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Hypersensitivity pneumonitis (HP) is characterized by a T-cell-mediated alveolitis, and the putative role of other inflammatory cells in its pathogenesis remains unclear. In this study we determined whether increased quantities of neutrophils were present in HP lungs, and if they were positive for gelatinase B and collagenase-2. Fifteen nonsmoking patients with subacute/chronic active HP were included. Lung samples were analyzed using myeloperoxidase antibody, and neutrophil/total cell ratio was evaluated by digital processing. All HP tissue samples exhibited variable quantities of neutrophils located inside vessels, and in the interstitial and alveolar spaces. Lung neutrophil percentage ranged from 0.7% to 4.8% (2.1 +/- 1.4%). There was a positive correlation between the percentage of lung neutrophils and the percentage of lung fibrosis (r = 0.6, p < 0.02). Tissue neutrophils showed intense immunoreactive collagenase-2 and gelatinase B staining. Additionally, gelatinolytic activities corresponding to progelatinases A and B and their activated forms, were several-fold increased in the bronchoalveolar lavage fluid (BALF) from patients with HP as compared with control subjects. These findings suggest that in HP lungs there is a persistent traffic of neutrophils loaded with gelatinase B and collagenase-2 that may play a role in the lung damage and in the fibrotic response.

Subacute hyperoxia may cause basement membrane disruption and subsequent fibrosis. To test the role of extracellular matrix degradation in hyperoxic damage, we analyzed the expression of gelatinases A and B and tissue inhibitors of metalloproteinases (TIMP)-1 and TIMP-2 in rats exposed to 85% O2. Oxygen-exposed rats were studied at 1, 3, 5, and 7 days, and compared with air-breathing rats. Lung mRNAs assayed by Northern and in situ hybridization showed an up-regulation of lung gelatinases A and B from the 3rd day on. Gelatinase A was localized in alveolar macrophages and in interstitial and alveolar epithelial cells. Gelatinase B mRNA and protein were localized in macrophages and bronchiolar and alveolar epithelial cells. Increased gelatinase A and B activities were demonstrated in bronchoalveolar lavage. TIMP-1 and TIMP-2 were constitutively expressed, and only TIMP-1 displayed a moderate increase with hyperoxia. To elucidate transcriptional mechanisms for increased gelatinase B expression after hyperoxia, nuclear transcription factor-kappabeta activation was explored. Oxidative stress significantly increased the lung expression of nuclear transcription factor-kappabeta (p65) protein, and nuclear transcription factor-kappabeta activation and increased levels of gelatinases A and B were found in isolated type II alveolar cells obtained from hyperoxic rats. Conceivably, subacute hyperoxia induces excessive gelatinase activity, which may contribute to lung damage.

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