Increased Mast Cell Density and Airway Responses to Allergic and Non-Allergic Stimuli in a Sheep Model of Chronic Asthma

BACKGROUND: Increased mast cell (MC) density and changes in their distribution in airway tissues is thought to contribute significantly to the pathophysiology of asthma. However, the time sequence for these changes and how they impact small airway function in asthma is not fully understood. The aim of the current study was to characterise temporal changes in airway MC density and correlate these changes with functional airway responses in sheep chronically challenged with house dust mite (HDM) allergen. METHODOLOGY/PRINCIPAL FINDINGS: MC density was examined on lung tissue from four spatially separate lung segments of allergic sheep which received weekly challenges with HDM allergen for 0, 8, 16 or 24 weeks. Lung tissue was collected from each segment 7 days following the final challenge. The density of tryptase-positive and chymase-positive MCs (MC(T) and MC(TC) respectively) was assessed by morphometric analysis of airway sections immunohistochemically stained with antibodies against MC tryptase and chymase. MC(T) and MC(TC) density was increased in small bronchi following 24 weeks of HDM challenges compared with controls (P<0.05). The MC(TC)/MC(T) ratio was significantly increased in HDM challenged sheep compared to controls (P<0.05). MC(T) and MC(TC) density was inversely correlated with allergen-induced increases in peripheral airway resistance after 24 weeks of allergen exposure (P<0.05). MC(T) density was also negatively correlated with airway responsiveness after 24 challenges (P<0.01). CONCLUSIONS: MC(T) and MC(TC) density in the small airways correlates with better lung function in this sheep model of chronic asthma. Whether this finding indicates that under some conditions mast cells have protective activities in asthma, or that other explanations are to be considered requires further investigation

A novel segmental challenge model for bleomycin-induced pulmonary fibrosis in sheep

Background: Idiopathic Pulmonary fibrosis (IPF) is a fatal respiratory disease, characterized by a progressive fibrosis and worsening lung function. While the outcomes of recent clinical trials have resulted in therapies to slow the progression of the disease, there is still a need to develop alternative therapies, which are able to prevent fibrosis. Aim: This study uses a segmental lung infusion of bleomycin (BLM) to investigate pulmonary fibrosis in a physiologically relevant large animal species. Methods: Two separate lung segments in eight sheep received two fortnightly challenges of either 3U or 30U BLM per segment, and a third segment received saline (control). Lung function was assessed using a wedged-bronchoscope procedure. Bronchoalveolar lavage fluid and lung tissue were assessed for inflammation, fibrosis and collagen content two weeks after the final dose of BLM. Results: Instillation of both BLM doses resulted in prominent fibrosis in the treated lobes. More diffuse fibrosis and loss of alveolar airspace was observed in high-dose BLM-treated segments, while multifocal fibrosis was seen in low-dose BLM-treated segments. Extensive and disorganised collagen deposition occurred in the BLM-treated lobes, compared to controls. Significant loss of lung compliance was also observed in the BLM-treated lobes, which did not occur in controls. Conclusions: Fibrosis comparable to IPF was induced into isolated lung segments, without compromising the respiratory functioning of the animal. This model may have potential for investigating novel therapies for IPF by allowing direct comparison of multiple treatments with internal controls, and sampling and drug delivery that are clinically relevant

The Effects of Tumstatin on Vascularity, Airway Inflammation and Lung Function in an Experimental Sheep Model of Chronic Asthma

Tumstatin, a protein fragment of the alpha-3 chain of Collagen IV, is known to be significantly reduced in the airways of asthmatics. Further, there is evidence that suggests a link between the relatively low level of tumstatin and the induction of angiogenesis and inflammation in allergic airway disease. Here, we show that the intra-segmental administration of tumstatin can impede the development of vascular remodelling and allergic inflammatory responses that are induced in a segmental challenge model of experimental asthma in sheep. In particular, the administration of tumstatin to lung segments chronically exposed to house dust mite (HDM) resulted in a significant reduction of airway small blood vessels in the diameter range 10(+)-20 mu m compared to controls. In tumstatin treated lung segments after HDM challenge, the number of eosinophils was significantly reduced in parenchymal and airway wall tissues, as well as in the bronchoalveolar lavage fluid. The expression of VEGF in airway smooth muscle was also significantly reduced in tumstatin-treated segments compared to control saline-treated segments. Allergic lung function responses were not attenuated by tumstatin administration in this model. The data are consistent with the concept that tumstatin can act to suppress vascular remodelling and inflammation in allergic airway disease

K(Ca)3.1 channel-blockade attenuates airway pathophysiology in a sheep model of chronic asthma.

BACKGROUND: The Ca[superscript: 2+]-activated K[superscript: +] channel K[subscript: Ca]3.1 is expressed in several structural and inflammatory airway cell types and is proposed to play an important role in the pathophysiology of asthma. The aim of the current study was to determine whether inhibition of K[subscript: Ca]3.1 modifies experimental asthma in sheep. METHODOLOGY AND PRINCIPAL FINDINGS: Atopic sheep were administered either 30 mg/kg Senicapoc (ICA-17073), a selective inhibitor of the K[subscript: Ca]3.1-channel, or vehicle alone (0.5% methylcellulose) twice daily (orally). Both groups received fortnightly aerosol challenges with house dust mite allergen for fourteen weeks. A separate sheep group received no allergen challenges or drug treatment. In the vehicle-control group, twelve weeks of allergen challenges resulted in a 60±19% increase in resting airway resistance, and this was completely attenuated by treatment with Senicapoc (0.25±12%; n = 10, P = 0.0147). The vehicle-control group had a peak-early phase increase in lung resistance of 82±21%, and this was reduced by 58% with Senicapoc treatment (24±14%; n = 10, P = 0.0288). Senicapoc-treated sheep also demonstrated reduced airway hyperresponsiveness, requiring a significantly higher dose of carbachol to increase resistance by 100% compared to allergen-challenged vehicle-control sheep (20±5 vs. 52±18 breath-units of carbachol; n = 10, P = 0.0340). Senicapoc also significantly reduced eosinophil numbers in bronchoalveolar lavage taken 48 hours post-allergen challenge, and reduced vascular remodelling. CONCLUSIONS: These findings suggest that K[subscript: Ca]3.1-activity contributes to allergen-induced airway responses, inflammation and vascular remodelling in a sheep model of asthma, and that inhibition of K[subscript: Ca]3.1 may be an effective strategy for blocking allergen-induced airway inflammation and hyperresponsiveness in humans