GM-CSF and the impaired pulmonary innate immune response following hyperoxic stress

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

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

Studying the Effects of Granulocyte-Macrophage Colony-Stimulating Factor on Fetal Lung Macrophages During the Perinatal Period Using the Mouse Model

Background: Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pro-inflammatory cytokine that is increased in the amniotic fluid in chorioamnionitis and elevated in the fetal lung with endotoxin exposure. Although GM-CSF has a pivotal role in fetal lung development, it stimulates pulmonary macrophages and is associated with the development of bronchopulmonary dysplasia (BPD). How antenatal GM-CSF results in recruitment of lung macrophage leading to BPD needs further elucidation. Hence, we used a transgenic and knock-out mouse model to study the effects of GM-CSF focusing on the fetal lung macrophage. Methods: Using bitransgenic (BTg) mice that conditionally over-expressed pulmonary GM-CSF after doxycycline treatment, and GM-CSF knock-out (KO) mice with no GM-CSF expression, we compared the ontogeny and immunophenotype of lung macrophages in BTg, KO and control mice at various prenatal and postnatal time points using flow cytometry and immunohistology. Results: During fetal life, compared to controls, BTg mice over-expressing pulmonary GM-CSF had increased numbers of lung macrophages that were CD68+ and these were primarily located in the interstitium rather than alveolar spaces. The lung macrophages that accumulated were predominantly CD11b+F4/80+ indicating immature macrophages. Conversely, lung macrophages although markedly reduced, were still present in GM-CSF KO mice. Conclusion: Increased exposure to GM-CSF antenatally, resulted in accumulation of immature macrophages in the fetal lung interstitium. Absence of GM-CSF did not abrogate but delayed the transitioning of interstitial macrophages. Together, these results suggest that other perinatal factors may be involved in modulating the maturation of alveolar macrophages in the developing fetal lung.

The protective effects of granulocyte-macrophage colony-stimulating factor against radiation-induced lung injury

Background

Radiation-induced lung injury (RILI) is a common complication of thoracic cancer radiation therapy. Currently, there is no effective treatment for RILI. RILI is associated with chronic inflammation, this injury is perpetuated by the stimulation of chemokines and proinflammatory cytokines. Recent studies have demonstrated that granulocyte-macrophage colony-stimulating factor (GM-CSF) plays a pivotal role in inflammation and fibrosis. This study aimed to investigate the protective effect of GM-CSF against the development of RILI in lung tissue.

Method

First, a single fraction of radiation at a dose of 16 Gy was targeted at the entire thorax of wild-type (WT) C57BL/6 mice and GM-CSF^–/– mice to induce RILI. Second, we detected the radioprotective effects of GM-CSF by measuring the inflammatory biomarkers and fibrosis alteration on radiated lung tissues. Furthermore, we investigated the potential mechanism of GM-CSF protective effects in RILI.

Results

The GM-CSF^–/– mice sustained more severe RILI than the WT mice. RILI was significantly alleviated by GM-CSF treatment. Intraperitoneally administered GM-CSF significantly inhibited inflammatory cytokine production and decreased epithelial-mesenchymal transition (EMT) in the RILI mouse model.

Conclusions

GM-CSF was shown to be an important modulator of RILI through regulating inflammatory cytokines, which provides a new strategy for the prevention and treatment of RILI.

Macrophage responses associated with COVID-19: A pharmacological perspective

COVID-19 has caused worldwide death and economic destruction. The pandemic is the result of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which has demonstrated high rates of infectivity leading to great morbidity and mortality in vulnerable populations. At present, scientists are exploring various approaches to curb this pandemic and alleviate its health consequences, while racing to develop a vaccine. A particularly insidious aspect of COVID-19 is the delayed overactivation of the body's immune system that is manifested as the cytokine storm. This unbridled production of pro-inflammatory cytokines and chemokines can directly or indirectly cause massive organ damage and failure. Systemic vascular endothelial inflammation and thrombocytopenia are potential consequences as well. In the case of COVID-19, the cytokine storm often fits the pattern of the macrophage activation syndrome with lymphocytopenia. The basis for the imbalance between the innate and adaptive immune systems is not clearly defined, but highlights the effect of SARS-CoV-2 on macrophages. Here we discuss the potential underlying basis for the impact of SARS-CoV-2 on macrophages, both direct and indirect, and potential therapeutic targets. These include granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 6 (IL-6), interferons, and CXCL10 (IP-10). Various biopharmaceuticals are being repurposed to target the cytokine storm in COVID-19 patients. In addition, we discuss the rationale for activating the macrophage alpha 7 nicotinic receptors as a therapeutic target. A better understanding of the molecular consequences of SARS-CoV-2 infection of macrophages could lead to novel and more effective treatments for COVID-19.

Hyperoxia and modulation of pulmonary vascular and immune responses in COVID-19

Oxygen is the most commonly used therapy in hospitalized patients with COVID-19. In those patients who develop worsening pneumonia and acute respiratory distress syndrome (ARDS), high concentrations of oxygen may need to be administered for prolonged time periods, often together with mechanical ventilation. Hyperoxia, although lifesaving and essential for maintaining adequate oxygenation in the short term, may have adverse long-term consequences upon lung parenchymal structure and function. How hyperoxia per se impacts lung disease in COVID-19 has remained largely unexplored. Numbers of experimental studies have previously established that hyperoxia is associated with deleterious outcomes inclusive of perturbations in immunologic responses, abnormal metabolic function, and alterations in hemodynamics and alveolar barrier function. Such changes may ultimately progress into clinically evident lung injury and adverse remodeling and result in parenchymal fibrosis when exposure is prolonged. Given that significant exposure to hyperoxia in patients with severe COVID-19 may be unavoidable to preserve life, these sequelae of hyperoxia, superimposed on the cytopathic effects of SARS-CoV-2 virus, may well impact pathogenesis of COVID-19-induced ARDS.

GM-CSF-based treatments in COVID-19: reconciling opposing therapeutic approaches

Therapeutics against coronavirus disease 2019 (COVID-19) are urgently needed. Granulocyte–macrophage colony-stimulating factor (GM-CSF), a myelopoietic growth factor and pro-inflammatory cytokine, plays a critical role in alveolar macrophage homeostasis, lung inflammation and immunological disease. Both administration and inhibition of GM-CSF are currently being therapeutically tested in COVID-19 clinical trials. This Perspective discusses the pleiotropic biology of GM-CSF and the scientific merits behind these contrasting approaches.

Recombinant granulocyte–macrophage colony-stimulating factor (GM-CSF) as well as antibodies targeted at GM-CSF or its receptor are being tested in clinical trials for coronavirus disease 2019 (COVID-19). This Perspective introduces the pleiotropic functions of GM-CSF and explores the rationale behind these different approaches.

Characterization of pulmonary immune responses to hyperoxia by high-dimensional mass cytometry analyses

Prolonged exposure to hyperoxia has deleterious effects on the lung, provoking both inflammation and alveolar injury. The elements of hyperoxic injury, which result in high rates of lethality in experimental models, are thought to include multicellular immune responses. To characterize these alterations in immune cell populations, we performed time-of-flight mass cytometry (CyTOF) analysis of CD45-expressing immune cells in whole lung parenchyma and the bronchoalveolar space of mice, exposed to 48 hours of hyperoxia together with normoxic controls. At the tested time point, hyperoxia exposure resulted in decreased abundance of immunoregulatory populations (regulatory B cells, myeloid regulatory cells) in lung parenchyma and markedly decreased proliferation rates of myeloid regulatory cells, monocytes and alveolar macrophages. Additionally, hyperoxia caused a shift in the phenotype of alveolar macrophages, increasing proportion of cells with elevated CD68, CD44, CD11c, PD-L1, and CD205 expression levels. These changes occurred in the absence of histologically evident alveolar damage and abundance of neutrophils in the parenchyma or alveolar space did not change at these time points. Collectively, these findings demonstrate that pulmonary response to hyperoxia involves marked changes in specific subsets of myeloid and lymphoid populations. These findings have important implications for therapeutic targeting in acute lung injury.

Current Pharmacological Approach to ARDS: The Place of Bosentan

Acute respiratory distress syndrome is characterized by dyspnea at presentation, tachypnea on physical examination, findings of bilateral infiltration in chest radiography, refractory hypoxia, and high mortality. Although the main treatment approach is to address the underlying disease, there are also pharmacological and nonpharmacological options for supportive treatment. There is currently no pharmacological agent with proven efficacy in this syndrome, and many drugs are being studied for this purpose. One of these is the endothelin receptor antagonist bosentan.

Consequences of Hypoxia for the Pulmonary Alveolar Epithelial Cell Innate Immune Response

Pulmonary innate immune responses involve a highly regulated multicellular network to defend the enormous surface area of the lung. Disruption of these responses renders the host susceptible to pneumonia. Alveolar epithelial cells (AEC) are a critical source of innate immune molecules such as GM-CSF, which determine the functional maturation of alveolar macrophages. In many pulmonary diseases, heterogeneous ventilation leads to regional hypoxia in the lung. The effect of hypoxia on AEC innate immune function is unknown. We now report that exposure of primary murine AEC to hypoxia (1% oxygen) for 24 h results in significant suppression of key innate immune molecules, including GM-CSF, CCL2, and IL-6. This exposure did not cause toxicity but did induce stabilization of hypoxia-inducible factor 1α protein (HIF-1α) and shift to glycolytic metabolism. Focusing on GM-CSF, we found that hypoxia greatly decreased the rate of GM-CSF transcription. Hypoxia both decreased NF-κB signaling in AEC and induced chromosomal changes, resulting in decreased accessibility in the GM-CSF proximal promoter of target sequences for NF-κB binding. In mice exposed to hypoxia in vivo (12% oxygen for 2 d), lung GM-CSF protein expression was reduced. In vivo phagocytosis of fluorescent beads by alveolar macrophages was also suppressed, but this effect was reversed by treatment with GM-CSF. These studies suggest that in critically ill patients, local hypoxia may contribute to the susceptibility of poorly ventilated lung units to infection through complementary effects on several pathways, reducing AEC expression of GM-CSF and other key innate immune molecules.

Effects of vitamin B-6 supplementation on oxidative stress and inflammatory response in neonatal rats receiving hyperoxia therapy

Hyperoxia is often used in the treatment of neonates. However, protracted use of hyper-oxia leads to significant morbidity. The purpose of this study was to evaluate the effects of vitamin B-6 supplementation on oxidative stress and inflammatory responses in neonatal rats undergoing hyperoxia therapy. The study consisted of 2 parts: a survival study and a vitamin B-6 efficacy study for 16 days. Neonatal rats were randomly divided into either the control group, B-6 group (subcutaneously injected with 90 mg/kg/d of pyridoxal 5′-phosphate [PLP]), O₂ group (treated with 85% oxygen), or O₂ + B-6 group (simultaneously treated with 85% oxygen and 90 mg/kg/d PLP). After the survival study was done, the vitamin B-6 efficacy study was performed with duplicate neonatal rats sacrificed on the 3rd, 6th, 9th, and 16th day. Serum inflammatory cytokines, tissue pathology, and malondialdehyde (MDA) levels were measured. In the survival study, the survival rate of neonatal rats in the control, B-6, O₂, and O₂ + B-6 group on the 16th day were 100%, 100%, 25%, and 62.50%, respectively. The efficacy study showed lung polymorphonuclear granulocyte (PMN) and macrophage infiltration, increased liver hemopoiesis, and higher MDA levels in liver homogenates at days 3 through 16 in the O₂ group. Vitamin B-6 supplementation considerably increased serum inflammatory cytokines in either the 6th or 9th day and decreased liver MDA level before the 6th day. These results indicate that neonatal rats receiving hyperoxia treatment suffered divergent serum inflammatory responses and were in increased liver oxidative stress. Vitamin B-6 supplementation seemed to improve survival rates, change systemic inflammatory response, and decrease liver oxidative stress while neonatal rats were under hyperoxia treatment.

Hyperbaric hyperoxia alters innate immune functional properties during NASA Extreme Environment Mission Operation (NEEMO)

BACKGROUND

Spaceflight is associated with immune dysregulation which is considered as risk factor for the performance of exploration-class missions. Among the consequences of confinement and other environmental factors of living in hostile environments, the role of different oxygen concentrations is of importance as either low (e.g. as considered for lunar or Martian habitats) or high (e.g. during extravehicular activities) can trigger immune dysfunction. The aim of this study was to investigate the impact of increased oxygen availability--generated through hyperbaricity--on innate immune functions in the course of a 14 days NEEMO mission.

METHODS

6 male subjects were included into a 14 days undersea deployment at the Aquarius station (Key Largo, FL, USA). The underwater habitat is located at an operating depth of 47 ft. The 2.5 times higher atmospheric pressure in the habitat leads to hyperoxia. The collection of biological samples occurred 6 days before (L-6), at day 7 (MD7) and 11/13 (MD11/13) during the mission, and 90 days thereafter (R). Blood analyses included differential blood cell count, ex vivo innate immune activation status and inhibitory competences of granulocytes.

RESULTS

The absolute leukocyte count showed an increase during deployment as well as the granulocyte and monocyte count. Lymphocyte count was decreased on MD7. The assessments of native adhesion molecules on granulocytes (CD11b, CD62L) indicated a highly significant cellular activation (L-6 vs. MD7/MD13) during mission. In contrast, granulocytes were more sensitive towards anti-inflammatory stimuli (adenosine) on MD13.

CONCLUSION

Living in the NEEMO habitat for 14 days induced significant immune alterations as seen by an activation of adhesion molecules and vice versa higher sensitivity towards inhibition. This investigation under hyperbaric hyperoxia is important especially for Astronauts' immune competence during extravehicular activities when exposed to similar conditions.

Polymorphisms in key pulmonary inflammatory pathways and the development of acute respiratory distress syndrome

PURPOSE/AIM

Acute Respiratory Distress Syndrome (ARDS) is an important clinical and public health problem. Why some at-risk individuals develop ARDS and others do not is unclear but may be related to differences in inflammatory and cell signaling systems. The Receptor for Advanced Glycation Endproducts (RAGE) and Granulocyte-Monocyte Stimulating Factor (GM-CSF) pathways have recently been implicated in pulmonary pathophysiology; whether genetic variation within these pathways contributes to ARDS risk or outcome is unknown.

MATERIALS AND METHODS

We studied 842 patients from three centers in Utah and 14 non-Utah ARDS Network centers. We studied patients at risk for ARDS and patients with ARDS to determine whether Single Nucleotide Polymorphisms (SNPs) in the RAGE and GM-CSF pathways were associated with development of ARDS. We studied 29 SNPs in 5 genes within the two pathways and controlled for age, sepsis as ARDS risk factor, and severity of illness, while targeting a false discovery rate of ≤ 5%. In a secondary analysis we evaluated associations with mortality.

RESULTS

Of 842 patients, 690 had ARDS, and 152 were at-risk. Sepsis was the risk factor for ARDS in 250 (30%) patients. When controlling for age, APACHE III score, sepsis as risk factor, and multiple comparisons, no SNPs were significantly associated with ARDS. In a secondary analysis, only rs743564 in CSF2 approached significance with regard to mortality (OR 2.17, unadjusted p = 0.005, adjusted p = 0.15).

CONCLUSIONS

Candidate SNPs within 5 genes in the RAGE and GM-CSF pathways were not significantly associated with development of ARDS in this multi-centric cohort.

Contrasting effects of hyperoxia on GM-CSF gene transcription in alveolar epithelial cells and T cells

Granulocyte/macrophage colony-stimulating factor (GM-CSF) is critically important for normal pulmonary innate immunity and for functional maturation of alveolar macrophages. Alveolar epithelial cells (AEC) are a major source of GM-CSF in the lung and express this growth factor constitutively, whereas most other cells, including T cells, express GM-CSF following inflammatory stimulation. AEC expression of GM-CSF is suppressed by oxidative stress, at least in part through induction of microRNA leading to increased mRNA turnover. In this report, we compare and contrast the effect of hyperoxia on transcriptional aspects of gene regulation of GM-CSF in lung epithelia and T cells of human and mouse origin. Similar to primary murine AEC, human H820 cells that express multiple characteristics of normal alveolar epithelial cells express GM-CSF constitutively, with decreased expression and increased mRNA turnover following exposure to hyperoxia. In contrast, hyperoxia induces augmented GM-CSF expression in human and murine activated T cells, in association with enhanced GM-CSF mRNA stability. Alveolar epithelial cells demonstrate constitutive transcription, with the proximal promoter in an open configuration in normoxia, without change in hyperoxia. Conversely, in both human and murine T cells, hyperoxia increased GM-CSF gene transcription. The proximal promoter was in a closed configuration in unstimulated T cells but became accessible upon activation and still more accessible in activated T cells exposed to hyperoxia. These fundamental differences in molecular regulation of GM-CSF expression highlight the distinctive niche of alveolar epithelial cell expression of GM-CSF and offer insights into the biology of GM-CSF in the setting of acute lung injury.

Key role of microRNA in the regulation of granulocyte macrophage colony-stimulating factor expression in murine alveolar epithelial cells during oxidative stress

GM-CSF is an endogenous pulmonary cytokine produced by normal alveolar epithelial cells (AEC) that is a key defender of the alveolar space. AEC GM-CSF expression is suppressed by oxidative stress through alternations in mRNA turnover, an effect that is reversed by treatment with recombinant GM-CSF. We hypothesized that specific microRNA (miRNA) would play a key role in AEC GM-CSF regulation. A genome-wide miRNA microarray identified 19 candidate miRNA altered in primary AEC during oxidative stress with reversal by treatment with GM-CSF. Three of these miRNA (miR 133a, miR 133a*, and miR 133b) are also predicted to bind the GM-CSF 3'-untranslated region (UTR). PCR for the mature miRNA confirmed induction during oxidative stress that was reversed by treatment with GM-CSF. Experiments using a GM-CSF 3'-UTR reporter construct demonstrated that miR133a and miR133b effects on GM-CSF expression are through interactions with the GM-CSF 3'-UTR. Using lentiviral transduction of specific mimics and inhibitors in primary murine AEC, we determined that miR133a and miR133b suppress GM-CSF expression and that their inhibition both reverses oxidant-induced suppression of GM-CSF expression and increases basal expression of GM-CSF in cells in normoxia. In contrast, these miRNAs are not active in regulation of GM-CSF expression in murine EL4 T cells. Thus, members of the miR133 family play key roles in regulation of GM-CSF expression through effects on mRNA turnover in AEC during oxidative stress. Increased understanding of GM-CSF gene regulation may provide novel miRNA-based interventions to augment pulmonary innate immune defense in lung injury.

Growth factors and cytokines in acute lung injury

Cytokines and growth factors play an integral role in the maintenance of immune homeostasis, the generation of protective immunity, and lung reparative processes. However, the dysregulated expression of cytokines and growth factors in response to infectious or noxious insults can initiate and perpetuate deleterious lung inflammation and fibroproliferation. In this article, we will comprehensively review the contribution of individual cytokines and growth factors and cytokine networks to key pathophysiological events in human and experimental acute lung injury (ALI), including inflammatory cell recruitment and activation, alveolar epithelial injury and repair, angiogenesis, and matrix deposition and remodeling. The application of cytokines/growth factors as prognostic indicators and therapeutic targets in human ALI is explored.

Innate Immune Responses in Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is a common complication of mechanical ventilation, resulting in substantial morbidity, mortality, and health care cost. Early upper airway colonization by pathogenic bacteria and microaspiration are the primary pathogenic events leading to VAP. Patients at risk for VAP have defects in structural/mechanical defenses of the respiratory tract. In addition, critical illness, including sepsis, trauma, and postoperative states, is associated with profound defects in both innate and acquired antibacterial immunity, influencing antimicrobial effector functions of both leukocytes and structural/parenchymal cells. Factors present within the lung microenvironment, including alveolar stretch, cyclical atelectasis, changes in oxygen tension, and respiratory tract microbiota, substantially impact antibacterial host responses. Mechanisms accounting for dysregulated immune homeostasis are incompletely understood, but likely involve: (1) alterations in the balance of pro- and anti-inflammatory cytokines; (2) changes in pathogen recognition receptor and G-protein coupled receptor expression and downstream signaling cascades; and (3) dysregulated cell death responses. Antibiotics and preventive strategies are the mainstay of therapy in patients with VAP. However, novel approaches are needed to reverse immunological reprogramming that occurs during critical illness and/or mechanical ventilation, and to identify patients who are most likely to benefit from immunomodulatory therapy.

Effect of alveolar epithelial cell plasticity on the regulation of GM-CSF expression

Local pulmonary expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) is critically important for defense of the pulmonary alveolar space. It is required for surfactant homeostasis and pulmonary innate immune responses and is protective against lung injury and aberrant repair. Alveolar epithelial cells (AEC) are a major source of GM-CSF; however, the control of homeostatic expression of GM-CSF is incompletely characterized. Increasing evidence suggests considerable plasticity of expression of AEC phenotypic characteristics. We tested the hypothesis that this plasticity extends to regulation of expression of GM-CSF using 1) MLE-12 cells (a commonly used murine cell line expressing some features of normal type II AEC, 2) primary murine AEC incubated under standard conditions [resulting in rapid spreading and loss of surfactant protein C (SP-C) expression with induction of the putative type I cell marker (T1α)], or 3) primary murine AEC on a hyaluronic acid/collagen matrix in defined medium, resulting in preservation of SP-C expression. AEC in standard cultures constitutively express abundant GM-CSF, with further induction in response to IL-1β but little response to TNF-α. In contrast, primary cells cultured to preserve SP-C expression and MLE-12 cells both express little GM-CSF constitutively, with significant induction in response to TNF-α and limited response to IL-1β. We conclude that constitutive and cytokine-induced expression of GM-CSF by AEC varies in concert with other cellular phenotypic characteristics. These changes may have important implications both for the maintenance of normal pulmonary homeostasis and for the process of repair following lung injury.

A randomized trial of recombinant human granulocyte-macrophage colony stimulating factor for patients with acute lung injury

RATIONALE

Despite recent advances in critical care and ventilator management, acute lung injury and acute respiratory distress syndrome continue to cause significant morbidity and mortality. Granulocyte-macrophage colony stimulating factor may be beneficial for patients with acute respiratory distress syndrome.

OBJECTIVES

To determine whether intravenous infusion of granulocyte-macrophage colony stimulating factor would improve clinical outcomes for patients with acute lung injury/acute respiratory distress syndrome.

DESIGN

A randomized, double-blind, placebo-controlled clinical trial of human recombinant granulocyte-macrophage colony stimulating factor vs. placebo. The primary outcome was days alive and breathing without mechanical ventilatory support within the first 28 days after randomization. Secondary outcomes included mortality and organ failure-free days.

SETTING

Medical and surgical intensive care units at three academic medical centers.

PATIENTS

One hundred thirty individuals with acute lung injury of at least 3 days duration were enrolled, out of a planned cohort of 200 subjects.

INTERVENTIONS

Patients were randomized to receive human recombinant granulocyte-macrophage colony stimulating factor (64 subjects, 250 μg/M) or placebo (66 subjects) by intravenous infusion daily for 14 days. Patients received mechanical ventilation using a lung-protective protocol.

MEASUREMENTS AND MAIN RESULTS

There was no difference in ventilator-free days between groups (10.7 ± 10.3 days placebo vs. 10.8 ± 10.5 days granulocyte-macrophage colony stimulating factor, p = .82). Differences in 28-day mortality (23% in placebo vs. 17% in patients receiving granulocyte-macrophage colony stimulating factor (p = .31) and organ failure-free days (12.8 ± 11.3 days placebo vs. 15.7 ± 11.9 days granulocyte-macrophage colony stimulating factor, p = .16) were not statistically significant. There were similar numbers of serious adverse events in each group.

CONCLUSIONS

In a randomized phase II trial, granulocyte-macrophage colony stimulating factor treatment did not increase the number of ventilator-free days in patients with acute lung injury/acute respiratory distress syndrome. A larger trial would be required to determine whether treatment with granulocyte-macrophage colony stimulating factor might alter important clinical outcomes, such as mortality or multiorgan failure. (ClinicalTrials.gov number, NCT00201409 [ClinicalTrials.gov]).

TLR4-dependent GM-CSF protects against lung injury in Gram-negative bacterial pneumonia

Toll-like receptors (TLRs) are required for protective host defense against bacterial pathogens. However, the role of TLRs in regulating lung injury during Gram-negative bacterial pneumonia has not been thoroughly investigated. In this study, experiments were performed to evaluate the role of TLR4 in pulmonary responses against Klebsiella pneumoniae (Kp). Compared with wild-type (WT) (Balb/c) mice, mice with defective TLR4 signaling (TLR4(lps-d) mice) had substantially higher lung bacterial colony-forming units after intratracheal challenge with Kp, which was associated with considerably greater lung permeability and lung cell death. Reduced expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA and protein was noted in lungs and bronchoalveolar lavage fluid of TLR4 mutant mice postintratracheal Kp compared with WT mice, and primary alveolar epithelial cells (AEC) harvested from TLR4(lps-d) mice produced significantly less GM-CSF in vitro in response to heat-killed Kp compared with WT AEC. TLR4(lps-d) AEC underwent significantly more apoptosis in response to heat-killed Kp in vitro, and treatment with GM-CSF protected these cells from apoptosis in response to Kp. Finally, intratracheal administration of GM-CSF in TLR4(lps-d) mice significantly decreased albumin leak, lung cell apoptosis, and bacteremia in Kp-infected mice. Based on these observations, we conclude that TLR4 plays a protective role on lung epithelium during Gram-negative bacterial pneumonia, an effect that is partially mediated by GM-CSF.

GM-CSF provides autocrine protection for murine alveolar epithelial cells from oxidant-induced mitochondrial injury

Exposure of mice to hyperoxia induces alveolar epithelial cell (AEC) injury, acute lung injury and death. Overexpression of granulocyte-macrophage colony-stimulating factor (GM-CSF) in the lung protects against these effects, although the mechanisms are not yet clear. Hyperoxia induces cellular injury via effects on mitochondrial integrity, associated with induction of proapoptotic members of the Bcl-2 family. We hypothesized that GM-CSF protects AEC through effects on mitochondrial integrity. MLE-12 cells (a murine type II cell line) and primary murine type II AEC were subjected to oxidative stress by exposure to 80% oxygen and by exposure to H(2)O(2). Exposure to H(2)O(2) induced cytochrome c release and decreased mitochondrial reductase activity in MLE-12 cells. Incubation with GM-CSF significantly attenuated these effects. Protection induced by GM-CSF was associated with Akt activation. GM-CSF treatment also resulted in increased expression of the antiapoptotic Bcl-2 family member, Mcl-1. Primary murine AEC were significantly more tolerant of oxidative stress than MLE-12 cells. In contrast to MLE-12 cells, primary AEC expressed significant GM-CSF at baseline and demonstrated constitutive activation of Akt and increased baseline expression of Mcl-1. Treatment with exogenous GM-CSF further increased Akt activation and Mcl-1 expression in primary AEC. Conversely, suppression of AEC GM-CSF expression by use of GM-CSF-specific small interfering RNA resulted in decreased tolerance of oxidative stress, Furthermore, silencing of Mcl-1 prevented GM-CSF-induced protection. We conclude that GM-CSF protects alveolar epithelial cells against oxidative stress-induced mitochondrial injury via the Akt pathway and its downstream components, including Mcl-1. Epithelial cell-derived GM-CSF may contribute to intrinsic defense mechanisms limiting lung injury.

Acute lung injury: how macrophages orchestrate resolution of inflammation and tissue repair

Lung macrophages are long living cells with broad differentiation potential, which reside in the lung interstitium and alveoli or are organ-recruited upon inflammatory stimuli. A role of resident and recruited macrophages in initiating and maintaining pulmonary inflammation in lung infection or injury has been convincingly demonstrated. More recent reports suggest that lung macrophages are main orchestrators of termination and resolution of inflammation. They are also initiators of parenchymal repair processes that are essential for return to homeostasis with normal gas exchange. In this review we will discuss cellular cross-talk mechanisms and molecular pathways of macrophage plasticity which define their role in inflammation resolution and in initiation of lung barrier repair following lung injury.

Erythromycin prevents the pulmonary inflammation induced by exposure to cigarette smoke

The effect of erythromycin on the inflammation caused by exposure to cigarette smoke was investigated in this study. Mice were exposed either to cigarette smoke or to environmental air (control), and some mice exposed to cigarette smoke were treated with oral erythromycin (100 mg/kg/day for 8 days). Pulmonary inflammation was assessed by determining the cellular content of bronchoalveolar lavage (BAL) fluid. The messenger RNA (mRNA) levels of various mediators, including keratinocyte-derived chemokine (KC), macrophage inflammatory protein (MIP)-2, surfactant protein (SP)-D, granulocyte macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor (TNF)-α, interleukin (IL)-6 in lung tissue were determined using quantitative reverse transcription polymerase chain reaction (qRT-PCR) assays. The exposure to cigarette smoke increased significantly the numbers of neutrophils (P = 0.029), macrophages (P = 0.029), and lymphocytes (P = 0.029) recovered in BAL fluid. Moreover, mRNA levels of KC (P = 0.029), MIP-2 (P = 0.029), SP-D (P = 0.029), and GM-CSF (P = 0.057) in the lung tissue were higher in mice exposed to cigarette smoke than in mice exposed to environmental air. In the erythromycin-treated mice that were exposed also to cigarette smoke, both neutrophil and lymphocyte counts were significantly lower in the BAL fluid than those in the vehicle-treated mice (P = 0.029). Erythromycin-treated mice exposed to cigarette smoke showed a trend of lower mRNA levels of KC and TNF-α in the lung tissue than those in the vehicle-treated mice, although the statistical significance was not achieved (P = 0.057). Our data demonstrated that erythromycin prevented lung inflammation induced by cigarette smoke, in parallel to the reduced mRNA levels of KC and TNF-α.

Hydrogen peroxide enhances phagocytosis of Pseudomonas aeruginosa in hyperoxia

Mechanical ventilation with hyperoxia is a necessary treatment for patients with respiratory distress. However, patients on mechanical ventilation have increased susceptibility to infection. Studies including ours have shown that reactive oxygen species (ROS), generated by exposure to prolonged hyperoxia, can cause a decrease in the phagocytic activity of alveolar macrophages. Hydrogen peroxide (H₂O₂) is a form of ROS generated under hyperoxic conditions. In this study, we examined whether treatment with H₂O₂ directly affects macrophage phagocytic ability in RAW 264.7 cells that were exposed to either 21% O₂ (room air) or 95% O₂ (hyperoxia). Moderate concentrations (ranging from 10 to 250 μM) of H₂O₂ significantly enhanced macrophage phagocytic activity and restored hyperoxia-suppressed phagocytosis through attenuation of hyperoxia-induced disorganization of actin cytoskeleton and actin oxidation. These results indicate that H₂O₂ at low-moderate concentrations can be beneficial to host immune responses by improving macrophage phagocytic activity.

Cytokine networks in the infected lung

The generation of an innate immune response is essential for rapid clearance of microbes from the respiratory tract, whereas acquired immunity is required for the generation of cellular immunity necessary for the killing of certain intracellular pathogens and the development of immunological memory. Cytokines play an integral role in host defense by serving as leukocyte chemoattractants, leukocyte-activating factors or afferent signals in the induction or regulation of other effector molecules. This review assesses the contribution of cytokine networks to the generation of antimicrobial host defenses in the lung, with an emphasis on cytokines/cytokine networks that are instrumental in innate antibacterial responses, including mucosal immunity, and also introduces networks that instruct the development of adaptive immunity.

Moderate oxygen augments lipopolysaccharide-induced lung injury in mice

Despite the associated morbidity and mortality, underlying mechanisms leading to the development of acute lung injury (ALI) remain incompletely understood. Frequently, ALI develops in the hospital, coinciding with institution of various therapies, including the use of supplemental oxygen. Although pathological evidence of hyperoxia-induced ALI in humans has yet to be proven, animal studies involving high oxygen concentration reproducibly induce ALI. The potentially injurious role of lower and presumably safer oxygen concentrations has not been well characterized in any species. We hypothesized that in the setting of a preexisting insult to the lung, the addition of moderate-range oxygen can augment lung injury. Our model of low-dose intratracheal LPS (IT LPS) followed by 60% oxygen caused a significant increase in ALI compared with LPS or oxygen alone with increased alveolar neutrophils, histological injury, and epithelial barrier permeability. In the LPS plus oxygen group, regulatory T cell number was reduced, and macrophage activation markers were increased, compared with LPS alone. Antibody-mediated depletion of neutrophils significantly abrogated the observed lung injury for all measured factors. The enhanced presence of alveolar neutrophils in the setting of LPS and oxygen is due, at least in part, to elevated chemokine gradients signaling neutrophils to the alveolar space. We believe these results strongly support an effect of lower concentrations of oxygen to augment the severity of a mild preexisting lung injury and warrants further investigation in both animals and humans.

Mechanisms of suppression of alveolar epithelial cell GM-CSF expression in the setting of hyperoxic stress

Pulmonary expression of granulocyte/macrophage colony-stimulating factor (GM-CSF) is critically important for normal functional maturation of alveolar macrophages. We found previously that lung GM-CSF is dramatically suppressed in mice exposed to hyperoxia. Alveolar epithelial cells (AEC) are a major source of GM-CSF in the peripheral lung, and in vivo hyperoxia resulted in greatly reduced expression of GM-CSF protein by AEC ex vivo. We now explore the mechanisms responsible for this effect, using primary cultures of murine AEC exposed to hyperoxia in vitro. Exposure of AEC to 80% oxygen/5% CO(2) for 48 h did not induce overt toxicity, but resulted in significantly decreased GM-CSF protein and mRNA expression compared with cells in normoxia. Similar effects were seen when AEC were stressed with serum deprivation, an alternative inducer of oxidative stress. The effects in AEC were opposite those in a murine lung epithelial cell line (MLE-12 cells), in which hyperoxia induced GM-CSF expression. Both hyperoxia and serum deprivation resulted in increased intracellular reactive oxygen species (ROS) in AEC. Hyperoxia and serum deprivation induced significantly accelerated turnover of GM-CSF mRNA. Treatment of AEC with catalase during oxidative stress preserved GM-CSF protein and mRNA and was associated with stabilization of GM-CSF mRNA. We conclude that hyperoxia-induced suppression of AEC GM-CSF expression is a function of ROS-induced destabilization of GM-CSF mRNA. We speculate that AEC oxidative stress results in significantly impaired pulmonary innate immune defense due to effects on local GM-CSF expression in the lung.

Nebulized antithrombin limits bacterial outgrowth and lung injury in Streptococcus pneumoniae pneumonia in rats

INTRODUCTION

Disturbed alveolar fibrin turnover is a cardinal feature of severe pneumonia. Clinical studies suggest that natural inhibitors of coagulation exert lung-protective effects via anticoagulant and possibly also anti-inflammatory pathways. Intravenous infusion of the natural anticoagulants increases the risk of bleeding. Local administration may allow for higher treatment dosages and increased local efficacy while at the same time reducing the risk of bleeding. We evaluated the effect of nebulized anticoagulants on pulmonary coagulopathy and inflammation in a rat model of Streptococcus pneumoniae pneumonia.

METHODS

In this randomized controlled in vivo laboratory study rats were challenged intratracheally with S. pneumoniae, inducing pneumonia, and randomized to treatment with normal saline (placebo), recombinant human activated protein C (rh-APC), plasma-derived antithrombin (AT), heparin or danaparoid, by means of nebulization.

RESULTS

S. pneumoniae infection increased pulmonary levels of thrombin-antithrombin complexes and fibrin degradation products. All nebulized anticoagulants significantly limited pulmonary coagulopathy. None of the agents except danaparoid resulted in changes in systemic coagulopathy. Treatment with plasma-derived AT reduced outgrowth of S. pneumoniae and histopathologic damage in lungs. In vitro experiments confirmed outgrowth was reduced in bronchoalveolar lavage fluid (BALF) from rats treated with plasma-derived AT compared with placebo. Neutralizing of cationic components in BALF diminished the inhibitory effects on bacterial outgrowth of BALF, suggesting a role for cationic antimicrobial proteins.

CONCLUSIONS

Nebulization of anticoagulants attenuates pulmonary coagulopathy during S. pneumoniae pneumonia in rats while only danaparoid affects systemic coagulation. Nebulized plasma-derived AT reduces bacterial outgrowth and exerts significant lung-protective effects.

Granulocyte-macrophage colony-stimulating factor to reverse sepsis-associated immunosuppression: a double-blind, randomized, placebo-controlled multicenter trial

RATIONALE

Sustained sepsis-associated immunosuppression is associated with uncontrolled infection, multiple organ dysfunction, and death.

OBJECTIVES

In the first controlled biomarker-guided immunostimulatory trial in sepsis, we tested whether granulocyte-macrophage colony-stimulating factor (GM-CSF) reverses monocyte deactivation, a hallmark of sepsis-associated immunosuppression (primary endpoint), and improves the immunological and clinical course of patients with sepsis.

METHODS

In a prospective, randomized, double-blind, placebo-controlled, multicenter trial, 38 patients (19/group) with severe sepsis or septic shock and sepsis-associated immunosuppression (monocytic HLA-DR [mHLA-DR] <8,000 monoclonal antibodies (mAb) per cell for 2 d) were treated with GM-CSF (4 microg/kg/d) or placebo for 8 days. The patients' clinical and immunological course was followed up for 28 days.

MEASUREMENTS AND MAIN RESULTS

Both groups showed comparable baseline mHLA-DR levels (5,609 +/- 3,628 vs. 5,659 +/- 3,332 mAb per cell), which significantly increased within 24 hours in the GM-CSF group. After GM-CSF treatment, mHLA-DR was normalized in 19/19 treated patients, whereas this occurred in 3/19 control subjects only (P < 0.001). GM-CSF also restored ex-vivo Toll-like receptor 2/4-induced proinflammatory monocytic cytokine production. In patients receiving GM-CSF, a shorter time of mechanical ventilation (148 +/- 103 vs. 207 +/- 58 h, P = 0.04), an improved Acute Physiology and Chronic Health Evaluation-II score (P = 0.02), and a shorter length of both intrahospital and intensive care unit stay was observed (59 +/- 33 vs. 69 +/- 46 and 41 +/- 26 vs. 52 +/- 39 d, respectively, both not significant). Side effects related to the intervention were not noted.

CONCLUSIONS

Biomarker-guided GM-CSF therapy in sepsis is safe and effective for restoring monocytic immunocompetence. Use of GM-CSF may shorten the time of mechanical ventilation and hospital/intensive care unit stay. A multicenter trial powered for the improvement of clinical parameters and mortality as primary endpoints seems indicated. Clinical trial registered with www.clinicaltrials.gov (NCT00252915).

Neuroimmune regulation in immunocompetence, acute illness, and healing

Adaptive immunocompetence is maintained by growth hormone (GH), prolactin (PRL), and vasopressin (VP). Innate or natural immunocompetence depends on cytokines, hormones (especially of the hypothalamus-pituitary-adrenal axis), and catecholamines. The acute phase response (APR, or acute febrile illness) is an emergency defense reaction whereby the adaptive, T cell-dependent, immune reactions are suppressed and the innate immune function is dramatically amplified. Infection and various forms of injury induce APR. Cytokines [interleukin (IL)-1beta, tumor necrosis factor-alpha, and IL-6] stimulate corticotropin-releasing hormone (CRH) and VP secretion and cause a "sympathetic outflow." Colony-stimulating factors activate leukocytes. CRH is a powerful activator of the pituitary adrenocortical axis and elevates glucocorticoid (GC) levels. Cytokines, GCs, and catecholamines play fundamental roles in the amplification of natural immune defense mechanisms. VP supports the APR at this stage. However, VP remains active and is elevated for a longer period than is CRH. VP, but not CRH, is elevated during chronic inflammatory diseases. VP controls adaptive immune function and stimulates adrenocorticotropic hormone (ACTH) and PRL secretion. PRL maintains the function of the thymus and of the T cell-dependent adaptive immune system. The ACTH-adrenal axis stimulates natural immunity and of suppressor/regulatory T cells, which suppress the adaptive immune system. VP also has a direct effect on lymphoid cells, the significance of which remains to be elucidated. It is suggested that VP regulates the process of recovery from acute illness.

Prenatal administration of granulocyte-macrophage colony-stimulating factor increases mesenchymal vascular endothelial growth factor expression and maturation in fetal rat lung

The aim of this study was to determine influence of prenatal granulocyte-macrophage colony-stimulating factor (GM-CSF) administration on lung growth, maturation, and vascular endothelial growth factor (VEGF) expression. Twenty Wistar rats received sterile saline (1 mL) or recombinant human GM-CSF (50 micro g/kg) on day 16 of pregnancy. Rats were sacrificed on days 18 and 20 of gestation. H-score for VEGF was calculated immunohistochemically. Alveolar VEGF expression on days 18 and 20 of gestation was significantly higher in the GM-CSF group (P < .01). Increase in VEGF with prenatal GM-CSF administration indicates that GM-CSF may stimulate lung growth and maturation and may be protective against lung disease due to prematurity.

Critical roles of inflammation and apoptosis in improved survival in a model of hyperoxia-induced acute lung injury in Pneumocystis murina-infected mice

Pneumocystis infections increase host susceptibility to additional insults that would be tolerated in the absence of infection, such as hyperoxia. In an in vivo model using CD4-depleted mice, we previously demonstrated that Pneumocystis murina pneumonia causes significant mortality following an otherwise nonlethal hyperoxic insult. Infected mice demonstrated increased pulmonary inflammation and alveolar epithelial cell apoptosis compared to controls. To test the mechanisms underlying these observations, we examined expression of components of the Fas-Fas ligand pathway in P. murina-infected mice exposed to hyperoxia. Hyperoxia alone increased expression of Fas on the surface of type II alveolar epithelial cells; conversely, infection with P. murina led to increased lung expression of Fas ligand. We hypothesized that inhibition of inflammatory responses or direct inhibition of alveolar epithelial cell apoptosis would improve survival in P. murina-infected mice exposed to hyperoxia. Mice were depleted of CD4(+) T cells and infected with P. murina and then were exposed to >95% oxygen for 4 days, followed by return to normoxia. Experimental groups received vehicle, dexamethasone, or granulocyte-macrophage colony-stimulating factor (GM-CSF). Compared with the vehicle-treated group, treatment with dexamethasone reduced Fas ligand expression and significantly improved survival. Similarly, treatment with GM-CSF, an agent we have shown protects alveolar epithelial cells against apoptosis, decreased Fas ligand expression and also improved survival. Our results suggest that the dual stresses of P. murina infection and hyperoxia induce lung injury via activation of the Fas-Fas ligand pathway and that corticosteroids and GM-CSF reduce mortality in P. murina-infected mice exposed to hyperoxic stress by inhibition of inflammation and apoptosis.

Paradoxical role of alveolar macrophage-derived granulocyte-macrophage colony-stimulating factor in pulmonary host defense post-bone marrow transplantation

Impaired host defense post-bone marrow transplant (BMT) is related to overproduction of prostaglandin E(2) (PGE(2)) by alveolar macrophages (AMs). We show AMs post-BMT overproduce granulocyte-macrophage colony-stimulating factor (GM-CSF), whereas GM-CSF in lung homogenates is impaired both at baseline and in response to infection post-BMT. Homeostatic regulation of GM-CSF may occur by hematopoietic/structural cell cross talk. To determine whether AM overproduction of GM-CSF influenced immunosuppression post-BMT, we compared mice that received BMT from wild-type donors (control BMT) or mice that received BMT from GM-CSF-/- donors (GM-CSF-/- BMT) with untransplanted mice. GM-CSF-/- BMT mice were less susceptible to pneumonia with Pseudomonas aeruginosa compared with control BMT mice and showed antibacterial responses equal to or better than untransplanted mice. GM-CSF-/- BMT AMs displayed normal phagocytosis and a trend toward enhanced bacterial killing. Surprisingly, AMs from GM-CSF-/- BMT mice overproduced PGE(2), but expression of the inhibitory EP(2) receptor was diminished. As a consequence of decreased EP(2) receptor expression, we found diminished accumulation of cAMP in response to PGE(2) stimulation in GM-CSF-/- BMT AMs compared with control BMT AMs. In addition, GM-CSF-/- BMT AMs retained cysteinyl leukotriene production and normal TNF-alpha response compared with AMs from control BMT mice. GM-CSF-/- BMT neutrophils also showed improved bacterial killing. Although genetic ablation of GM-CSF in hematopoietic cells post-BMT improved host defense, transplantation of wild-type bone marrow into GM-CSF-/- recipients demonstrated that parenchymal cell-derived GM-CSF is necessary for effective innate immune responses post-BMT. These results highlight the complex regulation of GM-CSF and innate immunity post-BMT.