Cedric Hubeau

Cytokine Pathways in Allergic Disease

Cytokines are critical in allergic intercellular communication networks, and they contribute to disease pathology through the recruitment and activation of pro-inflammatory leukocytes and in chronic disease to pro-fibrotic/remodeling events. Th2 cytokines predominate primarily in mild to moderate allergic asthma, although clinical trials with inhibitors of IL-4 and IL-5 have not provided the robust efficacy observed in animal models of allergy. These results not only highlight the complexity of allergic disease, but they also point to the importance of other cytokine networks in driving pathology. The heterogeneous nature of the disease is emphasized by the fact that the Th2/Th1/Th17 cytokine balance can be influenced by the initiating allergic trigger. For example, the house dust mite allergen Der p 2 mimics the activity of MD-2 by presenting lipopolysaccharide to Toll-like receptor-4 for the activation of inflammatory genes including innate-type cytokines. Here we discuss the functions of the novel cytokine players, thymic stromal lymphopoetin (TSLP), IL-33, IL-25, and IL-9 and delineate nonredundant roles for IL-4 and IL-13 in allergic disease. Persistent efforts in the characterization of these and other cytokine networks will be essential for understanding the complex pathogenic mechanisms that underpin allergic disease and for guiding targeted therapeutic interventions.

Chitinase Dependent Control of Protozoan Cyst Burden in the Brain

Chronic infections represent a continuous battle between the hosts immune system and pathogen replication. Many protozoan parasites have evolved a cyst lifecycle stage that provides it with increased protection from environmental degradation as well as endogenous host mechanisms of attack. In the case of Toxoplasma gondii, these cysts are predominantly found in the immune protected brain making clearance of the parasite more difficult and resulting in a lifelong infection. Currently, little is known about the nature of the immune response stimulated by the presence of these cysts or how they are able to propagate. Here we establish a novel chitinase-dependent mechanism of cyst control in the infected brain. Despite a dominant Th1 immune response during Toxoplasma infection there exists a population of alternatively activated macrophages (AAMØ) in the infected CNS. These cells are capable of cyst lysis via the production of AMCase as revealed by live imaging, and this chitinase is necessary for protective immunity within the CNS. These data demonstrate chitinase activity in the brain in response to a protozoan pathogen and provide a novel mechanism to facilitate cyst clearance during chronic infections.

Interleukin-6 neutralization alleviates pulmonary inflammation in mice exposed to cigarette smoke and poly(I:C)

Increased systemic and pulmonary levels of IL-6 (interleukin-6) are associated with the severity of exacerbations and decline of lung function in patients with COPD (chronic obstructive pulmonary disease). Whether IL-6 is directly involved or plays a bystander role in the pathophysiology of COPD remains unclear. Here we hypothesized that neutralizing circulating levels of IL-6 would modulate episodes of acute pulmonary inflammation following CS (cigarette smoke) exposure and virus-like challenges. For this purpose, we used a model where C57BL/6 mice were exposed to CS twice daily via a nose-only system, and concomitant periodic intranasal challenge with poly(I:C), a synthetic ligand for TLR3 (Toll-like receptor 3) that mimics the encounter with double stranded RNA that is carried by influenza-like viruses. This protocol recapitulates several aspects of acute pulmonary inflammation associated with COPD, including prominent airway neutrophilia, insensitivity to steroid treatment and increased levels of several inflammatory cytokines in BAL (bronchoalveolar lavage) samples. Although IL-6-deficient mice exposed to CS/poly(I:C) developed pulmonary inflammation similar to WT (wild-type) controls, WT mice exposed to CS/poly(I:C) and treated intraperitoneally with IL-6-neutralizing antibodies showed significantly lower blood counts of lymphocytes and monocytes, lower BAL levels of IL-6 and CXCL1 (CXC chemokine ligand 1)/KC (keratinocyte chemoattractant), as well as reduced numbers of BAL neutrophils, lymphocytes and macrophages. Our results thus indicate that the systemic neutralization of IL-6 significantly reduces CS/poly(I:C)-induced pulmonary inflammation, which may be a relevant approach to the treatment of episodes of acute pulmonary inflammation associated with COPD.

Acidic Mammalian Chitinase Is Not a Critical Target for Allergic Airway Disease

The expression of acidic mammalian chitinase (AMCase) is associated with Th2-driven respiratory disorders. To investigate the potentially pathological role of AMCase in allergic airway disease (AAD), we sensitized and challenged mice with ovalbumin or a combination of house dust mite (HDM) plus cockroach allergen. These mice were treated or not treated with small molecule inhibitors of AMCase, which significantly reduced allergen-induced chitinolytic activity in the airways, but exerted no apparent effect on pulmonary inflammation per se. Transgenic and AMCase-deficient mice were also submitted to protocols of allergen sensitization and challenge, yet we found little or no difference in the pattern of AAD between mutant mice and wild-type (WT) control mice. In a separate model, where mice were challenged only with intratracheal instillations of HDM without adjuvant, total bronchoalveolar lavage (BAL) cellularity, inflammatory infiltrates in lung tissues, and lung mechanics remained comparable between AMCase-deficient mice and WT control mice. However BAL neutrophil and lymphocyte counts were significantly increased in AMCase-deficient mice, whereas concentrations in BAL of IL-13 were significantly decreased compared with WT control mice. These results indicate that, although exposure to allergen stimulates the expression of AMCase and increased chitinolytic activity in murine airways, the overexpression or inhibition of AMCase exerts only a subtle impact on AAD. Conversely, the increased numbers of neutrophils and lymphocytes in BAL and the decreased concentrations of IL-13 in AMCase-deficient mice challenged intratracheally with HDM indicate that AMCase contributes to the Th1/Th2 balance in the lungs. This finding may be of particular relevance to patients with asthma and increased airway neutrophilia.

Modulation of IL-17A and TL1A largely abrogates house dust mite-induced lung inflammation in murine model of allergic airway disease

Recent studies suggest a role for Th17 responses in the increased airway neutrophilia associated with severe asthma. House dust mite (HDM) is a natural allergen to which asthmatics are often sensitized. Mice repeatedly challenged with HDM extract developed robust airway neutrophilia rapidly evolving into asthma-like disease with increased numbers of eosinophils and lymphocytes in bronchoalveolar lavages (BAL) as well as inflammatory infiltrates, vascular/muscular hypertrophy, interstitial fibrosis, epithelial hyperplasia and mucus accumulation in lung tissues. RNA and protein screening revealed a robust Th17 component post-HDM exposure. We thus evaluated whether IL-17A deficiency could modulate HDM-induced allergic airway disease. Airway neutrophilia was indeed abrogated in IL-17A deficient mice weekly challenged with HDM (acute model), however total BAL cellularity and lung mechanics remained comparable to those of HDM-challenged WT mice. In contrast, IL-17A deficient mice daily exposed to HDM (chronic model) had decreased BAL cellularity associated with reduced numbers of BAL macrophages, neutrophils, eosinophils and lymphocytes. Interestingly antibody neutralization of TL1A, a member of the TNF superfamily known to promote Th2 and Th17 responses, reduced BAL cellularity to baseline levels in HDM-challenged WT mice. Our results thus indicate that targeting Th17 responses can alleviate HDM-induced airway neutrophilia, and can also broadly modulate allergic airway disease.

Acidic mammalian chitinase is not a critical target for allergic airway disease in mice

The expression of acidic mammalian chitinase (AMCase) is associated with Th2-driven respiratory disorders. To investigate the potentially pathological role of AMCase in allergic airway disease (AAD), we sensitized and challenged mice with ovalbumin or a combination of house dust mite (HDM) plus cockroach allergen. These mice were treated or not treated with small molecule inhibitors of AMCase, which significantly reduced allergen-induced chitinolytic activity in the airways, but exerted no apparent effect on pulmonary inflammation per se. Transgenic and AMCase-deficient mice were also submitted to protocols of allergen sensitization and challenge, yet we found little or no difference in the pattern of AAD between mutant mice and wild-type (WT) control mice. In a separate model, where mice were challenged only with intratracheal instillations of HDM without adjuvant, total bronchoalveolar lavage (BAL) cellularity, inflammatory infiltrates in lung tissues, and lung mechanics remained comparable between AMCase-deficient mice and WT control mice. However BAL neutrophil and lymphocyte counts were significantly increased in AMCase-deficient mice, whereas concentrations in BAL of IL-13 were significantly decreased compared with WT control mice. These results indicate that, although exposure to allergen stimulates the expression of AMCase and increased chitinolytic activity in murine airways, the overexpression or inhibition of AMCase exerts only a subtle impact on AAD. Conversely, the increased numbers of neutrophils and lymphocytes in BAL and the decreased concentrations of IL-13 in AMCase-deficient mice challenged intratracheally with HDM indicate that AMCase contributes to the Th1/Th2 balance in the lungs. This finding may be of particular relevance to patients with asthma and increased airway neutrophilia.

Interleukin-6 neutralization alleviates acute exacerbation-like disease in a model of cigarette smoke-induced pulmonary inflammation

Increased systemic and pulmonary levels of interleukin (IL)-6 have been associated with the severity of acute exacerbations and accelerated decline of lung function in COPD patients. The demonstration that IL-6 plays a pivotal role in AE-related pulmonary symptoms and therefore represents a therapeutic target for the treatment of COPD, remains elusive. We used a murine model where C57BL/6 female mice are exposed to cigarette smoke (CS) twice daily through a nose-only system, while being punctually challenged intranasally with poly I:C, a synthetic ligand for Toll Like Receptor-3 (TLR3). This protocol recapitulates several aspects of pulmonary inflammation as seen in acute exacerbations of COPD, including prominent airway neutrophilia as well as increased levels of type I interferon, GM-CSF, IL-6, KC, MIP-1 alpha, RANTES, and TNF-alpha in bronchoalveolar lavage (BAL) samples. Using this model, IL-6 deficient mice showed a susceptibility to CS-induced pulmonary inflammation that, overall, was comparable to that found with wild-type (WT) control mice. In contrast, using the same model with WT mice treated intraperitoneally with IL-6 neutralizing antibodies (rat IgG1, clone MP5-20F3, 25 mg/kg thrice weekly) diminished blood counts of lymphocytes (p=0.0070) and monocytes (p=0.0091), while this treatment also depleted BAL levels of IL-6 (p=0.0002) and reduced BAL levels of KC (p=0.0220). Total BAL cellularity was found to be largely decreased (p<0.0001) as well as BAL numbers of neutrophils (p=0.0031), lymphocytes (p<0.0001) and macrophages (p<0.0001), while inflammatory infiltrates seemed reduced in lung tissue sections from treated mice. Our results show that the neutralization of IL-6 largely abrogates pulmonary inflammation in CS-exposed mice, and therefore indicate that IL-6 may be a valid therapeutic target for the treatment of COPD, in particular in episodes of acute exacerbation.