Johan Kips

The ENFUMOSA cross-sectional European multicentre study of the clinical phenotype of chronic severe asthma

Since severe asthma is a poorly understood, major health problem, 12 clinical specialist centres in nine European countries formed a European Network For Understanding Mechanisms Of Severe Asthma (ENFUMOSA). In a cross-sectional observational study, a total of 163 subjects with severe asthma were compared with 158 subjects whose asthma was controlled by low doses of inhaled corticosteroids (median dose of beclomethasone equivalents 666 µg). Despite being treated with higher doses of inhaled corticosteroids (median dose 1773 µg) and for a third of the severe asthmatics also being treated with regular, oral-steroid therapy (median daily dose 19 mg), the subjects with severe asthma met the inclusion criteria. The criteria required subjects to have undergone at least one asthma exacerbation in the past year requiring oral steroid treatment. Females dominated the severe asthma group (female/male ratio 4.4:1 versus 1.6:1 in the controlled asthmatics), and compared with controlled asthmatics, they had a predominantly neutrophilic inflammation (sputum neutrophils, 36 versus 28%) and evidence of ongoing mediator release but less atopy. From these findings and other physiological and clinical data reported in this paper, it is suggested that severe asthma might be a different form of asthma rather than an increase in asthma symptoms. The findings prompt for longitudinal studies and interventions to define the mechanisms in severe asthma.

Attenuation of allergic airway inflammation in IL‐4 deficient mice

To investigate the role of IL‐4 in vivo in allergic asthma, we developed a murine model of allergen‐induced airway inflammation. Repealed daily exposures of actively immunised C57BL/6 mice to aerosolized ovalbumin (OVA) induced a peribronchial inflammation and an increase in eosinophils and lymphocytes in bronchoalveolar‐lavage(BAL) fluid. In IL‐4 deficient (IL4−/−) mice, treated in the same way, there were substantially fewer eosinophils in BAL and much less peribronchial inflammation compared with wild type mice. In this model, mast cell deficient (W/Wv) mice developed a similar degree of BAL eosinophilia and peribronchial inflammation as wild type mice, demonstrating that the mast cell is not required for the induction of chronic airway inflammation. In contrast, BAL eosinophilia and airway inflammation were absent in OVA‐treated MHC ClassII deficient (B6.Aa−/−) mice which lack mature CD4+ T lymphocytes. In conclusion, these results indicate that IL‐4 is a central mediator of allergic airway inflammation, regulating antigen‐induced eosinophil recruitment into the airways by a T cell dependent mechanism.

Murine models of asthma.

In vivo animal models can offer valuable information on several aspects of asthma pathogenesis and treatment. The mouse is increasingly used in these models, mainly because this species allows for the application in vivo of a broad range of immunological tools, including gene deletion technology. Mice, therefore, seem particularly useful to further elucidate factors influencing the response to inhaled allergens. Examples include: the role of immunoregulatory mechanisms that protect against T‐helper cell type 2 cell development; the trafficking of T‐cells; and the contribution of the innate immunity. However, as for other animal species, murine models also have limitations. Mice do not spontaneously develop asthma and no model mimics the entire asthma phenotype. Instead, mice should be used to model specific traits of the human disease. The present task force report draws attention to specific aspects of lung structure and function that need to be borne in mind when developing such models and interpreting the results. In particular, efforts should be made to develop models that mimic the lung function changes characteristic of asthma as closely as possible. A large section of this report is therefore devoted to an overview of airway function and its measurement in mice.

Airway eosinophilia is not a requirement for allergen-induced airway hyperresponsiveness.

House dust mites (HDMs) are the major source of perennial allergens causing human allergic asthma. Animal models mimicking as closely as possible the allergic features observed in human asthma are therefore interesting tools for studying the immunological and pathophysiological mechanisms involved. Especially the role of eosinophils and allergen‐specific immunoglobulin (Ig) E in the pathophysiology of airway hyperresponsiveness (AHR) remains a subject of intense debate.

Cytokines in asthma

The airway inflammation underlying asthma is regulated by a network of mutually interacting cytokines. The exact functional role of each individual cytokine in the pathogenesis of the disease remains to be fully established. Type 2 T‐helper cells are currently considered to play a crucial role in this process. In vivo animal data suggest a sequential involvement of interleukin (IL)‐4 and IL‐5 in the induction of allergen-induced airway changes. The potential role of other type 2 T‐helper cell-like cytokines in asthma is increasingly being recognized. In particular, IL‐4 and -13 display a large degree of redundancy. Whereas IL‐4 seems to be crucial in the primary allergen sensitization process, IL-13 might be more important during secondary exposure to aerosolized allergen. Animal models also indicate that T‐cell-derived cytokine production, rather than eosinophil influx or immunoglobulin‐E synthesis, is causally related to altered airway behaviour. An important aspect when evaluating the functional role of cytokines in a complex disease such as asthma is the interaction with other cytokines in the microenvironment. Increased expression of pro-inflammatory cytokines such as tumour necrosis factor‐α can further enhance the inflammatory process, and is increasingly linked to disease severity. In addition, decreased expression of immunoregulatory cytokines, including interleukin-12, interleukin-18 or interferon gamma could also strengthen the type 2 T‐helper cell-driven inflammatory process.

Endogenous interleukin-10 suppresses allergen-induced airway inflammation and nonspecific airway responsiveness.

The airway inflammation observed in asthma is orchestrated by activated Th‐2 lymphocytes relevant for the induction of altered airway responsiveness. An increasing body of evidence is accumulating that not only the pro‐inflammatory cytokines interleukin (IL)‐4 and IL‐5 but also the immunomodulating cytokines IL‐12 and possibly IL‐10 are crucial for regulating the allergic airway inflammation.

THE POTENTIAL ROLE OF TUMOUR NECROSIS FACTOR ALPHA IN ASTHMA

It has clearly been established over the past few years that asthma is accompanied by airway inflammation [1-3]. This chronic inflammatory state is considered to be intimately related to the pathogenesis of non-speciflc bronchial hyperresponsiveness (BHR), a key feature in asthma [4]. Various aspects in the pathogenesis of the allergic airway inflammation and its precise relationship to bronchial hyperresponsiveness, however, remain unclear. One of the pieces of the puzzle concerns the significance of cytokines in this process. The importance of these cytokines in the orchestration of an allergic inflammatory response is currently emerging. Various cytokines or their mRNA precursors have been shown to be present in bronchial biopsies or bronchoalveolar lavage (BAL) fluid from asthmatics. These include tumour necrosis factor a (TNFa), interleukin-1 (IL-1), IL-2, IL-3, IL-4, IL-5, IL-6 and granulocyte macrophage colony stimulating factor (GMCSF) [5-9]. The exact role of each of these cytokines in the pathogenesis of asthma remains to be fully established.

Importance of lnterleukin-4 and lnterleukin-12 in Allergen-Induced Airway Changes in Mice

T helper 2 (Th2)-like cells are thought to play a crucial role in the pathogenesis of atopic asthma. In this study, we attempted to evaluate the in vivo effect of suppressing Th2 cell development on allergen-induced airway changes. Repeated exposure of actively sensitized C57Bl/6 mice to aerosolized ovalbumin (OA) causes, in comparison to saline-exposed control animals, synthesis of specific IgE, increase of eosinophils in bronchoalveolar lavage fluid and airway hyperresponsiveness. These effects are not observed in OA-exposed, sensitized IL-4-knockout mice. Likewise, these effects are inhibited in OA-exposed C57Bl/6 mice treated with IL-12 during initial antigen exposure. These results suggest that suppressing Th2 cell development in vivo might have profound inhibitory effects on allergen-induced airway changes.

Sequential Development of Airway Hyperresponsiveness and Acute Airway Obstruction in a Mouse Model of Allergic Inflammation

Background: Mouse models have been established mirroring key features of human bronchial asthma including airway hyperresponsiveness (AHR). Acute airway obstruction in response to an allergen challenge, however, remains to be demonstrated in these models. Objective: A mouse model of allergic lung inflammation was employed to analyze the development of specific (allergen-induced) and nonspecific (methacholine-induced) airway obstruction. Methods: Mice were sensitized to ovalbumin (OVA) and challenged with OVA aerosol twice each week during four weeks. Changes in lung functions were determined by noninvasive head-out body plethysmography. The development of acute airway obstruction after OVA challenge and AHR after methacholine aerosol application were assessed by a decrease in the mid-expiratory flow rate (EF50). Results: Two airway challenges were sufficient to induce AHR (5.7 vs. 15 mg/ml methacholine). Further OVA challenges reduced the baseline EF50 from 1.85 to 1.20 ml/s (4th week) and induced acute airway obstruction. The OVA-induced obstruction was maximal in the 4th week (EF50 = 0.91 ml/s). Conclusion: The development of acute airway obstruction in allergen-sensitized mice was demonstrated by means of head-out body plethysmography. In our model, AHR was observed before the development of airway obstruction.

Intranasal and inhaled fluticasone propionate for pollen-induced rhinitis and asthma.

Background:  Studies suggest that nasal treatment might influence lower airway symptoms and function in patients with comorbid rhinitis and asthma. We investigated the effect of intranasal, inhaled corticosteroid or the combination of both in patients with both pollen‐induced rhinitis and asthma.