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1.  A20-Deficient Mast Cells Exacerbate Inflammatory Responses In Vivo 
PLoS Biology  2014;12(1):e1001762.
Mast cells, best known as effector cells in pathogenic immunoglobulin-mediated responses, can sense a variety of “danger” signals; if manipulated to enhance their resulting inflammatory responses, they also exacerbate inflammatory diseases such as arthritis and lung inflammation.
Mast cells are implicated in the pathogenesis of inflammatory and autoimmune diseases. However, this notion based on studies in mast cell-deficient mice is controversial. We therefore established an in vivo model for hyperactive mast cells by specifically ablating the NF-κB negative feedback regulator A20. While A20 deficiency did not affect mast cell degranulation, it resulted in amplified pro-inflammatory responses downstream of IgE/FcεRI, TLRs, IL-1R, and IL-33R. As a consequence house dust mite- and IL-33-driven lung inflammation, late phase cutaneous anaphylaxis, and collagen-induced arthritis were aggravated, in contrast to experimental autoimmune encephalomyelitis and immediate anaphylaxis. Our results provide in vivo evidence that hyperactive mast cells can exacerbate inflammatory disorders and define diseases that might benefit from therapeutic intervention with mast cell function.
Author Summary
Mast cells mediate allergic and anaphylactic immune reactions. They are also equipped with innate pattern recognition, cytokine, and alarmin receptors, which induce inflammatory responses. Correlative studies in human patients hinted at roles for mast cells in autoimmune and inflammatory diseases. However, studies using mast cell-deficient mice have yielded contradictory results in this context. In this study we determined that A20, the negative feedback regulator, restricts inflammation downstream of the mast cell antigen (allergen) receptor module, innate pattern recognition receptors, and the alarmin receptor IL-33R. By mast cell–specific ablation of A20 we established a mouse model for exaggerated inflammatory but normal anaphylactic mast cell signaling. With these mice we evaluated the impact of increased mast cell-mediated inflammation under experimental conditions aimed at mimicking several inflammatory human diseases. Our results demonstrated that the lack of A20 from mast cells exacerbated disease in mouse models for rheumatoid arthritis and innate forms of asthma, but did not impact disease progression in a mouse model for multiple sclerosis. Our data provide direct evidence that enhanced inflammatory mast cell responses can contribute to disease pathology and do so via sensing and amplifying local inflammatory reactions driven by “danger” stimuli and/or tissue damage that leads to the release of alarmins.
doi:10.1371/journal.pbio.1001762
PMCID: PMC3891641  PMID: 24453940
2.  Granuloma Formation in Pulmonary Sarcoidosis 
Sarcoidosis is a granulomatous disorder of unknown cause, affecting multiple organs, but mainly the lungs. The exact order of immunological events remains obscure. Reviewing current literature, combined with careful clinical observations, we propose a model for granuloma formation in pulmonary sarcoidosis. A tight collaboration between macrophages, dendritic cells, and lymphocyte subsets, initiates the first steps toward granuloma formation, orchestrated by cytokines and chemokines. In a substantial part of pulmonary sarcoidosis patients, granuloma formation becomes an on-going process, leading to debilitating disease, and sometimes death. The immunological response, determining granuloma sustainment is not well understood. An impaired immunosuppressive function of regulatory T cells has been suggested to contribute to the exaggerated response. Interestingly, therapeutical agents commonly used in sarcoidosis, such as glucocorticosteroids and anti-TNF agents, interfere with granuloma integrity and restore the immune homeostasis in autoimmune disorders. Increasing insight into their mechanisms of action may contribute to the search for new therapeutical targets in pulmonary sarcoidosis.
doi:10.3389/fimmu.2013.00437
PMCID: PMC3857538  PMID: 24339826
pulmonary sarcoidosis; granuloma; formation; integrity; dendritic cells; T helper 1 cells; T helper 17 cells; regulatory T cells
3.  Cellular networks controlling Th2 polarization in allergy and immunity 
In contrast to the development of Th1 (type 1 T helper cells), Th17 and Treg (regulatory T cells), little is known of the mechanisms governing Th2 development, which is important for immunity to helminths and for us to understand the pathogenesis of allergy. A picture is emerging in which mucosal epithelial cells instruct dendritic cells to promote Th2 responses in the absence of IL-12 (interleukin 12) production and provide instruction through thymic stromal lymphopoieitin (TSLP) or granulocyte-macrophage colony stimulating factor (GM-CSF). At the same time, allergens, helminths and chemical adjuvants elicit the response of innate immune cells like basophils, which provide more polarizing cytokines and IL-4 and reinforce Th2 immunity. This unique communication between cells will only be fully appreciated if we study Th2 immunity in vivo and in a tissue-specific context, and can only be fully understood if we compare several models of Th2 immune response induction.
doi:10.3410/B4-6
PMCID: PMC3292286  PMID: 22403589
4.  Inflammatory dendritic cells—not basophils—are necessary and sufficient for induction of Th2 immunity to inhaled house dust mite allergen 
The Journal of Experimental Medicine  2010;207(10):2097-2111.
It is unclear how Th2 immunity is induced in response to allergens like house dust mite (HDM). Here, we show that HDM inhalation leads to the TLR4/MyD88-dependent recruitment of IL-4 competent basophils and eosinophils, and of inflammatory DCs to the draining mediastinal nodes. Depletion of basophils only partially reduced Th2 immunity, and depletion of eosinophils had no effect on the Th2 response. Basophils did not take up inhaled antigen, present it to T cells, or express antigen presentation machinery, whereas a population of FceRI+ DCs readily did. Inflammatory DCs were necessary and sufficient for induction of Th2 immunity and features of asthma, whereas basophils were not required. We favor a model whereby DCs initiate and basophils amplify Th2 immunity to HDM allergen.
doi:10.1084/jem.20101563
PMCID: PMC2947072  PMID: 20819925
5.  Effect of Cigarette Smoke Extract on Dendritic Cells and Their Impact on T-Cell Proliferation 
PLoS ONE  2009;4(3):e4946.
Chronic obstructive pulmonary disease (COPD) is characterized by chronic airway inflammation. Cigarette smoke has been considered a major player in the pathogenesis of COPD. The inflamed airways of COPD patients contain several inflammatory cells including neutrophils, macrophages,T lymphocytes, and dendritic cells (DCs). The relative contributions of these various inflammatory cells to airway injury and remodeling are not well documented. In particular, the potential role of DCs as mediators of inflammation in the smoker's airways and COPD patients is poorly understood. In the current study we analyzed the effects of cigarette smoke extract on mouse bone marrow derived DC and the production of chemokines and cytokines were studied. In addition, we assessed CSE-induced changes in cDC function in the mixed lymphocyte reaction (MLR) examining CD4+ and CD8+ T cell proliferation. Cigarette smoke extract induces the release of the chemokines CCL3 and CXCL2 (but not cytokines), via the generation of reactive oxygen species (ROS). In a mixed-leukocyte reaction assay, cigarette smoke-primed DCs potentiate CD8+T cell proliferation via CCL3. In contrast, proliferation of CD4+T cells is suppressed via an unknown mechanism. The cigarette smoke-induced release of CCL3 and CXCL2 by DCs may contribute to the influx of CD8+T cells and neutrophils into the airways, respectively.
doi:10.1371/journal.pone.0004946
PMCID: PMC2655711  PMID: 19293939
6.  Clearance of influenza virus from the lung depends on migratory langerin+CD11b− but not plasmacytoid dendritic cells 
The Journal of Experimental Medicine  2008;205(7):1621-1634.
Although dendritic cells (DCs) play an important role in mediating protection against influenza virus, the precise role of lung DC subsets, such as CD11b− and CD11b+ conventional DCs or plasmacytoid DCs (pDCs), in different lung compartments is currently unknown. Early after intranasal infection, tracheal CD11b−CD11chi DCs migrated to the mediastinal lymph nodes (MLNs), acquiring co-stimulatory molecules in the process. This emigration from the lung was followed by an accumulation of CD11b+CD11chi DCs in the trachea and lung interstitium. In the MLNs, the CD11b+ DCs contained abundant viral nucleoprotein (NP), but these cells failed to present antigen to CD4 or CD8 T cells, whereas resident CD11b−CD8α+ DCs presented to CD8 cells, and migratory CD11b−CD8α− DCs presented to CD4 and CD8 T cells. When lung CD11chi DCs and macrophages or langerin+CD11b−CD11chi DCs were depleted using either CD11c–diphtheria toxin receptor (DTR) or langerin-DTR mice, the development of virus-specific CD8+ T cells was severely delayed, which correlated with increased clinical severity and a delayed viral clearance. 120G8+ CD11cint pDCs also accumulated in the lung and LNs carrying viral NP, but in their absence, there was no effect on viral clearance or clinical severity. Rather, in pDC-depleted mice, there was a reduction in antiviral antibody production after lung clearance of the virus. This suggests that multiple DCs are endowed with different tasks in mediating protection against influenza virus.
doi:10.1084/jem.20071365
PMCID: PMC2442640  PMID: 18591406
7.  Alum adjuvant boosts adaptive immunity by inducing uric acid and activating inflammatory dendritic cells 
Alum (aluminum hydroxide) is the most widely used adjuvant in human vaccines, but the mechanism of its adjuvanticity remains unknown. In vitro studies showed no stimulatory effects on dendritic cells (DCs). In the absence of adjuvant, Ag was taken up by lymph node (LN)–resident DCs that acquired soluble Ag via afferent lymphatics, whereas after injection of alum, Ag was taken up, processed, and presented by inflammatory monocytes that migrated from the peritoneum, thus becoming inflammatory DCs that induced a persistent Th2 response. The enhancing effects of alum on both cellular and humoral immunity were completely abolished when CD11c+ monocytes and DCs were conditionally depleted during immunization. Mechanistically, DC-driven responses were abolished in MyD88-deficient mice and after uricase treatment, implying the induction of uric acid. These findings suggest that alum adjuvant is immunogenic by exploiting “nature's adjuvant,” the inflammatory DC through induction of the endogenous danger signal uric acid.
doi:10.1084/jem.20071087
PMCID: PMC2292225  PMID: 18362170
8.  The Balance between Plasmacytoid DC versus Conventional DC Determines Pulmonary Immunity to Virus Infections 
PLoS ONE  2008;3(3):e1720.
Background
Respiratory syncytial virus (RSV) infects nearly all infants by age 2 and is a leading cause of bronchiolitis. RSV may employ several mechanisms to induce immune dysregulation, including dendritic cell (DC) modulation during the immune response to RSV.
Methods and Findings
Expansion of cDC and pDC by Flt3L treatment promoted an anti-viral response with reduced pathophysiology characterized by decreased airway hyperreactivity, reduced Th2 cytokines, increased Th1 cytokines, and a reduction in airway inflammation and mucus overexpression. These protective aspects of DC expansion could be completely reversed by depleting pDCs during the RSV infection. Expansion of DCs by Flt3L treatment enhanced in CD8+ T cell responses, which was reversed by depletion of pDC.
Conclusions
These results indicate that a balance between cDC and pDC in the lung and its lymph nodes is crucial for the outcome of a pulmonary infection. Increased pDC numbers induced by Flt3L treatment have a protective impact on the nature of the overall immune environment.
doi:10.1371/journal.pone.0001720
PMCID: PMC2249704  PMID: 18320041
9.  Activation of the D prostanoid 1 receptor suppresses asthma by modulation of lung dendritic cell function and induction of regulatory T cells 
Prostaglandins (PGs) can enhance or suppress inflammation by acting on different receptors expressed by hematopoietic and nonhematopoietic cells. Prostaglandin D2 binds to the D prostanoid (DP)1 and DP2 receptor and is seen as a critical mediator of asthma causing vasodilation, bronchoconstriction, and inflammatory cell influx. Here we show that inhalation of a selective DP1 agonist suppresses the cardinal features of asthma by targeting the function of lung dendritic cells (DCs). In mice treated with DP1 agonist or receiving DP1 agonist-treated DCs, there was an increase in Foxp3+ CD4+ regulatory T cells that suppressed inflammation in an interleukin 10–dependent way. These effects of DP1 agonist on DCs were mediated by cyclic AMP–dependent protein kinase A. We furthermore show that activation of DP1 by an endogenous ligand inhibits airway inflammation as chimeric mice with selective hematopoietic loss of DP1 had strongly enhanced airway inflammation and antigen-pulsed DCs lacking DP1 were better at inducing airway T helper 2 responses in the lung. Triggering DP1 on DCs is an important mechanism to induce regulatory T cells and to control the extent of airway inflammation. This pathway could be exploited to design novel treatments for asthma.
doi:10.1084/jem.20061196
PMCID: PMC2118726  PMID: 17283205
10.  Inhaled iloprost suppresses the cardinal features of asthma via inhibition of airway dendritic cell function 
Journal of Clinical Investigation  2007;117(2):464-472.
Inhalation of iloprost, a stable prostacyclin (PGI2) analog, is a well-accepted and safe treatment for pulmonary arterial hypertension. Although iloprost mainly acts as a vasodilator by binding to the I prostanoid (IP) receptor, recent evidence suggests that signaling via this receptor also has antiinflammatory effects through unclear mechanisms. Here we show in a murine model of asthma that iloprost inhalation suppressed the cardinal features of asthma when given during the priming or challenge phase. As a mechanism of action, iloprost interfered with the function of lung myeloid DCs, critical antigen-presenting cells of the airways. Iloprost treatment inhibited the maturation and migration of lung DCs to the mediastinal LNs, thereby abolishing the induction of an allergen-specific Th2 response in these nodes. The effect of iloprost was DC autonomous, as iloprost-treated DCs no longer induced Th2 differentiation from naive T cells or boosted effector cytokine production in primed Th2 cells. These data should pave the way for a clinical effectiveness study using inhaled iloprost for the treatment of asthma.
doi:10.1172/JCI28949
PMCID: PMC1783814  PMID: 17273558
11.  Local application of FTY720 to the lung abrogates experimental asthma by altering dendritic cell function 
Journal of Clinical Investigation  2006;116(11):2935-2944.
Airway DCs play a crucial role in the pathogenesis of allergic asthma, and interfering with their function could constitute a novel form of therapy. The sphingosine 1–phosphate receptor agonist FTY720 is an oral immunosuppressant that retains lymphocytes in lymph nodes and spleen, thus preventing lymphocyte migration to inflammatory sites. The accompanying lymphopenia could be a serious side effect that would preclude the use of FTY720 as an antiasthmatic drug. Here we show in a murine asthma model that local application of FTY720 via inhalation prior to or during ongoing allergen challenge suppresses Th2-dependent eosinophilic airway inflammation and bronchial hyperresponsiveness without causing lymphopenia and T cell retention in the lymph nodes. Effectiveness of local treatment was achieved by inhibition of the migration of lung DCs to the mediastinal lymph nodes, which in turn inhibited the formation of allergen-specific Th2 cells in lymph nodes. Also, FTY720-treated DCs were intrinsically less potent in activating naive and effector Th2 cells due to a reduced capacity to form stable interactions with T cells and thus to form an immunological synapse. These data support the concept that targeting the function of airway DCs with locally acting drugs is a powerful new strategy in the treatment of asthma.
doi:10.1172/JCI28295
PMCID: PMC1626118  PMID: 17080194

Results 1-11 (11)