenotypic and functional transformation in response to acute allergic airway inflammation. The phenotype and functional characteristics of AMs obtained from human subjects with asthma after subsegmental bronchoprovocation with allergen was studied. Using macrophage-depleted mice, the role and trafficking of AM populations was determined using an acute allergic lung inflammation model. We observed that depletion of AMs in a mouse allergic asthma model attenuates Th2-type allergic lung inflammation and its consequent airway remodeling. In both human and mouse, endobronchial challenge with allergen induced a marked increase in monocyte chemotactic proteins (MCPs) in bronchoalveolar fluid, concomitant with the rapid appearance of a monocyte-derived population of AMs. Furthermore, airway allergen challenge of allergic subjects with mild asthma skewed the pattern of AM gene expression toward high levels of the receptor for MCP1 (CCR2/MCP1R) and expression of M2 phenotypic proteins, whereas most proinflammatory genes were highly suppressed. CCL2/MCP-1 gene expression was prominent in bronchial epithelial cells in a mouse allergic asthma model, and in vitro studies indicate that bronchial epithelial cells produced abundant MCP-1 in response to house dust mite allergen. Thus, our study indicates that bronchial allergen challenge induces the recruitment of blood monocytes along a chemotactic gradient generated by allergen-exposed bronchial epithelial cells.

The lung communication network

The different types of cells in the lung, from the conducting airway epithelium to the alveolar epithelium and the pulmonary vasculature, are interconnected by gap junctions. The specific profile of gap junction proteins, the connexins, expressed in these different cell types forms compartments of intercellular communication that can be further shaped by the release of extracellular nucleotides via pannexin1 channels. In this review, we focus on the physiology of connexins and pannexins and describe how this lung communication network modulates lung function and host defenses in conductive and respiratory airways.

Connexins: Intercellular Signal Transmitters in Lymphohematopoietic Tissues

Life-long hematopoietic demands are met by a pool of hematopoietic stem cells (HSC) with self-renewal and multipotential differentiation ability. Humoral and paracrine signals from the bone marrow (BM) hematopoietic microenvironment control HSC activity. Cell-to-cell communication through connexin (Cx) containing gap junctions (GJs) allows pluricellular coordination and synchronization through transfer of small molecules with messenger activity. Hematopoietic and surrounding nonhematopoietic cells communicate each other through GJs, which regulate fetal and postnatal HSC content and function in hematopoietic tissues. Traffic of HSC between peripheral blood and BM is also dependent on Cx proteins. Cx mutations are associated with human disease and hematopoietic dysfunction and Cx signaling may represent a target for therapeutic intervention. In this review, we illustrate and highlight the importance of Cxs in the regulation of hematopoietic homeostasis under normal and pathological conditions.

Brief Glutamine Pretreatment Increases Alveolar Macrophage CD163/Heme Oxygenase-1/p38-MAPK Dephosphorylation Pathway and Decreases Capillary Damage but Not Neutrophil Recruitment in IL-1/LPS-Insufflated Rats

Background

Glutamine (GLN) attenuates acute lung injury (ALI) but its effect on alveolar macrophages is unknown. We hypothesized that GLN pretreatment would induce the anti-inflammatory CD163/heme oxygenase (HO)-1/p38-MAPK dephosphorylation pathway in alveolar macrophages and reduce ALI in rats insufflated with interleukin-1 (IL-1) and lipopolysaccharide (LPS).

Methods

Male Sprague-Dawley rats were randomized to the following groups: GLN-IL-1/LPS-, GLN+IL-1/LPS-, GLN-IL-1/LPS+, and GLN+IL-1/LPS+. GLN pretreatment was given via gavage (1g/kg L-alanyl-L-glutamine) daily for 2 days. ALI was subsequently induced by insufflating 50ng IL-1 followed by 5mg/kg E.coli LPS. After 24h, bronchoalveolar lavage (BAL) protein, lactate dehydrogenase (LDH) and neutrophil concentrations were analyzed. BAL alveolar macrophage CD163+ expression, HO-1 and p38-MAPK concentrations were measured, as well as alveolar macrophage tumor necrosis factor (TNF)-α and interleukin (IL)-10 concentrations. Histology and immunofluorescence studies were also performed.

Results

Following IL-1/LPS insufflation, GLN pretreated rats had significantly decreased BAL protein and LDH concentrations, but not BAL neutrophil counts, compared to non-GLN pretreated rats. The number of alveolar macrophages and the number of CD163+ macrophages were significantly increased in GLN pretreated IL-1/LPS-insufflated rats compared to non-GLN pretreated, IL-1/LPS-insufflated rats. GLN pretreatment before IL-1/LPS also significantly increased HO-1 concentrations and dephosphorylated p38-MAPK levels but not cytokine levels in alveolar macrophages. Immunofluorescence localized CD163 and HO-1 in alveolar macrophages.

Conclusion

Short-term GLN pretreatment activates the anti-inflammatory CD163/HO-1/p38-MAPK dephosphorylation pathway of alveolar macrophages and decreases capillary damage but not neutrophil recruitment in IL-1/LPS-insufflated rats.

Multidimensional immunolabeling and 4D time-lapse imaging of vital ex vivo lung tissue

During the last decades, the study of cell behavior was largely accomplished in uncoated or extracellular matrix (ECM)-coated plastic dishes. To date, considerable cell biological efforts have tried to model in vitro the natural microenvironment found in vivo. For the lung, explants cultured ex vivo as lung tissue cultures (LTCs) provide a three-dimensional (3D) tissue model containing all cells in their natural microenvironment. Techniques for assessing the dynamic live interaction between ECM and cellular tissue components, however, are still missing. Here, we describe specific multidimensional immunolabeling of living 3D-LTCs, derived from healthy and fibrotic mouse lungs, as well as patient-derived 3D-LTCs, and concomitant real-time four-dimensional multichannel imaging thereof. This approach allowed the evaluation of dynamic interactions between mesenchymal cells and macrophages with their ECM. Furthermore, fibroblasts transiently expressing focal adhesions markers incorporated into the 3D-LTCs, paving new ways for studying the dynamic interaction between cellular adhesions and their natural-derived ECM. A novel protein transfer technology (FuseIt/Ibidi) shuttled fluorescently labeled α-smooth muscle actin antibodies into the native cells of living 3D-LTCs, enabling live monitoring of α-smooth muscle actin-positive stress fibers in native tissue myofibroblasts residing in fibrotic lesions of 3D-LTCs. Finally, this technique can be applied to healthy and diseased human lung tissue, as well as to adherent cells in conventional two-dimensional cell culture. This novel method will provide valuable new insights into the dynamics of ECM (patho)biology, studying in detail the interaction between ECM and cellular tissue components in their natural microenvironment.

Mycobacterium tuberculosis Differentially Activates cGAS- and Inflammasome-Dependent Intracellular Immune Responses through ESX-1

Cytosolic detection of microbial products is essential for the initiation of an innate immune response against intracellular pathogens such as Mycobacterium tuberculosis (Mtb). During Mtb infection of macrophages, activation of cytosolic surveillance pathways is dependent on the mycobacterial ESX-1 secretion system and leads to type I interferon (IFN) and interleukin-1β (IL-1β) production. Whereas the inflammasome regulates IL-1β secretion, the receptor(s) responsible for the activation of type I IFNs has remained elusive. We demonstrate that the cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) is essential for initiating an IFN response to Mtb infection. cGAS associates with Mtb DNA in the cytosol to stimulate cyclic GAMP (cGAMP) synthesis. Notably, activation of cGAS-dependent cytosolic host responses can be uncoupled from inflammasome activation by modulating the secretion of ESX-1 substrates. Our findings identify cGAS as an innate sensor of Mtb and provide insight into how ESX-1 controls the activation of specific intracellular recognition pathways.