Phenotypic comparison of allergic airway responses to house dust mite in three rat strains

Specific allergen immunotherapy attenuates allergic airway inflammation in a rat model of Alstonia scholaris pollen induced airway allergy

Pollen grains are well established to be an important cause of respiratory allergy. Current pharmacologic therapies for allergic asthma do not cure the disease. Allergen specific immunotherapy is the only treatment method which re-directs the immune system away from allergic response leading to a long lasting effect. The mechanism by which immunotherapy achieves this goal is an area of active research world-wide. The present experimental study was designed to develop an experimental model of allergic lung inflammation based on a relevant human allergen, Alstonia scholaris pollen, and to establish the immunological and cellular features of specific allergen immunotherapy using this same pollen extract. Our results revealed that Alstonia scholaris pollen sensitization and challenge causes eosinophilic airway inflammation with mucin hypersecretion. This is associated with increased total IgE, increased expression of FcɛRI on lung mast cells and increased levels of IL-4, IL-5 & IL-13 as confirmed by ELISA, in-situ immunofluorescence and FACS assay. Allergen specific immunotherapy reduced airway inflammation and also decreased total IgE level, FcɛRI expression, IL-4, IL-5 & IL-13 levels. It was further noted that the reduction of these levels was more by intra-nasal route than by intra-peritoneal route. Thus we present a novel animal model of Alstonia scholaris pollen allergic disease and specific allergen immunotherapy which will pave the way towards the development of better treatment modalities.

Angiogenesis and airway reactivity in asthmatic Brown Norway rats

Expanded and aberrant bronchial vascularity, a prominent feature of the chronic asthmatic airway, might explain persistent airway wall edema and sustained leukocyte recruitment. Since it is well established that there are causal relationships between exposure to house dust mite (HDM) and the development of asthma, determining the effects of HDM in rats, mammals with a bronchial vasculature similar to humans, provides an opportunity to study the effects of bronchial angiogenesis on airway function directly. We studied rats exposed bi-weekly to HDM (Der p 1; 50 μg/challenge by intranasal aspiration, 1, 2, 3 weeks) and measured the time course of appearance of increased blood vessels within the airway wall. Results demonstrated that within 3 weeks of HDM exposure, the number of vessels counted within airway walls of bronchial airways (0.5-3 mm perimeter) increased significantly. These vascular changes were accompanied by increased airway responsiveness to methacholine. A shorter exposure regimen (2 weeks of bi-weekly exposure) was insufficient to cause a significant increase in functional vessels or reactivity. Yet, 19F/1H MR imaging at 3T following αvβ3-targeted perfluorocarbon nanoparticle infusion revealed a significant increase in 19F signal in rat airways after 2 weeks of bi-weekly HDM, suggesting earlier activation of the process of neovascularization. Although many antigen-induced mouse models exist, mice lack a bronchial vasculature and consequently lack the requisite human parallels to study bronchial edema. Overall, our results provide an important new model to study the impact of bronchial angiogenesis on chronic inflammation and airways hyperreactivity.

Vagal afferents contribute to exacerbated airway responses following ozone and allergen challenge

Brown-Norway rats (n=113) sensitized and challenged with nDer f 1 allergen were used to examine the contribution of lung sensory nerves to ozone (O(3)) exacerbation of asthma. Prior to their third challenge rats inhaled 1.0ppm O(3) for 8h. There were three groups: (1) control; (2) vagus perineural capsaicin treatment (PCT) with or without hexamethonium; and (3) vagotomy. O(3) inhalation resulted in a significant increase in lung resistance (R(L)) and an exaggerated response to subsequent allergen challenge. PCT abolished the O(3)-induced increase in R(L) and significantly reduced the increase in R(L) induced by a subsequent allergen challenge, while hexamethonium treatment reestablished bronchoconstriction induced by allergen challenge. Vagotomy resulted in a significant increase in the bronchoconstriction induced by O(3) inhalation and subsequent challenge with allergen. In this model of O(3) exacerbation of asthma, vagal C-fibers initiate reflex bronchoconstriction, vagal myelinated fibers initiate reflex bronchodilation, and mediators released within the airway initiate bronchoconstriction.

Moving towards a new generation of animal models for asthma and COPD with improved clinical relevance

Asthma and chronic obstructive pulmonary disease (COPD) are complex inflammatory airway diseases characterised by airflow obstruction that remain leading causes of hospitalization and death worldwide. Animal modelling systems that accurately reflect disease pathophysiology continue to be essential to the development of new therapies for both conditions. In this review, we describe preclinical in vivo models that recapitulate many of the features of asthma and COPD. Specifically, we discuss the pro's and con's of the standard models and highlight recently developed systems designed to more accurately reflect the complexity of both diseases. For instance, clinically relevant allergens (i.e. house dust mite) are now being used to mimic the inflammatory changes and airway remodelling that result after chronic allergen exposures. Additionally, systems are being developed to mimic steroid-resistant and viral exacerbations of allergic inflammation - aspects of asthma where there is an acute need for new therapies. Similarly, COPD models have evolved to align with the improved clinical understanding of the factors contributing to disease progression. This includes using cigarette smoke to model not only airway inflammation and remodelling, but some systemic changes (e.g. hypertension and skeletal muscle alterations) that are thought to influence disease. Further, mouse genetics are being exploited to gain insights into the genetics of COPD susceptibility. The new models of asthma and COPD described herein demonstrate that improved clinical understanding of the diseases and better preclinical models is an iterative process that will hopefully lead to therapies that can effectively manage severe asthma and COPD.

BN.MES-Cyba(mes) congenic rats manifest focal necrosis with eosinophilic infiltration in the liver without blood eosinophilia

The Matsumoto Eosinophilia Shinshu (MES) rat strain develops hereditary blood eosinophilia and eosinophil-related inflammatory lesions in organs due to the mutant Cyba(mes) gene. We hypothesized that a new eosinophilia model with a different phenotype could be established by changing the genetic background of rats. We bred and characterized a congenic strain, in which the mutant Cyba(mes) gene was introduced into the background of a BN strain (BN.MES-Cyba(mes)). The congenic rats showed robust proliferation of eosinophils in the bone marrow. Nonetheless, blood eosinophil levels of the rats remained within the normal range. In addition, the rats manifested focal necrosis with eosinophilic infiltration in the liver, a phenotype rarely observed in the original MES rat strain. These results imply the presence of genetic polymorphisms between MES and BN strains which modulate the mobilization of eosinophils to the peripheral circulation and organs. The newly established BN.MES-Cyba(mes) congenic rat strain, together with the original MES strain, will provide useful models for elucidating the molecular genetic mechanisms involved in the development and trafficking of eosinophils.

Effects of Hemoglobin Vesicles, a Liposomal Artificial Oxygen Carrier, on Hematological Responses, Complement and Anaphylactic Reactions in Rats

Hemoglobin vesicle (HbV), a liposomal oxygen carrier containing human hemoglobin, was intravenously infused into rats. After the infusion of saline, the HbV or empty vesicle (EV), numbers of red cells, leukocytes and platelets in peripheral blood were unchanged during the observation period of one week in addition to each time point among three groups. However, the lymphocyte ratio transiently decreased and the granulocyte ratio increased in the HbV and EV groups at 6 h after the infusion. Those changes returned to the initial value one day after the infusion and those were maintained for the subsequent observation period. No dramatic change was seen in the ratio of CD4(+)/CD8(+) T cells. A transient decrease of the complement titer was observed three days after the infusion of HbV and EV, although the consumption of complement titer was not detected in rat serum by mixing HbV or EV in vitro, indicating that the transient decrease of complement titer in vivo was not due to the consumption of complement due to the interaction with HbV or EV. Multiple infusions of HbV caused the decrease of complement titer only after the first infusion and no allergic reaction was observed. No anaphylactic shock was observed in rats administered with EV several times, while ovalbumin (OVA) sensitized rats died with symptoms of respiratory distress after the second OVA administration. These results indicate that HbV could be administered without serious clinical symptoms or adverse reactions.

Nicotine primarily suppresses lung Th2 but not goblet cell and muscle cell responses to allergens

Allergic asthma, an inflammatory disease characterized by the infiltration and activation of various leukocytes, the production of Th2 cytokines and leukotrienes, and atopy, also affects the function of other cell types, causing goblet cell hyperplasia/hypertrophy, increased mucus production/secretion, and airway hyperreactivity. Eosinophilic inflammation is a characteristic feature of human asthma, and recent evidence suggests that eosinophils also play a critical role in T cell trafficking in animal models of asthma. Nicotine is an anti-inflammatory, but the association between smoking and asthma is highly contentious and some report that smoking cessation increases the risk of asthma in ex-smokers. To ascertain the effects of nicotine on allergy/asthma, Brown Norway rats were treated with nicotine and sensitized and challenged with allergens. The results unequivocally show that, even after multiple allergen sensitizations, nicotine dramatically suppresses inflammatory/allergic parameters in the lung including the following: eosinophilic/lymphocytic emigration; mRNA and/or protein expression of the Th2 cytokines/chemokines IL-4, IL-5, IL-13, IL-25, and eotaxin; leukotriene C(4); and total as well as allergen-specific IgE. Although nicotine did not significantly affect hexosaminidase release, IgG, or methacholine-induced airway resistance, it significantly decreased mucus content in bronchoalveolar lavage; interestingly, however, despite the strong suppression of IL-4/IL-13, nicotine significantly increased the intraepithelial-stored mucosubstances and Muc5ac mRNA expression. These results suggest that nicotine modulates allergy/asthma primarily by suppressing eosinophil trafficking and suppressing Th2 cytokine/chemokine responses without reducing goblet cell metaplasia or mucous production and may explain the lower risk of allergic diseases in smokers. To our knowledge this is the first direct evidence that nicotine modulates allergic responses.

Development and characterisation of a novel and rapid lung eosinophil influx model in the rat

Eosinophils play a major role in the development and severity of asthma. Robust and rapid preclinical animal models are desirable to profile novel therapeutics inhibiting the influx of eosinophils into the airways. To develop a rapid, airway eosinophil recruitment model in the rat, Brown-Norway (BN) rats were immunised with ovalbumin (OVA)/alum on day 0, 1 and 2 and challenged with OVA aerosol on day 5 and 6. On day 7 bronchoalveolar lavage fluid (BALF) was analysed for eosinophil numbers, eosinophil peroxidase (EPO) activity and cytokines. Lung sections were also examined. The immunised animals showed a strong selective influx of eosinophils into the airways correlating with enhanced EPO activity, Interleukin (IL-4), IL-5 and monocytes chemo attractant protein levels in the BALF in comparison to sham-sensitised rats. In addition the immunised rats developed goblet cell metaplasia in the lung and showed OVA specific IgG1 and IgE levels in the serum but no airway hyperreactivity after metacholine challenge. Airway inflammation was suppressed by applying the steroids Budesonide (intra tracheally) and Prednisolone (per orally), Roflumilast a phosphodiesterase-4 inhibitor, and the H1 receptor antagonists Epinastine and Ketotifen. Montelukast, a Leukotriene receptor antagonist and Chromoglycate, a mast cell stabiliser, had no effect in this model. In summary, in this novel preclinical rat model therapeutics expected to inhibit the development of airway eosinophilia can rapidly be tested.

Enhanced glucocorticoid receptor signaling in T cells impacts thymocyte apoptosis and adaptive immune responses

To study the effect of enhanced glucocorticoid signaling on T cells, we generated transgenic rats overexpressing a mutant glucocorticoid receptor with increased ligand affinity in the thymus. We found that this caused massive thymocyte apoptosis at physiological hormone levels, which could be reversed by adrenalectomy. Due to homeostatic proliferation, a considerable number of mature T lymphocytes accumulated in the periphery, responding normally to costimulation but exhibiting a perturbed T-cell repertoire. Furthermore, the transgenic rats showed increased resistance to experimental autoimmune encephalomyelitis, which manifests in a delayed onset and milder disease course, impaired leukocyte infiltration into the central nervous system and a distinct cytokine profile. In contrast, the ability of the transgenic rats to mount an allergic airway response to ovalbumin was not compromised, although isotype switching of antigen-specific immunoglobulins was altered. Collectively, our findings suggest that endogenous glucocorticoids impact T-cell development and favor the selection of Th2- over Th1-dominated adaptive immune responses.

Local pulmonary immune stimulation by the Toll-like receptor 2 and 6 ligand MALP-2 in rats is age dependent

Recent studies indicate that the pulmonary immune response in humans and experimental animals is different in newborn, adult and elderly age groups. The aim of this study was to investigate the influence of age on the leukocyte composition in different lung compartments and peripheral blood of weaned and adult rats. A mycoplasma-like inflammatory response was mimicked by intratracheal application of the synthetic macrophage-activating lipopeptide-2 (MALP-2) which activates macrophages and other cells via the Toll-like receptor (TLR) 2 and 6. TLR 2 and 6 mRNA expressions were investigated by semiquantitative RT-PCR in cells of the bronchoalveolar lavage (BAL) and lung interstitium. Weaned Lewis rats (3-4 weeks old) and adults (12-14 months old) were treated with vehicle control or MALP-2. Cytokines and cell infiltration were measured in the BAL and lung interstitium. In control rats, no differences in TLR 2 and 6 mRNA expression level were found between the age groups. After MALP-2 treatment, the maximum of MCP-1 concentration in the BAL fluid was reached in weaned rats after 4h and in adults after 2h. The TNF-alpha maximum was measured after 2h in both age groups. Three days after MALP-2 the numbers of different leukocyte subsets were significantly increased in the BAL of both groups. In contrast, in the lung interstitium MALP-2 induced a leukocyte increase in adult rats but not in weaned rats. In conclusion, data on pulmonary immune responses from one age group and one lung compartment should not be generalized or extrapolated to other groups.

Leukocyte infiltration of the periarterial space of the lung after allergen provocation in a rat asthma model

The periarterial space has recently been described and its physiological and pathophysiological role during inflammatory and allergic reactions has been reviewed. The present studies used a light-/electron-microscopic approach to characterize the periarterial space in an asthma model in Brown Norway rats. After repeated sensitization with ovalbumin and heat-killed Bordetella pertussis bacilli, airway challenge was carried out after 1 further week. Four or 24 h after challenge, rats were fixed by perfusion or instillation and processed for microscopy. Several periarterial capillaries and connective tissue characterized the tissue between small pulmonary arteries, bronchioles and alveolar septa. Additionally, a partly pronounced interstitial edema was seen independent of the kind of fixation. Not only small arteries but also arterioles and venules were partly surrounded by edematous fluid already visible by light microscopy. Within the connective tissue and within the periarterial fluid, numerous leukocytes, predominantly eosinophils, were found. However, leukocytes were detected only rarely in the vascular lumen. Only sporadically were eosinophils seen in the wall of small arteries or venules. Eosinophils transmigrating the endothelium of capillaries or arterioles were not visible 4 or 24 h after challenge. Thus, granulocytes transmigrate in the periarterial space very rapidly or even earlier than 4 h after challenge. The location of transmigration in the periarterial space needs further investigation.

Localization of Eutr2, a locus controlling susceptibility to DES-induced uterine inflammation and pyometritis, to RNO5 using a congenic rat strain

In some rat strains chronic administration of exogenous estrogens induces pyometritis, an inflammation of the uterus associated with infection, suggesting that there is genetic variation in susceptibility to estrogen-induced inflammation and pyometritis. In this article we report that following 10 weeks of treatment with the synthetic estrogen diethylstilbestrol (DES), Fisher 344 (F344) rats exhibit modest uterine inflammation and a 0% incidence of pyometritis. By contrast, under identical experimental conditions, Brown Norway (BN) rats exhibit significant inflammation and a 100% incidence of pyometritis. Similarly, we also observed profound uterine inflammation and a 100% incidence of pyometritis in a congenic rat strain in which a segment of RNO5 from the BN strain is carried on the F344 strain. These data suggest that a locus on RNO5 controls both the magnitude of DES-induced uterine inflammation and susceptibility to DES-induced pyometritis. This locus, designated Eutr2, resides within the same segment of RNO5 as the Eutr1 locus, which confers susceptibility to E2-induced pyometritis in an F2 population generated in a cross between the BN and August x Copenhagen 9935, Irish (ACI) strains.

The Periarterial Space in the Lung: Its Important Role in Lung Edema, Transplantation, and Microbial or Allergic Inflammation

In mammal lungs different compartments for leukocytes can be identified during health and disease, e.g. lung interstitium, bronchoalveolar space, the epithelium and lamina propria of the air-conducting part. A so far neglected compartment is the space around the branches of the pulmonary arteries, characterized by a unique architecture of capillaries running in parallel to the pulmonary artery. This compartment - the periarterial space - is described and its physiological and pathophysiological role reviewed. The periarterial space is infiltrated by different leukocyte subsets during edema formation in the early stages of a lung transplant rejection and, in particular, during inflammatory and allergic reactions. The periarterial compartment seems to be of major relevance in all these situations.