Chest
Volume 110, Issue 2, August 1996, Pages 383-391
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Clinical Investigations: Interstitial Lung Disease
Mast Cells in Bronchiolitis Obliterans Organizing Pneumonia: Mast Cell Hyperplasia and Evidence for Extracellular Release of Tryptase

https://doi.org/10.1378/chest.110.2.383Get rights and content

Idiopathic bronchiolitis obliterans organizing pneumonia (BOOP) is characterized by air space inflammation and fibrosis of unknown origin. The pathogenesis of the inflammatory reaction and fibrosis in fibrotic lung disorders remains unclear; however, recent attention has focused on the potential role of the mast cell in the genesis of fibrosis. To determine whether mast cells are implicated in the pathogenesis of BOOP, mast cells were identified in BAL fluid and in transbronchial lung biopsy specimens from 11 patients affected by BOOP and 17 control subjects. Mast cells and tryptase were significantly increased in BAL fluid of patients with BOOP (p=0.001 and p=0.03, respectively). In lung tissue of patients with BOOP, there was an increased number of mast cells per square millimeter of lung tissue with respect to control group (p=0.001). Seventy-three percent of mast cells were found in the alveolar septa, 18% within alveoli often plunged in organizing pneumonia, 4% among alveolar lining cells, and 6% along blood vessels. No mast cells were located within alveoli in control subjects. Mast cell degranulation was evident in lung tissue specimens of patients with BOOP but not in those of control subjects (p=0.01). This study shows the importance of mast cells and mast cell activation in the pathogenesis of BOOP.

Section snippets

Subjects

Light microscopic studies were made of transbronchial lung biopsy specimens and BAL from 11 patients with BOOP (5 men; mean age, 62.8±2.3 years; 4 smokers) without any personal or family history of allergic disease and 17 control subjects (Table 1).

Diagnosis was made on the following: (1) consistent clinical history and radiologic findings, as described;2 (2) typical histologic pattern of BOOP at transbronchial biopsy (the essential pathologic feature was the presence of buds of granulation

Clinical Features, Radiologic Findings, and Pulmonary Function Analyses

All patients were symptomatic at the beginning of the study. Likewise, they showed a characteristic restrictive pattern with a variable decrease of vital capacity (7 patients [64%] had SVC <80% of predicted) and diffusing capacity (8 patients [73%] had Dco/VA <80% of predicted). An obstructive defect (FEV1/FVC ratio <70%) was found in 27% (3/11) of patients with BOOP. Small airway obstruction (FEF25–75 <70%) was found in 82% (9/11) of patients. No differences were observed between smoker and

DISCUSSION

Several cytologic changes were found in BAL fluid from patients with BOOP: total cell numbers were higher, lymphocytes represented the predominant cell type, and mast cells and eosinophil percentages increased significantly. Tryptase levels were higher in BAL fluid from patients with BOOP and correlated positively with mast cell numbers and percentages. Mast cell numbers were increased showing degranulating aspects in transbronchial biopsy specimens from patients with BOOP. These changes, when

ACKNOWLEDGMENTS

We thank Iris Spanevello for expert technical assistance and Elizabeth de Young for the English-language version of this article.

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    Partly supported by a grant from Ministero dell'Università e Ricerca Scientifica.

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