François Erard

Toll-Like Receptor 2 (TLR2)-Dependent-Positive and TLR2-Independent-Negative Regulation of Proinflammatory Cytokines by Mycobacterial Lipomannans

Lipoarabinomannans (LAM) and lipomannans (LM) are integral parts of the mycobacterial cell wall recognized by cells involved in the innate immune response and have been found to modulate the cytokine response. Typically, mannosylated LAM from pathogenic mycobacteria have been reported to be anti-inflammatory, whereas phosphoinositol-substituted LAM from nonpathogenic species are proinflammatory molecules. In this study, we show that LM from several mycobacterial species, including Mycobacterium chelonae, Mycobacterium kansasii, and Mycobacterium bovis bacillus Calmette-Guérin, display a dual function by stimulating or inhibiting proinflammatory cytokine synthesis through different pathways in murine primary macrophages. LM, but none of the corresponding LAM, induce macrophage activation characterized by cell surface expression of CD40 and CD86 and by TNF and NO secretion. This activation is dependent on the presence of Toll-like receptor (TLR) 2 and mediated through the adaptor protein myeloid differentiation factor 88 (MyD88), but independent of either TLR4 or TLR6 recognition. Surprisingly, LM exerted also a potent inhibitory effect on TNF, IL-12p40, and NO production by LPS-activated macrophages. This TLR2-, TLR6-, and MyD88-independent inhibitory effect is also mediated by LAM from M. bovis bacillus Calmette-Guérin but not by LAM derived from M. chelonae and M. kansasii. This study provides evidence that mycobacterial LM bear structural motifs susceptible to interact with different pattern recognition receptors with pro- or anti-inflammatory effects. Thus, the ultimate response of the host may therefore depend on the prevailing LM or LAM in the mycobacterial envelope and the local host cell receptor availability.

IL-33-activated dendritic cells are critical for allergic airway inflammation

IL‐33, a new member of the IL‐1 family cytokine, is involved in Th2‐type responses in a wide range of diseases and signals through the ST2 receptor expressed on many immune cells. Since the effects of IL‐33 on DCs remain controversial, we investigated the ability of IL‐33 to modulate DC functions in vitro and in vivo. Here, we report that IL‐33 activates myeloid DCs to produce IL‐6, IL‐1b, TNF, CCL17 and to express high levels of CD40, CD80 OX40L and CCR7. Importantly, IL‐33‐activated DCs prime naive lymphocytes to produce the Th2 cytokines IL‐5 and IL‐13, but not IL‐4. In vivo, IL‐33 exposure induces DC recruitment and activation in the lung. Using an OVA‐induced allergic lung inflammation model, we demonstrate that the reduced airway inflammation in ST2‐deficient mice correlates with the failure in DC activation and migration to the draining LN. Finally, we show that adoptive transfer of IL‐33‐activated DCs exacerbates lung inflammation in a DC‐driven model of allergic airway inflammation. These data demonstrate for the first time that IL‐33 activates DCs during antigen presentation and thereby drives a Th2‐type response in allergic lung inflammation.

Toll-Like Receptor 2 Is Required for Optimal Control of Listeria monocytogenes Infection

ABSTRACT The control of Listeria monocytogenes infection depends on the rapid activation of the innate immune system, likely through Toll-like receptors (TLR), since mice deficient for the common adapter protein of TLR signaling, myeloid differentiation factor 88 (MyD88), succumb to Listeria infection. In order to test whether TLR2 is involved in the control of infections, we compared the host response in TLR2-deficient mice with that in wild-type mice. Here we show that TLR2-deficient mice are more susceptible to systemic infection by Listeria than are wild-type mice, with a reduced survival rate, increased bacterial burden in the liver, and abundant and larger hepatic microabscesses containing increased numbers of neutrophils. The production of tumor necrosis factor, interleukin-12, and nitric oxide and the expression of the costimulatory molecules CD40 and CD86, which are necessary for the control of infection, were reduced in TLR2-deficient macrophages and dendritic cells stimulated by Listeria and were almost abolished in the absence of MyD88, coincident with the high susceptibility of MyD88-deficient mice to in vivo infection. Therefore, the present data demonstrate a role for TLR2 in the control of Listeria infection, but other MyD88-dependent signals may contribute to host resistance.

Dual Role of IL-22 in Allergic Airway Inflammation and its Cross-talk with IL-17A

RATIONALE IL-22 has both proinflammatory and antiinflammatory properties. Its role in allergic lung inflammation has not been explored. OBJECTIVES To investigate the expression and roles of IL-22 in the onset and resolution of experimental allergic asthma and its cross-talk with IL-17A. METHODS IL-22 expression was assessed in patient samples and in the lung of mice immunized and challenged with ovalbumin. IL-22 functions in allergic airway inflammation were evaluated using mice deficient in IL-22 or anti-IL-22 neutralizing antibodies. Moreover, the effects of recombinant IL-22 and IL-17A neutralizing antibodies were investigated. MEASUREMENTS AND MAIN RESULTS Increased pulmonary IL-22 expression is found in the serum of patients with asthma and mice immunized and challenged with ovalbumin. Allergic lung inflammation is IL-22 dependent because eosinophil recruitment, Th2 cytokine including IL-13 and IL-33, chemokine production, airway hyperreactivity, and mucus production are drastically reduced in mice deficient in IL-22 or by IL-22 antibody neutralization during immunization of wild-type mice. By contrast, IL-22 neutralization during antigen challenge enhanced allergic lung inflammation with increased Th2 cytokines. Consistent with this, recombinant IL-22 given with allergen challenge protects mice from lung inflammation. Finally, IL-22 may regulate the expression and proinflammatory properties of IL-17A in allergic lung inflammation. CONCLUSIONS IL-22 is required for the onset of allergic asthma, but functions as a negative regulator of established allergic inflammation. Our study reveals that IL-22 contributes to the proinflammatory properties of IL-17A in experimental allergic asthma.

Dominant-Negative Inhibitors of Soluble TNF Attenuate Experimental Arthritis without Suppressing Innate Immunity to Infection

TNF is a pleiotropic cytokine required for normal development and function of the immune system; however, TNF overexpression also induces inflammation and is associated with autoimmune diseases. TNF exists as both a soluble and a transmembrane protein. Genetic studies in mice have suggested that inflammation in disease models involves soluble TNF (solTNF) and that maintenance of innate immune function involves transmembrane TNF (tmTNF). These findings imply that selective pharmacologic inhibition of solTNF may be anti-inflammatory and yet preserve innate immunity to infection. To address this hypothesis, we now describe dominant-negative inhibitors of TNF (DN-TNFs) as a new class of biologics that selectively inhibits solTNF. DN-TNFs blocked solTNF activity in human and mouse cells, a human blood cytokine release assay, and two mouse arthritis models. In contrast, DN-TNFs neither inhibited the activity of human or mouse tmTNF nor suppressed innate immunity to Listeria infection in mice. These results establish DN-TNFs as the first selective inhibitors of solTNF, demonstrate that inflammation in mouse arthritis models is primarily driven by solTNF, and suggest that the maintenance of tmTNF activity may improve the therapeutic index of future anti-inflammatory agents.

TLR5 signaling stimulates the innate production of IL-17 and IL-22 by CD3(neg)CD127+ immune cells in spleen and mucosa.

In adaptive immunity, Th17 lymphocytes produce the IL-17 and IL-22 cytokines that stimulate mucosal antimicrobial defenses and tissue repair. In this study, we observed that the TLR5 agonist flagellin induced swift and transient transcription of genes encoding IL-17 and IL-22 in lymphoid, gut, and lung tissues. This innate response also temporarily enhanced the expression of genes associated with the antimicrobial Th17 signature. The source of the Th17-related cytokines was identified as novel populations of CD3negCD127+ immune cells among which CD4-expressing cells resembling lymphoid tissue inducer cells. We also demonstrated that dendritic cells are essential for expression of Th17-related cytokines and so for stimulation of innate cells. These data define that TLR-induced activation of CD3negCD127+ cells and production of Th17-related cytokines may be crucial for the early defenses against pathogen invasion of host tissues.

Toll-like receptor and tumour necrosis factor dependent endotoxin-induced acute lung injury

Recent studies on endotoxin/lipopolysaccharide (LPS)‐induced acute inflammatory response in the lung are reviewed. The acute airway inflammatory response to inhaled endotoxin is mediated through Toll‐like receptor 4 (TLR4) and CD14 signalling as mice deficient for TLR4 or CD14 are unresponsive to endotoxin. Acute bronchoconstriction, tumour necrosis factor (TNF), interleukin (IL)‐12 and keratinocyte‐derived chemokine (KC) production, protein leak and neutrophil recruitment in the lung are abrogated in mice deficient for the adaptor molecules myeloid differentiation factor 88 (MyD88) and Toll/Interleukin‐1 receptor (TIR)‐domain‐containing adaptor protein (TIRAP), but independent of TIR‐domain‐containing adaptor‐inducing interferon‐beta (TRIF). In particular, LPS‐induced TNF is required for bronchoconstriction, but dispensable for inflammatory cell recruitment. Lipopolysaccharide induces activation of the p38 mitogen‐activated protein kinase (MAPK). Inhibition of pulmonary MAPK activity abrogates LPS‐induced TNF production, bronchoconstriction, neutrophil recruitment into the lungs and broncho‐alveolar space. In conclusion, TLR4‐mediated, bronchoconstriction and acute inflammatory lung pathology to inhaled endotoxin are dependent on TLR4/CD14/MD2 expression using the adapter proteins TIRAP and MyD88, while TRIF, IL‐1R1 or IL‐18R signalling pathways are dispensable. Further downstream in this axis of signalling, TNF blockade reduces only acute bronchoconstriction, while MAPK inhibition abrogates completely endotoxin‐induced inflammation.

Inflammasome–IL-1–Th17 response in allergic lung inflammation

Allergic asthma has increased dramatically in prevalence and severity over the last three decades. Both clinical and experimental data support an important role of Th2 cell response in the allergic response. Recent investigations revealed that airway exposure to allergen in sensitized individuals causes the release of ATP and uric acid, activating the NLRP3 inflammasome complex and cleaving pro-IL-1β to mature IL-1β through caspase-1. The production of pro-IL-1β requires a toll-like receptor (TLR) 4 signal which is provided by the allergen. IL-1β creates a pro-inflammatory milieu with the production of IL-6 and chemokines which mobilize neutrophils and enhance Th17 cell differentiation in the lung. Here, we review our results showing that NLRP3 inflammasome activation is required to develop allergic airway inflammation in mice and that IL-17 and IL-22 production by Th17 cells plays a critical role in established asthma. Therefore, inflammasome activation leading to IL-1β production contributes to the control of allergic asthma by enhancing Th17 cell differentiation.

Acylation determines the toll-like receptor (TLR)-dependent positive versus TLR2-, mannose receptor-, and SIGNR1-independent negative regulation of pro-inflammatory cytokines by mycobacterial lipomannan.

Mycobacterium tuberculosis lipomannans (LMs) modulate the host innate immune response. The total fraction of Mycobacterium bovis BCG LM was shown both to induce macrophage activation and pro-inflammatory cytokines through Toll-like receptor 2 (TLR2) and to inhibit pro-inflammatory cytokine production by lipopolysaccharide (LPS)-activated macrophages through a TLR2-independent pathway. The pro-inflammatory activity was attributed to tri- and tetra-acylated forms of BCG LM but not the mono- and di-acylated ones. Here, we further characterize the negative activities of M. bovis BCG LM on primary murine macrophage activation. We show that di-acylated LMs exhibit a potent inhibitory effect on cytokine and NO secretion by LPS-activated macrophages. The inhibitory activity of mycobacterial mannose-capped lipoarabino-mannans on human phagocytes was previously attributed to their binding to the C-type lectins mannose receptor or specific intracellular adhesion molecule-3 grabbing nonintegrin (DC-SIGN). However, we found that di-acylated LM inhibition of LPS-induced tumor necrosis factor secretion by murine macrophages was independent of TLR2, mannose receptor, or the murine ortholog SIGNR1. We further determined that tri-acyl-LM, an agonist of TLR2/TLR1, promoted interleukin-12 p40 and NO secretion through the adaptor proteins MyD88 and TIRAP, whereas the fraction containing tetra-acylated LM activated macrophages in a MyD88-dependent fashion, mostly through TLR4. TLR4-dependent pro-inflammatory activity was also seen with M. tuberculosis LM, composed mostly of tri-acylated LM, suggesting that acylation degree per se might not be sufficient to determine TLR2 versus TLR4 usage. Therefore, LM acylation pattern determines the anti-inflammatory versus pro-inflammatory effects of LM through different pattern recognition receptors or signaling pathways and may represent an additional mean of regulating the host innate immunity by mycobacteria.

NLRP3 inflammasome is required in murine asthma in the absence of aluminum adjuvant

To cite this article: Besnard A‐G, Guillou N, Tschopp J, Erard F, Couillin I, Iwakura Y, Quesniaux V, Ryffel B, Togbe D. NLRP3 inflammasome is required in murine asthma in the absence of aluminum adjuvant. Allergy 2011; 66: 1047–1057.