Bruno Schnyder

Interleukin-17 is a negative regulator of established allergic asthma

T helper (Th)17 cells producing interleukin (IL)-17 play a role in autoimmune and allergic inflammation. Here, we show that IL-23 induces IL-17 in the lung and IL-17 is required during antigen sensitization to develop allergic asthma, as shown in IL-17R–deficient mice. Since IL-17 expression increased further upon antigen challenge, we addressed its function in the effector phase. Most strikingly, neutralization of IL-17 augmented the allergic response in sensitized mice. Conversely, exogenous IL-17 reduced pulmonary eosinophil recruitment and bronchial hyperreactivity, demonstrating a novel regulatory role of IL-17. Mechanistically, IL-17 down modulated eosinophil-chemokine eotaxin (CCL11) and thymus- and activation-regulated chemokine/CCL17 (TARC) in lungs in vivo and ex vivo upon antigen restimulation. In vitro, IL-17 reduced TARC production in dendritic cells (DCs)—the major source of TARC—and antigen uptake by DCs and IL-5 and IL-13 production in regional lymph nodes. Furthermore, IL-17 is regulated in an IL-4–dependent manner since mice deficient for IL-4Rα signaling showed a marked increase in IL-17 concentration with inhibited eosinophil recruitment. Therefore, endogenous IL-17 is controlled by IL-4 and has a dual role. Although it is essential during antigen sensitization to establish allergic asthma, in sensitized mice IL-17 attenuates the allergic response by inhibiting DCs and chemokine synthesis.

IL-1R1/MyD88 signaling and the inflammasome are essential in pulmonary inflammation and fibrosis in mice

The molecular mechanisms of acute lung injury resulting in inflammation and fibrosis are not well established. Here we investigate the roles of the IL-1 receptor 1 (IL-1R1) and the common adaptor for Toll/IL-1R signal transduction, MyD88, in this process using a murine model of acute pulmonary injury. Bleomycin insult results in expression of neutrophil and lymphocyte chemotactic factors, chronic inflammation, remodeling, and fibrosis. We demonstrate that these end points were attenuated in the lungs of IL-1R1- and MyD88-deficient mice. Further, in bone marrow chimera experiments, bleomycin-induced inflammation required primarily MyD88 signaling from radioresistant resident cells. Exogenous rIL-1beta recapitulated a high degree of bleomycin-induced lung pathology, and specific blockade of IL-1R1 by IL-1 receptor antagonist dramatically reduced bleomycin-induced inflammation. Finally, we found that lung IL-1beta production and inflammation in response to bleomycin required ASC, an inflammasome adaptor molecule. In conclusion, bleomycin-induced lung pathology required the inflammasome and IL-1R1/MyD88 signaling, and IL-1 represented a critical effector of pathology and therapeutic target of chronic lung inflammation and fibrosis.

Cigarette Smoke-Induced Pulmonary Inflammation Is TLR4/MyD88 and IL-1R1/MyD88 Signaling Dependent

Acute cigarette smoke exposure of the airways (two cigarettes twice daily for three days) induces acute inflammation in mice. In this study, we show that airway inflammation is dependent on Toll-like receptor 4 and IL-1R1 signaling. Cigarette smoke induced a significant recruitment of neutrophils in the bronchoalveolar space and pulmonary parenchyma, which was reduced in TLR4-, MyD88-, and IL-1R1-deficient mice. Diminished neutrophil influx was associated with reduced IL-1, IL-6, and keratinocyte-derived chemokine levels and matrix metalloproteinase-9 activity in the bronchoalveolar space. Further, cigarette smoke condensate (CSC) induced a macrophage proinflammatory response in vitro, which was dependent on MyD88, IL-1R1, and TLR4 signaling, but not attributable to LPS. Heat shock protein 70, a known TLR4 agonist, was induced in the airways upon smoke exposure, which probably activates the innate immune system via TLR4/MyD88, resulting in airway inflammation. CSC-activated macrophages released mature IL-1β only in presence of ATP, whereas CSC alone promoted the TLR4/MyD88 signaling dependent production of IL-1α and pro-IL-1β implicating cooperation between TLRs and the inflammasome. In conclusion, acute cigarette exposure results in LPS-independent TLR4 activation, leading to IL-1 production and IL-1R1 signaling, which is crucial for cigarette smoke induced inflammation leading to chronic obstructive pulmonary disease with emphysema.

Both Hemopoietic and Resident Cells Are Required for MyD88-Dependent Pulmonary Inflammatory Response to Inhaled Endotoxin

Inhaled endotoxin induces an inflammatory response that contributes to the development and severity of asthma and other forms of airway disease. Here, we show that inhaled endotoxin-induced acute bronchoconstriction, TNF, IL-12p40, and KC production, protein leak, and neutrophil recruitment in the lung are abrogated in mice deficient for the adaptor molecule MyD88. Bronchoconstriction, inflammation, and protein leak are normal in Toll/IL-1R domain-containing adaptor inducing IFN-β-deficient mice. MyD88 is involved in TLR, but also in IL-1R-associated kinase 1-mediated IL-1R and -18R signaling. We exclude a role for IL-1 and IL-18 pathways in this response, as IL-1R1 and caspase-1 (ICE)-deficient mice develop lung inflammation while TLR4-deficient mice are unresponsive to inhaled LPS. Significantly, using bone marrow chimera, we demonstrate that both hemopoietic and resident cells are necessary for a full MyD88-dependent response to inhaled endotoxin; bronchoconstriction depends on resident cells while cytokine secretion is mediated by hemopoietic cells.

Dual Effects of p38 MAPK on TNF-Dependent Bronchoconstriction and TNF-Independent Neutrophil Recruitment in Lipopolysaccharide-Induced Acute Respiratory Distress Syndrome

The administration of endotoxins from Gram-negative bacteria induces manifestations reminding of acute respiratory distress syndrome. p38 MAPKs have been implicated in this pathology. In this study, we show that the specific p38 α,β MAPK inhibitor, compound 37, prevents LPS-induced bronchoconstriction and neutrophil recruitment into the lungs and bronchoalveolar space in a dose-dependent manner in C57BL/6 mice. Furthermore, TNF induction and TNF signals were blocked. In TNF-deficient mice, bronchoconstriction, but not neutrophil sequestration, in the lung was abrogated after LPS administration. Therefore, TNF inhibition does not explain all of the effects of the p38 MAPK inhibitor. The p38 α,β MAPK inhibitor also prevented LPS-induced neutrophilia in TNF-deficient mice. In conclusion, LPS provokes acute bronchoconstriction that is TNF dependent and p38 MAPK mediated, whereas the neutrophil recruitment is independent of TNF but depends on LPS/TLR4-induced signals mediated by p38 MAPK.

Nonredundant roles of TIRAP and MyD88 in airway response to endotoxin, independent of TRIF, IL-1 and IL-18 pathways

Inhaled endotoxins induce an acute inflammatory response in the airways mediated through Toll-like receptor 4 (TLR4) and myeloid differentiation factor 88 (MyD88). However, the relative roles of the TLR4 adaptor proteins TIRAP and TRIF and of the MyD88-dependent IL-1 and IL-18 receptor pathways in this response are unclear. Here, we demonstrate that endotoxin-induced acute bronchoconstriction, vascular damage resulting in protein leak, Th1 cytokine and chemokine secretion and neutrophil recruitment in the airways are abrogated in mice deficient for either TIRAP or MyD88, but not in TRIF deficient mice. The contribution of other TLR-independent, MyD88-dependent signaling pathways was investigated in IL-1R1, IL-18R and caspase-1 (ICE)-deficient mice, which displayed normal airway responses to endotoxin. In conclusion, the TLR4-mediated, bronchoconstriction and acute inflammatory lung pathology to inhaled endotoxin critically depend on the expression of both adaptor proteins, TIRAP and MyD88, suggesting cooperative roles, while TRIF, IL-1R1, IL-18R signaling pathways are dispensable.

Petasites extract Ze 339 (PET) inhibits allergen‐induced Th2 responses, airway inflammation and airway hyperreactivity in mice

Background: The herbal Petasites hybridus (butterbur) extract (Ze 339, PET) is known to have leukotriene inhibiting properties, and therefore might inhibit allergic diseases.

T cell-derived TNF down-regulates acute airway response to endotoxin

Acute and chronic airway inflammations caused by environmental agents including endotoxin represent an increasing health problem. Local TNF production may contribute to lung dysfunction and inflammation, although pulmonary neutrophil recruitment occurs in the absence of TNF. First, we demonstrate that membrane‐bound TNF is sufficient to mediate the inflammatory responses to lipopolysaccharide (LPS). Secondly, using cell type‐specific TNF‐deficient mice we show that TNF derived from either macrophage/neutrophil (M/N) or T lymphocytes have differential effects on LPS‐induced respiratory dysfunction (enhanced respiratory pause, Penh) and pulmonary neutrophil recruitment. While Penh, vascular leak, neutrophil recruitment, TNF, and thymus‐ and activation‐regulated chemokine/CCL17 (TARC) expression in the lung were reduced in M/N‐deficient mice, T cell‐specific TNF‐deficient mice displayed augmented Penh, vascular leak, neutrophil influx, increased CD11c+ cells and expression of TNF, TARC and murine CXC chemokines KC/CXCL1 in the lung. In conclusion, inactivation of TNF in either M/N or T cells has differential effects on LPS‐induced lung disease, suggesting that selective deletion of TNF in T cells may aggravate airway pathology.

Neutrophil Inhibitory Factor Selectively Inhibits the Endothelium-Driven Transmigration of Eosinophils In Vitro and Airway Eosinophilia in OVA-Induced Allergic Lung Inflammation

Leukocyte adhesion molecules are involved in cell recruitment in an allergic airway response and therefore provide a target for pharmaceutical intervention. Neutrophil inhibitory factor (NIF), derived from canine hookworm (Ancylostoma caninum), binds selectively and competes with the A-domain of CD11b for binding to ICAM-1. The effect of recombinant NIF was investigated. Intranasal administration of rNIF reduced pulmonary eosinophilic infiltration, goblet cell hyperplasia, and Th2 cytokine production in OVA-sensitized mice. In vitro, transendothelial migration of human blood eosinophils across IL-4-activated umbilical vein endothelial cell (HUVEC) monolayers was inhibited by rNIF (IC50: 4.6 ± 2.6 nM; mean ± SEM), but not across TNF or IL-1-activated HUVEC monolayers. Treatment of eosinophils with rNIF together with mAb 60.1 directed against CD11b or mAb 107 directed against the metal ion-dependent adhesion site (MIDAS) of the CD11b A-domain resulted in no further inhibition of transendothelial migration suggesting shared functional epitopes. In contrast, rNIF increased the inhibitory effect of blocking mAbs against CD18, CD11a, and VLA-4. Together, we show that rNIF, a selective antagonist of the A-domain of CD11b, has a prominent inhibitory effect on eosinophil transendothelial migration in vitro, which is congruent to the in vivo inhibition of OVA-induced allergic lung inflammation.

Histamine scavenging attenuates endotoxin-induced acute lung injury

Histamine is an important mediator of early and late inflammatory responses. Here we asked whether scavenging of endogenous histamine by the arthropod‐derived histamine binding protein EV131 diminishes acute respiratory distress syndrome (ARDS) induced by inhaled endotoxin. We demonstrate that EV131 (360 μg given intranasally) reduced endotoxin‐induced bronchoconstriction and recruitment of neutrophils. Furthermore, EV131 administration diminished TNF‐α and protein leak in the bronchoalveolar lavage fluid. The data suggest that histamine attenuates endotoxin‐induced bronchoconstriction and neutrophil recruitment. Therefore, scavenging of histamine by EV131 may represent a novel therapeutic strategy in ARDS.