OMIP-92: Characterization of rat macrophage subsets, lymphocytes, and granulocytes in bronchoalveolar lavage fluid.

Airway inflammation is a defense mechanism against inhaled agents characterized by infiltration of circulating immune cells. Given the inconsistent cellular identification across pre-clinical rat model, we have developed a flow cytometry panel of six colors to characterize macrophages subsets, lymphocytes and granulocytes in bronchoalveolar lavage fluid (BAL). Rats were challenged with intratracheal instillation of lipopolysaccharide (LPS). BAL were harvested 24 h after one LPS exposure in rats. This flow cytometry panel involve the description of macrophage subsets, T and B lymphocytes and neutrophils, which are central to airway immune responses, as based on scientific literature. By using a relatively small number of parameters to identify multiple cell types, additional parameters can be used for project/disease-specific activation markers.

CD200Fc limits dendritic cell and B-cell activation during chronic allergen exposures.

Allergic asthma is a chronic inflammatory disease characterized by Th2, conventional dendritic cell, and B-cell activation. In addition to excessive inflammation, asthma pathogenesis includes dysregulation of anti-inflammatory pathways, such as the CD200/CD200R pathway. Thus, we investigated whether a CD200R agonist, CD200Fc, could disrupt the inflammatory cascade in chronic allergic asthma pathogenesis using a mice model of experimental asthma. Mice were exposed to house dust mites for 5 wk, and CD200Fc treatment was initiated after chronic inflammation was established (starting on week 4). We demonstrate that chronic house dust mite exposure altered CD200 and CD200R expression on lung immune cell populations, including upregulation of CD200 on alveolar macrophages and reduced expression of CD200 on conventional dendritic cells. CD200Fc treatment does not change bronchoalveolar cellular infiltration, but it attenuates B-cell activation and skews the circulating immunoglobulin profile toward IgG2a. This is accompanied by reduced activation of conventional dendritic cells, including lower expression of CD40, especially on conventional dendritic cell subset 2 CD200R+. Furthermore, we confirm that CD200Fc can directly modulate conventional dendritic cell activation in vitro using bone marrow-derived dendritic cells. Thus, the CD200/CD200R pathway is dysregulated during chronic asthma pathogenesis, and the CD200R agonist modulates B-cell and dendritic cell activation but, in our chronic model, is not sufficient to alter inflammation measured in bronchoalveolar lavage.

Specificity of CD200/CD200R pathway in LPS-induced lung inflammation.

Introduction: At lung mucosal surfaces, immune cells must initiate inflammatory response against pathogen without inducing tissue damage. Loss of this equilibrium can lead to acute respiratory distress syndrome (ARDS), a severe lung inflammatory disease characterized by excessive inflammation and dysregulation of anti-inflammatory pathways. Methods: To investigate the role of anti-inflammatory pathway CD200/CD200R in lung inflammatory response, we administered LPS intratracheally in CD200 KO and wild type (WT) rats. Inflammation was evaluated using bronchoalveolar lavage (BAL) cellularity. Lung injury was measured by total protein level in BAL fluid, and levels of proinflammatory cytokines (TNF, IL-6) and chemokines (CXCL2, CCL2) were determined in BAL supernatants. In a second series of experiments, recombinant CD200Fc was administered to KO rats to restore the anti-inflammatory response. Results: At baseline, CD200 KO rats did not show sign of inflammation, however KO rats had lower number of alveolar macrophages. In addition, LPS administration induced greater pulmonary edema in CD200 KO rats. This was accompanied with a higher recruitment of neutrophils as well as levels of TNF, IL-6, CXCL2, and CCL2 in BAL compared to WT rats. CD200Fc administration in KO rats reduced neutrophil accumulation and TNF and CXCL2 levels in BAL. Interestingly, the increased inflammatory response of CD200 KO rats could be attributed to greater activation potential of alveolar macrophages with higher levels of ERK and P-ERK MAPK. Conclusion: This study shows that lung inflammatory response is exacerbated in absence of CD200 in an experimental model of ARDS in rats. In addition, CD200/CD200R pathway shows selective regulation of acute lung inflammation and cannot completely abrogate the complex LPS-induced inflammatory response. However, addition of CD200 agonist in a multi-target therapy strategy could have beneficial impacts.

Cross-Talk Between Alveolar Macrophages and Lung Epithelial Cells is Essential to Maintain Lung Homeostasis.

The main function of the lung is to perform gas exchange while maintaining lung homeostasis despite environmental pathogenic and non-pathogenic elements contained in inhaled air. Resident cells must keep lung homeostasis and eliminate pathogens by inducing protective immune response and silently remove innocuous particles. Which lung cell type is crucial for this function is still subject to debate, with reports favoring either alveolar macrophages (AMs) or lung epithelial cells (ECs) including airway and alveolar ECs. AMs are the main immune cells in the lung in steady-state and their function is mainly to dampen inflammatory responses. In addition, they phagocytose inhaled particles and apoptotic cells and can initiate and resolve inflammatory responses to pathogens. Although AMs release a plethora of mediators that modulate immune responses, ECs also play an essential role as they are more than just a physical barrier. They produce anti-microbial peptides and can secrete a variety of mediators that can modulate immune responses and AM functions. Furthermore, ECs can maintain AMs in a quiescent state by expressing anti-inflammatory membrane proteins such as CD200. Thus, AMs and ECs are both very important to maintain lung homeostasis and have to coordinate their action to protect the organism against infection. Thus, AMs and lung ECs communicate with each other using different mechanisms including mediators, membrane glycoproteins and their receptors, gap junction channels, and extracellular vesicles. This review will revisit characteristics and functions of AMs and lung ECs as well as different communication mechanisms these cells utilize to maintain lung immune balance and response to pathogens. A better understanding of the cross-talk between AMs and lung ECs may help develop new therapeutic strategies for lung pathogenesis.

CD200 in asthma.

Constant exposure to foreign particles in the airways requires tight immune regulation in order to maintain sufficient anti-microbial defences, while preventing immunopathological responses that could impair gas exchange. Dysregulation of immunoregulatory pathways has been associated with asthma and allergy. This review will focus on the CD200 regulatory pathway and its role in the asthmatic cascade. CD200 and its receptors are highly expressed in the lung, on epithelial cells and leukocytes, and emerging evidence links dysregulation of the CD200 pathway with asthma. Moreover, pharmacological modulation of CD200 receptors was shown to improve clinical and inflammatory outcomes of preclinical asthma models. Therefore, the involvement of CD200 in asthma is increasingly recognized and preclinical studies support the contention that it could constitute an additional target to alleviate asthma exacerbation and/or reduce disease severity.

Lung CD200 Receptor Activation Abrogates Airway Hyperresponsiveness in Experimental Asthma.

In allergic asthma, homeostatic pathways are dysregulated, which leads to an immune response toward normally innocuous antigens. The CD200-CD200 receptor pathway is a central regulator of inflammation, and CD200 expression was recently found to be down-regulated in circulating leukocytes of patients with asthma. Given the antiinflammatory properties of CD200, we investigated whether local delivery of recombinant CD200 (rCD200) could reinstate lung homeostasis in an experimental model of asthma. Brown Norway rats were sensitized with ovalbumin (OVA) and alum. rCD200 was intratracheally administered 24 hours before OVA challenge, and airway responsiveness to methacholine was measured 24 hours after the allergen challenge. Inflammation was also assessed by measuring cell recruitment and cytokine levels in bronchoalveolar lavages, as well as lung and draining lymph node accumulation of dendritic cells (DCs) and T cells. In sensitized rats, rCD200 abolished airway hyperresponsiveness, whereas the sham treatment had no effect. In addition, rCD200 strongly reduced OVA-induced lung accumulation of myeloid DCs, CD4(+) T cells, and T helper type 2 cells. This was associated with a strong reduction of OVA-induced IL-13 level and with an increase of IL-10 in supernatants of bronchoalveolar lavages. Lung eosinophilia and draining lymph node accumulation of myeloid DCs and T cells were not affected by rCD200. Overall, these data reveal that rCD200 can inhibit airway hyperresponsiveness in a model of asthma by a multistep mechanism associated with local alterations of the T cell response and the cytokine milieu.

Fibroblast growth factor-2 is a sputum remodeling biomarker of severe asthma.

OBJECTIVE: Given the large phenotypic diversity of asthma, our aim was to characterize molecular profiles related to asthma severity using selected remodeling biomarkers in induced sputum. METHODS: Induced sputum from healthy controls, patients with mild to moderate asthma and severe asthma were collected. Twelve selected biomarkers previously associated to airway remodeling such as connective tissue growth factor (CTGF), fibroblast growth factor (FGF)-2, matrix metalloproteinase (MMP)-1, MMP-2, MMP-3, MMP-7, MMP-8, MMP-9, MMP-12, MMP-13, procollagen type 1 and tissue inhibitor of metalloproteinase (TIMP)-1 were measured in sputum samples using ELISA or Luminex technology. FGF-2 level was also evaluated in bronchial biopsies using immunohistochemistry. RESULTS: Sputum of severe asthma was characterized by reduced percentage of macrophages and increased percentage of neutrophils and eosinophils. FGF-2, MMP-1 and TIMP-1 levels increased with asthma severity. Interestingly, only FGF-2 level inversely correlated with FEV1/FVC ratio. Although percentage of eosinophils correlated with asthma severity, it did not correlate with FGF-2 levels. Increased levels of FGF-2 with asthma severity were confirmed in bronchial biopsies by immunohistochemistry. CONCLUSIONS: Level of FGF-2 in induced sputum represents a relevant remodeling biomarker of asthma severity and significantly correlates with pulmonary function. FGF-2 sputum biomarker is proposed to reveal the phenotype of asthma characterized by fixed airflow obstruction.

Alveolar macrophages reduce airway hyperresponsiveness and modulate cytokine levels.

The authors have recently demonstrated that alveolar macrophages (AMs) are important in protecting against early phase reactions and airway hyperresponsiveness following allergen challenge. To further understand the mechanisms involved, the authors investigated the capacity of AMs to modulate airway inflammation and cytokine levels in bronchoalveolar lavage (BAL). AMs from allergy-susceptible Brown Norway (BN) rats or allergy-resistant Sprague-Dawley (SD) rats were transferred into AM-depleted BN rats 24 hours prior to allergen challenge. Methacholine-induced airway hyperresponsiveness was examined 24 hours following ovalbumin challenge. Total cells, cell types, and cytokine levels (tumor necrosis factor [TNF], interleukin [IL]-4, IL-10, IL-12 and IL-13) in BAL were measured 24 hours after allergen challenge. The transfer of AMs from SD rats into AM-depleted BN rats 24 hours before allergen challenge eliminated methacholine-induced airway hyperresponsiveness, but did not modify the number and the type of inflammatory cells in BAL. Levels of IL-13 and TNF were significantly higher in BAL of BN rats compared with SD rats. Interestingly, IL-13 and TNF levels were significantly increased and inhibited, respectively, in BN rats that received AMs from SD rats compared with BN rats. Our data suggest that AM modulation of cytokine milieu is involved in the reduction of airway hyperresponsiveness.

Alveolar macrophages in allergic asthma: an expression signature characterized by heat shock protein pathways.

The implication of alveolar macrophages (AM) in asthma, a T(h)2 disease, has not been well characterized. Thus, the goal of this study is to better characterize AM phenotype of allergic asthmatic compared with normal subjects using genomic expression analyses. Microarray analyses were performed with AM isolated from bronchoalveolar lavage. Robust multiarray analysis (RMA) normalization and Smyth's moderated t test were used to select differentially expressed genes. Fifty differentially expressed genes were identified. Nineteen have been classified in categories linked to stress or immune responses and among them; nine are part of the heat shock protein (HSP) family. Difference of expression for three (HSPD1, PRNP, SERPINH1) of the five selected genes were validated using real-time reverse transcription-polymerase chain reaction. Enzyme-linked immunosorbent assay was used to measure the protein level of heat shock protein 60 (HSP60), the protein encoded by HSPD1, and showed difference in AM protein level between allergic asthmatic and control subjects. In summary, this study suggests that HSP gene family, particularly HSP60, is involved in AM functions in a context of allergic asthma. These results also support the involvement of AM immune functions in the development of an allergic asthmatic response.

Coumarinic derivatives show anti-inflammatory effects on alveolar macrophages, but their anti-elastase activity is essential to reduce lung inflammation in vivo.

We have previously demonstrated the potency of coumarinic derivatives to inhibit human leukocyte elastase. Given the anti-inflammatory activities of some coumarins, we investigated the capacity of our coumarinic derivatives to inhibit inflammation and whether their anti-elastase activity was essential for their anti-inflammatory functions. All compounds studied were coumarinic derivatives displaying differential anti-proteinase activity. Coumarinic derivatives 1, 2, and 3 efficiently inhibited human leukocyte elastase in vitro, whereas the coumarinic derivative 4 did not show inhibitory activity. The anti-inflammatory effect of these compounds and a coumarin control, scopoletin, on interleukin-6 (IL-6), tumor necrosis factor (TNF), and macrophage chemotactic protein-1 (MCP-1) release was studied using lipopolysaccharide (LPS)-stimulated alveolar macrophages. The in vivo effect of compound 2, that inhibits elastase, and compound 4, that does not show proteinase inhibition, was investigated using a mouse model of LPS-induced lung inflammation and elastase-induced acute lung injury. All investigated coumarinic derivatives, regardless of their anti-proteinase activity, significantly inhibited IL-6 and TNF production by LPS-stimulated alveolar macrophages. However, only compounds 2, 3, and 4 significantly reduced MCP-1 release. Compound 2 attenuated LPS-induced leukocyte recruitment in bronchoalveolar lavage, whereas no inhibition was observed with compound 4 devoid of elastase inhibitory capacity. Interestingly, MCP-1 level was reduced in bronchoalveolar lavage of compound 4 treated mice, whereas TNF and IL-6 levels were not modulated by coumarins. Furthermore, compound 2, but not 4, reduced elastase induced lung injury. Our data suggest that although coumarinic derivatives have anti-inflammatory properties, their anti-elastase activity is essential to reduce lung inflammation in vivo.

Alveolar macrophage cytotoxic activity is inhibited by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a carcinogenic component of cigarette smoke.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a carcinogenic compound of cigarette smoke that generates electrophilic intermediates capable of damaging DNA. Recently, we have shown that NNK can modulate mediator production by alveolar macrophages (AM) and bronchial and alveolar epithelial cells, suggesting that cigarette smoke can alter lung immune response. Thus, we investigated the effect of NNK and cigarette smoke extract (CSE) on AM capacity to eliminate tumoral cells. Rat AM cell line, NR8383, was treated with NNK (500 microM) or CSE (3%) and stimulated with lipopolysaccharide (10 ng/ml). The release of cytotoxic mediators, tumor necrosis factor (TNF) and reactive oxygen species (ROS), was measured in cell-free supernatants using ELISA and superoxide anion production. TNF- and ROS-dependent cytotoxicity were studied using a (51)Chromium-release assay and WEHI-164 and P-815 cell lines. Treatment of AM with NNK and CSE for 18 h significantly inhibited AM TNF release. CSE exposure resulted in a significant increase of ROS production, whereas NNK did not. TNF-dependent cytotoxic activity of NR8383 and freshly isolated rat AM was significantly inhibited after treatment with NNK and CSE. Interestingly, although ROS production was stimulated by CSE and not affected by NNK, CSE inhibited AM ROS-dependent cytotoxicity. These results suggest that NNK may be one of the cigarette smoke components responsible for the reduction of pulmonary cytotoxicity. Thus, NNK may have a double pro-carcinogenic effect by contributing to DNA adduct formation and inhibiting AM cytotoxicity against tumoral cells.

Antigen sensitization modulates alveolar macrophage functions in an asthma model.

We have previously demonstrated that adoptive transfer of alveolar macrophages from allergy-resistant rats to alveolar macrophage-depleted allergic rats prevents airway hyperresponsiveness development, suggesting an important role for alveolar macrophages in asthma pathogenesis. Given that ovalbumin sensitization can modulate alveolar macrophage cytokine production, we investigated the role of sensitized and unsensitized alveolar macrophages in an asthma model. Alveolar macrophages from unsensitized or sensitized Brown Norway rats were transferred to alveolar macrophage-depleted sensitized rats 24 h before allergen challenge. Airway responsiveness to methacholine and airway inflammation were measured the following day. Methacholine concentration needed to increase lung resistance by 200% was significantly higher in alveolar macrophage-depleted sensitized rats that received unsensitized alveolar macrophages compared with alveolar macrophage-depleted sensitized rats that received sensitized alveolar macrophages. Tumor necrosis factor levels in bronchoalveolar lavage fluid of sensitized rats that received unsensitized alveolar macrophages were significantly lower compared with rats that received sensitized alveolar macrophages. Interestingly, alveolar macrophages of unsensitized animals showed higher phagocytosis activity compared with alveolar macrophages of sensitized rats, suggesting that sensitization modulates alveolar macrophage phagocytosis function. Our data suggest an important role of allergen sensitization on alveolar macrophage function in asthma pathogenesis.

Cytokine production by alveolar macrophages is down regulated by the alpha-methylhydroxylation pathway of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).

NNK, a nicotine-derived nitrosamine, is a potent lung carcinogen that generates electrophilic intermediates capable of damaging DNA. The effects of NNK on the immune response, which may facilitate lung carcinogenesis, are poorly understood. Alveolar macrophages (AM), a key cell in the maintenance of lung homeostasis, metabolize NNK via two major metabolic activation pathways: alpha-methylhydroxylation and alpha-methylenehydroxylation. We have shown previously that NNK inhibits the production of interleukin-12 (IL-12) and tumor necrosis factor (TNF), but stimulates the production of IL-10 and prostaglandin E(2) (PGE(2)) by AM. In the present study, we investigated the contribution of each activation pathway in the modulation of AM function. We used two precursors, 4-[(acetoxymethyl)-nitrosamino]-1-(3-pyridyl)-1-butanone (NNKOAc) and N-nitro(acetoxymethyl)methylamine (NDMAOAc), which generate the reactive electrophilic intermediates [4-(3-pyridyl)-4-oxo-butanediazohydroxide and methanediazohydroxide, respectively] in high yield and exclusively. Rat AM cell line, NR8383, was stimulated and treated with different concentrations of NNKOAc or NDMAOAc (12, 25 and 50 microM). Mediator release was measured in cell-free supernatants. NNKOAc significantly inhibited the production of IL-10, IL-12, TNF and nitric oxide but increased the release of PGE(2) and cyclooxygenase-2 expression suggesting that the alpha-methylhydroxylation pathway might be responsible for NNK modulation of AM cytokine release. In contrast, NDMAOAc did not modulate AM mediator production. However, none of these precursors, alone or in combination, could explain the stimulation of AM IL-10 production by NNK. Our results suggest that the alpha-methylhydroxylation of NNK leading to DNA pyridyloxobutylation also modulates cytokine production in NNK-treated AM.

Adoptive transfer of alveolar macrophages abrogates bronchial hyperresponsiveness.

Increasing evidence suggests that alveolar macrophages (AM) are involved in asthma pathogenesis. To better understand the role that these cells play, we investigated the capacity of AM from allergy-resistant rat, Sprague Dawley (SD), to modulate airway hyperresponsiveness of allergy-susceptible rat, Brown Norway (BN). AM of ovalbumin (OVA)-sensitized BN rats were eliminated by intratracheal instillation of liposomes containing clodronate. AM from OVA-sensitized SD rats were transferred into AM-depleted BN rats 24 h before allergen challenge. Airway responsiveness to methacholine was measured the following day. Instillation of liposomes containing clodronate in BN rats eliminated 85% AM after 3 d compared with saline liposomes. Methacholine concentration needed to increase lung resistance by 200% (EC200RL) was significantly lower in OVA-challenged BN rats (27.9 +/- 2.8 mg/ml) compared with SD rats (63.9 +/- 8.6 mg/ml). However, when AM from SD rats were transferred into AM-depleted BN rats, airway responsiveness (64.0 +/- 11.3 mg/ml) was reduced to the level of naïve rats (54.4 +/- 3.7 mg/ml) in a dose-dependent manner. Interestingly, transfer of AM from BN rats into SD rats did not modulate airway responsiveness. To our knowledge, this is the first direct evidence showing that AM may protect against the development of airway hyperresponsiveness.

Endothelins regulate mediator production of rat tissue-cultured mucosal mast cells. Up-regulation of Th1 and inhibition of Th2 cytokines.

Mast cells have been shown to produce endothelin-1 (ET-1) and to express ET receptors. Thus, we postulated that ETs modulate mast cell mediator production in an autocrine manner. Rat tissue-cultured mast cells (RCMC-1) were incubated with exogenous ET-1 or ET-3, and beta-hexosaminidase release and TNF, IL-4, IL-10, IL-12, IL-13, macrophage inflammatory protein-1alpha (MIP-1alpha), and nitric oxide (NO) production were investigated. ET-1 and -3 induced the release of beta-hexosaminidase and TNF and of mRNA expression. An antagonist of the ET(B) receptor subtype abrogated ET-stimulated TNF release, although ET(A) and ET(B) receptors have been identified by immunocytochemistry. It is interesting that ET-1 and ET-3 inhibited (25-30%) mRNA expression of Th2-type cytokines (IL-4, IL-10, and IL-13) and increased IL-12 release (39% and 41%, respectively) without affecting MIP-1alpha and NO production. Thus, our data suggest that ETs may play an important role in modulating the cytokine network by regulating Th1/Th2 cytokine production by mast cells.

Characterization of lung hyperresponsiveness, inflammation, and alveolar macrophage mediator production in allergy resistant and susceptible rats.

To better understand asthma pathogenesis, we characterized airway responsiveness, lung inflammation, and mediator production of alveolar macrophages (AM) after allergen sensitization and challenge in two strains of rats showing different susceptibilities in developing airway allergic reactions. Airway responsiveness to acethylcholine was measured 24 h after ovalbumin (OVA) challenge, whereas bronchoalveolar lavages were performed 5 min, 8 h, and 24 h after challenge. Brown Norway rats showed airway hyperresponsiveness after challenge, whereas lung resistance remained unchanged in Sprague-Dawley rats. Interestingly, Sprague-Dawley rats developed a neutrophilic inflammation, whereas both neutrophils and eosinophils were increased in Brown Norway rats. AM mediator production varied with time with a lower tumor necrosis factor (TNF) and interleukin (IL)-10 release at 8 h after challenge. OVA challenge stimulated spontaneous TNF and IL-10 release by AM isolated 24 h after challenge in both strains of rats, although AM from Brown Norway rats released significantly more IL-10 and TNF. Furthermore, nitric oxide production was increased only in OVA-challenged (24 h) Brown Norway rats. Our results suggest that AM may participate to the expansion of Th2 inflammation in Brown Norway rats and that differences in AM mediator production may explain, in part, distinct allergic susceptibilities in these two strains of rats.