Distinct macrophage subpopulations characterize acute infection and chronic inflammatory lung disease

Granulocyte-CSF links destructive inflammation and comorbidities in obstructive lung disease

Chronic obstructive pulmonary disease (COPD) is an incurable inflammatory lung disease that afflicts millions of people worldwide, and it is the fourth leading cause of death. Systemic comorbidities affecting the heart, skeletal muscle, bone, and metabolism are major contributors to morbidity and mortality. Given the surprising finding in large prospective clinical biomarker studies that peripheral white blood cell count is more closely associated with disease than inflammatory biomarkers, we probed the role of blood growth factors. Using the SHIP-1-deficient COPD mouse model, which manifests a syndrome of destructive lung disease and a complex of comorbid pathologies, we have identified a critical and unexpected role for granulocyte-CSF (G-CSF) in linking these conditions. Deletion of G-CSF greatly reduced airway inflammation and lung tissue destruction, and attenuated systemic inflammation, right heart hypertrophy, loss of fat reserves, and bone osteoporosis. In human clinical translational studies, bronchoalveolar lavage fluid of patients with COPD demonstrated elevated G-CSF levels. These studies suggest that G-CSF may play a central and unforeseen pathogenic role in COPD and its complex comorbidities, and identify G-CSF and its regulators as potential therapeutic targets.

Characterization of Immune Cells in Human Adipose Tissue by Using Flow Cytometry

Infiltration of immune cells in the subcutaneous and visceral adipose tissue (AT) deposits leads to a low-grade inflammation contributing to the development of obesity-associated complications such as type 2 diabetes. To quantitatively and qualitatively investigate the immune cell subsets in human AT deposits, we have developed a flow cytometry approach. The stromal vascular fraction (SVF), containing the immune cells, is isolated from subcutaneous and visceral AT biopsies by collagenase digestion. Adipocytes are removed after centrifugation. The SVF cells are stained for multiple membrane-bound markers selected to differentiate between immune cell subsets and analyzed using flow cytometry. As a result of this approach, pro- and anti-inflammatory macrophage subsets, dendritic cells (DCs), B-cells, CD4⁺ and CD8⁺ T-cells, and NK cells can be detected and quantified. This method gives detailed information about immune cells in AT and the amount of each specific subset. Since there are numerous fluorescent antibodies available, our flow cytometry approach can be adjusted to measure various other cellular and intracellular markers of interest.

Dysregulated Functions of Lung Macrophage Populations in COPD

Chronic obstructive pulmonary disease (COPD) is a diverse respiratory disease characterised by bronchiolitis, small airway obstruction, and emphysema. Innate immune cells play a pivotal role in the disease's progression, and in particular, lung macrophages exploit their prevalence and strategic localisation to orchestrate immune responses. To date, alveolar and interstitial resident macrophages as well as blood monocytes have been described in the lungs of patients with COPD contributing to disease pathology by changes in their functional repertoire. In this review, we summarise recent evidence from human studies and work with animal models of COPD with regard to altered functions of each of these myeloid cell populations. We primarily focus on the dysregulated capacity of alveolar macrophages to secrete proinflammatory mediators and proteases, induce oxidative stress, engulf microbes and apoptotic cells, and express surface and intracellular markers in patients with COPD. In addition, we discuss the differences in the responses between alveolar macrophages and interstitial macrophages/monocytes in the disease and propose how the field should advance to better understand the implications of lung macrophage functions in COPD.

Toll-like receptor 2 and 4 have opposing roles in the pathogenesis of cigarette smoke-induced chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is the third leading cause of morbidity and death and imposes major socioeconomic burdens globally. It is a progressive and disabling condition that severely impairs breathing and lung function. There is a lack of effective treatments for COPD, which is a direct consequence of the poor understanding of the underlying mechanisms involved in driving the pathogenesis of the disease. Toll-like receptor (TLR)2 and TLR4 are implicated in chronic respiratory diseases, including COPD, asthma and pulmonary fibrosis. However, their roles in the pathogenesis of COPD are controversial and conflicting evidence exists. In the current study, we investigated the role of TLR2 and TLR4 using a model of cigarette smoke (CS)-induced experimental COPD that recapitulates the hallmark features of human disease. TLR2, TLR4, and associated coreceptor mRNA expression was increased in the airways in both experimental and human COPD. Compared with wild-type (WT) mice, CS-induced pulmonary inflammation was unaltered in TLR2-deficient ( Tlr2-/-) and TLR4-deficient ( Tlr4-/-) mice. CS-induced airway fibrosis, characterized by increased collagen deposition around small airways, was not altered in Tlr2-/- mice but was attenuated in Tlr4-/- mice compared with CS-exposed WT controls. However, Tlr2-/- mice had increased CS-induced emphysema-like alveolar enlargement, apoptosis, and impaired lung function, while these features were reduced in Tlr4-/- mice compared with CS-exposed WT controls. Taken together, these data highlight the complex roles of TLRs in the pathogenesis of COPD and suggest that activation of TLR2 and/or inhibition of TLR4 may be novel therapeutic strategies for the treatment of COPD.

SHIP negatively regulates type II immune responses in mast cells and macrophages

SHIP is a hematopoietic-specific lipid phosphatase that dephosphorylates PI3K-generated PI(3,4,5)-trisphosphate. SHIP removes this second messenger from the cell membrane blunting PI3K activity in immune cells. Thus, SHIP negatively regulates mast cell activation downstream of multiple receptors. SHIP has been referred to as the "gatekeeper" of mast cell degranulation as loss of SHIP dramatically increases degranulation or permits degranulation in response to normally inert stimuli. SHIP also negatively regulates Mϕ activation, including both pro-inflammatory cytokine production downstream of pattern recognition receptors, and alternative Mϕ activation by the type II cytokines, IL-4, and IL-13. In the SHIP-deficient (SHIP-/- ) mouse, increased mast cell and Mϕ activation leads to spontaneous inflammatory pathology at mucosal sites, which is characterized by high levels of type II inflammatory cytokines. SHIP-/- mast cells and Mϕs have both been implicated in driving inflammation in the SHIP-/- mouse lung. SHIP-/- Mϕs drive Crohn's disease-like intestinal inflammation and fibrosis, which is dependent on heightened responses to innate immune stimuli generating IL-1, and IL-4 inducing abundant arginase I. Both lung and gut pathology translate to human disease as low SHIP levels and activity have been associated with allergy and with Crohn's disease in people. In this review, we summarize seminal literature and recent advances that provide insight into SHIP's role in mast cells and Mϕs, the contribution of these cell types to pathology in the SHIP-/- mouse, and describe how these findings translate to human disease and potential therapies.

Effect of anti-podoplanin antibody administration during lipopolysaccharide-induced lung injury in mice

Introduction

Acute respiratory distress syndrome (ARDS) is a devastating pulmonary condition in the critically ill patient. A therapeutic intervention is yet to be found that can prevent progression to ARDS. We recently demonstrated that the interaction between podoplanin expressed on inflammatory alveolar macrophages (iAMs) and its endogenous ligand, platelet C-type lectin-like 2 (CLEC-2), protects against exaggerated lung inflammation during a mouse model of ARDS. In this study, we aim to investigate the therapeutic use of a crosslinking/activating anti-podoplanin antibody (α-PDPN, clone 8.1.1) during lipopolysaccharide (LPS)-induced lung inflammation in mice.

Methods

Intravenous administration of α-PDPN was performed 6 hours after intratracheal LPS in wildtype, C57Bl/6 mice. Lung function decline was measured by pulse oximetry as well as markers of local inflammation including bronchoalveolar lavage neutrophilia and cytokine/chemokine expression. In parallel, alveolar macrophages were isolated and cultured in vitro from haematopoietic-specific podoplanin-deficient mice (Pdpn^fl/flVAV1cre⁺) and floxed-only controls treated with or without LPS in the presence or absence of α-PDPN.

Results

Lung function decline as well as alveolar neutrophil recruitment was significantly decreased in mice treated with the crosslinking/activating α-PDPN in vivo. Furthermore, we demonstrate that, in vitro, activation of podoplanin on iAMs regulates their secretion of proinflammatory cytokines and chemokines.

Conclusions

These data confirm the importance of the CLEC-2–podoplanin pathway during intratracheal (IT)-LPS and demonstrate the beneficial effect of targeting podoplanin during IT-LPS in mice possibly via modulation of local cytokine/chemokine expression. Moreover, these data suggest that podoplanin-targeted therapies may have a beneficial effect in patients at risk of developing ARDS.

Aspirin-triggered resolvin D1 reduces pneumococcal lung infection and inflammation in a viral and bacterial coinfection pneumonia model

Formyl peptide receptor 2/lipoxin A4 (LXA4) receptor (Fpr2/ALX) co-ordinates the transition from inflammation to resolution during acute infection by binding to distinct ligands including serum amyloid A (SAA) and Resolvin D1 (RvD1). Here, we evaluated the proresolving actions of aspirin-triggered RvD1 (AT-RvD1) in an acute coinfection pneumonia model. Coinfection with Streptococcus pneumoniae and influenza A virus (IAV) markedly increased pneumococcal lung load and neutrophilic inflammation during the resolution phase. Fpr2/ALX transcript levels were increased in the lungs of coinfected mice, and immunohistochemistry identified prominent Fpr2/ALX immunoreactivity in bronchial epithelial cells and macrophages. Levels of circulating and lung SAA were also highly increased in coinfected mice. Therapeutic treatment with exogenous AT-RvD1 during the acute phase of infection (day 4–6 post-pneumococcal inoculation) significantly reduced the pneumococcal load. AT-RvD1 also significantly reduced neutrophil elastase (NE) activity and restored total antimicrobial activity in bronchoalveolar lavage (BAL) fluid (BALF) of coinfected mice. Pneumonia severity, as measured by quantitating parenchymal inflammation or alveolitis was significantly reduced with AT-RvD1 treatment, which also reduced the number of infiltrating lung neutrophils and monocytes/macrophages as assessed by flow cytometry. The reduction in distal lung inflammation in AT-RvD1-treated mice was not associated with a significant reduction in inflammatory and chemokine mediators. In summary, we demonstrate that in the coinfection setting, SAA levels were persistently increased and exogenous AT-RvD1 facilitated more rapid clearance of pneumococci in the lungs, while concurrently reducing the severity of pneumonia by limiting excessive leukocyte chemotaxis from the infected bronchioles to distal areas of the lungs.

Platelet CLEC-2 protects against lung injury via effects of its ligand podoplanin on inflammatory alveolar macrophages in the mouse

There is no therapeutic intervention proven to prevent acute respiratory distress syndrome (ARDS). Novel mechanistic insights into the pathophysiology of ARDS are therefore required. Platelets are implicated in regulating many of the pathogenic processes that occur during ARDS; however, the mechanisms remain elusive. The platelet receptor CLEC-2 has been shown to regulate vascular integrity at sites of acute inflammation. Therefore the purpose of this study was to establish the role of CLEC-2 and its ligand podoplanin in a mouse model of ARDS. Platelet-specific CLEC-2-deficient, as well as alveolar epithelial type I cell (AECI)-specific or hematopoietic-specific podoplanin deficient, mice were established using cre-loxP strategies. Combining these with intratracheal (IT) instillations of lipopolysaccharide (LPS), we demonstrate that arterial oxygen saturation decline in response to IT-LPS in platelet-specific CLEC-2-deficient mice is significantly augmented. An increase in bronchoalveolar lavage (BAL) neutrophils and protein was also observed 48 h post-IT-LPS, with significant increases in pro-inflammatory chemokines detected in BAL of platelet-specific CLEC-2-deficient animals. Deletion of podoplanin from hematopoietic cells but not AECIs also reduces lung function and increases pro-inflammatory chemokine expression following IT-LPS. Furthermore, we demonstrate that following IT-LPS, platelets are present in BAL in aggregates with neutrophils, which allows for CLEC-2 interaction with podoplanin expressed on BAL inflammatory alveolar macrophages. Taken together, these data suggest that the platelet CLEC-2-podoplanin signaling axis regulates the severity of lung inflammation in mice and is a possible novel target for therapeutic intervention in patients at risk of developing ARDS.

Characterisation of lung macrophage subpopulations in COPD patients and controls

Lung macrophage subpopulations have been identified based on size. We investigated characteristics of small and large macrophages in the alveolar spaces and lung interstitium of COPD patients and controls. Alveolar and interstitial cells were isolated from lung resection tissue from 88 patients. Macrophage subpopulation cell-surface expression of immunological markers and phagocytic ability were assessed by flow cytometry. Inflammatory related gene expression was measured. Alveolar and interstitial macrophages had subpopulations of small and large macrophages based on size and granularity. Alveolar macrophages had similar numbers of small and large cells; interstitial macrophages were mainly small. Small macrophages expressed significantly higher cell surface HLA-DR, CD14, CD38 and CD36 and lower CD206 compared to large macrophages. Large alveolar macrophages showed lower marker expression in COPD current compared to ex-smokers. Small interstitial macrophages had the highest pro-inflammatory gene expression levels, while large alveolar macrophages had the lowest. Small alveolar macrophages had the highest phagocytic ability. Small alveolar macrophage CD206 expression was lower in COPD patients compared to smokers. COPD lung macrophages include distinct subpopulations; Small interstitial and small alveolar macrophages with more pro-inflammatory and phagocytic function respectively, and large alveolar macrophages with low pro-inflammatory and phagocytic ability.

White matter damage after traumatic brain injury: A role for damage associated molecular patterns

Traumatic brain injury (TBI) is a leading cause of mortality and long-term morbidity worldwide. Despite decades of pre-clinical investigation, therapeutic strategies focused on acute neuroprotection failed to improve TBI outcomes. This lack of translational success has necessitated a reassessment of the optimal targets for intervention, including a heightened focus on secondary injury mechanisms. Chronic immune activation correlates with progressive neurodegeneration for decades after TBI; however, significant challenges remain in functionally and mechanistically defining immune activation after TBI. In this review, we explore the burgeoning evidence implicating the acute release of damage associated molecular patterns (DAMPs), such as adenosine 5'-triphosphate (ATP), high mobility group box protein 1 (HMGB1), S100 proteins, and hyaluronic acid in the initiation of progressive neurological injury, including white matter loss after TBI. The role that pattern recognition receptors, including toll-like receptor and purinergic receptors, play in progressive neurological injury after TBI is detailed. Finally, we provide support for the notion that resident and infiltrating macrophages are critical cellular targets linking acute DAMP release with adaptive immune responses and chronic injury after TBI. The therapeutic potential of targeting DAMPs and barriers to clinical translational, in the context of TBI patient management, are discussed.

Development and Functional Differentiation of Tissue-Resident Versus Monocyte-Derived Macrophages in Inflammatory Reactions

Mononuclear phagocytes are key cells in tissue integrity and defense. Tissue-resident macrophages are abundantly present in all tissues of the body and have a complex role in ensuring tissue functions and homeostatic balance. Circulating blood monocytes can enter tissue both in steady-state conditions, for helping in replenishing the tissue-resident macrophage pool and, in particular, for acting as potent effector cells during inflammatory events such as infections, traumas, and diseases. The heterogeneity of monocytes and macrophages depends on their ontogeny, their tissue location, and their functional programming, with both monocytes and macrophages able to exert distinct or similar functions depending on the tissue-specific and stimulus-specific microenvironment. In this short review, we will review the current hypotheses on tissue-resident macrophage ontogeny and functions, as compared to blood-derived monocytes, with a particular focus on inflammatory conditions.

The inhibitor of semicarbazide-sensitive amine oxidase, PXS-4728A, ameliorates key features of chronic obstructive pulmonary disease in a mouse model

BACKGROUND AND PURPOSE

Chronic obstructive pulmonary disease (COPD) is a major cause of illness and death, often induced by cigarette smoking (CS). It is characterized by pulmonary inflammation and fibrosis that impairs lung function. Existing treatments aim to control symptoms but have low efficacy, and there are no broadly effective treatments. A new potential target is the ectoenzyme, semicarbazide-sensitive mono-amine oxidase (SSAO; also known as vascular adhesion protein-1). SSAO is elevated in smokers' serum and is a pro-inflammatory enzyme facilitating adhesion and transmigration of leukocytes from the vasculature to sites of inflammation.

EXPERIMENTAL APPROACH

PXS-4728A was developed as a low MW inhibitor of SSAO. A model of COPD induced by CS in mice reproduces key aspects of human COPD, including chronic airway inflammation, fibrosis and impaired lung function. This model was used to assess suppression of SSAO activity and amelioration of inflammation and other characteristic features of COPD.

KEY RESULTS

Treatment with PXS-4728A completely inhibited lung and systemic SSAO activity induced by acute and chronic CS-exposure. Daily oral treatment inhibited airway inflammation (immune cell influx and inflammatory factors) induced by acute CS-exposure. Therapeutic treatment during chronic CS-exposure, when the key features of experimental COPD develop and progress, substantially suppressed inflammatory cell influx and fibrosis in the airways and improved lung function.

CONCLUSIONS AND IMPLICATIONS

Treatment with a low MW inhibitor of SSAO, PXS-4728A, suppressed airway inflammation and fibrosis and improved lung function in experimental COPD, demonstrating the therapeutic potential of PXS-4728A for this debilitating disease.

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.

Saikosaponin A inhibits influenza A virus replication and lung immunopathology

Fatal influenza outcomes result from a combination of rapid virus replication and collateral lung tissue damage caused by exaggerated pro-inflammatory host immune cell responses. There are few therapeutic agents that target both biological processes for the attenuation of influenza-induced lung pathology. We show that Saikosaponin A, a bioactive triterpene saponin with previouslyestablished anti-inflammatory effects, demonstrates both in vitro and in vivo anti-viral activity against influenza A virus infections. Saikosaponin A attenuated the replication of three different influenza A virus strains, including a highly pathogenic H5N1 strain, in human alveolar epithelial A549 cells. This anti-viral activity occurred through both downregulation of NF-κB signaling and caspase 3-dependent virus ribonucleoprotein nuclear export as demonstrated by NF-κB subunit p65 and influenza virus nucleoprotein nuclear translocation studies in influenza virus infected A549 cells. Critically, Saikosaponin A also attenuated viral replication, aberrant pro-inflammatory cytokine production and lung histopathology in the widely established H1N1 PR8 model of influenza A virus lethality in C57BL/6 mice. Flow cytometry studies of mouse bronchoalveolar lavage cells revealed that SSa exerted immunomodulatory effects through a selective attenuation of lung neutrophil and monocyte recruitment during the early peak of the innate immune response to PR8 infection. Altogether, our results indicate that Saikosaponin A possesses novel therapeutic potential for the treatment of pathological influenza virus infections.

Advances in understanding COPD

In recent years, thousands of publications on chronic obstructive pulmonary disease (COPD) and its related biology have entered the world literature, reflecting the increasing scientific and medical interest in this devastating condition. This article is a selective review of several important emerging themes that offer the hope of creating new classes of COPD medicines. Whereas basic science is parsing molecular pathways in COPD, its comorbidities, and asthma COPD overlap syndrome (ACOS) with unprecedented sophistication, clinical translation is disappointingly slow. The article therefore also considers solutions to current difficulties that are impeding progress in translating insights from basic science into clinically useful treatments.

Aspirin-triggered resolvin D1 is produced during self-resolving gram-negative bacterial pneumonia and regulates host immune responses for the resolution of lung inflammation

Bacterial pneumonia is a leading cause of morbidity and mortality worldwide. Host responses to contain infection and mitigate pathogen-mediated lung inflammation are critical for pneumonia resolution. Aspirin-triggered resolvin D1 (AT-RvD1; 7S,8R,17R-trihydroxy-4Z,9E,11E,13Z,15E,19Z-docosahexaenoic acid) is a lipid mediator (LM) that displays organ-protective actions in sterile lung inflammation, and regulates pathogen-initiated cellular responses. Here, in a self-resolving murine model of Escherichia coli pneumonia, LM metabololipidomics performed on lungs obtained at baseline, 24, and 72 h after infection uncovered temporal regulation of endogenous AT-RvD1 production. Early treatment with exogenous AT-RvD1 (1 h post infection) enhanced clearance of E. coli and Pseudomonas aeruginosa in vivo, and lung macrophage phagocytosis of fluorescent bacterial particles ex vivo. Characterization of macrophage subsets in the alveolar compartment during pneumonia identified efferocytosis by infiltrating macrophages (CD11b(Hi) CD11c(Low)) and exudative macrophages (CD11b(Hi) CD11c(Hi)). AT-RvD1 increased efferocytosis by these cells ex vivo, and accelerated neutrophil clearance during pneumonia in vivo. These anti-bacterial and pro-resolving actions of AT-RvD1 were additive to antibiotic therapy. Taken together, these findings suggest that the pro-resolving actions of AT-RvD1 during pneumonia represent a novel host-directed therapeutic strategy to complement the current antibiotic-centered approach for combatting infections.

An Epithelial Integrin Regulates the Amplitude of Protective Lung Interferon Responses against Multiple Respiratory Pathogens

The healthy lung maintains a steady state of immune readiness to rapidly respond to injury from invaders. Integrins are important for setting the parameters of this resting state, particularly the epithelial-restricted αVβ6 integrin, which is upregulated during injury. Once expressed, αVβ6 moderates acute lung injury (ALI) through as yet undefined molecular mechanisms. We show that the upregulation of β6 during influenza infection is involved in disease pathogenesis. β6-deficient mice (β6 KO) have increased survival during influenza infection likely due to the limited viral spread into the alveolar spaces leading to reduced ALI. Although the β6 KO have morphologically normal lungs, they harbor constitutively activated lung CD11b+ alveolar macrophages (AM) and elevated type I IFN signaling activity, which we traced to the loss of β6-activated transforming growth factor-β (TGF-β). Administration of exogenous TGF-β to β6 KO mice leads to reduced numbers of CD11b+ AMs, decreased type I IFN signaling activity and loss of the protective phenotype during influenza infection. Protection extended to other respiratory pathogens such as Sendai virus and bacterial pneumonia. Our studies demonstrate that the loss of one epithelial protein, αVβ6 integrin, can alter the lung microenvironment during both homeostasis and respiratory infection leading to reduced lung injury and improved survival.

A pathogenic role for tumor necrosis factor-related apoptosis-inducing ligand in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a life-threatening inflammatory respiratory disorder, often induced by cigarette smoke (CS) exposure. The development of effective therapies is impaired by a lack of understanding of the underlining mechanisms. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytokine with inflammatory and apoptotic properties. We interrogated a mouse model of CS-induced experimental COPD and human tissues to identify a novel role for TRAIL in COPD pathogenesis. CS exposure of wild-type mice increased TRAIL and its receptor messenger RNA (mRNA) expression and protein levels, as well as the number of TRAIL(+)CD11b(+) monocytes in the lung. TRAIL and its receptor mRNA were also increased in human COPD. CS-exposed TRAIL-deficient mice had decreased pulmonary inflammation, pro-inflammatory mediators, emphysema-like alveolar enlargement, and improved lung function. TRAIL-deficient mice also developed spontaneous small airway changes with increased epithelial cell thickness and collagen deposition, independent of CS exposure. Importantly, therapeutic neutralization of TRAIL, after the establishment of early-stage experimental COPD, reduced pulmonary inflammation, emphysema-like alveolar enlargement, and small airway changes. These data provide further evidence for TRAIL being a pivotal inflammatory factor in respiratory diseases, and the first preclinical evidence to suggest that therapeutic agents that target TRAIL may be effective in COPD therapy.

Depletion of Alveolar Macrophages Does Not Prevent Hantavirus Disease Pathogenesis in Golden Syrian Hamsters

Andes virus (ANDV) is associated with a lethal vascular leak syndrome in humans termed hantavirus pulmonary syndrome (HPS). The mechanism for the massive vascular leakage associated with HPS is poorly understood; however, dysregulation of components of the immune response is often suggested as a possible cause. Alveolar macrophages are found in the alveoli of the lung and represent the first line of defense to many airborne pathogens. To determine whether alveolar macrophages play a role in HPS pathogenesis, alveolar macrophages were depleted in an adult rodent model of HPS that closely resembles human HPS. Syrian hamsters were treated, intratracheally, with clodronate-encapsulated liposomes or control liposomes and were then challenged with ANDV. Treatment with clodronate-encapsulated liposomes resulted in significant reduction in alveolar macrophages, but depletion did not prevent pathogenesis or prolong disease. Depletion also did not significantly reduce the amount of virus in the lung of ANDV-infected hamsters but altered neutrophil recruitment, MIP-1α and MIP-2 chemokine expression, and vascular endothelial growth factor (VEGF) levels in hamster bronchoalveolar lavage (BAL) fluid early after intranasal challenge. These data demonstrate that alveolar macrophages may play a limited protective role early after exposure to aerosolized ANDV but do not directly contribute to hantavirus disease pathogenesis in the hamster model of HPS.

IMPORTANCE

Hantaviruses continue to cause disease worldwide for which there are no FDA-licensed vaccines, effective postexposure prophylactics, or therapeutics. Much of this can be attributed to a poor understanding of the mechanism of hantavirus disease pathogenesis. Hantavirus disease has long been considered an immune-mediated disease; however, by directly manipulating the Syrian hamster model, we continue to eliminate individual immune cell types. As the most numerous immune cells present in the respiratory tract, alveolar macrophages are poised to defend against hantavirus infection, but those antiviral responses may also contribute to hantavirus disease. Here, we demonstrate that, like in our prior T and B cell studies, alveolar macrophages neither prevent hantavirus infection nor cause hantavirus disease. While these studies reflect pathogenesis in the hamster model, they should help us rule out specific cell types and prompt us to consider other potential mechanisms of disease in an effort to improve the outcome of human HPS.

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.

Targeting myeloid cells in the tumor microenvironment enhances vaccine efficacy in murine epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is typically diagnosed at advanced stages, and is associated with a high relapse rate. Patients in remission are ideal candidates for immunotherapy aimed at cure or prolonging disease-free periods. However, immunosuppressive pathways in the tumor microenvironment are obstacles to durable anti-tumor immunity. In a metastatic syngeneic mouse model of EOC, immunosuppressive macrophages and myeloid-derived suppressor cells (MDSCs) accumulate in the local tumor environment. In addition, resident peritoneal macrophages from non-tumor-bearing mice were highly immunosuppressive, abrogating stimulated T cell proliferation in a cell contact-dependent manner. Immunization with microparticles containing TLR9 and NOD-2 ligands (MIS416) significantly prolonged survival in tumor-bearing mice. The strategy of MIS416 immunization followed by anti-CD11b administration further delayed tumor progression, thereby establishing the proof of principle that myeloid depletion can enhance vaccine efficacy. In patients with advanced EOC, ascites analysis showed substantial heterogeneity in the relative proportions of myeloid subsets and their immunosuppressive properties. Together, these findings point to immunosuppressive myeloid cells in the EOC microenvironment as targets to enhance vaccination. Further studies of myeloid cell accumulation and functional phenotypes in the EOC microenvironment may identify patients who are likely to benefit from vaccination combined with approaches that deplete tumor-associated myeloid cells.

Expression Profiling of Macrophages Reveals Multiple Populations with Distinct Biological Roles in an Immunocompetent Orthotopic Model of Lung Cancer

Macrophages represent an important component of the tumor microenvironment and play a complex role in cancer progression. These cells are characterized by a high degree of plasticity, and they alter their phenotype in response to local environmental cues. Whereas the M1/M2 classification of macrophages has been widely used, the complexity of macrophage phenotypes has not been well studied, particularly in lung cancer. In this study we employed an orthotopic immunocompetent model of lung adenocarcinoma in which murine lung cancer cells are directly implanted into the left lobe of syngeneic mice. Using multimarker flow cytometry, we defined and recovered several distinct populations of monocytes/macrophages from tumors at different stages of progression. We used RNA-seq transcriptional profiling to define distinct features of each population and determine how they change during tumor progression. We defined an alveolar resident macrophage population that does not change in number and expresses multiple genes related to lipid metabolism and lipid signaling. We also defined a population of tumor-associated macrophages that increase dramatically with tumor and selectively expresses a panel of chemokine genes. A third population, which resembles tumor-associated monocytes, expresses a large number of genes involved in matrix remodeling. By correlating transcriptional profiles with clinically prognostic genes, we show that specific monocyte/macrophage populations are enriched in genes that predict outcomes in lung adenocarcinoma, implicating these subpopulations as critical determinants of patient survival. Our data underscore the complexity of monocytes/macrophages in the tumor microenvironment, and they suggest that distinct populations play specific roles in tumor progression.

CD11b immunophenotyping identifies inflammatory profiles in the mouse and human lungs

The development of easily accessible tools for human immunophenotyping to classify patients into discrete disease endotypes is advancing personalized therapy. However, no systematic approach has been developed for the study of inflammatory lung diseases with often complex and highly heterogeneous disease etiologies. We have devised an internally standardized flow cytometry approach that can identify parallel inflammatory alveolar macrophage phenotypes in both the mouse and human lungs. In mice, lung innate immune cell alterations during endotoxin challenge, influenza virus infection, and in two genetic models of chronic obstructive lung disease could be segregated based on the presence or absence of CD11b alveolar macrophage upregulation and lung eosinophilia. Additionally, heightened alveolar macrophage CD11b expression was a novel feature of acute lung exacerbations in the SHIP-1(-/-) model of chronic obstructive lung disease, and anti-CD11b antibody administration selectively blocked inflammatory CD11b(pos) but not homeostatic CD11b(neg) alveolar macrophages in vivo. The identification of analogous profiles in respiratory disease patients highlights this approach as a translational avenue for lung disease endotyping and suggests that heterogeneous innate immune cell phenotypes are an underappreciated component of the human lung disease microenvironment.

Carbon black nanoparticles induce biphasic gene expression changes associated with inflammatory responses in the lungs of C57BL/6 mice following a single intratracheal instillation

Inhalation of carbon black nanoparticles (CBNPs) causes pulmonary inflammation; however, time course data to evaluate the detailed evolution of lung inflammatory responses are lacking. Here we establish a time-series of lung inflammatory response to CBNPs. Female C57BL/6 mice were intratracheally instilled with 162 μg CBNPs alongside vehicle controls. Lung tissues were examined 3h, and 1, 2, 3, 4, 5, 14, and 42 days (d) post-exposure. Global gene expression and pulmonary inflammation were assessed. DNA damage was evaluated in bronchoalveolar lavage (BAL) cells and lung tissue using the comet assay. Increased neutrophil influx was observed at all time-points. DNA strand breaks were increased in BAL cells 3h post-exposure, and in lung tissues 2-5d post-exposure. Approximately 2600 genes were differentially expressed (± 1.5 fold; p ≤ 0.05) across all time-points in the lungs of exposed mice. Altered transcript levels were associated with immune-inflammatory response and acute phase response pathways, consistent with the BAL profiles and expression changes found in common respiratory infectious diseases. Genes involved in DNA repair, apoptosis, cell cycle regulation, and muscle contraction were also differentially expressed. Gene expression changes associated with inflammatory response followed a biphasic pattern, with initial changes at 3h post-exposure declining to base-levels by 3d, increasing again at 14 d, and then persisting to 42 d post-exposure. Thus, this single CBNP exposure that was equivalent to nine 8-h working days at the current Danish occupational exposure limit induced biphasic inflammatory response in gene expression that lasted until 42 d post-exposure, raising concern over the chronic effects of CBNP exposure.

Deletion of 5-Lipoxygenase in the Tumor Microenvironment Promotes Lung Cancer Progression and Metastasis through Regulating T Cell Recruitment

Eicosanoids, including PGs, produced by cyclooxygenases (COX), and leukotrienes, produced by 5-lipoxygenase (5-LO) have been implicated in cancer progression. These molecules are produced by both cancer cells and the tumor microenvironment (TME). We previously reported that both COX and 5-LO metabolites increase during progression in an orthotopic immunocompetent model of lung cancer. Although PGs in the TME have been well studied, less is known regarding 5-LO products produced by the TME. We examined the role of 5-LO in the TME using a model in which Lewis lung carcinoma cells are directly implanted into the lungs of syngeneic WT mice or mice globally deficient in 5-LO (5-LO-KO). Unexpectedly, primary tumor volume and liver metastases were increased in 5-LO-KO mice. This was associated with an ablation of leukotriene (LT) production, consistent with production mainly mediated by the microenvironment. Increased tumor progression was partially reproduced in global LTC4 synthase KO or mice transplanted with LTA4 hydrolase-deficient bone marrow. Tumor-bearing lungs of 5-LO-KO had decreased numbers of CD4 and CD8 T cells compared with WT controls, as well as fewer dendritic cells. This was associated with lower levels of CCL20 and CXL9, which have been implicated in dendritic and T cell recruitment. Depletion of CD8 cells increased tumor growth and eliminated the differences between WT and 5-LO mice. These data reveal an antitumorigenic role for 5-LO products in the microenvironment during lung cancer progression through regulation of T cells and suggest that caution should be used in targeting this pathway in lung cancer.

Lethal influenza infection: Is a macrophage to blame?

Alveolar macrophages (AMs) are critical for immunity against influenza A virus (IAV) infection. Depletion, hyporeactivity, and disruption of AM development and differentiation are all associated with lethal IAV infection. AMs drive the innate immune response that limits IAV infection. AMs are crucial for steady-state homeostasis of pulmonary surfactant, and in turn surfactant proteins regulate AMs and participate in host defense against IAV. Known factors that are necessary for AM function and differentiation in vivo include surfactant proteins, the growth factor GM-CSF, the hormone receptor PPARγ, and the transcription factors PU.1 and Bach2. Although PU.1 and PPARγ are downstream effectors of GM-CSF, Bach2 works independently. GM-CSF and Bach2-deficient AMs have phenotypes with immature or alternatively activated states of differentiation, respectively, and both extremes are unsuitable for surfactant homeostasis. The activation state of AMs and the local microenvironment may determine the development of symptomatic versus asymptomatic IAV infection in different individuals.

A far-red fluorescent probe for flow cytometry and image-based functional studies of xenobiotic sequestering macrophages

Clofazimine (CFZ) is an optically active, red-colored chemotherapeutic agent that is FDA approved for the treatment of leprosy and is on the World Health Organization's list of essential medications. Interestingly, CFZ massively accumulates in macrophages where it forms crystal-like drug inclusions (CLDIs) after oral administration of the drug in animals and humans. The analysis of the fluorescence spectra of CLDIs formed by resident tissue macrophages revealed that CFZ, when accumulated as CLDIs, undergoes a red shift in fluorescence excitation (from Ex: 540-570 to 560-600 nm) and emission (Em: 560-580 to 640-700 nm) signal relative to the soluble and free-base crystal forms of CFZ. Using epifluorescence microscopy, CLDI(+) cells could be identified, relative to CLDI(-) cells, based on a >3-fold increment in mean fluorescence signal at excitation 640 nm and emission at 670 nm. Similarly, CLDI(+) cells could be identified by flow cytometry, based on a >100-fold increment in mean fluorescence signal using excitation lasers at 640 nm and emission detectors >600 nm. CLDI's fluorescence excitation and emission was orthogonal to that of cell viability dyes such as propidium iodide and 4,6-diamidino-2-phenylindole dihydrochloride (DAPI), cellular staining dyes such as Hoechst 33342 (nucleus) and FM 1-43 (plasma membrane), as well as many other fluorescently tagged antibodies used for immunophenotyping analyses. In vivo, >85% of CLDI(+) cells in the peritoneal exudate were F4/80(+) macrophages and >97% of CLDI(+) cells in the alveolar exudate were CD11c(+). Most importantly, the viability of cells was minimally affected by the presence of CLDIs. Accordingly, these results establish that CFZ fluorescence in CLDIs is suitable for quantitative flow cytometric phenotyping analysis and functional studies of xenobiotic sequestering macrophages.

Morphological and Functional Alterations of Alveolar Macrophages in a Murine Model of Chronic Inflammatory Lung Disease

Purpose

Chronic lung inflammation commonly induces a multitude of structural and functional adaptations within the lung tissue and airspaces. Yet the impact of a persistent inflammatory environment on alveolar macrophages is still incompletely understood. Here, we examined morphology and function of alveolar macrophages in a transgenic mouse model of chronic lung disease.

Methods

Imaging flow cytometry, flow cytometry, and microscopic evaluation of alveolar macrophages isolated from healthy and inflamed lungs were performed. Gene expression of polarization markers was compared by quantitative real-time RT-PCR. The pro-inflammatory immune response of alveolar macrophages toward bacterial ligands was assessed in in vivo clodronate-liposome depletion studies.

Results

Chronic lung inflammation is associated with a substantially altered, activated alveolar macrophage morphology, and blunted TNF-α response by these cells following stimulation with ligands derived from the respiratory pathogen Streptococcus pneumoniae.

Conclusions

These results demonstrate pleiotropic effects of pulmonary inflammation on alveolar macrophage phenotype and function and suggest a functional impairment of these cells during infection with airborne pathogens.

In vivo compartmental analysis of leukocytes in mouse lungs

The lung has a unique structure consisting of three functionally different compartments (alveolar, interstitial, and vascular) situated in an extreme proximity. Current methods to localize lung leukocytes using bronchoalveolar lavage and/or lung perfusion have significant limitations for determination of location and phenotype of leukocytes. Here we present a novel method using in vivo antibody labeling to enable accurate compartmental localization/quantification and phenotyping of mouse lung leukocytes. Anesthetized C57BL/6 mice received combined in vivo intravenous and intratracheal labeling with fluorophore-conjugated anti-CD45 antibodies, and lung single-cell suspensions were analyzed by flow cytometry. The combined in vivo intravenous and intratracheal CD45 labeling enabled robust separation of the alveolar, interstitial, and vascular compartments of the lung. In naive mice, the alveolar compartment consisted predominantly of resident alveolar macrophages. The interstitial compartment, gated by events negative for both intratracheal and intravenous CD45 staining, showed two conventional dendritic cell populations, as well as a Ly6C^lo monocyte population. Expression levels of MHCII on these interstitial monocytes were much higher than on the vascular Ly6C^lo monocyte populations. In mice exposed to acid aspiration-induced lung injury, this protocol also clearly distinguished the three lung compartments showing the dynamic trafficking of neutrophils and exudative monocytes across the lung compartments during inflammation and resolution. This simple in vivo dual-labeling technique substantially increases the accuracy and depth of lung flow cytometric analysis, facilitates a more comprehensive examination of lung leukocyte pools, and enables the investigation of previously poorly defined “interstitial” leukocyte populations during models of inflammatory lung diseases.

Intrapulmonary administration of bone-marrow derived M1/M2 macrophages to enhance the resolution of LPS-induced lung inflammation: noninvasive monitoring using free-breathing MR and CT imaging protocols

Background

Alveolar macrophages, with their high functional plasticity, were reported to orchestrate the induction and resolution of inflammatory processes in chronic pulmonary diseases. Noninvasive imaging modalities that offer simultaneous monitoring of inflammation progression and tracking of macrophages subpopulations involved in the inflammatory cascade, can provide an ideal and specific diagnostic tool to visualize the action mechanism in its initial stages. Therefore, the purpose of the current study was to evaluate the role of M1 and M2 macrophages in the resolution of lipopolysaccharide (LPS)-induced lung inflammation and monitor this process using noninvasive free-breathing MRI and CT protocols.

Methods

Bone-marrow derived macrophages were first polarized to M1 and M2 macrophages and then labeled with superparamagnetic iron oxide nanoparticles. BALB/c mice with lung inflammation received an intrapulmonary instillation of these ex vivo polarized M1 or M2 macrophages. The biodistribution of macrophages subpopulations and the subsequent resolution of lung inflammation were noninvasively monitored using MRI and micro-CT. Confirmatory immunohistochemistry analyses were performed on lung tissue sections using specific macrophage markers.

Results

As expected, large inflammatory areas noninvasively imaged using pulmonary MR and micro-CT were observed within the lungs following LPS challenge. Subsequent intrapulmonary administration of M1 and M2 macrophages resulted in a significant decrease in inflammation starting from 72 h. Confirmatory immunohistochemistry analyses established a progression of lung inflammation with LPS and its subsequent reduction with both macrophages subsets. An enhanced resolution of inflammation was observed with M2 macrophages compared to M1.

Conclusions

The current study demonstrated that ex vivo polarized macrophages decreased LPS-induced lung inflammation. Noninvasive free-breathing MR and CT imaging protocols enabled efficient monitoring of progression and resolution of lung inflammation.

Rhinovirus infection induces interleukin-13 production from CD11b-positive, M2-polarized exudative macrophages

Rhinovirus (RV) causes asthma exacerbations. Previously, we showed that adherent bronchoalveolar cells from allergen-treated mice produce IL-13 when stimulated with RV ex vivo, implicating cells of the monocyte/macrophage lineage in viral-induced airway inflammation. In this study, we hypothesized that RV infection of allergen-treated mice results in IL-13 production by CD11b+ exudative macrophages in vivo. We sensitized and challenged BALB/c mice with ovalbumin (OVA), after which mice were inoculated with RV or sham HeLa cell lysate. After 1 day, lungs were harvested, and cell suspensions were analyzed by flow cytometry. We repeated this process in IL-13 reporter mice, CD11b-DTR mice in which diphtheria toxin selectively depletes CD11b+ cells, and chemokine receptor 2 (CCR2) null mice. We found that lungs of mice infected with RV alone showed increases in CD45+, CD68+, F4/80+, Ly6C+, and CD11b(high) cells, indicating an influx of inflammatory monocytes and exudative macrophages. The combination of OVA and RV had synergistic effects on the exudative macrophage number. However, CD11b+ cells from OVA-treated, RV-infected mice showed M2 polarization, including expression of CD206 and CD301 and production of IL-13. Similar results were obtained in IL-13 reporter mice. Diphtheria toxin depleted CD11b+, IL-13-producing cells in OVA-treated, RV-infected, CD11b-DTR mice, decreasing airway inflammation and responsiveness. CD11b+, Ly6C+ cells were reduced in CCR2 knockout mice. We conclude that, in contrast to naive mice, RV infection of mice with allergic airways disease induces an influx of IL-13-producing CD11b+ exudative macrophages bearing M2 macrophage markers. This finding further implicates alternatively activated macrophages in RV-induced asthma exacerbations.

Alendronate inhalation ameliorates elastase-induced pulmonary emphysema in mice by induction of apoptosis of alveolar macrophages

Alveolar macrophages play a crucial role in the pathogenesis of emphysema, for which there is currently no effective treatment. Bisphosphonates are widely used to treat osteoclast-mediated bone diseases. Here we show that delivery of the nitrogen-containing bisphosphonate alendronate via aerosol inhalation ameliorates elastase-induced emphysema in mice. Inhaled, but not orally ingested, alendronate inhibits airspace enlargement after elastase instillation, and induces apoptosis of macrophages in bronchoalveolar fluid via caspase-3- and mevalonate-dependent pathways. Cytometric analysis indicates that the F4/80(+)CD11b(high)CD11c(mild) population characterizing inflammatory macrophages, and the F4/80(+)CD11b(mild)CD11c(high) population defining resident alveolar macrophages take up substantial amounts of the bisphosphonate imaging agent OsteoSense680 after aerosol inhalation. We further show that alendronate inhibits macrophage migratory and phagocytotic activities and blunts the inflammatory response of alveolar macrophages by inhibiting nuclear factor-κB signalling. Given that the alendronate inhalation effectively induces apoptosis in both recruited and resident alveolar macrophages, we suggest this strategy may have therapeutic potential for the treatment of emphysema.

[The rat submandibular lymph node after introduction in mandibular bone defect ultipotent mesenchymal cells adsorbed on polyhydroxyalkanoate scaffold]

The reactions of rat regional lymph nodes, caused by implantation of the autologous multipotent mesenchymal stromal cells of a bone marrow origin (AMMSCBM) for acceleration of bone defect regeneration in bottom jaw experiment were studied by methods of fluorescent light microscopy. After introduction in an injury site of a bottom jaw bone of polyhydroxyalkanoate with adsorbed AMMSCBM with a transfected GFP gene the numerous large macrophages with a set of oval fluorescent inclusions in cytoplasm appear in lymph nodules of submandibular lymph nodes. The number of such macrophages increases within 2 weeks after operation, and further starts decreasing. Probably, entered via such way the AMMSCBM partially are phagocytized by macrophages. At destruction of the structures created from AMMSCBM, debris also are phagocytized by macrophages. In that and other case these macrophages appear in the germinative centers of lymph nodules in lymph nodes where initiation of immunity reactions against DNA and same GFP isn't excluded.

T-cell-restricted T-bet overexpression induces aberrant hematopoiesis of myeloid cells and impairs function of macrophages in the lung

Although overexpression of T-bet, a master transcription factor in type-1 helper T lymphocytes, has been reported in several hematologic and immune diseases, its role in their pathogenesis is not fully understood. In the present study, we used transgenic model mice (T-bet(tg/wt) and T-bet(tg/tg)) to investigate the effects of T-bet overexpression selectively in T lymphocytes on the development of hematologic and immune diseases. The results showed that T-bet overexpression in T cells spontaneously induced maturation arrest in the mononuclear phagocyte lineage, as well as spontaneous dermatitis and pulmonary alveolar proteinosis (PAP)-like disease in T-bet(tg/wt) and T-bet(tg/tg) mice, respectively. T-bet(tg/tg) alveoli with the PAP phenotype showed remarkable reorganization of alveolar mononuclear phagocyte subpopulations and impaired function, in addition to augmented T-cell infiltration. In addition, PAP development in T-bet(tg/tg) mice was found to be associated with increased migration of myeloid cells from the bone marrow into the peripheral blood. These findings reveal an unexpected link between T-bet overexpression in T lymphocytes and the development of PAP caused by reorganization of mononuclear phagocytes in the lung, and provide new insight into the molecular pathogenesis of secondary PAP accompanied by hematologic disorders.

Role of alveolar macrophages in chronic obstructive pulmonary disease

Alveolar macrophages (AMs) represent a unique leukocyte population that responds to airborne irritants and microbes. This distinct microenvironment coordinates the maturation of long-lived AMs, which originate from fetal blood monocytes and self-renew through mechanisms dependent on GM-CSF and CSF-1 signaling. Peripheral blood monocytes can also replenish lung macrophages; however, this appears to occur in a stimuli specific manner. In addition to mounting an appropriate immune response during infection and injury, AMs actively coordinate the resolution of inflammation through efferocytosis of apoptotic cells. Any perturbation of this process can lead to deleterious responses. In chronic obstructive pulmonary disease (COPD), there is an accumulation of airway macrophages that do not conform to the classic M1/M2 dichotomy. There is also a skewed transcriptome profile that favors expression of wound-healing M2 markers, which is reflective of a deficiency to resolve inflammation. Endogenous mediators that can promote an imbalance in inhibitory M1 vs. healing M2 macrophages are discussed, as they are the plausible mechanisms underlying why AMs fail to effectively resolve inflammation and restore normal lung homeostasis in COPD.

The role of macrophages in influenza A virus infection

ABSTRACT: 

The importance of macrophages in the control of infections has long been documented, but macrophages have also been shown to contribute to severe influenza A virus infections. Macrophage function ranges from highly proinflammatory to wound healing and regulatory and a picture of diverse subsets with considerable plasticity in function and phenotype is emerging. Within the lung three subsets of macrophage populations have been identified: resident alveolar macrophages, interstitial macrophages and exudate-derived macrophages. Here we review model systems and techniques for defining macrophage function in vivo and discuss macrophage infection in vitro. The use of detailed phenotypic approaches and techniques to dissect the role of individual macrophage subsets in vivo promises rapid advances in this area of research.

Alterations in macrophages and monocytes from tumor-bearing mice: evidence of local and systemic immune impairment

Macrophages are cells of the innate immune system involved in critical activities such as maintaining tissue homeostasis and immune surveillance. Pro-inflammatory macrophages M1 are responsible for the inflammatory response, while M2 macrophages are associated with the immunosuppressive repair phase of tissue remodeling. Most cancers are associated with chronic inflammation, and a high number of macrophages in tumors have been associated with tumor progression. Much effort has been made in elucidating the mechanisms through which macrophages contribute to tumor development, yet much less is known about the initial mechanisms by which tumors modify macrophages. Our work has focused on identifying the mechanisms by which macrophages from tumor hosts are modified by tumors. We have shown that peritoneal macrophages are significantly altered in mice bearing advanced mammary tumors and are not M1 or M2 polarized, but express a mixture of both transcriptional programs. These macrophages are less differentiated and more prone to apoptosis, resulting in increased myelopoiesis as a compensation to regenerate macrophage progenitors in the marrow. Macrophages in the tumor microenvironment are also neither M1 nor M2 cells and through a display of different mechanisms are even more impaired than their peripheral counterparts. Finally, systemic blood monocytes, precursors of tissue macrophages, are also altered in tumor bearers and show a mixed program of pro- and anti-inflammatory functions. We conclude that there is evidence for local and systemic immune impairment in tumor hosts.

SAA drives proinflammatory heterotypic macrophage differentiation in the lung via CSF-1R-dependent signaling

Serum amyloid A (SAA) is expressed locally in chronic inflammatory conditions such as chronic obstructive pulmonary disease (COPD), where macrophages that do not accord with the classic M1/M2 paradigm also accumulate. In this study, the role of SAA in regulating macrophage differentiation was investigated in vitro using human blood monocytes from healthy subjects and patients with COPD and in vivo using an airway SAA challenge model in BALB/c mice. Differentiation of human monocytes with SAA stimulated the proinflammatory monokines IL-6 and IL-1β concurrently with the M2 markers CD163 and IL-10. Furthermore, SAA-differentiated macrophages stimulated with lipopolysaccharide (LPS) expressed markedly higher levels of IL-6 and IL-1β. The ALX/FPR2 antagonist WRW4 reduced IL-6 and IL-1β expression but did not significantly inhibit phagocytic and efferocytic activity. In vivo, SAA administration induced the development of a CD11c(high)CD11b(high) macrophage population that generated higher levels of IL-6, IL-1β, and G-CSF following ex vivo LPS challenge. Blocking CSF-1R signaling effectively reduced the number of CD11c(high)CD11b(high) macrophages by 71% and also markedly inhibited neutrophilic inflammation by 80%. In conclusion, our findings suggest that SAA can promote a distinct CD11c(high)CD11b(high) macrophage phenotype, and targeting this population may provide a novel approach to treating chronic inflammatory conditions associated with persistent SAA expression.

Characterization of the inflammatory infiltrate in Streptococcus pneumoniae pneumonia in young and elderly patients

There is an increased susceptibility and mortality in the elderly due to pneumonia caused by Streptococcus pneumoniae. We aimed to assess the inflammatory cell composition with respect to age in pneumococcal pneumonia patients. Neutrophilic granulocytes and various lymphocyte and macrophage subpopulations were immunohistochemically quantified on lung tissue specimens of young (n = 5; mean age 8.4 years), middle-aged (n = 8; mean age 55.9 years) and elderly (n = 9; mean age 86.6 years) pneumonia patients with microbiologically proven S. pneumoniae pneumonia. We discovered a higher percentage of neutrophilic granulocytes in elderly as opposed to young patients (95 vs. 75%, p = 0.012). Conversely, young patients versus elderly patients had more alveolar macrophages (CD11c+: 20 vs. 9%, p = 0.029) and M1 macrophages (CD14+: 30 vs. 10%, p = 0.012 and HLA-DR+: 52 vs. 11%, p = 0.019). There was no significant difference concerning M2 macrophages and lymphocytes. Comparison of young patients with middle-aged patients showed similar significant results for alveolar macrophages (p = 0.019) and subsignificant results for M1 macrophages and neutrophilic granulocytes (p < 0.08). This is the first study characterizing the inflammatory infiltrate of pneumococcal pneumonia in situ. Our observations improve the understanding of the innate immune mechanisms of pneumococcal lung infection and point at the potential of therapies for restoring macrophage function and decreasing neutrophilic influx in order to help prevent or cure pneumonia.

Persistent lung inflammation and fibrosis in serum amyloid P component (APCs-/-) knockout mice

Fibrosing diseases, such as pulmonary fibrosis, cardiac fibrosis, myelofibrosis, liver fibrosis, and renal fibrosis are chronic and debilitating conditions and are an increasing burden for the healthcare system. Fibrosis involves the accumulation and differentiation of many immune cells, including macrophages and fibroblast-like cells called fibrocytes. The plasma protein serum amyloid P component (SAP; also known as pentraxin-2, PTX2) inhibits fibrocyte differentiation in vitro, and injections of SAP inhibit fibrosis in vivo. SAP also promotes the formation of immuno-regulatory Mreg macrophages. To elucidate the endogenous function of SAP, we used bleomycin aspiration to induce pulmonary inflammation and fibrosis in mice lacking SAP. Compared to wildtype C57BL/6 mice, we find that in Apcs^-/- “SAP knock-out” mice, bleomycin induces a more persistent inflammatory response and increased fibrosis. In both C57BL/6 and Apcs^-/- mice, injections of exogenous SAP reduce the accumulation of inflammatory macrophages and prevent fibrosis. The types of inflammatory cells present in the lungs following bleomycin-aspiration appear similar between C57BL/6 and Apcs^-/- mice, suggesting that the initial immune response is normal in the Apcs^-/- mice, and that a key endogenous function of SAP is to promote the resolution of inflammation and fibrosis.

Reprint of: A rapid increase in macrophage-derived versican and hyaluronan in infectious lung disease

The goals of this study were to characterize the changes in chondroitin sulfate proteoglycans and hyaluronan in lungs in acute response to gram-negative bacterial infection and to identify cellular components responsible for these changes. Mice were treated with intratracheal (IT) live Escherichia coli, E. coli lipopolysaccharide (LPS), or PBS. Both E. coli and LPS caused rapid selective increases in mRNA expression of versican and hyaluronan synthase (Has) isoforms 1 and 2 associated with increased immunohistochemical and histochemical staining for versican and hyaluronan in the lungs. Versican was associated with a subset of alveolar macrophages. To examine whether macrophages contribute to versican and hyaluronan accumulation, in vitro studies with primary cultures of bone marrow-derived and alveolar macrophages were performed. Unstimulated macrophages expressed very low levels of versican and hyaluronan synthase mRNA, with no detectible versican protein or hyaluronan product. Stimulation with LPS caused rapid increases in versican mRNA and protein, a rapid increase in Has1 mRNA, and concomitant inhibition of hyaluronidases 1 and 2, the major hyaluronan degrading enzymes. Hyaluronan could be detected following chloroquine pre-treatment, indicating rapid turnover and degradation of hyaluronan by macrophages. In addition, the effects of LPS, the M1 macrophage classical activation agonist, were compared to those of IL-4/IL-13 or IL-10, the M2a and M2c alternative activation agonists, respectively. Versican and Has1 increased only in response to M1 activation. Finally, the up-regulation of versican and Has1 in the whole lungs of wild-type mice following IT LPS was completely abrogated in TLR-4(-/-) mice. These findings suggest that versican and hyaluronan synthesis may play an important role in the innate immune response to gram-negative lung infection.

MR imaging and targeting of a specific alveolar macrophage subpopulation in LPS-induced COPD animal model using antibody-conjugated magnetic nanoparticles

Purpose

Targeting and noninvasive imaging of a specific alveolar macrophage subpopulation in the lung has revealed the importance for early and better diagnosis and therapy of chronic obstructive pulmonary disease (COPD). In this study, the in vivo effect of pulmonary administration of iron oxide nanoparticles on the polarization profile of macrophages was assessed, and a noninvasive free-breathing magnetic resonance imaging (MRI) protocol coupled with the use of biocompatible antibody-conjugated superparamagnetic iron oxide (SPIO) nanoparticles was developed to enable specific targeting and imaging of a particular macrophage subpopulation in lipopolysaccharide-induced COPD mice model.

Materials and methods

Enzyme-linked immunosorbent assay, Real-time polymerase chain reaction, and flow cytometry analysis were performed to assess the biocompatibility of PEGylated dextran-coated SPIO nanoparticles. Specific biomarkers for M1 and M2 macrophages subsets were selected for conjugation with magnetic nanoparticles. MRI protocol using ultra-short echo time sequence was optimized to enable simultaneous detection of inflammation progress in the lung and detection of macrophages subsets. Flow cytometry and immunohistochemistry analysis were finally performed to confirm MRI readouts and to characterize the polarization profile of targeted macrophages.

Results

The tested SPIO nanoparticles, under the current experimental conditions, were found to be biocompatible for lung administration in preclinical settings. Cluster of differentiation (CD)86- and CD206-conjugated magnetic nanoparticles enabled successful noninvasive detection of M1 and M2 macrophage subpopulations, respectively, and were found to co-localize with inflammatory regions induced by lipopolysaccharide challenge. No variation in the polarization profile of targeted macrophages was observed, even though a continuum switch in their polarization might occur. However, further confirmatory studies are required to conclusively establish this observation.

Conclusion

Coupling of magnetic iron oxide nanoparticles with a specific antibody targeted to a particular macrophage subpopulation could offer a promising strategy for an early and better diagnosis of pulmonary inflammatory diseases using noninvasive MRI.

New insights into the role of the aryl hydrocarbon receptor in the function of CD11c⁺ cells during respiratory viral infection

The aryl hydrocarbon receptor (AHR) has garnered considerable attention as a modulator of CD4(+) cell lineage development and function. It also regulates antiviral CD8(+) T-cell responses, but via indirect mechanisms that have yet to be determined. Here, we show that during acute influenza virus infection, AHR activation skews dendritic-cell (DC) subsets in the lung-draining lymph nodes, such that there are fewer conventional CD103(+) DCs and CD11b(+) DCs. Sorting DC subsets reveals AHR activation reduces immunostimulatory function of CD103(+) DCs in the mediastinal lymph nodes, and decreases their frequency in the lung. DNA-binding domain Ahr mutants demonstrate that alterations in DC subsets require the ligand-activated AHR to contain its inherent DNA-binding domain. To evaluate the intrinsic role of AHR in DCs, conditional knockouts were created using Cre-LoxP technology, which revealed that AHR in CD11c(+) cells plays a key role in controlling the acquisition of effector CD8(+) T cells in the infected lung. However, AHR within other leukocyte lineages contributes to diminished naïve CD8(+) T-cell activation in the draining lymphoid nodes. These findings indicate DCs are among the direct targets of AHR ligands in vivo, and AHR signaling modifies host responses to a common respiratory pathogen by affecting the complex interplay of multiple cell types.

Flow cytometric analysis of macrophages and dendritic cell subsets in the mouse lung

The lung hosts multiple populations of macrophages and dendritic cells, which play a crucial role in lung pathology. The accurate identification and enumeration of these subsets are essential for understanding their role in lung pathology. Flow cytometry is a mainstream tool for studying the immune system. However, a systematic flow cytometric approach to identify subsets of macrophages and dendritic cells (DCs) accurately and consistently in the normal mouse lung has not been described. Here we developed a panel of surface markers and an analysis strategy that accurately identify all known populations of macrophages and DCs, and their precursors in the lung during steady-state conditions and bleomycin-induced injury. Using this panel, we assessed the polarization of lung macrophages during the course of bleomycin-induced lung injury. Alveolar macrophages expressed markers of alternatively activated macrophages during both acute and fibrotic phases of bleomycin-induced lung injury, whereas markers of classically activated macrophages were expressed only during the acute phase. Taken together, these data suggest that this flow cytometric panel is very helpful in identifying macrophage and DC populations and their state of activation in normal, injured, and fibrotic lungs.

SHIP-1 deficiency in the myeloid compartment is insufficient to induce myeloid expansion or chronic inflammation

SHIP-1 has an important role in controlling immune cell function through its ability to downmodulate PI3K signaling pathways that regulate cell survival and responses to stimulation. Mice deficient in SHIP-1 display several chronic inflammatory phenotypes including antibody-mediated autoimmune disease, Crohn's disease-like ileitis and a lung disease reminiscent of chronic obstructive pulmonary disease. The ileum and lungs of SHIP-1-deficient mice are infiltrated at an early age with abundant myeloid cells and the mice have a limited lifespan primarily thought to be due to the consolidation of lungs with spontaneously activated macrophages. To determine whether the myeloid compartment is the key initiator of inflammatory disease in SHIP-1-deficient mice, we examined two independent strains of mice harboring myeloid-restricted deletion of SHIP-1. Contrary to expectations, conditional deletion of SHIP-1 in myeloid cells did not result in consolidating pneumonia or segmental ileitis typical of germline SHIP-1 deficiency. In addition, other myeloid cell abnormalities characteristic of germline loss of SHIP-1, including flagrant splenomegaly and enhanced myelopoiesis, were absent in mice lacking SHIP-1 in myeloid cells. This study indicates that the spontaneous inflammatory disease characteristic of germline SHIP-1 deficiency is not initiated solely by LysM-positive myeloid cells but requires the simultaneous loss of SHIP-1 in other hematolymphoid lineages.

Influenza infection suppresses NADPH oxidase-dependent phagocytic bacterial clearance and enhances susceptibility to secondary methicillin-resistant Staphylococcus aureus infection

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a leading contributor to mortality during recent influenza pandemics. The mechanism for this influenza-induced susceptibility to secondary S. aureus infection is poorly understood. In this study, we show that innate antibacterial immunity was significantly suppressed during the recovery stage of influenza infection, even though MRSA superinfection had no significant effect on viral burdens. Compared with mice infected with bacteria alone, postinfluenza MRSA-infected mice exhibited impaired bacterial clearance, which was not due to defective phagocyte recruitment, but rather coincided with reduced intracellular reactive oxygen species levels in alveolar macrophages and neutrophils. NADPH oxidase is responsible for reactive oxygen species production during phagocytic bacterial killing, a process also known as oxidative burst. We found that gp91(phox)-containing NADPH oxidase activity in macrophages and neutrophils was essential for optimal bacterial clearance during respiratory MRSA infections. In contrast to wild-type animals, gp91(phox-/-) mice exhibited similar defects in MRSA clearance before and after influenza infection. Using gp91(phox+/-) mosaic mice, we further demonstrate that influenza infection inhibits a cell-intrinsic contribution of NADPH oxidase to phagocyte bactericidal activity. Taken together, our results establish that influenza infection suppresses NADPH oxidase-dependent bacterial clearance and leads to susceptibility to secondary MRSA infection.

A rapid increase in macrophage-derived versican and hyaluronan in infectious lung disease

The goals of this study were to characterize the changes in chondroitin sulfate proteoglycans and hyaluronan in lungs in acute response to gram-negative bacterial infection and to identify cellular components responsible for these changes. Mice were treated with intratracheal (IT) live Escherichia coli, E. coli lipopolysaccharide (LPS), or PBS. Both E. coli and LPS caused rapid selective increases in mRNA expression of versican and hyaluronan synthase (Has) isoforms 1 and 2 associated with increased immunohistochemical and histochemical staining for versican and hyaluronan in the lungs. Versican was associated with a subset of alveolar macrophages. To examine whether macrophages contribute to versican and hyaluronan accumulation, in vitro studies with primary cultures of bone marrow-derived and alveolar macrophages were performed. Unstimulated macrophages expressed very low levels of versican and hyaluronan synthase mRNA, with no detectible versican protein or hyaluronan product. Stimulation with LPS caused rapid increases in versican mRNA and protein, a rapid increase in Has1 mRNA, and concomitant inhibition of hyaluronidases 1 and 2, the major hyaluronan degrading enzymes. Hyaluronan could be detected following chloroquine pre-treatment, indicating rapid turnover and degradation of hyaluronan by macrophages. In addition, the effects of LPS, the M1 macrophage classical activation agonist, were compared to those of IL-4/IL-13 or IL-10, the M2a and M2c alternative activation agonists, respectively. Versican and Has1 increased only in response to M1 activation. Finally, the up-regulation of versican and Has1 in the whole lungs of wild-type mice following IT LPS was completely abrogated in TLR-4(-/-) mice. These findings suggest that versican and hyaluronan synthesis may play an important role in the innate immune response to gram-negative lung infection.