Persistent airway hyperresponsiveness and histologic alterations after chronic antigen challenge in cats

We studied the effect of chronic immune sensitization on the airway reactivity and associated cytologic and histologic alterations in initially nonatopic cats, a species that spontaneously develops idiopathic asthma. Seven cats were sensitized by intramuscular injection of Ascaris suum antigen (AA) for 4 wk, and four other cats served as sham controls. Airway sensitization was demonstrated by an increased response to nebulized AA in sensitized animals (RL = 45.9 +/- 6.1 cm H2O/L/s, versus a baseline response of 24.7 +/- 1.5 cm H2O/L/s, p < 0.01), and hyperresponsiveness was demonstrated by an increased response to acetylcholine (ACh)-challenge 24 h after AA (approximately 1.0 log decrease in PD200, p < 0.01). The number of eosinophils in the sensitized animals' bronchoalveolar lavage (BAL) fluid increased 12-fold (p < 0.01 versus control) in response to AA challenge; 32 +/- 5% of the BAL eosinophils had a specific density < 1.050, versus 8 +/- 2% prior to AA challenge (p < 0.05). There was no change in airway reactivity, eosinophil recovery, or density in the control group 24 h after sham challenge with saline. The same seven sensitized cats further received nebulized AA three times weekly for 4 to 6 wk, after which BAL samples were again obtained and ACh dose-response curves generated 72 h after the final administration of nebulized AA. Airway hyperresponsiveness increased (approximately 1.5 log decrease in PD200, p < 0.001) and the number of eosinophils recovered in BAL fluid was increased 11-fold (p < 0.05). Necropsy specimens demonstrated bronchoconstriction in AA-challenged animals but not controls; luminal narrowing was accompanied by: (1) a 29.0 +/- 0.34% increase in smooth-muscle thickness (p < 0.05); (2) goblet-cell and submucosal-gland hypertrophy and hyperplasia; and (3) epithelial erosion and eosinophilic infiltration. We demonstrate in nonhuman species persistent airway hyperreactivity associated with a complete constellation of histologic changes in epithelium, smooth muscle, and mucus glands, and cytologic changes in BAL fluid, all induced by immune sensitization. Our data suggest that chronic immune sensitization per se could be a salient factor in causing many of the changes associated with chronic bronchial asthma.

Morphologic and morphometric characterization of lung collagen content in clinically normal adult thoroughbreds in race training

Interstitial and bronchointerstitial pulmonary patterns are commonly observed in thoracic radiographs of Thoroughbreds. Prominent interstitial and bronchointerstitial pulmonary patterns are observed in clinically normal horses, and in horses with respiratory tract disease. Until recently, the relevance of these pulmonary patterns was not known. Previous studies indicated that bronchiolitis, bronchiolar epithelial hyperplasia, epithelial metaplasia, and bronchial arteriolar recruitment correlated strongly with the prominence of the interstitial and bronchointerstitial pulmonary patterns observed radiographically. We examined the content and distribution of collagen in the lungs of 7 clinically normal Thoroughbreds in race training. After standardized fixation, lung tissue was treated with a compound that selectively stains collagen. Standard morphometric techniques were used to determine the volume density of parenchymal tissue and parenchymal airspace, mean linear intercept (estimate of alveolar size), alveolar surface area-to-volume ratio, percentage of parenchyma composed of collagen, percentage of airway wall composed of collagen, and airway wall thickness. These values were compared with radiographic and histopathologic scores obtained from the same horses. The volume density of parenchymal tissue and small airway wall thickness correlated strongly with the prominence of the bronchial and bronchointerstitial pulmonary patterns observed radiographically. Small airway thickness was also highly correlated with the perceived prominence of the interstitial pulmonary patterns observed radiographically, and morphometric estimates of parenchymal tissue and parenchymal collagen. There were also strong correlations between the volume density of parenchymal tissue, the percentage of parenchymal collagen, peribronchiolar mononuclear cell infiltrates, and bronchiolar mucosal plication estimates.(ABSTRACT TRUNCATED AT 250 WORDS)

Augmented muscarinic responsiveness caused by 5-lipoxygenase products secreted from alveolar macrophages in isolated-perfused rat lung

We examined the effect of activated alveolar macrophages (AM) on airway responsiveness to muscarinic stimulation in 33 adult Sprague-Dawley rats. An isolated-perfused lung preparation was used to ensure precise and uniform delivery of cells into peripheral airways. The bronchoconstrictor response to acetylcholine (ACh) delivered into the pulmonary arterial circulation was augmented in 8 rats after infusion of 3 x 10(6) AM activated with 10(-6) M f-met-leu-phe and 5 micrograms/ml of cytochalasin B. Lung resistance (RL) caused by 10(-6) mol ACh increased 2.5-fold from 0.10 +/- 0.004 cm H2O/ml/s before infusion of activated AM to 0.35 +/- 0.05 cm H2O/ml/s after infusion of activated AM (N = 8; p < 0.05); the response to ACh was not augmented after infusion of nonactivated AM (N = 7) or vehicle control (N = 6). Baseline RL before ACh was similar in all three groups (p NS). Perfusion with activated AM also significantly increased the wet/dry (W/D) lung weight ratios (7.1 +/- 0.5) compared with nonactivated AM (5.2 +/- 0.1) or vehicle control (5.5 +/- 0.3) (p < 0.05 versus either nonactivated AM or vehicle control). A63162, a 5-lipoxygenase inhibitor, but not indomethacin, a cyclooxygenase inhibitor, completely inhibited augmentation of bronchoconstrictor responses to ACh caused by activated AM and also completely attenuated the increase in W/D lung weight ratios. A highly significant (p < 0.01) correlation (R = 0.76) between W/D lung weight ratios and RL was observed after 10(-6) mol ACh (the greatest dose of ACh administered). Baseline RL was equivalent for all groups before and after infusion of cells or vehicle.(ABSTRACT TRUNCATED AT 250 WORDS)