Fibroproliferation and mast cells in the acute respiratory distress syndrome

Development of Adaptive Immunity and Its Role in Lung Remodeling

Asthma is characterized by airflow limitations resulting from bronchial closure, which can be either reversible or fixed due to changes in airway tissue composition and structure, also known as remodeling. Airway remodeling is defined as increased presence of mucins-producing epithelial cells, increased thickness of airway smooth muscle cells, angiogenesis, increased number and activation state of fibroblasts, and extracellular matrix (ECM) deposition. Airway inflammation is believed to be the main cause of the development of airway remodeling in asthma. In this chapter, we will review the development of the adaptive immune response and the impact of its mediators and cells on the elements defining airway remodeling in asthma.

Titration of Ventilator Settings to Target Driving Pressure and Mechanical Power

PURPOSE

Driving pressure (ΔP) and mechanical power (MP) may be important mediators of lung injury in acute respiratory distress syndrome (ARDS) however there is little evidence for strategies directed at lowering these parameters. We applied predictive modeling to estimate the effects of modifying ventilator parameters on ΔP and MP.

METHODS

2,622 ARDS patients (Berlin criteria) from the Medical Information Mart for Intensive Care IV database (MIMIC-IV version1.0) admitted to the intensive care unit (ICU) at Beth Israel Deaconess Medical Center between 2008 and 2019 were included. Flexible confounding-adjusted regression models for time varying data were fit to estimate the effects of adjusting PEEP and tidal volume (VT) on ΔP, and adjusting VT and respiratory rate (f) on MP.

RESULTS

Reduction in VT reduced ΔP and MP, with more pronounced effect on MP with lower compliance. Strategies reducing f, consistently increased MP (when VT was adjusted to maintain consistent minute ventilation). Adjustment of PEEP yielded a U-shaped effect on ΔP.

CONCLUSIONS

This novel conditional modeling confirmed expected response patterns for ΔP, with the response to adjustments depending on patients' lung mechanics. Furthermore a VT -driven approach should be favored over a f -driven approach when aiming to reduce MP.

Uncovering the Mast Cell Response to Mycobacterium tuberculosis

The immunologic mechanisms that contribute to the response to Mycobacterium tuberculosis infection still represent a challenge in the clinical management and scientific understanding of tuberculosis disease. In this scenario, the role of the different cells involved in the host response, either in terms of innate or adaptive immunity, remains key for defeating this disease. Among this coordinated cell response, mast cells remain key for defeating tuberculosis infection and disease. Together with its effector’s molecules, membrane receptors as well as its anatomical locations, mast cells play a crucial role in the establishment and perpetuation of the inflammatory response that leads to the generation of the granuloma during tuberculosis. This review highlights the current evidences that support the notion of mast cells as key link to reinforce the advancements in tuberculosis diagnosis, disease progression, and novel therapeutic strategies. Special focus on mast cells capacity for the modulation of the inflammatory response among patients suffering multidrug resistant tuberculosis or in co-infections such as current COVID-19 pandemic.

Decline in Mast Cell Density During Diffuse Alveolar Damage in Idiopathic Pulmonary Fibrosis

Mast cells (MCs) are known to be involved in the pathogenesis of idiopathic pulmonary fibrosis (IPF), although their role in acute exacerbations of IPF has not been investigated. The aims of the study were to evaluate the numbers of MCs in fibrotic and non-fibrotic areas of lung tissue specimens of idiopathic pulmonary fibrosis (IPF) patients with or without an acute exacerbation of IPF, and to correlate the MC density with clinical parameters. MCs of IPF patients were quantified from surgical lung biopsy (SLB) specimens (n = 47) and lung tissue specimens taken at autopsy (n = 7). MC density was higher in the fibrotic areas of lung tissue compared with spared alveolar areas or in controls. Female gender, low diffusion capacity for carbon monoxide, diffuse alveolar damage, and smoking were associated with a low MC density. MC densities of fibrotic areas had declined significantly in five subjects in whom both SLB in the stable phase and autopsy after an acute exacerbation of IPF had been performed. There were no correlations of MC densities with survival time or future acute exacerbations. The MC density in fibrotic areas was associated with several clinical parameters. An acute exacerbation of IPF was associated with a significant decline in MC counts. Further investigations will be needed to clarify the role of these cells in IPF and in the pathogenesis of acute exacerbation as this may help to identify some potential targets for medical treatment for this serious disease.

iRGD conjugated nimbolide liposomes protect against endotoxin induced acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a deadly respiratory illness associated with refractory hypoxemia and pulmonary edema. The recent pandemic outbreak of COVID-19 is associated with severe pneumonia and inflammatory cytokine storm in the lungs. The anti-inflammatory phytomedicine nimbolide (NIM) may not be feasible for clinical translation due to poor pharmacokinetic properties and lack of suitable delivery systems. To overcome these barriers, we have developed nimbolide liposomes conjugated with iRGD peptide (iRGD-NIMLip) for targeting lung inflammation. It was observed that iRGD-NIMLip treatment significantly inhibited oxidative stress and cytokine storm compared to nimbolide free-drug (f-NIM), nimbolide liposomes (NIMLip), and exhibited superior activity compared to dexamethasone (DEX). iRGD-NIMLip abrogated the LPS induced p65 NF-κB, Akt, MAPK, Integrin β3 and β5, STAT3, and DNMT1 expression. Collectively, our results demonstrate that iRGD-NIMLip could be a promising novel drug delivery system to target severe pathological consequences observed in ARDS and COVID-19 associated cytokine storm.

COVID-19 Usurps Host Regulatory Networks

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes coronavirus disease 2019 (COVID-19). SARS-CoV-2 binds the angiotensin-converting enzyme 2 (ACE2) on the cell surface and this complex is internalized. ACE2 serves as an endogenous inhibitor of inflammatory signals associated with four major regulator systems: the renin-angiotensin-aldosterone system (RAAS), the complement system, the coagulation cascade, and the kallikrein-kinin system (KKS). Understanding the pathophysiological effects of SARS-CoV-2 on these pathways is needed, particularly given the current lack of proven, effective treatments. The vasoconstrictive, prothrombotic and pro-inflammatory conditions induced by SARS-CoV-2 can be ascribed, at least in part, to the activation of these intersecting physiological networks. Moreover, patients with immune deficiencies, hypertension, diabetes, coronary heart disease, and kidney disease often have altered activation of these pathways, either due to underlying disease or to medications, and may be more susceptible to SARS-CoV-2 infection. Certain characteristic COVID-associated skin, sensory, and central nervous system manifestations may also be linked to viral activation of the RAAS, complement, coagulation, and KKS pathways. Pharmacological interventions that target molecules along these pathways may be useful in mitigating symptoms and preventing organ or tissue damage. While effective anti-viral therapies are critically needed, further study of these pathways may identify effective adjunctive treatments and patients most likely to benefit.

Repositioning Chromones for Early Anti-inflammatory Treatment of COVID-19

The COVID-19 pandemic is posing an unprecedented sanitary threat. In the absence of specific vaccines and anti-SARS-CoV-2 drugs, medicines that may assist in tackling the emergency and limiting the high number of fatalities are urgently needed. The repositioning of available drugs to treat COVID-19 is the only and rapid option in the face of the lack of direct antiviral agents and vaccines available. In this light it is important to focus on available drugs, which, based on their pharmacodynamics, could plausibly attenuate viral growth as well as COVID-19’s worst complications. This is the case of chloroquine and tocilizumab which seem to limit virus replication and the severity of interstitial pneumonia, respectively. However, these treatments, particularly those aimed at containing inflammation, are still reserved for the most severe cases. This commentary elaborates on the pharmacological rationale of repositioning the mast cell stabilizer chromones as an adjunctive treatment for SARS‐CoV‐2 infection, and proposes their practical clinical testing as an early, safe, and cost-effective anti-inflammatory intervention in COVID-19 to limit the eventual secondary progression toward life-threatening respiratory complications.

Role of mast cells and eosinophils in different stages of trinitrobenzenosulphonic acid-induced rat colitis

The present study aimed to elucidate the effect of mast cells (MCs) and eosinophils (Eos) in trinitrobenzenosulphonic acid (TNBS)-induced colitis in SD rats. A rat model of ulcerative colitis (UC) was established by intracolonic injection of 100 mg/kg TNBS (in 0.3 ml 50% ethanol). At 6, 11, 16, 21 days after TNBS injection, the rats were sacrificed to determine the colon injury scores, the counts, distribution, and ultrastructure of mast cells (MCs) and eosinophils (Eos), the concentration of whole blood, and colon histamine. The results showed that after TNBS injection, for 6 days, colon injury score was significantly increased in the distal colon of the rats (P < 0.01 vs. control), accompanied by markedly increased whole blood histamine level and Eos count (P < 0.01), but decreased colon histamine concentration (P < 0.01). At the following 11, 16, 21 days' detection, MCs count and colon histamine level were gradually increased while Eos count and blood histamine were decreased during 21 days' detection period. Furthermore, the correlation analysis revealed that the Eos counts were positively correlated with the colon injury score and blood histamine content (P < 0.05, respectively). The MCs count was negatively associated with the blood histamine content (P < 0.05), but positively associated with the colon tissue histamine content (P < 0.01). In conclusion, though no correlation was found between MCs and Eos counts in the TNBS-induced colitis in this study, their relationship with whole blood and colon histamine appear to play different roles in both the acute and repair stages of colitis.

Hyperglycemia induces epithelial-mesenchymal transition in the lungs of experimental diabetes mellitus

Diabetes mellitus (DM) reduces lung function and increases the risk of asthma, chronic obstructive pulmonary disease, pneumonia, and pulmonary fibrosis. Epithelial-mesenchymal transition (EMT) plays a crucial role in the development of pulmonary fibrosis. The pathogenesis of pulmonary fibrosis in diabetes remains unknown. We investigated the effects of hyperglycemia on EMT in the lungs of gerbils with streptozotocin (STZ)-induced diabetes. Diabetic gerbils exhibited a significantly lower volume fraction of the alveolar airspace and significantly higher septal thickness, volume fraction of the alveolar wall, and lung injury scores than did nondiabetic gerbils. The percentage of 8-hydroxy-2'-deoxyguanosine-positive cells and transforming growth factor-β-positive cells was significantly higher, the expression of E-cadherin was significantly lower, and the expression of N-cadherin was significantly higher in diabetic gerbils than in nondiabetic gerbils. These EMT characteristics were associated with a significant increase in α-smooth muscle actin (SMA) expression and collagen deposition in the lungs of diabetic gerbils. The increased α-SMA expression was co-localized with surfactant protein-C in alveolar type II cells in hyperglycemic animals. In conclusion, our study demonstrates that hyperglycemia induces EMT and contributes to lung fibrosis in an experimental DM model.

Combined pirfenidone, azithromycin and prednisolone in post-H1N1 ARDS pulmonary fibrosis

There are no specific data on the management of pulmonary fibrosis post-H1N1 ARDS. We present the cases of three patients who responded positively to treatment with pirfenidone, azithromycin and prednisolone. Three males, aged 40, 45 and 59 years, had H1N1 ARDS requiring mechanical ventilation for two weeks or longer. After weaning off ventilation, they had persistent symptoms and hypoxemia at rest despite receiving prednisolone and home oxygen for at least three weeks following discharge. Computed tomography (CT) of the chest showed fibrosis and traction bronchiectasis. At presentation, they could not perform spirometry. Investigations ruled out infection. Pirfenidone (600 mg daily escalated to maximum tolerable dose of 2.4 gm daily) and azithromycin (500 mg thrice weekly) were added off-label to prednisolone. In one patient pirfenidone was discontinued after three months due to an adverse reaction and azithromycin was continued for nine months. At one year follow-up, all patients had symptomatic improvement, better effort tolerance, regression of opacities and no progression of fibrosis on CT, and improvement in spirometry and six minute walk tests. Pirfenidone and azithromycin added to prednisolone may have led to clinical and radiological improvement. The current experience suggests that this treatment approach to pulmonary fibrosis post-H1N1 ARDS be studied further. (Sarcoidosis Vasc Diffuse Lung Dis 2018; 35: 85-90).

The Processes and Mechanisms of Cardiac and Pulmonary Fibrosis

Fibrosis is the formation of fibrous connective tissue in response to injury. It is characterized by the accumulation of extracellular matrix components, particularly collagen, at the site of injury. Fibrosis is an adaptive response that is a vital component of wound healing and tissue repair. However, its continued activation is highly detrimental and a common final pathway of numerous disease states including cardiovascular and respiratory disease. Worldwide, fibrotic diseases cause over 800,000 deaths per year, accounting for ~45% of total deaths. With an aging population, the incidence of fibrotic disease and subsequently the number of fibrosis-related deaths will rise further. Although, fibrosis is a well-recognized cause of morbidity and mortality in a range of disease states, there are currently no viable therapies to reverse the effects of chronic fibrosis. Numerous predisposing factors contribute to the development of fibrosis. Biological aging in particular, interferes with repair of damaged tissue, accelerating the transition to pathological remodeling, rather than a process of resolution and regeneration. When fibrosis progresses in an uncontrolled manner, it results in the irreversible stiffening of the affected tissue, which can lead to organ malfunction and death. Further investigation into the mechanisms of fibrosis is necessary to elucidate novel, much needed, therapeutic targets. Fibrosis of the heart and lung make up a significant proportion of fibrosis-related deaths. It has long been established that the heart and lung are functionally and geographically linked when it comes to health and disease, and thus exploring the processes and mechanisms that contribute to fibrosis of each organ, the focus of this review, may help to highlight potential avenues of therapeutic investigation.

Airway and parenchyma immune cells in influenza A(H1N1)pdm09 viral and non-viral diffuse alveolar damage

Background

Diffuse alveolar damage (DAD), which is the histological surrogate for acute respiratory distress syndrome (ARDS), has a multifactorial aetiology. Therefore it is possible that the immunopathology differs among the various presentations of DAD. The aim of this study is to compare lung immunopathology of viral (influenza A(H1N1)pdm09) to non-viral, extrapulmonary aetiologies in autopsy cases with DAD.

Methods

The lung tissue of 44 patients, was divided in the H1N1 group (n = 15) characterized by severe pulmonary injury due to influenza A(H1N1)pdm09 infection; the ARDS group (n = 13), characterized by patients with DAD due to non-pulmonary causes; and the Control group (n = 16), consisting of patients with non-pulmonary causes of death. Immunohistochemistry and image analysis were used to quantify, in the parenchyma and small airways, several immune cell markers.

Results

Both DAD groups had higher expression of neutrophils and macrophages in parenchyma and small airways. However, there was a higher expression of CD4+ and CD8+ T lymphocytes, CD83+ dendritic cells, granzyme A+ and natural killer + cell density in the lung parenchyma of the H1N1 group (p < 0.05). In the small airways, there was a lower cell density of tryptase + mast cells and dendritic + cells and an increase of IL-17 in both DAD groups (p < 0.05).

Conclusion

DAD due to viral A(H1N1)pdm09 is associated with a cytotoxic inflammatory phenotype, with partially divergent responses in the parenchyma relative to the small airways. In non-viral DAD, main immune cell alterations were found at the small airway level, reinforcing the role of the small airways in the pathogenesis of the exudative phase of DAD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-017-0630-x) contains supplementary material, which is available to authorized users.

Corticosteroids in ARDS: The Never-Ending Story

This feature examines the impact of pharmacologic interventions on the treatment of the critically ill patient — an area of health care that has become increasingly complex. Recent advances in drug therapy (including evolving and controversial data) for adult intensive-care-unit patients will be reviewed and assessed in terms of clinical, humanistic, and economic outcomes.

Lipopolysaccharide-induced endotoxemia in corn oil-preloaded mice causes an extended course of lung injury and repair and pulmonary fibrosis: A translational mouse model of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by acute hypoxemia respiratory failure, bilateral pulmonary infiltrates, and pulmonary edema of non-cardiac origin. Effective treatments for ARDS patients may arise from experimental studies with translational mouse models of this disease that aim to delineate the mechanisms underlying the disease pathogenesis. Mouse models of ARDS, however, can be limited by their rapid progression from injured to recovery state, which is in contrast to the course of ARDS in humans. Furthermore, current mouse models of ARDS do not recapitulate certain prominent aspects of the pathogenesis of ARDS in humans. In this study, we developed an improved endotoxemic mouse model of ARDS resembling many features of clinical ARDS including extended courses of injury and recovery as well as development of fibrosis following i.p. injection of lipopolysaccharide (LPS) to corn oil-preloaded mice. Compared with mice receiving LPS alone, those receiving corn oil and LPS exhibited extended course of lung injury and repair that occurred over a period of >2 weeks instead of 3–5days. Importantly, LPS challenge of corn oil-preloaded mice resulted in pulmonary fibrosis during the repair phase as often seen in ARDS patients. In summary, this simple novel mouse model of ARDS could represent a valuable experimental tool to elucidate mechanisms that regulate lung injury and repair in ARDS patients.

Mast cells and their activation in lung disease

Mast cells and their activation contribute to lung health via innate and adaptive immune responses to respiratory pathogens. They are also involved in the normal response to tissue injury. However, mast cells are involved in disease processes characterized by inflammation and remodeling of tissue structure. In these diseases mast cells are often inappropriately and chronically activated. There is evidence for activation of mast cells contributing to the pathophysiology of asthma, pulmonary fibrosis, and pulmonary hypertension. They may also play a role in chronic obstructive pulmonary disease, acute respiratory distress syndrome, and lung cancer. The diverse mechanisms through which mast cells sense and interact with the external and internal microenvironment account for their role in these diseases. Newly discovered mechanisms of redistribution and interaction between mast cells, airway structural cells, and other inflammatory cells may offer novel therapeutic targets in these disease processes.

Swine flu fibrosis: Regressive or progressive?

Swine flu influenza had spread the world over in 2009. The main pathology was bilateral pneumonia. Majority of these cases recovered from pneumonia fully. Though in some cases, pulmonary fibrosis was reported as a sequel. However, long-term progression of such pulmonary fibrosis is uncertain. We are hereby reporting two cases of swine flu that showed residual pulmonary fibrosis. The clinical and laboratory parameters were also recorded. In both the cases, radiological shadows and spirometric values did not show deterioration. We conclude that swine flu pulmonary fibrosis is not a progressive condition.

Mechanical Stress and the Induction of Lung Fibrosis via the Midkine Signaling Pathway

RATIONALE

Lung-protective ventilatory strategies have been widely used in patients with acute respiratory distress syndrome (ARDS), but the ARDS mortality rate remains unacceptably high and there is no proven pharmacologic therapy.

OBJECTIVES

Mechanical ventilation can induce oxidative stress and lung fibrosis, which may contribute to high dependency on ventilator support and increased ARDS mortality. We hypothesized that the novel cytokine, midkine (MK), which can be up-regulated in oxidative stress, plays a key role in the pathogenesis of ARDS-associated lung fibrosis.

METHODS

Blood samples were collected from 17 patients with ARDS and 10 healthy donors. Human lung epithelial cells were challenged with hydrogen chloride followed by mechanical stretch for 72 hours. Wild-type and MK gene-deficient (MK(-/-)) mice received two-hit injury of acid aspiration and mechanical ventilation, and were monitored for 14 days.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of MK were higher in patients with ARDS than in healthy volunteers. Exposure to mechanical stretch of lung epithelial cells led to an epithelial-mesenchymal transition profile associated with increased expression of angiotensin-converting enzyme, which was attenuated by silencing MK, its receptor Notch2, or NADP reduced oxidase 1. An increase in collagen deposition and hydroxyproline level and a decrease in lung tissue compliance seen in wild-type mice were largely attenuated in MK(-/-) mice.

CONCLUSIONS

Mechanical stretch can induce an epithelial-mesenchymal transition phenotype mediated by the MK-Notch2-angiotensin-converting enzyme signaling pathway, contributing to lung remodeling. The MK pathway is a potential therapeutic target in the context of ARDS-associated lung fibrosis.

Tryptase is involved in the development of early ventilator-induced pulmonary fibrosis in sepsis-induced lung injury

Introduction

Most patients with sepsis and acute lung injury require mechanical ventilation to improve oxygenation and facilitate organ repair. Mast cells are important in response to infection and resolution of tissue injury. Since tryptase secreted from mast cells has been associated with tissue fibrosis, we hypothesized that tryptase would be involved in the early development of ventilator-induced pulmonary fibrosis in a clinically relevant model of sepsis-induced lung injury.

Methods

Prospective, randomized, controlled animal study using Sprague-Dawley rats. Sepsis was induced by cecal ligation and perforation. Animals were randomized to spontaneous breathing or two ventilatory strategies for 4 h: protective ventilation with tidal volume (VT) = 6 ml/kg plus 10 cmH₂O positive end-expiratory pressure (PEEP) or injurious ventilation with VT = 20 ml/kg plus 2 cmH₂O PEEP. Healthy, non-ventilated animals served as non-septic controls. We studied the following end points: histology, serum cytokine levels, hydroxyproline content, tryptase and proteinase-activated receptor-2 (PAR-2) protein level in lung homogenates, and tryptase and PAR-2 immunohistochemical localization in the lungs.

Results

All septic animals developed acute lung injury. Animals ventilated with high VT had a significant increase of pulmonary fibrosis, hydroxyproline content, tryptase and PAR-2 protein levels compared to septic controls (P <0.0001). However, protective ventilation attenuated sepsis-induced lung injury and decreased lung tryptase and PAR-2 protein levels. Immunohistochemical staining confirmed the presence of tryptase and PAR-2 in the lungs.

Conclusions

Mechanical ventilation modified tryptase and PAR-2 in injured lungs. Increased levels of these proteins were associated with development of sepsis and ventilator-induced pulmonary fibrosis early in the course of sepsis-induced lung injury.

Sepsis-induced lung inflammation is modulated by insulin

BACKGROUND

We have previously shown that diabetic rats are more susceptible to sepsis, but that the Acute lung injury (ALI) secondary to sepsis is less intense than in non-diabetics. In the present study, we further investigated the ALI-secondary to sepsis in diabetic rats and the effect of insulin treatment.

METHODS

Diabetes was induced in male Wistar rats by alloxan and sepsis by cecal ligation and puncture surgery (CLP). Some diabetic rats were given neutral protamine Hagedorn (NPH) insulin (4 IU, s.c.) 2 h before CLP. Six h later, the lungs were examined for edema, cell infiltration and prostaglandin-E2 (PGE2) levels in the bronchoalveolar lavage (BAL).

RESULTS

The results confirmed that leukocyte infiltration and edema were milder in diabetic rats with sepsis. After insulin treatment, the lung inflammation in diabetics increased to levels comparable to the non-diabetics. The BAL concentration of PGE2 was also lower in diabetics with sepsis, and increased after insulin treatment. Sepsis was followed by early fibroblast activation in the lung parenchyma, evaluated by increased transforming growth factor (TGF)-β and smooth muscle actin (α-SMA) expression, as well as an elevated number of cells with myofibroblasts morphology. These events were significantly lower in diabetic rats and increased after insulin treatment.

CONCLUSION

The results show that insulin modulates the early phase of inflammation and myofibroblast differentiation in diabetic rats.

Activation of the renin-angiotensin system in hyperoxia-induced lung fibrosis in neonatal rats

BACKGROUND

Oxygen toxicity plays an important role in lung injury and may lead to bronchopulmonary dysplasia. We previously demonstrated that hyperoxia activated the renin-angiotensin system (RAS) in cultured human fetal lung fibroblasts.

OBJECTIVE

To examine whether the upregulation of RAS components is associated with hyperoxia-induced lung fibrosis in neonatal Sprague-Dawley rats.

METHODS

Experimental rat pups were exposed to 1 week of >95% O(2) and a further 2 weeks of 60% O(2). Control pups were exposed to room air over the same periods. Lung tissues were taken for biochemical and histochemical assays on postnatal days 7 and 21.

RESULTS

Hyperoxia significantly increased total collagen content and the expression of type I collagen and alpha smooth muscle actin when compared to control rats. RAS components including angiotensinogen, angiotensin-converting enzyme, angiotensin II, and angiotensin II type 1 receptor were significantly upregulated by hyperoxia. The results also demonstrated that only the extracellular signal-regulated kinase (ERK) signaling pathway was activated by hyperoxia exposure. p38 mitogen-activated protein kinase and c-Jun N-terminal kinase were not activated.

CONCLUSIONS

Local RAS activation is involved in the pathogenesis of hyperoxia-induced lung fibrosis in neonatal rats. ERK phosphorylation might mediate angiotensin II type 1 receptor activation.

Immune response CC chemokines CCL2 and CCL5 are associated with pulmonary sarcoidosis

Background

Pulmonary sarcoidosis involves an intense leukocyte infiltration of the lung with the formation of non-necrotizing granulomas. CC chemokines (chemokine (C-C motif) ligand 2 (CCL2)-CCL5) are chemoattractants of mononuclear cells and act through seven transmembrane G-coupled receptors. Previous studies have demonstrated conflicting results with regard to the associations of these chemokines with sarcoidosis. In an effort to clarify previous discrepancies, we performed the largest observational study to date of CC chemokines in bronchoalveolar lavage fluid (BALF) from patients with pulmonary sarcoidosis.

Results

BALF chemokine levels from 72 patients affected by pulmonary sarcoidosis were analyzed by enzyme-linked immunosorbent assay (ELISA) and compared to 8 healthy volunteers. BALF CCL3 and CCL4 levels from pulmonary sarcoidosis patients were not increased compared to controls. However, CCL2 and CCL5 levels were elevated, and subgroup analysis showed higher levels of both chemokines in all stages of pulmonary sarcoidosis. CCL2, CCL5, CC chemokine receptor type 1 (CCR1), CCR2 and CCR3 were expressed from mononuclear cells forming the lung granulomas, while CCR5 was only found on mast cells.

Conclusions

These data suggest that CCL2 and CCL5 are important mediators in recruiting CCR1, CCR2, and CCR3 expressing mononuclear cells as well as CCR5-expressing mast cells during all stages of pulmonary sarcoidosis.

Small airway remodeling in acute respiratory distress syndrome: a study in autopsy lung tissue

INTRODUCTION

Airway dysfunction in patients with the Acute Respiratory Distress Syndrome (ARDS) is evidenced by expiratory flow limitation and dynamic hyperinflation. These functional alterations have been attributed to closure/obstruction of small airways. Airway morphological changes have been reported in experimental models of acute lung injury, characterized by epithelial necrosis and denudation in distal airways. To date, however, no study has focused on the morphological airway changes in lungs from human subjects with ARDS. The aim of this study is to evaluate structural and inflammatory changes in distal airways in ARDS patients.

METHODS

We retrospectively studied autopsy lung tissue from subjects who died with ARDS and from control subjects who died of non pulmonary causes. Using image analysis, we quantified the extension of epithelial changes (normal, abnormal and denudated epithelium expressed as percentages of the total epithelium length), bronchiolar inflammation, airway wall thickness, and extracellular matrix (ECM) protein content in distal airways. The Student's t-test or the Mann-Whitney test was used to compare data between the ARDS and control groups. Bonferroni adjustments were used for multiple tests. The association between morphological and clinical data was analyzed by Pearson rank test.

RESULTS

Thirty-one ARDS patients (A: PaO2/FiO2 ≤200, 45 ± 14 years, 16 males) and 11 controls (C: 52 ± 16 years, 7 males) were included in the study. ARDS airways showed a shorter extension of normal epithelium (A:32.9 ± 27.2%, C:76.7 ± 32.7%, P < 0.001), a larger extension of epithelium denudation (A:52.6 ± 35.2%, C:21.8 ± 32.1%, P < 0.01), increased airway inflammation (A:1(3), C:0(1), P = 0.03), higher airway wall thickness (A:138.7 ± 54.3 μm, C:86.4 ± 33.3 μm, P < 0.01), and higher airway content of collagen I, fibronectin, versican and matrix metalloproteinase-9 (MMP-9) compared to controls (P ≤0.03). The extension of normal epithelium showed a positive correlation with PaO2/FiO2 (r2 = 0.34; P = 0.02) and a negative correlation with plateau pressure (r2 = 0.27; P = 0.04). The extension of denuded epithelium showed a negative correlation with PaO2/FiO2 (r2 = 0.27; P = 0.04).

CONCLUSIONS

Structural changes in small airways of patients with ARDS were characterized by epithelial denudation, inflammation and airway wall thickening with ECM remodeling. These changes are likely to contribute to functional airway changes in patients with ARDS.

Keratinocyte growth factor expression is suppressed in early acute lung injury/acute respiratory distress syndrome by smad and c-Abl pathways

OBJECTIVE

Keratinocyte growth factor (KGF) is expressed primarily by fibroblasts, is important for alveolar epithelial proliferation/function, and protects against lung injury in multiple animal models. We wished to determine whether acute lung injury/acute respiratory distress syndrome (ALI/ARDS) alveolar fluid induces KGF and fibroblast genes important for alveolar repair.

DESIGN

A single-center cohort study enrolling patients between 2004 and 2006.

SETTING

A medical intensive care unit of a tertiary care medical center.

PATIENTS

Adult patients meeting the American-European Consensus Conference definition of ALI/ARDS.

INTERVENTIONS

Patients with ALI/ARDS were enrolled, and lavage fluid was collected within 48 hours of intubation. Lavage fluid was also collected from two control cohorts. The patients with ALI/ARDS were followed for 28 days or until death.

MEASUREMENT AND MAIN RESULTS

Fifteen patients with ALI/ARDS, five patients with cardiogenic edema, and five normal lung parenchyma controls were enrolled from 2004 to 2006. Primary normal human lung fibroblasts were incubated with bronchoalveolar lavage fluid and assessed for KGF, connective tissue growth factor, alpha-smooth muscle actin, and collagen 1 expression by real-time reverse transcriptase-polymerase chain reaction. Fibroblasts incubated with ALI/ARDS lavage fluid expressed 50% less KGF messenger RNA than those incubated with lavage fluid from CE patients (p < 0.01) and 33% than normal parenchymal controls (p < 0.03). Lavage fluid from patients with ALI/ARDS induced more connective tissue growth factor (p < 0.05), collagen 1 (p < 0.03), and alpha-smooth muscle actin (p < 0.04) than from CE patients. Preincubation of normal human lung fibroblasts with the transforming growth factor (TGF)-beta1 receptor/smad phosphorylation inhibitor SB431542 increased ALI/ARDS-induced KGF expression by 40% (p < 0.04). In cultured human lung fibroblasts, TGF-beta1 suppressed KGF messenger RNA and protein expression, which were reversed by SB431542 and by the c-Abl inhibitor, imatinib mesylate, but not by the p38 map kinase inhibitor, SB203580.

CONCLUSIONS

ALI/ARDS alveolar fluid suppresses KGF expression, in part, due to TGF-beta1. TGF-beta1 suppression of KGF requires both smad phosphorylation and c-Abl activation.

What have anatomic and pathologic studies taught us about acute lung injury and acute respiratory distress syndrome?

PURPOSE OF REVIEW

Acute lung injury and acute respiratory distress syndrome are defined as morphologic and functional manifestations of pulmonary injury of various causes. Acute lung injury and acute respiratory distress syndrome may result from direct effects on epithelial lung cells or from indirect effects on endothelial lung cells, reflecting lung involvement as part of a more distant systemic inflammatory response. This review addresses anatomic/pathologic differences between acute lung injury and acute respiratory distress syndrome lungs.

RECENT FINDINGS

It is well established that acute lung injury and acute respiratory distress syndrome are characterized by local and intense inflammatory responses, with accumulation of several types of cells and soluble mediators. There are parallel anti-inflammatory response and lung remodeling, with deposition of collagen. Patient outcome will depend on resolution of the initial event and on the balance between the inflammatory and remodeling responses. Several trials have attempted to modify both responses, but all have yielded negative results.

SUMMARY

An appreciation of the acute respiratory distress syndrome must take into account anatomic/pathologic characteristics, which depend upon the initial cause. Consideration of each pathologic mechanism will permit more precise clinical management and probably improved outcomes.

Bronchoalveolar lavage fluid from patients with acute lung injury/acute respiratory distress syndrome induces myofibroblast differentiation

OBJECTIVE

Myofibroblasts express alpha-smooth muscle actin (alphaSMA), are important in tissue repair, and are present in the early phase of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). We wished to determine whether bronchoalveolar lavage fluid (BALF) from ALI/ARDS patients can induce myofibroblast differentiation and if this induction is associated with outcome.

DESIGN

A single-center cohort study enrolling patients between 2002 and 2005.

SETTING

Medical intensive care unit of a tertiary care medical center.

PATIENTS

Adult patients meeting the American-European Consensus Conference definition of ALI/ARDS.

INTERVENTIONS

BALF was collected from ALI/ARDS patients within 48 hrs of intubation and incubated with normal human lung fibroblasts in vitro, and alphaSMA expression was assessed by reverse transcription polymerase chain reaction. BALF was also collected and tested from negative control patients. ALI/ARDS patients were followed for 28 days or death.

MEASUREMENTS AND MAIN RESULTS

Thirty-one lung injury and 11 negative control patients were enrolled from 2002 to 2005. ALI/ ARDS BALF demonstrated potent alphaSMA induction with a mean value 92% greater than negative controls (34.5% +/- 7.6% vs. 18% +/- 2.4% of maximal transforming growth factor [TGF]-beta1 [5 ng/mL], p < .02). The specific TGF-beta1 receptor inhibitor SB431542 reduced ALI/ARDS BALF-stimulated alphaSMA induction by 52% (p < .005). There was no correlation between ALI/ARDS BALF-induced alphaSMA and procollagen 3 induction (r = -.08, p = .66). The odds ratio for survival was 6.75 (1.15-39.80) times higher for ALI/ARDS patients with alphaSMA induction between 15% and 75% of maximal TGF-beta1 induction (5 ng/mL) than outside this range.

CONCLUSIONS

ALI/ARDS BALF-induced myofibroblast differentiation is partially attributable to TGF-beta1. Procollagen 3 and alphaSMA are regulated by distinct mechanisms in ALI/ARDS and there may be an optimal level of myofibroblast induction that is associated with better outcome.

The alveolar-epithelial barrier: a target for potential therapy

During acute lung injury (ALI), the alveolar-capillary barrier is damaged, resulting in the accumulation of fluid and protein in the alveolar space characteristic of the acute respiratory distress syndrome (ARDS). Disordered epithelial repair may contribute to the development of fibrosis and worsen outcomes in patients who have lung injury. This article discusses novel emerging therapies based on these mechanisms that are designed to preserve the function and promote the repair of the alveolar epithelium in patients who have ALI/ARDS.

Marked stem cell factor expression in the airways of lung transplant recipients

BACKGROUND

Airways repair is critical to lung function following transplantation. We hypothesised that the stem cell factor (SCF) could play a role in this setting.

METHODS

We studied 9 lung transplant recipients (LTx recipients) during their first year postgraft, and evaluated SCF mRNA expression in bronchial biopsy specimens using on-line fluorescent PCR and SCF protein levels in bronchoalveolar lavage (BAL) and serum using ELISA. The expression of SCF receptor Kit was assessed using immunostaining of paraffin-embedded bronchial sections.

RESULTS

SCF mRNA was highly expressed during the early postgraft period [Month (M)1-M3] (300% increase vs controls: 356 vs 1.2 pg SCF/microg GAPDH cDNA, p < 0.001) and decreased thereafter (M4-M12: 187 pg/microg), although remaining at all times 10-100 times higher than in controls. While SCF protein levels in BAL were similar in LTx recipients and in controls, the SCF serum levels were at all times higher in LTx recipients than in controls (p < 0.05), with no relationship between these levels and the acute complications of the graft. Finally, Kit was strongly expressed by the mast cells as well as by the bronchial epithelium of LTx recipients.

CONCLUSION

SCF and Kit are expressed in bronchial biopsies from lung transplant recipients irrespective of the clinical status of the graft. A role for these factors in tissue repair following lung transplantation is hypothesised.

Constitutive activation of prosurvival signaling in alveolar mesenchymal cells isolated from patients with nonresolving acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a clinical syndrome characterized by stereotypic host inflammatory and repair cellular responses; however, mechanisms regulating the resolution of ARDS are poorly understood. Here, we report the isolation and characterization of a novel population of mesenchymal cells from the alveolar space of ARDS patients via fiber-optic bronchoscopy with bronchoalveolar lavage (BAL). BAL was performed on 17 patients during the course of ARDS. Immunofluorescence staining and multiparameter flow cytometric analysis defined a population of alveolar mesenchymal cells (AMCs) that are CD45-/prolyl-4-hydroxylase+/alpha-smooth muscle actin+/-. AMCs proliferated in ex vivo cell culture for multiple passages; early passage (3-5) cells were subsequently analyzed in 13 patients. AMCs isolated from patients with persistent or nonresolving ARDS (ARDS-NR, n = 4) demonstrate enhanced constitutive activation of prosurvival signaling pathways involving PKB/Akt, FKHR, and BCL-2 family proteins compared with AMCs from patients with resolving ARDS (ARDS-R, n = 9). Exogenous transforming growth factor-beta1 markedly induces PKB/Akt activation in AMCs from ARDS-R. ARDS-NR cells are more resistant to serum deprivation-induced apoptosis compared with ARDS-R. This study identifies a novel population of mesenchymal cells that can be isolated from the alveolar spaces of ARDS patients. AMCs in patients with ARDS-NR acquire an activational profile characterized by enhanced prosurvival signaling and an antiapoptotic phenotype. These findings support the concept that apoptosis of mesenchymal cells may be an essential component of normal repair and resolution of ARDS and suggest that dysregulation of this process may contribute to persistent ARDS.

c-Kit immunophenotyping and metalloproteinase expression profiles of mast cells in interstitial lung diseases

Diverse interstitial lung diseases (ILD) demonstrate mesenchymal infiltration by an abundance of activated mast cells whose role in parenchymal fibrogenesis remains unclear. Since mast cells differentiate in a dynamic, tissue-specific manner via signals transduced by c-Kit receptor, we examined the effect of ILD microenvironments on c-Kit expression and metalloproteinase phenotypes of mesenchymal mast cell populations. Immunohistochemical and flow cytometric analyses characterized surface expression of c-Kit on mast cells in tissues obtained from patients with idiopathic pulmonary fibrosis, systemic sclerosis, sarcoidosis, and lymphangioleiomyomatosis, thus identifying a unique immunophenotype not shared by normal lung mast cells. Isolation of c-Kit+/FcepsilonRI+/CD34- mast cells via immunocytometric sorting of heterogeneous cell populations from mechanically disaggregated lung tissues permitted analysis of gene expression patterns by two-step real-time polymerase chain reaction. Transcriptional profiling identified expression of c-Kit and the neutral serine proteases, tryptase and chymase, establishing the identity of sorted populations as mature mast cells. Mast cells harvested from ILD tissues demonstrated characteristic metalloproteinase phenotypes which included expression of matrix metalloproteinase (MMP)-1 and a disintegrin and metalloproteinase (ADAM)-9, -10, and -17. Immunohistochemical co-localization guided by gene profiling data confirmed expression of chymase, MMP-1, and ADAM-17 protein in subpopulations of mast cells in remodelling interstitium. Gene profiling of harvested mast cells also showed increased transcript copy numbers for TNFalpha and CC chemokine receptor 2, which play critical roles in lung injury. We conclude that ILD microenvironments induce unique c-Kit receptor and metalloproteinase mast cell phenotypes.

Role of mast cells in hepatic remodeling during cholestasis and its resolution: relevance to regulation of apoptosis

BACKGROUND/AIMS

Mast cells are thought to be related to fibrogenesis, but recent studies have shown that fibrosis of the liver can be induced even in mast cell-deficient rats. To clarify the significance of mast cell accumulation in cholestatic liver diseases, the relations between such accumulation, bile ductule proliferation and apoptosis of biliary epithelial cells were examined in the rats during cholestasis and its resolution.

METHODS

Cholestasis and its resolution were induced in rats by common bile duct ligation and spontaneous recanalization, respectively. The extent of bile ductule proliferation and the numbers of mast cells and apoptotic biliary epithelial cells were estimated quantitatively in liver sections.

RESULTS

Recanalization of the ligated common bile duct led to an abrupt and transient increase in the number of mast cells, although the number of proliferated bile ductules decreased rapidly. The number of apoptotic biliary epithelial cells of the proliferated bile ductules increased rapidly and transiently, and the change paralleled that of the mast cells.

CONCLUSIONS

Mast cells accumulating in the portal triads during cholestasis and its resolution may relate to the reduction of proliferated bile ductules, i.e., in hepatic remodeling, through the induction of apoptosis of biliary epithelial cells.

Time course of respiratory mechanics and pulmonary structural remodelling in acute lung injury

The aim of this study was to evaluate the time course of in vivo and in vitro respiratory mechanics and examine whether these parameters could reflect the temporal changes in lung parenchyma remodelling in paraquat (PQ)-induced lung injury. Measurements were done 1, 3 and 8 weeks after the intraperitoneal (i.p.) injection of saline (control) or paraquat (7mgkg(-1)) in rats. Airway and tissue resistances increased from control in PQ1 and PQ3 and returned to control values in PQ8, in accordance with the magnitude of bronchoconstriction. Viscoelastic/inhomogeneous pressure, tissue elastance, the number of polymorphonuclear cells, and collagen fibre content in lung parenchyma increased in PQ1 and remained elevated in PQ3 and PQ8. Static elastance increased in PQ1, returned to control values after 3 weeks, and was correlated with the volume fraction of collapsed alveoli. In conclusion, there is a restoration of normal alveolar-capillary lung units with a gradual improvement in airway and tissue resistances and static elastance. However, the on-going fibrotic process kept elevated tissue elastance and viscoelastic/inhomogeneous pressure.

Key role of mast cells and their major secretory products in inflammatory bowel disease

Historically, mast cells were known as a key cell type involved in type I hypersensitivity. Until last two decades, this cell type was recognized to be widely involved in a number of non-allergic diseases including inflammatory bowel disease (IBD). Markedly increased numbers of mast cells were observed in the mucosa of the ileum and colon of patients with IBD, which was accompanied by great changes of the content in mast cells such as dramatically increased expression of TNF-α, IL-16 and substance P. The evidence of mast cell degranulation was found in the wall of intestine from patients with IBD with immunohistochemistry technique. The highly elevated histamine and tryptase levels were detected in mucosa of patients with IBD, strongly suggesting that mast cell degranulation is involved in the pathogenesis of IBD. However, little is known of the actions of histamine, tryptase, chymase and carboxypeptidase in IBD. Over the last decade, heparin has been used to treat IBD in clinical practice. The low molecular weight heparin (LMWH) was effective as adjuvant therapy, and the patients showed good clinical and laboratory response with no serious adverse effects. The roles of PGD2, LTC4, PAF and mast cell cytokines in IBD were also discussed. Recently, a series of experiments with dispersed colon mast cells suggested there should be at least two pathways in man for mast cells to amplify their own activation-degranulation signals in an autocrine or paracrine manner. The hypothesis is that mast cell secretogogues induce mast cell degranulation, release histamine, then stimulate the adjacent mast cells or positively feedback to further stimulate its host mast cells through H₁ receptor. Whereas released tryptase acts similarly to histamine, but activates mast cells through its receptor PAR-2. The connections between current anti-IBD therapies or potential therapies for IBD with mast cells were discussed, implicating further that mast cell is a key cell type that is involved in the pathogenesis of IBD. In conclusion, while pathogenesis of IBD remains unclear, the key role of mast cells in this group of diseases demonstrated in the current review implicates strongly that IBD is a mast cell associated disease. Therefore, close attentions should be paid to the role of mast cells in IBD.

Effect of corticosteroid on lung parenchyma remodeling at an early phase of acute lung injury

In vivo (lung resistive and viscoelastic pressures and static elastance) and in vitro (tissue resistance, elastance, and hysteresivity) respiratory mechanics were analyzed 1 and 30 days after saline (control) or paraquat (P [10 and 25 mg/kg intraperitoneally]) injection in rats. Additionally, P10 and P25 were treated with methylprednisolone (2 mg/kg intravenously) at 1 or 6 hours after acute lung injury (ALI) induction. Collagen and elastic fibers were quantified. Lung resistive and viscoelastic pressures and static elastance were higher in P10 and P25 than in the control. Tissue elastance and resistance augmented from control to P10 (1 and 30 days) and P25. Hysteresivity increased in only P25. Methylprednisolone at 1 or 6 hours attenuated in vivo and in vitro mechanical changes in P25, whereas P10 parameters were similar to the control. Collagen increment was dose and time dependent. Elastic fibers increased in P25 and at 30 days in P10. Corticosteroid prevented collagen increment and avoided elastogenesis. In conclusion, methylprednisolone led to a complete maintenance of in vivo and in vitro respiratory mechanics in mild lesion, whereas it minimized the changes in tissue impedance and extracellular matrix in severe ALI. The beneficial effects of the early use of steroids in ALI remained unaltered at Day 30.

Acute respiratory distress syndrome: imaging of the injured lung

In patients with the acute respiratory distress syndrome (ARDS), there is non-specific but widespread exudation of oedema and inflammatory fluid into the lungs. The clinical corollary (dyspnoea, refractory hypoxia, reduced pulmonary compliance and diffuse pulmonary infiltrates) is catastrophic and generally associated with a poor outcome. Imaging is integral to the care of these critically ill patients on the intensive care unit. In the present review, the radiological changes on plain radiography and computed tomography (CT) in patients with ARDS are discussed. Particular attention is directed at the appearances on CT: the relationships between CT features, histopathological changes and the inevitable alterations in pulmonary physiology are explored.

Lung tissue mechanics and extracellular matrix remodeling in acute lung injury

This study was undertaken to test whether there is structural remodeling of lung parenchyma that could lead to tissue mechanical changes at an early phase of varying degrees of acute lung injury (ALI). Tissue resistance (R), dynamic elastance (E), and hysteresivity (eta) were analyzed during sinusoidal oscillations of rat lung parenchymal strips 24 h after intraperitoneal injection of saline (C) or paraquat (P [10, 15, 25, and 30 mg/kg]). These strips were also stained in order to quantify the amount of collagen and of three types of elastic fibers (elaunin, oxytalan, and fully developed elastic fibers) in the alveolar septa. E augmented progressively from C to P25, but the data from the P25 and P30 groups were not different (p < 0.0001). R and eta increased from C to P10 and from P15 to P25 (p < 0.001). Collagen fiber content increased exponentially with the severity of the injury. Elaunin and fully developed elastic fibers remained unchanged in the five groups, while oxytalan fibers increased only in the P25 and P30 groups. In conclusion, the pronounced mechanical changes at the tissue level and fibroelastogenesis happened at an early phase of the disease and even in mildly abnormal lung parenchyma.

KEYWORDS

elastance; collagen fibers; elastin; paraquat

Mast cell density and substance P-like immunoreactivity during the initiation and progression of lung lesions in ovine Mannheimia (Pasteurella) haemolytica pneumonia

To determine the density of mast cells (MCs) and the extent of substance P (SP) immunoreactivity during initiation and progression of pneumonic pasteurellosis (PP), 18 lambs were inoculated intrabronchially with Mannheimia (Pasteurella) haemolytica or saline, and lung tissue was collected at 1, 15 and 45 days post-inoculation (n=3, each group). Additionally, the left (non-inoculated) contralateral lungs in bacteria-inoculated animals were collected as controls. At 1 day after bacterial inoculation the lungs had typical M. haemolytica lesions. These pneumonic lesions had fewer numbers of MCs and reduced histamine content. Macrophages infiltrating some of the inflamed areas were strongly immunoreactive for SP. At 15 days, MCs remained scarce at sites where lung damage persisted, i.e. pyogranulomatous foci, but were increased in number in areas of interstitial damage. Pulmonary ganglion neurons were strongly immunoreactive for SP. By 45 days the fibrosing changes became more defined as pleural fibrosis, fibrosing alveolitis, alveolar epithelial hyperplasia and bronchiolitis obliterans. These lungs had increased numbers of MCs, but histamine content was not different from saline- and non-inoculated left lungs. Substance P immunoreactivity occurred only in nerves and was scarce and mild. This work demonstrates that MC density decreases initially with PP, but increases with progression of PP. SP fibres tend to be decreased during the initiation and at 45 days of PP, but other cells, such as macrophages and neuronal ganglion cells, produce substance P during progression of PP and thereby constitute an additional source of substance P.

Pulmonary pathology of acute respiratory distress syndrome

Lung morphology in ARDS reflects the rapid evolution from interstitial and alveolar edema to end-stage fibrosis consequent to injury of the alveolocapillary unit. This morphologic progression, termed diffuse alveolar damage, has been subdivided into sequentially occurring exudative, proliferative, and fibrotic phases. Pulmonary lesions correlate with the phase of alveolar damage rather than its specific cause. The pathologic features are consistent with the effects of a host of injurious stimuli and the complex interaction of inflammatory mediators on alveolar epithelial and capillary endothelial cells. Although ARDS frequently culminates in "interstitial" fibrosis, the organization of intraluminal exudate dominates the histologic picture in the proliferative phase and establishes the framework for subsequent fibrous remodeling of the lung. Involvement of the pulmonary vasculature is an important aspect of ARDS, from the initial phase of edema to the terminal stage of intractable pulmonary hypertension. Vascular lesions include thrombotic, fibroproliferative, and obliterative changes that, like the parenchymal lesions, correlate with the temporal phase of DAD. Although ARDS is characterized by extensive bilateral lung involvement, alveolar damage can also affect the lung in a localized fashion. RAD is associated with the same clinical risk factors as DAD, suggesting that there is a spectrum in the extent of lung involvement and disease severity in patients at risk for ARDS. The factors that govern which patients will develop the fulminant syndrome are poorly understood. It must be re-emphasized that the lung is stereotyped in its response to injury and, consequently, descriptive, or even quantitative, studies of lung morphology can only provide clues regarding the initiating factors and pathogenetic mechanisms of ARDS. Progress in understanding the pathogenesis of ARDS and development of rational approaches to therapy will ultimately depend on careful clinical and experimental studies and the application of immunohistochemical and molecular biology techniques to unravel basic mechanisms of cellular injury and response.

Mechanisms of repair and remodeling following acute lung injury

At present, we largely lack the ability to correlate the clinical course of ARDS patients with potential factors involved in the biochemical and cellular basis of lung repair. This requires very large patient databases with measurement of many biochemical parameters. Important mechanistic determinants during the repair phase can be sought by correlation with late outcomes, but a large-scale cooperative effort among multiple centers with sharing of follow-up data and patient specimens is essential. We also lack detailed human histologic material from many phases of ARDS and, particularly, know little of the long-term morphologic impact of ARDS in survivors. Establishment of a national registry that follows ARDS survivors and that would seek their cooperation in advance in obtaining autopsy specimens when they die of other causes would be very valuable. Correlating the pathology with their pulmonary function during recovery would give important insights into the reasons for the different patterns of abnormal pulmonary functions. The factors that determine the success of repair are of critical importance in testing new ARDS treatment strategies. Would accelerating the resolution of alveolar edema alter the course of subsequent fibrosis and inflammation? Does surfactant replacement therapy--a costly proposition in adults with ARDS--lead to better long-term outcomes in survivors? How much should we worry about the use of high levels of oxygen for support of arterial partial pressure of oxygen? Is it better to accept hyperoxia to avoid pressure or volume trauma induced by mechanical ventilation with higher minute ventilations? These major management issues all may affect the success of the late repair and recovery process. Intervention trials need to examine the long-term physiologic and functional outcomes.

Adult respiratory distress syndrome - an update

In adults, acute lung injury or adult respiratory distress syndrome (ARDS) may complicate a wide range of serious medical and surgical conditions, only some of which involve direct pulmonary insult. The characteristic histological feature of ARDS is an intense inflammatory process in the lungs, which may progress to fibrosis. The earliest physiological characteristic is an increase in the protein permeability across the endothelial and epithelial barriers of the lungs. This clinical syndrome is characterized by arterial hypoxaemia and bilateral radiographic infiltrates, which represent protein-rich oedema fluid. In addition there is a neutrophilic and macrophage infiltrate. Pulmonary endothelium is actively involved in the development of ARDS. It alters cell-cell adhesion as the initial step in leucocyte migration which, in turn, changes the permeability that allows protein-rich fluid to move into the interstitium. The quantity of this interstitial oedema may be sufficient to cause bulk flow through the epithelial barrier. There is probably independent epithelial injury. Finally, the endothelium can release and metabolize vasoactive and inflammatory substances, such as endothelins, nitric oxide and cytokines, etc. No single substance is responsible for acute lung injury, but rather a complex interplay exists between diverse pro- and anti-inflammatory mediators.