Kinetics of eosinophilia and eosinophil activation in the development of non-allergic bronchial hyperresponsiveness in guinea pigs injected with Sephadex beads

The changing role of eosinophils in long-term hyperreactivity following a single ozone exposure

Ozone hyperreactivity over 24 h is mediated by blockade of inhibitory M2 muscarinic autoreceptors by eosinophil major basic protein. Because eosinophil populations in the lungs fluctuate following ozone, the contribution of eosinophils to M2 dysfunction and airway hyperreactivity was measured over several days. After one exposure to ozone, M2 function, vagal reactivity, smooth muscle responsiveness, and inflammation were measured in anesthetized guinea pigs. Ozone-induced hyperreactivity to vagal stimulation persisted over 3 days. Although hyperreactivity one day after ozone is mediated by eosinophils, AbVLA-4 did not inhibit either eosinophil accumulation in the lungs or around the nerves or prevent hyperreactivity at this time point. Two days after ozone, eosinophils in BAL, around airway nerves and in lungs, were decreased, and neuronal M2 receptor function was normal, although animals were still hyperreactive to vagal stimulation. Depleting eosinophils with AbIL-5 prevented hyperreactivity, thus eosinophils contribute to vagal hyperreactivity by mechanisms separate from M2 receptor blockade. Three days after ozone, vagal hyperreactivity persisted, eosinophils were again elevated in BAL in lungs and around nerves, and M2 receptors were again dysfunctional. At this point, airway smooth muscle was also hyperresponsive to methacholine. Eosinophil depletion with AbIL-5, AbVLA-4, or cyclophosphamide protected M2 function 3 days after ozone and prevented smooth muscle hyperreactivity. However, vagal hyperreactivity was significantly potentiated by eosinophil depletion. The site of hyperreactivity, muscle or nerve, changes over 3 days after a single exposure to ozone. Additionally, the role of eosinophils is complex; they mediate hyperreactivity acutely while chronically may be involved in repair.

Role of tachykinins in sephadex-induced airway hyperreactivity and inflammation in guinea pigs

We have studied the effect of selective tachykinin NK(1) and NK(2) receptor antagonists on airway hyperreactivity to acetylcholine and increase of inflammatory cells on bronchoalveolar lavage fluid induced by sephadex beads (20 mg/kg, i.v.) in guinea pigs. Airway hyperreactivity was assessed by measuring the increase of bronchial insufflation pressure to acetylcholine (0.01-30 micromol/kg, i.v.) at 3 h (early phase) and 24 h (late phase) after sephadex administration. An increase in inflammatory cells in bronchoalveolar lavage fluid (eosinophils and macrophages) was detected at 24 h (from 11.6 x 10(6) to 49.3 x 10(6) cells) but not at 3 h from sephadex administration. Neurokinin A and substance P levels in bronchoalveolar lavage fluid showed a significant increase at 24 h (from 31.7+/-11.6 to 561+/-231 pg/ml and from 5.9+/-2.6 to 29.3+/-4.1 pg/ml for neurokinin A and substance P, respectively). At this time point, the tachykinin in bronchoalveolar lavage cellular content was depleted from 232+/-43 to 21+/-20 pg/sample and from 56.6+/-6.7 to 2+/-2 pg/sample for neurokinin A and substance P, respectively. Capsaicin pretreatment abolished the early but not the late phase of airway hyperreactivity induced by sephadex without modifying bronchoalveolar lavage total cells number and bronchoalveolar lavage levels of neurokinin A and substance P. Administration of the tachykinin NK(2) (nepadutant) and/or the NK(1) receptor antagonist (MEN 11467 or (1R,2S)-2-N[1(H)indol-3-yl-carbonyl]-1-N[N-(p-tolylacetyl)-N-(methyl)-D-3(2-naphthyl)alanyl)diaminocyclohexane)), 5 min before sephadex, prevented the early phase of airway hyperreactivity to acetylcholine but only nepadutant prevented the late phase. Nepadutant was able to abolish the early phase of airway hyperreactivity if given after sephadex administration and reduced by about 50% the increase of cell number in bronchoalveolar lavage fluid during the late phase, without affecting the levels of neurokinin A and substance P. These findings indicate an involvement of endogenous tachykinins in the genesis of airway hyperreactivity in a guinea-pig model of non-allergic asthma. Early airway hyperreactivity apparently involves release of tachykinins from capsaicin-sensitive afferent nerves acting via tachykinin NK(1)/NK(2) receptors. Late airway hyperreactivity involves tachykinins acting via tachykinin NK(2) receptors: inflammatory cells activated/recruited in response to sephadex challenge appear a likely source of tachykinins involved in the late phase of the response.

Critical role for T cells in Sephadex-induced airway inflammation: pharmacological and immunological characterization and molecular biomarker identification

Intratracheal instillation of Sephadex particles is a convenient model for assessing the impact of potential anti-inflammatory compounds on lung eosinophilia thought to be a key feature in asthma pathophysiology. However, the underlying cellular and molecular mechanisms involved are poorly understood. We have studied the time course of Sephadex-induced lung eosinophilia, changes in pulmonary T cell numbers, and gene and protein expression as well as the immunological and pharmacological modulation of these inflammatory indices in the Sprague Dawley rat. Sephadex increased T cell numbers (including CD4(+) T cells) and evoked a pulmonary eosinophilia that was associated with an increase in gene/protein expression of the Th2-type cytokines IL-4, IL-5, and IL-13 and eotaxin in lung tissue. Sephadex instillation also induced airway hyperreactivity to acetylcholine and bradykinin. A neutralizing Ab (R73) against the alphabeta-TCR caused 54% depletion of total (CD2(+)) pulmonary T cells accompanied by a significant inhibition of IL-4, IL-13 and eotaxin gene expression together with suppression (65% inhibition) of eosinophils in lung tissue 24 h after Sephadex treatment. Sephadex-induced eosinophilia and Th2 cytokine gene and/or protein expression were sensitive to cyclosporin A and budesonide, compounds that inhibit T cell function, suggesting a pivotal role for T cells in orchestrating Sephadex-induced inflammation in this model.

Involvement of bradykinin B1 and B2 receptors in pulmonary leukocyte accumulation induced by Sephadex beads in guinea pigs

The effects of selected bradykinin receptor antagonists on leukocyte infiltration into the lungs were studied in a model of guinea pig lung inflammation induced by the intravenous injection of Sephadex beads. The bradykinin B1 receptor antagonist, [Leu8]desArg9-BK (40 mg kg(-1) 24 h(-1)) and the bradykinin B2 receptor antagonist, DArg[Hyp3,Thi5,DTic7,Oic8]BK (code name HOE 140; 4 mg kg(-1) 24 h(-1)), administered intravenously by osmotic pumps, significantly reduced eosinophil counts by 33% and 42% in bronchoalveolar fluid, respectively. HOE 140 decreased neutrophil counts by 35%. LysLys[Hyp3,Igl5,D-Igl7,Oic8]desArg9BK+ ++ (code name B 9858), a newly described bradykinin B1 receptor antagonist, administered intraperitoneally (1 mg kg(-1)), decreased eosinophil and neutrophil counts by 45% in bronchoalveolar fluid. D-Arg[Hyp3,Igl5,D-Igl7,Oic8]BK (code name B 9430), a non-selective bradykinin B1/B2 receptor antagonist, also administered intraperitoneally (1 mg kg(-1)), decreased eosinophil and macrophage counts by 62% and 80% in bronchoalveolar fluid. These results suggest that bradykinin B1 and B2 receptors are involved in leukocyte recruitment in our model of lung inflammation.

Pulmonary inflammation without bronchial hyperresponsiveness in vivo or in vitro after sephadex instillation in pigs

1. In rodent models, Sephadex produces pulmonary inflammation that may be associated with bronchial hyperresponsiveness. In the present study we examined whether Sephadex-induced inflammation altered airway narrowing in pigs. 2. Twenty millilitres of 10 mg/mL Sephadex suspension was instilled twice intratracheally into anaesthetized pigs (days 1 and 7 of a 9 day study). In vivo bronchial responsiveness was assessed from the effect of acetylcholine (ACh) aerosol on airways resistance and dynamic compliance before Sephadex instillation and on days 3, 5 and 9. Lung histology and in vitro bronchial responsiveness was assessed on day 9. In vitro responsiveness was assessed by measuring the reduction in flow through perfused 2 mm i.d. bronchial segments in response to ACh applied luminally and adventitially. 3. Sephadex produced a focal peribronchial granulomatous reaction characterized by the presence of macrophages, eosinophils, neutrophils and giant cells. Changes in airway resistance and lung compliance in response to ACh did not change over the study period. The response of perfused bronchial segments to luminally or adventitially applied ACh was also unaltered. 4. Sephadex-induced pulmonary inflammation does not alter airway narrowing in vitro nor bronchial hyperresponsiveness in vivo in the pig.