Caveolin-1, the hallmark protein of caveolae, is highly expressed within the lung in the epithelium, endothelium, and in immune cells. In addition to its classical roles in cholesterol metabolism and endocytosis, caveolin-1 has also been shown to be important in inflammatory signaling pathways. In particular, caveolin-1 is known to associate with the nitric oxide synthase enzymes, downregulating their activity. Endotoxins, which are are composed mainly of lipopolysaccharide (LPS), are found ubiquitously in the environment and can lead to the development of airway inflammation and increased airway hyperresponsiveness (AHR).
We compared the acute responses of wild-type and caveolin-1 deficient mice after LPS aerosol, a well-accepted mode of endotoxin exposure, to investigate the role of caveolin-1 in the development of environmental lung injury.
Although the caveolin-1 deficient mice had greater lung inflammatory indices compared to wild-type mice, they exhibited reduced AHR following LPS exposure. The uncoupling of inflammation and AHR led us to investigate the role of caveolin-1 in the production of nitric oxide, which is known to act as a bronchodilator. The absence of caveolin-1 resulted in increased nitrite levels in the lavage fluid in both sham and LPS treated mice. Additionally, inducible nitric oxide synthase expression was increased in the lung tissue of caveolin-1 deficient mice following LPS exposure and administration of the potent and specific inhibitor 1400W increased AHR to levels comparable to wild-type mice.
We attribute the relative airway hyporesponsiveness in the caveolin-1 deficient mice after LPS exposure to the specific role of caveolin-1 in mediating nitric oxide production.
Caveolin-1; Lipopolysaccharide; Airway hyperresponsiveness; Nitric oxide; Lung injury; Cytokines
Proliferation and differentiation of the pulmonary epithelium after injury is a critical process in the defense against the external environment. Defects in this response can result in airway remodeling, such as mucus cell metaplasia (MCM), commonly seen in patients with chronic lung disease. We have previously shown that amphiregulin (AREG), a ligand to the epidermal growth factor receptor (EGFR), is induced during the repair/differentiation process elicited by naphthalene-induced lung injury. Thus, we hypothesized that AREG signaling plays an important role in epithelial proliferation and differentiation of the repairing airway. Mice deficient in AREG and lung epithelial EGFR were used to define roles for AREG-dependent EGFR signaling in airway repair and remodeling. We show that AREG and epithelial EGFR expression is dispensable to pulmonary epithelial repair after naphthalene-induced lung injury, but regulates secretory cell differentiation to a mucus-producing phenotype. We show that the pulmonary epithelium is the source of AREG, suggesting that naphthalene-induced MCM is mediated through an autocrine signaling mechanism. However, induction of MCM resulting from allergen exposure was independent of AREG. Our data demonstrate that AREG-dependent EGFR signaling in airway epithelial cells contributes to MCM in naphthalene-induced lung injury. We conclude that AREG may represent a determinant of nonallergic chronic lung diseases complicated by MCM.
Clara cells; epidermal growth factor receptor; amphiregulin; mucus cell metaplasia
Background: Low socioeconomic status is consistently associated with reduced physical and mental health, but the mechanisms remain unclear. Increased levels of urban air pollutants interacting with parental stress have been proposed to explain health disparities in respiratory disease, but the impact of such interactions on mental health is unknown.
Objectives: We aimed to determine whether prenatal air pollution exposure and stress during pregnancy act synergistically on offspring to induce a neuroinflammatory response and subsequent neurocognitive disorders in adulthood.
Methods: Mouse dams were intermittently exposed via oropharyngeal aspiration to diesel exhaust particles (DEP; 50 μg × 6 doses) or vehicle throughout gestation. This exposure was combined with standard housing or nest material restriction (NR; a novel model of maternal stress) during the last third of gestation.
Results: Adult (postnatal day 60) offspring of dams that experienced both stressors (DEP and NR) displayed increased anxiety, but only male offspring of this group had impaired cognition. Furthermore, maternal DEP exposure increased proinflammatory interleukin (IL)-1β levels within the brains of adult males but not females, and maternal DEP and NR both decreased anti-inflammatory IL-10 in male, but not female, brains. Similarly, only DEP/NR males showed increased expression of the innate immune recognition gene toll-like receptor 4 (Tlr4) and its downstream effector, caspase-1.
Conclusions: These results show that maternal stress during late gestation increases the susceptibility of offspring—particularly males—to the deleterious effects of prenatal air pollutant exposure, which may be due to a synergism of these factors acting on innate immune recognition genes and downstream neuroinflammatory cascades within the developing brain.
Citation: Bolton JL, Huff NC, Smith SH, Mason SN, Foster WM, Auten RL, Bilbo SD. 2013. Maternal stress and effects of prenatal air pollution on offspring mental health outcomes in mice. Environ Health Perspect 121:1075–1082; http://dx.doi.org/10.1289/ehp.1306560
Mycoplasma pneumoniae (Mp) frequently colonizes the airways of patients with chronic asthma and likely contributes to asthma exacerbations. We previously reported that mice lacking surfactant protein A (SP-A) have increased airway hyperresponsiveness (AHR) during M pneumoniae infection versus wild-type mice mediated by TNF-α. Mast cells (MCs) have been implicated in AHR in asthma models and produce and respond to TNF-α.
Determine the contribution of MC/TNF interactions to AHR in airways lacking functional SP-A during Mp infection. Methods: Bronchoalveolar lavage fluid was collected from healthy and asthmatic subjects to examine TNF-α levels and M pneumoniae positivity. To determine how SP-A interactions with MCs regulate airway homeostasis, we generated mice lacking both SP-A and MCs (SP-A−/−KitW-sh/W-sh) and infected them with M pneumoniae.
Our findings indicate that high TNF-α levels correlate with M pneumoniae positivity in human asthmatic patients and that human SP-A inhibits M pneumoniae–stimulated transcription and release of TNF-α by MCs, implicating a protective role for SP-A. MC numbers increase in M pneumoniae–infected lungs, and airway reactivity is dramatically attenuated when MCs are absent. Using SP-A−/−KitW-sh/W-sh mice engrafted with TNF-α−/− or TNF receptor (TNF-R)−/− MCs, we found that TNF-α activation of MCs through the TNF-R, but not MC-derived TNF-α, leads to augmented AHR during M pneumoniae infection when SP-A is absent. Additionally, M pneumoniae– infected SP-A−/−KitW-sh/W-sh mice engrafted with TNF-α−/− or TNF-R−/− MCs have decreased mucus production compared with that seen in mice engrafted with wild-type MCs, whereas burden was unaffected.
Our data highlight a previously unappreciated but vital role for MCs as secondary responders to TNF-α during the host response to pathogen infection.
Mast cells; TNF; Mycoplasma species; airway hyperres-ponsiveness; mucus
Hyaluronan is a high molecular weight component of pulmonary extracelluar matrix and lung injury can generate low molecular weight hyaluronan fragment (HA) that functions as endogenous ligand to cell surface receptors CD44 and toll like receptor 4 (TLR4). This leads to activation of intracellular NFκB signaling and pro-inflammatory cytokine production. Based on previous information that ozone exposure causes increased HA in bronchial alveolar lavage fluid (BALF) and ozone pre-exposure primes immune response to inhaled LPS, we hypothesized that HA production during ozone exposure augments the inflammatory response to LPS. We demonstrate that acute ozone exposure at 1ppm for 3 hours primes the immune response to low dose aerosolized LPS in C57BL/6J mice, resulting in increased neutrophil recruitment into the airspaces, increased levels of protein and pro-inflammatory cytokines in the BALF, and increased airway hyperresponsiveness (AHR). Intratracheal instillation of endotoxin-free HA (25 μg) enhances the biological response to inhaled LPS in a manner similar to ozone pre-exposure. In vitro studies using bone marrow-derived macrophages indicate that HA enhances LPS responses measured by TNFα production while immunofluorescence staining of murine alveolar macrophages demonstrates that HA induces TLR4 peripheralization and lipid raft co-localization. Collectively, our observations support that ozone primes macrophage responsiveness to low dose LPS, in part, due to hyaluronan-induced TLR4 peripheralization in lung macrophages.
environmental; ozone; lipopolysaccharide; hyaluronan; TLR4; toll-like receptor; innate immunity; macrophage; lung injury
Graft-versus-host-disease (GVHD) is a severe and frequent complication of allogeneic bone marrow transplantation (BMT) that involves the gastrointestinal tract and lungs. The pathobiology of GVHD is complex and involves immune cell recognition of host antigens as foreign. We hypothesize a central role for the collectin surfactant protein A (SP-A) in regulating the development of GVHD after allogeneic BMT.
C57BL/6 (H2b; WT) and SP-A deficient mice on C57BL/6 background (H2b; SP-A−/−) mice underwent allogeneic (Allo) or syngeneic (Syn) BMT with cells from either C3HeB/FeJ (H2k; SP-A−/−alloBMT or WTalloBMT) or C57Bl/6 (H2b; SP-A−/−synBMT or WTsynBMT) mice. 5 weeks post BMT, mice were necropsied and lung and gastrointestinal (GI) tissue were analyzed.
SP-A−/−alloBMT or WTalloBMT had no significant differences in lung pathology however, SP-A−/−alloBMT mice developed marked features of GI GVHD including decreased body weight, increased tissue inflammation and lymphocytic infiltration. SP-A−/−alloBMT mice also had increased colon expression of IL-1β, IL-6, TNF-α, and IFN-γ and as well as increased Th17 cells, and diminished regulatory T (Treg) cells.
Our results demonstrate the first evidence of a critical role for SP-A in modulating GI GVHD. In these studies, we demonstrate that mice deficient in SP-A that have undergone an alloBMT have a greater incidence of GI GVHD that is associated with increased Th17 cells and decreased Tregs. The results of these studies demonstrate that SP-A protects against the development of GI GVHD and establishes a role for SP-A in regulating the immune response in the GI tract.
Graft-versus-host disease; Surfactant Protein A; Th17; Regulatory T cells
Air pollutant exposure is linked with childhood asthma incidence and exacerbations, and maternal exposure to airborne pollutants during pregnancy increases airway hyperreactivity (AHR) in offspring. To determine if exposure to diesel exhaust (DE) during pregnancy worsened postnatal ozone-induced AHR, timed pregnant C57BL/6 mice were exposed to DE (0.5 or 2.0 mg/m3) 4 hours daily from Gestation Day 9–17, or received twice-weekly oropharyngeal aspirations of the collected DE particles (DEPs). Placentas and fetal lungs were harvested on Gestation Day 18 for cytokine analysis. In other litters, pups born to dams exposed to air or DE, or to dams treated with aspirated diesel particles, were exposed to filtered air or 1 ppm ozone beginning the day after birth, for 3 hours per day, 3 days per week for 4 weeks. Additional pups were monitored after a 4-week recovery period. Diesel inhalation or aspiration during pregnancy increased levels of placental and fetal lung cytokines. There were no significant effects on airway leukocytes, but prenatal diesel augmented ozone-induced elevations of bronchoalveolar lavage cytokines at 4 weeks. Mice born to the high-concentration diesel–exposed dams had worse ozone-induced AHR, which persisted in the 4-week recovery animals. Prenatal diesel exposure combined with postnatal ozone exposure also worsened secondary alveolar crest development. We conclude that maternal inhalation of DE in pregnancy provokes a fetal inflammatory response that, combined with postnatal ozone exposure, impairs alveolar development, and causes a more severe and long-lasting AHR to ozone exposure.
diesel; fetal inflammation; ozone; airway hyperreactivity
Emphysema is currently a leading cause of mortality with no known effective therapy to attenuate progressive loss of lung function. Previous work support that activation of nuclear factor erythroid 2-related factor 2 (Nrf2) is protective to the lung through induction of hundreds of antioxidant genes. In models of lung injury, the expression of NAD(P)H:quinine oxidoreductase 1 (NQO1) is upregulated in a manner dependent on Nrf2 and human emphysema is associated with reduced levels of NQO1. However, the functional role of NQO1 in emphysema remains unknown. In this study, we demonstrate the protective role of NQO1 in the development of emphysema using mouse models. NQO1 deficient animals demonstrate premature age-related emphysema and were more susceptible to both elastase and inhaled lipopolysaccharide (LPS) models of emphysema. The absence of NQO1 was associated with enhanced markers of oxidant stress. Treatment of NQO1 deficient animals with the antioxidant N-acetyl cysteine reversed the NQO1-dependent emphysematous changes. In vitro studies utilizing either inhibition or induction of NQO1 demonstrate a potent antioxidant role of NQO1 in macrophages, suggesting a role of macrophage-derived oxidants in the pathogenesis of emphysema. These novel findings support a functional role of NQO1 in protecting the lung from development of emphysema.
T-box expressed in T cells (T-bet) is a critical transcription factor for T helper (Th) 1 responses. Although Th1 cells are thought to contribute to certain alloimmune responses, their role in pulmonary graft-versus-host disease (GVHD) is uncertain. We have established a murine model of acute pulmonary GVHD after hematopoietic cell transplant (HCT) and inhaled LPS exposure. We tested the hypothesis that pulmonary GVHD can occur independent of Th1 cells using T-bet–deficient donors. B10.BR(H2k) mice underwent allogeneic (Allo) or syngeneic (Syn) HCT with cells from either C57Bl/6J(H2b) mice (Allo wild-type [WT] or SynWT) or C57Bl/6J mice lacking T-bet (AlloTbet−/− or SynTbet−/−). After HCT, mice were exposed daily to aerosolized LPS and subsequently bronchoalveolar lavage and lung tissue were analyzed for cytokines, lymphocytic inflammation, pathology, and fibrosis. Independent of LPS exposure, AlloTbet−/− mice developed pulmonary GVHD manifested by lymphocytic inflammation. Furthermore, AlloTbet−/− mice developed features of chronic pulmonary GVHD, including increased peribronchiolar fibrosis and collagen content. LPS exposure increased neutrophil recruitment and decreased static compliance in AlloTbet−/− mice as compared with LPS-exposed AlloWT mice or LPS-exposed SynTbet−/− mice. In addition, LPS-exposed AlloTbet−/− mice had increased pulmonary IL-17, IL-13, and Th17 cells, and diminished regulatory T cells compared with the other groups. Our results demonstrate that Th1 cytokines are dispensable in pulmonary GVHD. In the absence of T-bet, there is increased production of Th17 and Th2 cytokines that is associated with peribronchiolar fibrosis and is further enhanced by LPS. These results suggest that the interplay between local innate immunity and non-Th1 T cell subsets contribute to chronic pulmonary GVHD.
pulmonary graft-versus-host disease; T helper cell type 1; IL-17; LPS; peribronchiolar fibrosis
Background: The role of the Nlrp3 inflammasome in nonallergic airway hyperresponsiveness (AHR) has not previously been reported. Recent evidence supports both interleukin (IL) 1β and short fragments of hyaluronan (HA) as contributors to the biological response to inhaled ozone.
Objective: Because extracellular secretion of IL-1β requires activation of the inflammasome, we investigated the role of the inflammasome proteins ASC, caspase1, and Nlrp3 in the biological response to ozone and HA.
Methods: C57BL/6J wild-type mice and mice deficient in ASC, caspase1, or Nlrp3 were exposed to ozone (1 ppm for 3 hr) or HA followed by analysis of airway resistance, cellular inflammation, and total protein and cytokines in bronchoalveolar lavage fluid (BALF). Transcription levels of IL-1β and IL-18 were determined in two populations of lung macrophages. In addition, we examined levels of cleaved caspase1 and cleaved IL-1β as markers of inflammasome activation in isolated alveolar macrophages harvested from BALF from HA-treated mice.
Results: We observed that genes of the Nlrp3 inflammasome were required for development of AHR following exposure to either ozone or HA fragments. These genes are partially required for the cellular inflammatory response to ozone. The expression of IL-1β mRNA in alveolar macrophages was up-regulated after either ozone or HA challenge and was not dependent on the Nlrp3 inflammasome. However, soluble levels of IL-1β protein were dependent on the inflammasome after challenge with either ozone or HA. HA challenge resulted in cleavage of macrophage-derived caspase1 and IL-1β, suggesting a role for alveolar macrophages in Nlrp3-dependent AHR.
Conclusions: The Nlrp3 inflammasome is required for the development of ozone-induced reactive airways disease.
asthma; environment; extracellular matrix; innate immunity; ozone; toll-like receptor
Ozone exposure during early life has the potential to contribute to the development of asthma as well as to exacerbate underlying allergic asthma.
Scope of Review
Developmentally regulated aspects of sensitivity to ozone exposure and downstream biochemical and cellular responses.
Developmental differences in antioxidant defense responses, respiratory physiology, and vulnerabilities to cellular injury during particular developmental stages all contribute to disparities in the health effects of ozone exposure between children and adults.
Ozone exposure has the capacity to affect multiple aspects of the “effector arc” of airway hyperresponsiveness, ranging from initial epithelial damage and neural excitation to neural reprogramming during infancy.
Inhalation of ambient ozone alters populations of lung macrophages. However, the impact of altered lung macrophage populations on the pathobiology of ozone is poorly understood. We hypothesized that sub-populations of macrophages modulate the response to ozone. We exposed C57BL/6 mice to ozone (2 ppm × 3h) or filtered air. 24 h after the exposure, the lungs were harvested and digested and the cells underwent flow cytometry. Analysis revealed a novel macrophage subset present in ozone exposed mice, which were distinct from resident alveolar macrophages (AM) and identified by enhanced Gr-1+ expression (Gr-1 Macs). Further analysis identified that Gr-1+ Macs exhibited high expression of MARCO, CX3CR1, and NQO1. Gr-1+ Macs were present in the absence of CCR2, suggesting that they were not derived from a CCR2-dependent circulating intermediate. Using PKH26-PCL to label resident phagocytic cells, we demonstrated that Gr-1 Macs were derived from resident lung cells. This new subset was diminished in the absence of CX3CR1. Interestingly, CX3CR1-null mice exhibited enhanced responses to ozone, including increased airway hyperresponsiveness (AHR), exacerbated neutrophil influx, accumulation of 8-isoprostanes and protein carbonyls, and increased expression of cytokines (CXCL2, IL-1β, IL-6, CCL2, and TNF-α). Our results identify a novel subset of lung macrophages, which are derived from a resident intermediate, dependent upon CX3CR1, and appear to protect the host from the biological response to ozone.
The incidence and severity of allergic asthma have increased over the last century, particularly in the United States and other developed countries. This time frame was characterized by marked environmental changes, including enhanced hygiene, decreased pathogen exposure, increased exposure to inhaled pollutants, and changes in diet. Although iron is well-known to participate in critical biologic processes such as oxygen transport, energy generation, and host defense, iron deficiency remains common in the United States and world-wide. The purpose of these studies was to determine how dietary iron supplementation affected the severity of allergic inflammation in the lungs, using a classic model of IgE-mediated allergy in mice. Results showed that mice fed an iron-supplemented diet had markedly decreased allergen-induced airway hyperreactivity, eosinophil infiltration, and production of pro-inflammatory cytokines, compared with control mice on an unsupplemented diet that generated mild iron deficiency but not anemia. In vitro, iron supplementation decreased mast cell granule content, IgE-triggered degranulation, and production of pro-inflammatory cytokines post-degranulation. Taken together, these studies show that iron supplementation can decrease the severity of allergic inflammation in the lung, potentially via multiple mechanisms that affect mast cell activity. Further studies are indicated to determine the potential of iron supplementation to modulate the clinical severity of allergic diseases in humans.
Rationale: Previously, we demonstrated a candidate region for susceptibility to airspace enlargement on mouse chromosome 5. However, the specific candidate genes within this region accounting for emphysema-like changes remain unrecognized. c-Kit is a receptor tyrosine kinase within this candidate gene region that has previously been recognized to contribute to the survival, proliferation, and differentiation of hematopoietic stem cells. Increases in the percentage of cells expressing c-Kit have previously been associated with protection against injury-induced emphysema.
Objectives: Determine whether genetic variants of c-Kit are associated with spontaneous airspace enlargement.
Methods: Perform single-nucleotide polymorphism association studies in the mouse strains at the extremes of airspace enlargement phenotype for variants in c-Kit tyrosine kinase. Characterize mice bearing functional variants of c-Kit compared with wild-type controls for the development of spontaneous airspace enlargement. Epithelial cell proliferation was measured in culture.
Measurements and Main Results: Upstream regulatory single-nucleotide polymorphisms in the divergent mouse strains were associated with the lung compliance difference observed between the extreme strains. c-Kit mutant mice (KitW-sh/W-sh), when compared with genetic controls, developed altered lung histology, increased total lung capacity, increased residual volume, and increased lung compliance that persist into adulthood. c-Kit inhibition with imatinib attenuated in vitro proliferation of cells expressing epithelial cell adhesion molecule.
Conclusions: Our findings indicate that c-Kit sustains and/or maintains normal alveolar architecture in the lungs of mice. In vitro data suggest that c-Kit can regulate epithelial cell clonal expansion. The precise mechanisms that c-Kit contributes to the development of airspace enlargement and increased lung compliance remain unclear and warrants further investigation.
genetic; tyrosine kinase; SASH; chronic obstructive pulmonary disease; aging
Pulmonary graft-versus-host disease (GVHD) after hematopoietic cell transplant (HCT) and allograft rejection after lung transplant are parallel immunologic processes that lead to significant morbidity and mortality. Our murine model of pulmonary GVHD after inhaled lipopolysaccharide (LPS) suggests that innate immune activation potentiates pulmonary transplant-related alloimmunity. We hypothesized that the CXCR3 receptor is necessary for development of LPS-induced pulmonary GVHD.
Recipient mice underwent allogeneic or syngeneic HCT followed by inhaled LPS. CXCR3 receptor inhibition was performed by using either CXCR3-knockout donors or systemic anti-CXCR3 antibody blockade. Pulmonary histopathology, cellular sub-populations, cytokine proteins and transcripts were analyzed.
In comparison to lungs of LPS-unexposed and syngeneic controls, lungs of LPS-exposed allogeneic HCT mice demonstrated prominent lymphocytic perivascular and peribronchiolar infiltrates. This pathology was associated with increased CD4+ and CD8+ T cells as well as an increase in CXCR3 expression on T cells, a 2-fold upregulation of CXCR3 transcript and a 4-fold increase in its ligand CXCL10/IP10. CXCR3 inhibition using gene-knockout strategy or antibody blockade did not change the severity of pulmonary pathology (mean pathology score 6.5 for sufficient vs. 6.5 knockout, p=1.00; mean score 6.8 for antibody blockade vs. 7.4 control, p=0.46). CXCR3 inhibition did not prevent CD3 infiltration, nor prevent production of IL-12p40, nor significantly change other Th1, Th2, or Th17 cytokines in the lung.
In the setting of allogeneic HCT, innate immune activation by LPS potentiates pulmonary GVHD through CXCR3-independent mechanisms. Clinical strategies focused on inhibition of CXCR3 may prove insufficient to ameliorate transplant-related lung disease.
Pulmonary graft-versus-host disease; Lung rejection; CXCR3; Lipopolysaccharide; Innate immunity
Air spaces of the mammalian lung are lined by a specialized epithelium that is maintained by endogenous progenitor cells. Within bronchioles, the abundance and distribution of progenitor cells that contribute to epithelial homeostasis change as a function of maintenance versus repair. It is unclear whether functionally distinct progenitor pools or a single progenitor cell type maintain the epithelium and how the behavior is regulated in normal or disease states. To address these questions, we applied fractionation methods for the enrichment of distal airway progenitors. We show that bronchiolar progenitor cells can be subdivided into two functionally distinct populations that differ in their susceptibility to injury and contribution to repair. The proliferative capacity of these progenitors is confirmed in a novel in vitro assay. We show that both populations give rise to colonies with a similar dependence on stromal cell interactions and regulation by TGF-β. These findings provide additional insights into mechanisms of epithelial remodeling in the setting of chronic lung disease and offer hope that pharmacologic interventions may be developed to mitigate tissue remodeling.
bronchiolar stem cell; Clara; progenitor; fractionation; epithelium
IL-1α and IL-1β were evaluated for their ability to provide adjuvant activity for the induction of serum antibody responses when nasally-administered with protein antigens in mice and rabbits. In mice, intranasal (i.n.) immunization with pneumococcal surface protein A (PspA) or tetanus toxoid (TT) combined with IL-1β induced protective immunity that was equivalent to that induced by parenteral immunization. Nasal immunization of awake (i.e., not anesthetized) rabbits with IL-1-adjuvanted vaccines induced highly variable serum antibody responses and was not as effective as parenteral immunization for the induction of antigen-specific serum IgG. However, i.n. immunization of deeply anesthetized rabbits with rPA + IL-1α consistently induced rPA-specific serum IgG ELISA titers that were not significantly different than those induced by intramuscular (IM) immunization with rPA + alum although lethal toxin neutralizing titers induced by nasal immunization were lower than those induced by IM immunization. Gamma scintigraphy demonstrated that the enhanced immunogenicity of nasal immunization in anesthetized rabbits correlated with an increased nasal retention of i.n. delivered non-permeable radio-labeled colloidal particles. Our results demonstrate that, in mice, IL-1 is an effective adjuvant for nasally-administered vaccines for the induction of protective systemic immunity and that in non-rodent species, effective induction of systemic immunity with nasally-administered vaccines may require formulations that ensure adequate retention of the vaccine within the nasal cavity.
adjuvant; interleukin 1; nasal
Background: Our previous work demonstrated that the extracellular matrix protein mindin contributes to allergic airways disease. However, the role of mindin in nonallergic airways disease has not previously been explored.
Objectives: We hypothesized that mindin would contribute to airways disease after inhalation of either lipopolysaccharide (LPS) or ozone.
Methods: We exposed C57BL/6J and mindin-deficient (–/–) mice to aerosolized LPS (0.9 μg/m3 for 2.5 hr), saline, ozone (1 ppm for 3 hr), or filtered air (FA). All mice were evaluated 4 hr after LPS/saline
exposure or 24 hr after ozone/FA exposure. We characterized the physiological and biological responses by analysis of airway hyperresponsiveness (AHR) with a computer-controlled small-animal ventilator (FlexiVent), inflammatory cellular recruitment, total protein in bronchoalveolar lavage fluid (BALF), proinflammatory cytokine profiling, and ex vivo bronchial ring studies.
Results: After inhalation of LPS, mindin–/– mice demonstrated significantly reduced total cell and neutrophil recruitment into the airspace compared with their wild-type counterparts. Mindin–/– mice also exhibited reduced proinflammatory cytokine production and lower AHR to methacholine challenge by FlexiVent. After inhalation of ozone, mice had no detectible differences in cellular inflammation or total BALF protein dependent on mindin. However, mindin–/– mice were protected from increased proinflammatory cytokine production and AHR compared with their C57BL/6J counterparts. After ozone exposure, bronchial rings derived from mindin–/– mice demonstrated reduced constriction in response to carbachol.
Conclusions: These data demonstrate that the extracellular matrix protein mindin modifies the airway response to both LPS and ozone. Our data support a conserved role of mindin in production of proinflammatory cytokines and the development of AHR in two divergent models of reactive airways disease, as well as a role of mindin in airway smooth muscle contractility after exposure to ozone.
airway smooth muscle; endotoxin; innate immunity; lipopolysaccharide; LPS; lung; mindin; ozone; Tlr4; toll-like receptor
Premature infants are at increased risk of developing airway hyper-reactivity following oxidative stress and inflammation. Mast cells contribute to airway hyper-reactivity partly by mediator release, so we sought to determine if blocking mast cell degranulation or recruitment prevents hyperoxia-induced airway hyper-reactivity, mast cell accumulation, and airway smooth muscle changes. Rats were exposed at birth to air or 60% O2 for 14 days, inducing significantly increased airway hyper-reactivity (AHR) in the latter group, induced by nebulized methacholine challenge, measured by forced oscillometry. Daily treatment (postnatal days 1-14) with intraperitoneal cromolyn prevented hyperoxia-induced AHR, as did treatment with imatinib on postnatal days 5-14, compared with vehicle treated controls. Cromolyn prevented mast cell degranulation in the trachea but not hilar airways, and blocked mast cell accumulation in the hilar airways. Imatinib treatment completely blocked mast cell accumulation in tracheal/hilar airway tissues. Hyperoxia-induced AHR in neonatal rats is mediated, at least in part, via the mast cell.
Idiopathic pulmonary fibrosis (IPF) is a progressive disease causing unremitting extracellular matrix deposition with resultant distortion of pulmonary architecture and impaired gas exchange. β-arrestins regulate G-protein-coupled receptors through receptor desensitization while acting as signaling scaffolds that facilitate numerous effector pathways. Here we examine the role of β-arrestin1 and β-arrestin2 in the pathobiology of pulmonary fibrosis. In the bleomycin-induced mouse lung fibrosis model, loss of eitherβ-arrestin1 or β-arrestin2 results in protection from mortality, inhibition of matrix deposition, and protected lung function. Fibrosis is prevented despite preserved recruitment of inflammatory cells and fibroblast chemotaxis. However, isolated lung fibroblasts from bleomycin-treated β-arrestin null mice fail to invade extracellular matrix while displaying altered expression of genes involved in matrix production and degradation. Furthermore, knockdown of β-arrestin2 in fibroblasts from IPF patients attenuated the invasive phenotype. These data implicate β-arrestins as mediators of fibroblast invasion and development of pulmonary fibrosis, thus representing a potential target for therapeutic intervention for patients with IPF.
Rationale: Ozone is a common environmental air pollutant that contributes to hospitalizations for respiratory illness. The mechanisms, which regulate ozone-induced airway hyperresponsiveness, remain poorly understood. We have previously reported that toll-like receptor 4 (TLR4)–deficient animals are protected against ozone-induced airway hyperresponsiveness (AHR) and that hyaluronan (HA) mediates ozone-induced AHR. However, the relation between TLR4 and hyaluronan in the airway response to ozone remains unexplored.
Objectives: We hypothesized that HA acts as an endogenous TLR4 ligand for the development of AHR after ozone-induced environmental airway injury.
Methods: TLR4-deficient and wild-type C57BL/6 mice were exposed to either inhaled ozone or intratracheal HA and the inflammatory and AHR response was measured.
Measurements and Main Results: TLR4-deficient mice have similar levels of cellular inflammation, lung injury, and soluble HA levels as those of C57BL/6 mice after inhaled ozone exposure. However, TLR4-deficient mice are partially protected from AHR after ozone exposure as well as after direct intratracheal instillation of endotoxin-free low molecular weight HA. Similar patterns of TLR4-dependent cytokines were observed in the bronchial alveolar lavage fluid after exposure to either ozone or HA. Exposure to ozone increased immunohistological staining of TLR4 on lung macrophages. Furthermore, in vitro HA exposure of bone marrow–derived macrophages induced NF-κB and production of a similar pattern of proinflammatory cytokines in a manner dependent on TLR4.
Conclusions: Our observations support the observation that extracellular matrix HA contributes to ozone-induced airways disease. Furthermore, our results support that TLR4 contributes to the biological response to HA by mediating both the production of proinflammatory cytokines and the development of ozone-induced AHR.
environmental airways injury; asthma; toll-like receptor; macrophage; TNF-α
Allergic asthma is characterized by airway hyperresponsiveness, inflammation, and a cellular infiltrate dominated by eosinophils. Numerous epidemiological studies have related the exacerbation of allergic asthma with an increase in ambient inhalable particulate matter from air pollutants. This is because inhalable particles efficiently deliver airborne allergens deep into the airways, where they can aggravate allergic asthma symptoms. However, the cellular mechanisms by which inhalable particulate allergens (pAgs) potentiate asthmatic symptoms remain unknown, in part because most in vivo and in vitro studies exploring the pathogenesis of allergic asthma use soluble allergens (sAgs). Using a mouse model of allergic asthma, we found that, compared with their sAg counterparts, pAgs triggered markedly heightened airway hyperresponsiveness and pulmonary eosinophilia in allergen-sensitized mice. Mast cells (MCs) were implicated in this divergent response, as the differences in airway inflammatory responses provoked by the physical nature of the allergens were attenuated in MC-deficient mice. The pAgs were found to mediate MC-dependent responses by enhancing retention of pAg/IgE/FcεRI complexes within lipid raft–enriched, CD63+ endocytic compartments, which prolonged IgE/FcεRI-initiated signaling and resulted in heightened cytokine responses. These results reveal how the physical attributes of allergens can co-opt MC endocytic circuitry and signaling responses to aggravate pathological responses of allergic asthma in mice.
Rationale: Epidemiologic studies implicate air pollutant exposure during pregnancy as a risk factor for wheezing in offspring. Ozone exposure is linked to exacerbations of wheezing in children.
Objectives: To determine if maternal pulmonary exposure to traffic-related particles during pregnancy augments ozone–induced airway hyperresponsiveness in offspring.
Methods: C57BL6 time-mated mice were given NIST SRM#1648 (particulate matter [PM]) 0.48 mg, saline vehicle, or no treatment by tracheal insufflation twice weekly for 3 weeks. PM exposure augmented maternal lung inflammation and placental TNF-α, Keratinocyte-derived cytokine (KC), and IL-6 (measured at gestation Day 18). After parturition, dams and litters were exposed to air or ozone 1 ppm 3 h/d, every other day, thrice weekly for 4 weeks. Respiratory system resistance in pups was measured at baseline and after administration of nebulized methacholine.
Measurements and Main Results: Ozone increased airway hyperresponsiveness, but the increase was greatest in pups born to PM-treated dams. Whole-lung TNF-α, IL-1β, KC, IL-6, and MCP-1 were increased in ozone–treated pups, with the greatest increase in pups born to dams given PM. Airway epithelial mucous metaplasia estimated by periodic acid-Schiff Alcian blue staining was increased in ozone–exposed pups born to PM-treated dams. Alveolar development, determined by morphometry, and airway smooth muscle bulk, estimated using α-actin histochemistry, were unaffected by prenatal or postnatal treatment.
Conclusions: Maternal pulmonary exposure to PM during pregnancy augments placental cytokine expression and postnatal ozone–induced pulmonary inflammatory cytokine responses and ozone–induced airway hyperresponsiveness without altering airway structure.
Rationale: S-Nitrosothiols (SNO) inhibit immune activation of the respiratory epithelium and airway SNO levels are decreased in inflammatory lung disease. Ethyl nitrite (ENO) is a gas with chemical properties favoring SNO formation. Augmentation of airway SNO by inhaled ENO treatment may decrease lung inflammation and subsequent injury by inhibiting activation of the airway epithelium.
Objectives: To determine the effect of inhaled ENO on airway SNO levels and LPS-induced lung inflammation/injury.
Methods: Mice were treated overnight with inhaled ENO (10 ppm) or air, followed immediately by exposure to aerosolized LPS or saline. Parameters of inflammation and lung injury were quantified 1 hour after completion of the aerosol exposure and correlated to lung airway and tissue SNO levels.
Measurements and Main Results: Aerosolized LPS induced a decrease in airway and lung tissue SNO levels including S-nitrosylated NF-κB. The decrease in lung SNO was associated with an increase in lung NF-κB activity, cytokine/chemokine expression (keratinocyte-derived chemokine, tumor necrosis factor-α, and IL-6), airway neutrophil influx, and worsened lung compliance. Pretreatment with inhaled ENO restored airway SNO levels and reduced LPS-mediated NF-κB activation thereby inhibiting the downstream inflammatory response and preserving lung compliance.
Conclusions: Airway SNO serves an antiinflammatory role in the lung. Inhaled ENO can be used to augment airway SNO and protect from LPS-induced acute lung injury.
ethyl nitrite; NF-κB; nitric oxide; S-nitrosylation
One host susceptibility factor for ozone identified in epidemiologic studies is NAD(P)H quinone oxidoreductase 1 (NQO1). We hypothesized that after ozone exposure, NQO1 is required to increase 8-isoprostane (also known as F2-isoprostane) production, a recognized marker of ozone-induced oxidative stress, and to enhance airway inflammation and hyperresponsiveness. In this report, we demonstrate that in contrast to wild-type mice, NQO1-null mice are resistant to ozone and have blunted responses, including decreased production of F2-isoprostane and keratinocyte chemokine, decreased airway inflammation, and diminished airway hyperreponsiveness. Importantly, these results in mice correlate with in vitro findings in humans. In primary human airway epithelial cells, inhibition of NQO1 by dicumarol blocks ozone-induced F2-isoprostane production and IL-8 gene expression. Together, these results demonstrate that NQO1 modulates cellular redox status and influences the biologic and physiologic effects of ozone.
ozone; NAD(P)H quinone oxidoreductase 1; F2-isoprostane