Keratinocyte growth factor pretreatment is associated with decreased macrophage inflammatory protein-2alpha concentrations and reduced neutrophil recruitment in acid aspiration lung injury

Mesenchymal stem cell-based therapy as a new therapeutic approach for acute inflammation

Acute inflammatory diseases such as acute colitis, kidney injury, liver failure, lung injury, myocardial infarction, pancreatitis, septic shock, and spinal cord injury are significant causes of death worldwide. Despite advances in the understanding of its pathophysiology, there are many restrictions in the treatment of these diseases, and new therapeutic approaches are required. Mesenchymal stem cell-based therapy due to immunomodulatory and regenerative properties is a promising candidate for acute inflammatory disease management. Based on preclinical results, mesenchymal stem cells and their-derived secretome improved immunological and clinical parameters. Furthermore, many clinical trials of acute kidney, liver, lung, myocardial, and spinal cord injury have yielded promising results. In this review, we try to provide a comprehensive view of mesenchymal stem cell-based therapy in acute inflammatory diseases as a new treatment approach.

12/15-Lipoxygenase Deficiency Impairs Neutrophil Granulopoiesis and Lung Proinflammatory Responses to Aspergillus fumigatus

Development of invasive aspergillosis correlates with impairments in innate immunity. We and others have recently shown that arachidonic acid metabolism pathways, specifically the cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) pathways, participate in the induction of protective innate immune responses during invasive aspergillosis. Based on the high degree of cooperation and interconnection within the eicosanoid network, we hypothesized that 12/15-LOX is also active during invasive aspergillosis. We report in this study that mice deficient in the gene encoding 12/15-LOX (Alox15) are profoundly susceptible to invasive aspergillosis. Decreased survival correlated with increased fungal burden and evidence of increased lung damage. These defects were associated with very early (6 and 12 h) 12/15-LOX-dependent inflammatory cytokine (IL-1α, IL-1β, and TNF-α) and chemokine (CCL3 and CCL4) production. Neutrophil levels in the lung were blunted in the absence of 12/15-LOX, although neutrophil antifungal activity was intact. However, lower neutrophil levels in the lungs of Alox15^−/− mice were not a result of impaired recruitment or survival; rather, Alox15^−/− mice demonstrated impaired neutrophil granulopoiesis in the bone marrow intrinsically and after fungal exposure. Employing a lower inoculum to allow for better survival allowed the identification of 12/15-LOX-dependent induction of IL-17A and IL-22. Impaired IL-17A and IL-22 production correlated with reduced invariant NKT cell numbers as well as lower IL-23 levels. Together, these data indicate that 12/15-LOX is a critical player in induction of the earliest aspects of the innate immune response to Aspergillus fumigatus.

ATRA reduces inflammation and improves alveolar epithelium regeneration in emphysematous rat lung

INTRODUCTION

Pulmonary emphysema characterized by alveolar wall destruction is resultant of persistent chronic inflammation. All-trans retinoic acid (ATRA) has been reported to reverse elastase-induced emphysema in rats. However, the underlying molecular mechanisms are so far unknown.

OBJECTIVE

To investigate the therapeutic potential effect of ATRA via the amelioration of the ERK/JAK-STAT pathways in the lungs of emphysematous rats.

METHODS

In silico analysis was done to find the binding efficiency of ATRA with receptor and ligands of ERK & JAK-STAT pathway. Emphysema was induced by porcine pancreatic elastase in Sprague-Dawley rats and ATRA was supplemented as therapy. Lungs were harvested for histopathological, genomics and proteomics analysis.

RESULTS AND DISCUSSION

In silico docking, analysis confirms that ATRA interferes with the normal binding of ligands (TNF-α, IL6ST) and receptors (TNFR1, IL6) of ERK/JAK-STAT pathways respectively. ATRA restored the histology, proteases/antiproteases balance, levels of inflammatory markers, antioxidants, expression of candidate genes of ERK and JAK-STAT pathways in the therapy group.

CONCLUSION

ATRA ameliorates ERK/JAK-STAT pathway in emphysema condition, resulting in alveolar epithelium regeneration. Hence, ATRA may prove to be a potential drug in the treatment of emphysema.

Role of Common γ-Chain Cytokines in Lung Interleukin-22 Regulation after Acute Exposure to Aspergillus fumigatus

Humans are constantly exposed to the opportunistic mold Aspergillus fumigatus, and disease caused by this pathogen is often determined by the magnitude of local and systemic immune responses. We have previously shown a protective role for interleukin-22 (IL-22) after acute A. fumigatus exposure. Here, employing IL-22^Cre R26R^eYFP reporter mice, we identified iNKT cells, γδ T cells, and type 3 innate lymphoid cells (ILC3s) as lung cell sources of IL-22 in response to acute A. fumigatus exposure. As these cells often utilize common γ-chain cytokines for their development or maintenance, we determined the role of IL-7, IL-21, and IL-15 in lung IL-22 induction and A. fumigatus lung clearance. We observed that IL-7, IL-21, and IL-15 were essential for, partially required for, or negatively regulated the production of IL-22, respectively. Deficiency in IL-7 and IL-21, but not IL-15R, resulted in impaired fungal clearance. Surprisingly, however, the absence of IL-7, IL-21, or IL-15R signaling had no effect on neutrophil recruitment. The levels of IL-1α, an essential anti-A. fumigatus proinflammatory cytokine, were increased in the absence of IL-7 and IL-15R but decreased in the absence of IL-21. IL-7 was responsible for maintaining lung iNKT cells and γδ T cells, whereas IL-21 was responsible for maintaining lung iNKT cells and ILC3s. In contrast, IL-15R deficiency had no effect on the absolute numbers of any IL-22 cell source, rather resulting in enhanced per cell production of IL-22 by iNKT cells and γδ T cells. Collectively, these results provide insight into how the IL-22 response in the lung is shaped after acute A. fumigatus exposure.

Murine model of oropharyngeal gastric fluid aspiration-A new assessment method for intrapulmonary liquid distribution using digital pixel calculation

AIM OF THE STUDY

The aim of this study was to investigate a new method for visualization and quantification of intrapulmonary liquid distribution after oropharyngeal gastric fluid aspiration in mice.

MATERIAL AND METHODS

Eleven mice received oropharyngeal aspiration with a gastric fluid, India ink, and saline solution. Digital imaging and pixel calculation were used to analyze intrapulmonary fluid distribution selectively.

RESULTS

Digital pixel analysis and orophanryngeal aspiration are both safe techniques in mice and deliver reproducible/valid results. Analysis revealed an average aspirate distribution of 86.8% of the total lung area. The proportional amount of the left lung was significantly greater than that of the right lung (P = 0.023). The lobe with the lowest mean distribution was the right lower lobe (79.2% ± 4.4%).

CONCLUSION

Digital pixel calculation is a reliable method for quantitative, macroscopic evaluation of fluid distribution in the lung. This method is a useful tool for training purposes and it can be used to ensure interinvestigator reproducibility.

IL-33 Signaling Regulates Innate IL-17A and IL-22 Production via Suppression of Prostaglandin E2 during Lung Fungal Infection

Members of the IL-1 family play protective and regulatory roles in immune defense against the opportunistic mold Aspergillus fumigatus In this study, we investigated the IL-1 family member IL-33 in lung defense against A. fumigatus IL-33 was detected in the naive lung, which further increased after exposure to A. fumigatus in a dectin-1-independent manner. Mice deficient in the receptor for IL-33 (Il1rl1-/-) unexpectedly demonstrated enhanced lung clearance of A. fumigatus IL-33 functioned as a negative regulator of multiple inflammatory cytokines, as IL-1α, IL-1β, IL-6, IL-17A, and IL-22 were significantly elevated in fungal-exposed Il1rl1-/- mice. Subsequently, IL-33 administration to normal mice attenuated fungal-induced IL-17A and IL-22, but not IL-1α, IL-1β, or IL-6, production. IL-33-mediated regulation of IL-17A and IL-22 did not involve the modulation of IL-23 but rather PGE2; PGE2 was significantly increased in fungal-exposed Il1rl1-/- mice, and normal mice produced less PGE2 after fungal exposure when administered IL-33, suggesting that IL-33-mediated regulation of IL-17A and IL-22 occurred at the level of PGE2 This was confirmed by in vivo cyclooxygenase 2 inhibition, which attenuated fungal-induced IL-17A and IL-22, as well as IL-1α, IL-1β, and IL-6, production in Il1rl1-/- mice, resulting in impaired fungal clearance. We also show that a PGE2 receptor agonist increased, whereas a PGE2 synthase inhibitor decreased, the levels of IL-17A and IL-22 but not IL-1α, IL-1β, or IL-6. This study establishes novel mechanisms of innate IL-17A/IL-22 production via PGE2 and regulation of the PGE2/IL-17A/IL-22 axis via IL-33 signaling during lung fungal exposure.

Keratinocyte growth factor-2 inhibits bacterial infection with Pseudomonas aeruginosa pneumonia in a mouse model

To determine protective effects of concurrent administration of Keratinocyte growth factor-2 (KGF-2) with Pseudomonas aeruginosa (P. aeruginosa) inoculation on the induced pneumonia. KGF-2 (5 mg/kg) was concurrently administered into the left lobe of 55 mice with P. aeruginosa PAO1 (5 × 10(6) CFU, half-lethal dose); 55 mice in the control group were concurrently administered PBS with the PAO1. We detected and analyzed: body temperature; amount of P. aeruginosa in homogenates; count of total number of nucleated cells and of mononuclear macrophages; protein concentration in bronchoalveolar lavage fluid (BALF); lung wet-to-dry weight ratio; cytokines in BALF and blood; and lung morphology. To study survival rate, concurrent administration of KGF-2 (experimental group) versus PBS (control) with a lethal dose of PAO1 (1 × 10(7) CFU was performed, and survivorship was documented for 7 days post-inoculation. The bacterial CFU in lung homogenates was significantly decreased in the KGF-2 group compared to the control group. There were significantly more mononuclear macrophages in the BALF from the KGF-2 group than from the control group (p < 0.05). KGF-2 increased the surfactant protein and GM-CSF mRNA in lung at 6 h and 72 h after inoculation. Significant reduction of lung injury scores, protein concentrations, lung wet-to-dry weight ratio, and IL-6 and TNF-α levels was noted in the KGF-2 treated rats at 72 h after inoculation (p < 0.05). The 7-day survival rate of the KGF-2 group was significantly higher than that of the control group (p < 0.05). Concurrent administration of KGF-2 facilitates the clearance of P. aeruginosa from the lungs, attenuates P. aeruginosa-induced lung injury, and extends the 7-day survival rate in mice model with P. aeruginosa pneumonia.

Bayesian network analysis of multi-compartmentalized immune responses in a murine model of sepsis and direct lung injury

Background

Inflammatory disease processes involve complex and interrelated systems of mediators. Determining the causal relationships among these mediators becomes more complicated when two, concurrent inflammatory conditions occur. In those cases, the outcome may also be dependent upon the timing, severity and compartmentalization of the insults. Unfortunately, standard methods of experimentation and analysis of data sets may investigate a single scenario without uncovering many potential associations among mediators. However, Bayesian network analysis is able to model linear, nonlinear, combinatorial, and stochastic relationships among variables to explore complex inflammatory disease systems. In these studies, we modeled the development of acute lung injury from an indirect insult (sepsis induced by cecal ligation and puncture) complicated by a direct lung insult (aspiration). To replicate multiple clinical situations, the aspiration injury was delivered at different severities and at different time intervals relative to the septic insult. For each scenario, we measured numerous inflammatory cell types and cytokines in samples from the local compartments (peritoneal and bronchoalveolar lavage fluids) and the systemic compartment (plasma). We then analyzed these data by Bayesian networks and standard methods.

Results

Standard data analysis demonstrated that the lung injury was actually reduced when two insults were involved as compared to one lung injury alone. Bayesian network analysis determined that both the severity of lung insult and presence of sepsis influenced neutrophil recruitment and the amount of injury to the lung. However, the levels of chemoattractant cytokines responsible for neutrophil recruitment were more strongly linked to the timing and severity of the lung insult compared to the presence of sepsis. This suggests that something other than sepsis-driven exacerbation of chemokine levels was influencing the lung injury, contrary to previous theories.

Conclusions

To our knowledge, these studies are the first to use Bayesian networks together with experimental studies to examine the pathogenesis of sepsis-associated lung injury. Compared to standard statistical analysis and inference, these analyses elucidated more intricate relationships among the mediators, immune cells and insult-related variables (timing, compartmentalization and severity) that cause lung injury. Bayesian networks are an effective tool for evaluating complex models of inflammation.

Keratinocyte growth factor promotes epithelial survival and resolution in a human model of lung injury

RATIONALE

Increasing epithelial repair and regeneration may hasten resolution of lung injury in patients with the acute respiratory distress syndrome (ARDS). In animal models of ARDS, keratinocyte growth factor (KGF) reduces injury and increases epithelial proliferation and repair. The effect of KGF in the human alveolus is unknown.

OBJECTIVES

To test whether KGF can attenuate alveolar injury in a human model of ARDS.

METHODS

Volunteers were randomized to intravenous KGF (60 μg/kg) or placebo for 3 days, before inhaling 50 μg LPS. Six hours later, subjects underwent bronchoalveolar lavage (BAL) to quantify markers of alveolar inflammation and cell-specific injury.

MEASUREMENTS AND MAIN RESULTS

KGF did not alter leukocyte infiltration or markers of permeability in response to LPS. KGF increased BAL concentrations of surfactant protein D, matrix metalloproteinase (MMP)-9, IL-1Ra, granulocyte-macrophage colony-stimulating factor (GM-CSF), and C-reactive protein. In vitro, BAL fluid from KGF-treated subjects inhibited pulmonary fibroblast proliferation, but increased alveolar epithelial proliferation. Active MMP-9 increased alveolar epithelial wound repair. Finally, BAL from the KGF-pretreated group enhanced macrophage phagocytic uptake of apoptotic epithelial cells and bacteria compared with BAL from the placebo-treated group. This effect was blocked by inhibiting activation of the GM-CSF receptor.

CONCLUSIONS

KGF treatment increases BAL surfactant protein D, a marker of type II alveolar epithelial cell proliferation in a human model of acute lung injury. Additionally, KGF increases alveolar concentrations of the antiinflammatory cytokine IL-1Ra, and mediators that drive epithelial repair (MMP-9) and enhance macrophage clearance of dead cells and bacteria (GM-CSF). Clinical trial registered with ISRCTN 98813895.

Recombinant Human Keratinocyte Growth Factor Induces Akt Mediated Cell Survival Progression in Emphysematous Mice

INTRODUCTION

Emphysema has been associated with decreased VEGF and VEGFR-2 expression and the presence of high numbers of apoptotic alveolar cells. Keratinocyte growth factor stimulates VEGF synthesis which in turn confers normal lung structure maintenance via the Akt pathway. In this study the potential role of rHuKGF in the improvement of deregulated Akt mediated cell survival pathway in emphysematous mice was investigated.

METHODS

Three experimental groups, i.e., emphysema, treatment and control groups, were prepared. Lungs of mice were treated on 3 occasions by oropharyngeal instillation of 10mg rHuKGF per kg body weight after induction of emphysema with porcine pancreatic elastase. Subsequently, lung tissues from mice were collected for histopathology and molecular biology studies.

RESULTS AND DISCUSSION

Histopathology photomicrographs and destructive index analysis have shown that elastase-induced airspace enlargement and loss of alveoli recovered in the treatment group. rHuKGF stimulates VEGF production which in turn induces the Akt mediated cell survival pathway in emphysematous lungs. mRNA expression of VEGF, VEGFR, PI3K and Akt was significantly increased while Pten, Caspase-9 and Bad was notably decreased in treatment group when compared with emphysema group, being comparable with the control group. Moreover, VEGF protein expression was in accordance with that found for mRNA.

CONCLUSION

Therapeutic rHuKGF supplementation improves the deregulated Akt pathway in emphysema, resulting in alveolar cell survival through activation of the endogenous VEGF-dependent cell survival pathway. Hence rHuKGF may prove to be a potential drug in the treatment of emphysema.

Palifermin for the protection and regeneration of epithelial tissues following injury: new findings in basic research and pre-clinical models

Keratinocyte growth factor (KGF) is a paracrine-acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre-clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre-clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre-clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin.

Eosinophil deficiency compromises lung defense against Aspergillus fumigatus

Exposure to the mold Aspergillus fumigatus may result in allergic bronchopulmonary aspergillosis, chronic necrotizing pulmonary aspergillosis, or invasive aspergillosis (IA), depending on the host's immune status. Neutrophil deficiency is the predominant risk factor for the development of IA, the most life-threatening condition associated with A. fumigatus exposure. Here we demonstrate that in addition to neutrophils, eosinophils are an important contributor to the clearance of A. fumigatus from the lung. Acute A. fumigatus challenge in normal mice induced the recruitment of CD11b+ Siglec F+ Ly-6G(lo) Ly-6C(neg) CCR3+ eosinophils to the lungs, which was accompanied by an increase in lung Epx (eosinophil peroxidase) mRNA levels. Mice deficient in the transcription factor dblGATA1, which exhibit a selective deficiency in eosinophils, demonstrated impaired A. fumigatus clearance and evidence of germinating organisms in the lung. Higher burden correlated with lower mRNA expression of Epx (eosinophil peroxidase) and Prg2 (major basic protein) as well as lower interleukin 1β (IL-1β), IL-6, IL-17A, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), and CXCL1 levels. However, examination of lung inflammatory cell populations failed to demonstrate defects in monocyte/macrophage, dendritic cell, or neutrophil recruitment in dblGATA1-deficient mice, suggesting that the absence of eosinophils in dlbGATA1-deficient mice was the sole cause of impaired lung clearance. We show that eosinophils generated from bone marrow have potent killing activity against A. fumigtaus in vitro, which does not require cell contact and can be recapitulated by eosinophil whole-cell lysates. Collectively, our data support a role for eosinophils in the lung response after A. fumigatus exposure.

Paracrine factors from mesenchymal stem cells: a proposed therapeutic tool for acute lung injury and acute respiratory distress syndrome

Despite extensive researches in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), current pharmacological therapies and respiratory support are still the main methods to treat patients with ALI and ARDS and the effects remain limited. Hence, innovative therapies are needed to decrease the morbidity and mortality. Because of the proven therapeutic effects in other fields, mesenchymal stem cells (MSCs) might be considered as a promising alternative to treat ALI and ARDS. Numerous documents demonstrate that MSCs can exert multiple functions, such as engraftment, differentiation and immunoregulation, but now the key researches are concentrated on paracrine factors secreted by MSCs that can mediate endothelial and epithelial permeability, increase alveolar fluid clearance and other potential mechanisms. This review aimed to review the current researches in terms of the effects of MSCs on ALI and ARDS and to analyse these paracrine factors, as well as to predict the potential directions and challenges of the application in this field.

Chlorine gas exposure increases susceptibility to invasive lung fungal infection

Chlorine (Cl₂) is a highly irritating and reactive gas with potential occupational and environmental hazards. Acute exposure to Cl₂ induces severe epithelial damage, airway hyperreactivity, impaired alveolar fluid clearance, and pulmonary edema in the presence of heightened inflammation and significant neutrophil accumulation in the lungs. Herein, we investigated whether Cl₂ exposure affected the lung antimicrobial immune response leading to increased susceptibility to opportunistic infections. Mice exposed to Cl₂ and challenged intratracheally 24 h thereafter with the opportunistic mold Aspergillus fumigatus demonstrated an >500-fold increase in A. fumigatus lung burden 72 h postchallenge compared with A. fumigatus mice exposed to room air. Cl₂-exposed A. fumigatus challenged mice also demonstrated significantly higher lung resistance following methacholine challenge and increased levels of plasma proteins (albumin and IgG) in the bronchoalveolar lavage fluid. Despite enhanced recruitment of inflammatory cells to the lungs of Cl₂-exposed A. fumigatus challenged mice, these cells (>60% of which were neutrophils) demonstrated a profound impairment in generating superoxide. Significantly higher A. fumigatus burden in the lungs of Cl₂ exposed mice correlated with enhanced production of IL-6, TNF-α, CXCL1, CCL2, and CCL3. Surprisingly, however, Cl₂-exposed A. fumigatus challenged mice had a specific impairment in the production of IL-17A and IL-22 in the lungs compared with mice exposed to room air and challenged with A. fumigatus. In summary, our results indicate that Cl₂ exposure markedly impairs the antimicrobial activity and inflammatory reactivity of myeloid cells in the lung leading to increased susceptibility to opportunistic pathogens.

Therapeutic effects of human mesenchymal stem cells in ex vivo human lungs injured with live bacteria

RATIONALE

Mesenchymal stem cells secrete paracrine factors that can regulate lung permeability and decrease inflammation, making it a potentially attractive therapy for acute lung injury. However, concerns exist whether mesenchymal stem cells' immunomodulatory properties may have detrimental effects if targeted toward infectious causes of lung injury.

OBJECTIVES

Therefore, we tested the effect of mesenchymal stem cells on lung fluid balance, acute inflammation, and bacterial clearance.

METHODS

We developed an Escherichia coli pneumonia model in our ex vivo perfused human lung to test the therapeutic effects of mesenchymal stem cells on bacterial-induced acute lung injury.

MEASUREMENTS AND MAIN RESULTS

Clinical-grade human mesenchymal stem cells restored alveolar fluid clearance to a normal level, decreased inflammation, and were associated with increased bacterial killing and reduced bacteremia, in part through increased alveolar macrophage phagocytosis and secretion of antimicrobial factors. Keratinocyte growth factor, a soluble factor secreted by mesenchymal stem cells, duplicated most of the antimicrobial effects. In subsequent in vitro studies, we discovered that human monocytes expressed the keratinocyte growth factor receptor, and that keratinocyte growth factor decreased apoptosis of human monocytes through AKT phosphorylation, an effect that increased bacterial clearance. Inhibition of keratinocyte growth factor by a neutralizing antibody reduced the antimicrobial effects of mesenchymal stem cells in the ex vivo perfused human lung and monocytes grown in vitro injured with E. coli bacteria.

CONCLUSIONS

In E. coli-injured human lungs, mesenchymal stem cells restored alveolar fluid clearance, reduced inflammation, and exerted antimicrobial activity, in part through keratinocyte growth factor secretion.

Therapeutic potential of growth factors in pulmonary emphysematous condition

Pulmonary emphysema is a major manifestation of chronic obstructive pulmonary disease (COPD), which is characterized by progressive destruction of alveolar parenchyma with persistent inflammation of the small airways. Such destruction in the distal respiratory tract is irreversible and irreparable. All-trans-retinoic acid was suggested as a novel therapy for regeneration of lost alveoli in emphysema. However, profound discrepancies were evident between studies. At present, no effective therapeutic options are available that allow for the regeneration of lost alveoli in emphysematous human lungs. Recently, some reports on rodent's models have suggested the beneficial effects of various growth factors toward alveolar maintenance and repair processes.

Dissecting paracrine effectors for mesenchymal stem cells

There has been increasing interest in the application of mesenchymal stem cells (MSCs) in regenerative medicine in recent years. In this context, the beneficial effects of MSCs have been ascribed mainly to a paracrine action rather than to direct replacement of the injured tissue. Indeed, MSCs produce a great variety of trophic and immunomodulatory factors. In this chapter, we provide an overview of growth factors and chemokines involved in stimulation of cell proliferation, inhibition of apoptosis, enhancement of angiogenesis, and suppression of inflammatory and immune response. In addition, we discuss the emerging role of the extracellular vesicles released from MSCs as possible paracrine mediators.

Concise review: Mesenchymal stem cells for acute lung injury: role of paracrine soluble factors

Morbidity and mortality have declined only modestly in patients with clinical acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), despite extensive research into the pathophysiology. Current treatment remains primarily supportive with lung-protective ventilation and a fluid conservative strategy. Pharmacologic therapies that reduce the severity of lung injury in preclinical models have not yet been translated to effective clinical treatment options. Consequently, further research in translational therapies is needed. Cell-based therapy with mesenchymal stem cells (MSCs) is one attractive new therapeutic approach. MSCs have the capacity to secrete multiple paracrine factors that can regulate endothelial and epithelial permeability, decrease inflammation, enhance tissue repair, and inhibit bacterial growth. This review will focus on recent studies, which support the potential therapeutic use of MSCs in ALI/ARDS, with an emphasis on the role of paracrine soluble factors.

Keratinocyte Growth Factor Stimulates Macrophage Inflammatory Protein 3α and Keratinocyte-derived Chemokine Secretion by Mouse Uterine Epithelial Cells

PROBLEM

communication between uterine epithelial cells and the underlying stromal fibroblasts is critical for proper endometrial function. Stromal fibroblast-derived growth factors have been shown to regulate epithelial immune functions. The purpose of this study was to determine whether keratinocyte growth factor (KGF) regulates uterine epithelial cell chemokine and antimicrobial secretion.

METHOD OF STUDY

uterine epithelial cells were isolated from Balb/c mice and cultured in either 96-well plates or transwell inserts. Epithelial cells were treated with KGF, epidermal growth factor (EGF), or hepatocyte growth factor (HGF). Macrophage inflammatory protein 3α (MIP3α) and keratinocyte-derived chemokine (KC) levels were measured by ELISA.

RESULTS

keratinocyte growth factor stimulated the secretion of MIP3α and KC. The effects on MIP3α by KGF were specific because EGF and HGF had no effect. In contrast, KGF, EGF, and HGF had similar effects on KC. Furthermore, KGF administered to the apical side of epithelial cells had no effect on MIP3α or KC secretion, indicating that the KGF receptor is located on the basolateral surface of uterine epithelial cells.

CONCLUSION

we demonstrate that KGF plays a role in uterine epithelial cell secretion of MIP3α and KC, key immune mediators involved in the protection of mucosal surfaces in the female reproductive tract.

Chronic pulmonary LPS tolerance induces selective immunosuppression while maintaining the neutrophilic response

LPS challenge causes potent activation of innate immunity. Because LPS is ubiquitously present in ambient air, repeated inhalation may lead to activation of the pulmonary immune response. If this activation is unregulated, chronic LPS inhalation would lead to persistent inflammation and organ damage. We hypothesized that the lung uses the mechanism of LPS tolerance to maintain the balance between hypoinflammatory and hyperinflammatory states. We developed a model of chronic pulmonary LPS tolerance induced by pulmonary exposure to 1 microg LPS for 4 consecutive days. Mice were challenged with 10 microg of LPS 24 h later. TNF-alpha protein was significantly decreased in the bronchoalveolar lavage fluid of tolerant versus nontolerant mice, whereas IL-6 levels were significantly increased in the tolerant group. Tolerant mice were also protected from airway hyperresponsiveness. M2 and M3 muscarinic receptor mRNA was significantly decreased in the lungs of tolerant mice, suggesting a mechanism for the decreased airway hyperresponsiveness. CXCL2 was significantly reduced in tolerant mice, but CXCL1 was equivalent between groups. No difference was seen in neutrophil recruitment to the alveolar space. Interestingly, LPS tolerance does not confer cross-tolerance to the Toll-like receptor (TLR) 2 stimulus Pam3Cys. TNF-alpha and IL-6 concentrations were significantly increased in LPS-tolerant mice challenged with Pam3Cys; however, chemokine concentrations were unaffected. Our data show that repeated LPS inhalation results in differential regulation of cytokines but does not inhibit neutrophil recruitment. This unrestricted neutrophil recruitment may represent a mechanism by which individuals may be protected from pulmonary bacterial infection and pneumonia.

Francisella tularensis DeltapyrF mutants show that replication in nonmacrophages is sufficient for pathogenesis in vivo

The pathogenesis of Francisella tularensis has been associated with this bacterium's ability to replicate within macrophages. F. tularensis can also invade and replicate in a variety of nonphagocytic host cells, including lung and kidney epithelial cells and hepatocytes. As uracil biosynthesis is a central metabolic pathway usually necessary for pathogens, we characterized DeltapyrF mutants of both F. tularensis LVS and Schu S4 to investigate the role of these mutants in intracellular growth. As expected, these mutant strains were deficient in de novo pyrimidine biosynthesis and were resistant to 5-fluoroorotic acid, which is converted to a toxic product by functional PyrF. The F. tularensis DeltapyrF mutants could not replicate in primary human macrophages. The inability to replicate in macrophages suggested that the F. tularensis DeltapyrF strains would be attenuated in animal infection models. Surprisingly, these mutants retained virulence during infection of chicken embryos and in the murine model of pneumonic tularemia. We hypothesized that the F. tularensis DeltapyrF strains may replicate in cells other than macrophages to account for their virulence. In support of this, F. tularensis DeltapyrF mutants replicated in HEK-293 cells and normal human fibroblasts in vitro. Moreover, immunofluorescence microscopy showed abundant staining of wild-type and mutant bacteria in nonmacrophage cells in the lungs of infected mice. These findings indicate that replication in nonmacrophages contributes to the pathogenesis of F. tularensis.

Functional contribution of CXCR2 to lung injury after aspiration of acid and gastric particulates

The effects of individual ELR+ CXC chemokines have been documented in experimental models of acid aspiration. However, aspiration lung injury would be influenced by the combined effects of these chemokines and other factors related to their function. Therefore, the role of the chemokine receptor CXCR2 was examined in lung injury induced by aspiration of acid and acid with gastric particulates. Anesthetized mice were given intratracheal injections of saline, acid solution, or acid containing gastric particles. Within 6 h, bronchoalveolar lavage fluid neutrophils and albumin increased relative to the severity of the insult. Immunohistochemistry and RT-PCR demonstrated striking increases in pulmonary expression of CXCR2 after aspiration. In CXCR2-deficient mice, neutrophil recruitment to airways was significantly reduced after aspiration of either acid or acid with particles. However, lung injury scores were unaffected in Ccr2-/- mice in the acid + particles group. Esterase-stained lung tissue demonstrated that focal aggregates of inflammatory cells contained neutrophils in the Ccr2-/- mice. These studies suggest CXCR2 and its ligands are dominant mediators of neutrophil recruitment to airways after aspiration. However, CXCR2-independent mechanisms recruit neutrophils into areas of cellular aggregation after aspiration of acidified gastric particulates.

Potential application of mesenchymal stem cells in acute lung injury

Despite extensive research into the pathogenesis of acute lung injury and the acute respiratory distress syndrome (ALI/ARDS), mortality remains high at approximately 40%. Current treatment is primarily supportive, with lung-protective ventilation and a fluid conservative strategy. Pharmacologic therapies that reduce the severity of lung injury in experimental studies have not yet been translated into effective clinical treatment options. Therefore, innovative therapies are needed. Recent studies have suggested that bone-marrow-derived multipotent mesenchymal stem cells (MSC) may have therapeutic applications in multiple clinical disorders including myocardial infarction, diabetes, sepsis, hepatic and acute renal failure. Recently, MSC have been studied in several in vivo models of lung disease. This review focuses on first describing the existing experimental literature that has tested the use of MSC in models of ALI/ARDS, and then the potential mechanisms underlying their therapeutic use with an emphasis on secreted paracrine soluble factors. The review concludes with a discussion of future research directions required for potential clinical trials.

Pulmonary effects of keratinocyte growth factor in newborn rats exposed to hyperoxia

Acute lung injury and compromised alveolar development characterize bronchopulmonary dysplasia (BPD) of the premature neonate. High levels of keratinocyte growth factor (KGF), a cell-cell mediator with pleiotrophic lung effects, are associated with low BPD risk. KGF decreases mortality in hyperoxia-exposed newborn rodents, a classic model of injury-induced impaired alveolarization, although the pulmonary mechanisms of this protection are poorly defined. These were explored through in vitro and in vivo approaches in the rat. Hyperoxia decreased by 30% the rate of wound closure of a monolayer of fetal alveolar epithelial cells, due to cell death, which was overcome by recombinant human KGF (100 ng/ml). In rat pups exposed to >95% O2 from birth, increased viability induced by intraperitoneal injection of KGF (2 microg/g body wt) every other day was associated with prevention of neutrophil influx in bronchoalveolar lavage (BAL), prevention of decreases in whole lung DNA content and cell proliferation rate, partial prevention of apoptosis increase, and a markedly increased proportion of surfactant protein B-immunoreactive cells in lung parenchyma. Increased lung antioxidant capacity is likely to be due in part to enhanced CAAT/enhancer binding protein alpha expression. By contrast, KGF neither corrected changes induced by hyperoxia in parameters of lung morphometry that clearly indicated impaired alveolarization nor had any significant effect on tissue or BAL surfactant phospholipids. These findings evidence KGF alveolar epithelial cell protection, enhancing effects on alveolar repair capacity, and anti-inflammatory effects in the injured neonatal lung that may account, at least in part, for its ability to reduce mortality. They argue in favor of a therapeutic potential of KGF in the injured neonatal lung.

Local and systemic chemokine patterns in a human musculoskeletal trauma model

OBJECTIVE AND DESIGN

This prospective study aims to identify differences in local and systemic chemokines kinetics within 24 h of a standardised human surgical trauma (total hip arthroplasty) and their impact on systemic polymorphonuclear cells.

MATERIALS AND METHODS

We examined seven patients with coxarthrosis, but without comorbidity, who had a total hip arthroplasty. Local drained blood and systemic blood samples were collected at wound closure and at 1, 4, and 24 h after surgery. Chemokines were measured using a multiplex antibody bead kit. Venous whole blood cell counts were taken at the same points in time.

RESULTS

There is a significant postoperative local burst of CCL2 and CXCL8 while systemic levels stay unchanged. The systemic levels of CCL3, CCL4, CCL5, CCL11, CXCL9, and CXCL10 were significantly reduced at 24 h post-surgery, but local levels remain unchanged or had only modest changes. There was a significant postoperative rise in monocytes and neutrophils.

CONCLUSION

There is fundamental difference between local and systemic chemokine kinetics in the human trauma model studied. High postoperative concentrations of CCL2 and CXCL8 at the site of inflammation form a gradient that contributes to the recruitment of neutrophils and monocytes at the trauma site.

Acute pulmonary lipopolysaccharide tolerance decreases TNF-alpha without reducing neutrophil recruitment

Pulmonary LPS exposure plays a key role in exacerbation of lung diseases such as chronic obstructive pulmonary disease and asthma. However, little is known about the effects of repeated LPS exposure in the lung microenvironment. We have developed a novel murine model of pulmonary LPS tolerance induced by intratracheal (i.t.) administration of LPS. First, we show that pulmonary LPS exposure does not induce whole-body refractoriness to systemic LPS, because i.t. administration followed by i.p. administration did not decrease plasma TNF-alpha. However, a local refractory state can be induced with two i.t. LPS exposures. Pulmonary LPS tolerance was induced by i.t. administration of 100 ng LPS at time 0 and 48 h. Nontolerant mice received PBS at time 0 and LPS at 48 h. Bronchoalveolar lavage levels of TNF-alpha were significantly attenuated in tolerant mice vs nontolerant mice (1597 pg/ml vs 7261 pg/ml). TNF-alpha mRNA was significantly reduced in bronchoalveolar lavage cells (5-fold) and lung tissue (10-fold). No reduction was seen in neutrophil numbers in the bronchoalveolar lavage fluid, myeloperoxidase activity, or expression of neutrophil chemoattractants CXCL1 and CXCL2, reflecting the specificity of the response. The reduction in TNF-alpha was accompanied by a significant increase in soluble receptors, TNF-SRI (159 pg/ml vs 206 pg/ml) and TNF-SRII (1366 pg/m vs 2695 pg/ml). In conclusion, pulmonary LPS tolerance results in a specific reduction in TNF-alpha expression, while the neutrophilic response is unaffected. This response may be a mechanism to limit tissue damage by reducing TNF-alpha levels, while still maintaining the antimicrobial capacity of the lung.

Low-dose carbon monoxide treatment attenuates early pulmonary neutrophil recruitment after acid aspiration

Exogenous carbon monoxide (CO) has anti-inflammatory and cytoprotective properties that show promise in the treatment of numerous pulmonary diseases. However, the effectiveness of CO in acute pulmonary injury associated with direct lung insult has not been shown conclusively. The purpose of this study was to determine if exogenous CO would modulate the pulmonary inflammation and lung injury that develops after acid aspiration. Groups of mice were given intratracheal (IT) injections of either saline or an acidic solution. After the IT injection, some of the mice in each group were allowed to spontaneously inhale CO (500 ppm). Mice exposed to CO for 6 h after IT acid had a significant decrease in bronchoalveolar lavage (BAL) fluid neutrophil counts and in histological evidence of lung injury. These results could not be explained by changes in BAL fluid chemokine levels or altered CXCR2 expression. The reduced neutrophil recruitment was associated with a decrease in the percentage of peripheral blood neutrophils expressing CD11b protein. However, within 24 h, the BAL neutrophil counts increased and were not different from animals without CO exposure. In addition, indices of vascular integrity were not different between animals with acid aspiration regardless of CO exposure at the later time point. These results showed that CO can modulate the early development of acute lung inflammation in this model of acid aspiration. Although these effects were eventually overwhelmed, the results suggest that CO may have efficacy during the initial treatment of aspiration lung injury.

Keratinocyte-derived chemokine plays a critical role in the induction of systemic inflammation and tissue damage after trauma-hemorrhage

Neutrophil infiltration is a crucial step in the development of organ dysfunction after trauma. We have previously shown that keratinocyte-derived chemokine (KC), a chemoattractant for neutrophils, is up-regulated after trauma-hemorrhage. To determine the role of KC after trauma-hemorrhage, the effect of a KC-neutralizing antibody on the posttraumatic inflammatory response was examined. One hour before surgery, male C3H/HeN mice were treated with an anti-KC antibody or isotype control. Animals were subjected to sham operation or trauma-hemorrhage and resuscitated with Ringer lactate thereafter. They were killed 2 h later, and Kupffer cells were isolated. Plasma levels, Kupffer cell production, and lung and liver content of TNF-alpha, IL-6, IL-10, monocyte chemoattractant protein 1, macrophage inflammatory protein 1alpha, and KC were determined by BD cytometric bead arrays. Myeloperoxidase content in lung and liver were measured as a parameter for neutrophil infiltration, and wet-to-dry weight ratios of these organs were also determined. Hepatocyte damage was assessed by measuring alpha-gluthathione S-transferase concentration. Administration of the anti-KC antibody before trauma-hemorrhage prevented increases in KC plasma levels, which was accompanied by amelioration of neutrophil infiltration and edema formation in lung and liver after trauma-hemorrhage. No effect on other cytokines in plasma or Kupffer cell release was observed. These results suggest that KC plays a pivotal role in neutrophil infiltration and organ damage after trauma-hemorrhage and resuscitation.

Bleomycin-induced pulmonary fibrosis is attenuated by a monoclonal antibody targeting HER2

The importance of HER2/HER3 signaling in decreasing the effects of lung injury was recently demonstrated. Transgenic mice unable to signal through HER2/HER3 had significantly less bleomycin-induced pulmonary fibrosis and showed a survival benefit. Based on these data, we hypothesized that pharmacological blockade of HER2/HER3 in vivo in wild-type mice would have the same beneficial effects. We tested this hypothesis in a bleomycin lung injury model using 2C4, a monoclonal antibody directed against HER2 that blocks HER2/HER3 signaling. The administration of 2C4 before injury decreased the effects of bleomycin at days 15 and 21 after injury. HER2/HER3 blockade resulted in less collagen deposition (362.8 +/- 37.9 compared with 610.5 +/- 27.1 microg/mg; P = 0.03) and less lung morphological changes (injury score of 1.99 +/- 1.55 vs. 3.90 +/- 0.76; P < 0.04). In addition, HER2/HER3 blockade resulted in a significant survival advantage with 50% vs. 25% survival at 30 days (P = 0.04). These results confirm that HER2 signaling can be pharmacologically targeted to reduce lung fibrosis and remodeling after injury.

Attenuating burn wound inflammation improves pulmonary function and survival in a burn-pneumonia model

OBJECTIVE

We previously showed that topical inhibition of inflammatory signaling in burn wounds reduced systemic inflammatory response and burn-induced pulmonary inflammation. We hypothesized that this topical intervention would attenuate burn-induced lung injury, improve pulmonary function, protect lungs from bacterial invasion, and reduce mortality.

DESIGN

Controlled, in vivo, laboratory study.

SETTING

University laboratory.

SUBJECTS

Female mice, 8-10 wks old.

INTERVENTIONS

Animals received 30% total body surface area burn followed by topical application of a specific inhibitor of p38 mitogen-activated protein kinase, a key inflammatory signaling pathway, or vehicle to the wound. Twenty-four hours after injury, pulmonary collagen deposition and pulmonary function were assessed. One day postburn, some of the animals received intratracheal instillation of Klebsiella pneumoniae and were subsequently monitored for 7 days.

MEASUREMENTS AND MAIN RESULTS

Topical inhibition of p38 mitogen-activated protein kinase significantly decreased pulmonary collagen deposition and prevented a decline in pulmonary function at 1 day after burn injury. Compared with sham controls, animals with burn injury had a significantly higher mortality in response to intratracheal bacterial challenge. Application of p38 mitogen-activated protein kinase inhibitor to the burn wound attenuated pulmonary neutrophil infiltration and reduced the mortality rate to a level experienced by sham controls.

CONCLUSIONS

Inflammatory source control in burn wounds with topical p38 mitogen-activated protein kinase inhibition attenuates acute lung injury, avoids pulmonary dysfunction, protects lungs from bacterial challenge, and improves survival.

Keratinocyte growth factor protects against elastase-induced pulmonary emphysema in mice

Pulmonary emphysema is characterized by persistent inflammation and progressive alveolar destruction. The keratinocyte growth factor (KGF) favorably influences alveolar maintenance and repair and possesses anti-inflammatory properties. We aimed to determine whether exogenous KGF prevented or corrected elastase-induced pulmonary emphysema in vivo. Treatment with 5 mg x kg(-1) x day(-1) KGF before elastase instillation prevented pulmonary emphysema. This effect was associated with 1) a sharp reduction in bronchoalveolar lavage fluid total protein and inflammatory cell recruitment, 2) a reduction in the pulmonary expression of the chemokines CCL2 (or monocyte chemoattractant protein-1) and CXCL2 (or macrophage inflammatory protein-2alpha) and of the adhesion molecules ICAM-1 and VCAM-1, 3) a reduction in matrix metalloproteinase (MMP)-2 and MMP-9 activity at day 3, and 4) a major reduction in DNA damage detected by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) in alveolar cells at day 7. Treatment with KGF after elastase instillation had no effect on elastase-induced emphysema despite the conserved expression of the KGF receptor in the lungs of elastase-instilled animals as determined by immunohistochemistry. In vitro, KGF abolished the elastase-induced increase in CCL2, CXCL2, and ICAM-1 mRNA in the MLE-12 murine alveolar epithelial cell line. We conclude that KGF pretreatment protected against elastase-induced pulmonary inflammation, activation of MMPs, alveolar cell DNA damage, and subsequent emphysema in mice.

Contributions of mucosal immune cells to methotrexate-induced mucositis

The use of high doses of the anti-cancer drug methotrexate (MTX) is associated with intestinal damage. As a result, mucosal immune cells become increasingly exposed to a vast amount of microbial stimuli. We aimed at determining whether these cells are still functional during MTX treatment. Furthermore, we assessed if activation of the mucosal immune system would play a role in the pathogenesis of mucositis. A contributive role to mucositis for the adaptive immune system was established by showing that mucosal lymphocytes from MTX-treated mice secreted enhanced amounts of cytokines upon ex vivo polyclonal stimulation. Next, in vitro experiments revealed that macrophages were not affected by MTX in the capacity to produce tumor necrosis factor-alpha (TNF-alpha) and IL-10 after LPS exposure. Moreover, peritoneal macrophages from MTX-treated mice produced more IL-10 and TNF-alpha upon LPS stimulation, compared with cells derived from control mice. These data indicate a persistence of both innate and adaptive immune responses in this model. The clinical relevance of these findings was further established by the fact that LPS exposure prior to MTX treatment aggravated the course of mucositis. Furthermore, LPS-responsive mice recovered more slowly compared with LPS-unresponsive mice from MTX treatment. Finally, we found an increase in weight loss and intestinal damage upon MTX treatment in IL-10-deficient mice in comparison to wild-type controls, suggesting a protective role for IL-10 in mucositis. We conclude that mucosal immune responses remain resilient during MTX-induced mucositis. Whereas TNF-alpha production may contribute to mucosal damage, IL-10 may regulate by restricting excessive mucositis.

Aspiration pneumonitis primes the host for an exaggerated inflammatory response during pneumonia

OBJECTIVE

Nosocomial pneumonia is a feared complication in the critically ill patient. Aspiration pneumonitis is frequently complicated by infections. The objective of this study was to determine the influence of aspiration pneumonitis on the host response to a common nosocomial respiratory pathogen.

DESIGN

Controlled, in vivo laboratory study.

SETTING

Research laboratory of a health sciences university.

SUBJECTS

Female C57Bl/6 mice.

INTERVENTIONS

Mice received hydrochloric acid or saline intratracheally followed 16 hrs later by Klebsiella pneumoniae.

MEASUREMENTS AND MAIN RESULTS

Hydrochloric acid induced a mild aspiration pneumonitis. Nonetheless, hydrochloric acid aspiration resulted in a markedly increased inflammatory response in the lung on infection with K. pneumoniae. This enhanced inflammatory reaction was accompanied by a greatly increased outgrowth of K. pneumoniae in lungs of mice previously exposed to hydrochloric acid. Preexisting aspiration pneumonitis also triggered mouse lungs in vivo and alveolar macrophages ex vivo for enhanced release of proinflammatory mediators on stimulation with Klebsiella lipopolysaccharide. Inhibition of tumor necrosis factor-alpha resulted in an increased inflammatory reaction and enhanced bacterial outgrowth in mice with primary K. pneumoniae pneumonia, whereas it had no effect in mice with preexisting aspiration pneumonitis.

CONCLUSIONS

These data indicate a) that aspiration pneumonitis renders the host more susceptible to respiratory tract infection with K. pneumoniae, concurrently priming the lung for an exaggerated inflammatory response; and b) that although tumor necrosis factor-alpha plays a major role in the host response to primary infection, it does not affect lung inflammation or defense after aspiration pneumonitis.

Keratinocyte growth factor therapy in murine oleic acid-induced acute lung injury

Alveolar type II (ATII) cell proliferation and differentiation are important mechanisms in repair following injury to the alveolar epithelium. KGF is a potent ATII cell mitogen, which has been demonstrated to be protective in a number of animal models of lung injury. We have assessed the effect of recombinant human KGF (rhKGF) and liposome-mediated KGF gene delivery in vivo and evaluated the potential of KGF as a therapy for acute lung injury in mice. rhKGF was administered intratracheally in male BALB/c mice to assess dose response and time course of proliferation. SP-B immunohistochemistry demonstrated significant increases in ATII cell numbers at all rhKGF doses compared with control animals and peaked 2 days following administration of 10 mg/kg rhKGF. Protein therapy in general is very expensive, and gene therapy has been suggested as a cheaper alternative for many protein replacement therapies. We evaluated the effect of topical and systemic liposome-mediated KGF-gene delivery on ATII cell proliferation. SP-B immunohistochemistry showed only modest increases in ATII cell numbers following gene delivery, and these approaches were therefore not believed to be capable of reaching therapeutic levels. The effect of rhKGF was evaluated in a murine model of OA-induced lung injury. This model was found to be associated with significant alveolar damage leading to severe impairment of gas exchange and lung compliance. Pretreatment with rhKGF 2 days before intravenous OA challenge resulted in significant improvements in PO2, PCO2, and lung compliance. This study suggests the feasibility of KGF as a therapy for acute lung injury.

Prevention and reversal of pulmonary inflammation and airway hyperresponsiveness by dexamethasone treatment in a murine model of asthma induced by house dust

The morbidity and mortality from asthma in the Western world have increased 75% in the past 20 years. Recent studies have demonstrated that sensitization to cockroach allergens correlates strongly with the increased asthma morbidity for adults and children. We investigated whether dexamethasone administered before or after allergen challenge would inhibit the pulmonary inflammation and airway hyperresponsiveness in a mouse model of asthma induced by a house dust extract with high levels of cockroach allergens. For the prevention experiment, mice were treated with an intraperitoneal injection of dexamethasone 1 h before each pulmonary challenge, and airway hyperresponsiveness was measured 24 h after the last challenge. Mice were killed 48 h after the last challenge. For the reversal study, airway hyperresponsiveness was measured 24 h after the last challenge, and the mice were treated with dexamethasone. Dexamethasone treatment before allergen challenge significantly reduced the pulmonary recruitment of inflammatory cells, myeloperoxidase activity in the lung, airway hyperreactivity, and total serum IgE levels compared with PBS-treated mice. Additionally, dexamethasone treatment could significantly reduce the airway hyperreactivity of an established asthmatic response. These results demonstrate that dexamethasone not only prevents but also halts the asthmatic response induced by house dust containing cockroach allergens. This model exhibits several features of human asthma that may be exploited in the study of pathophysiological mechanisms and potential therapeutic interventions.