Collagenolytic activity in bronchoalveolar lavage fluid in canine pulmonary eosinophilia

We studied and characterized the collagenolytic matrix metalloproteinases (MMP-8 and MMP-13) in the pathogenesis of canine pulmonary eosinophilia (PE). Twenty dogs with PE and 16 healthy control dogs underwent similar clinical examination and collection of bronchoalveolar lavage fluid (BALF). Analyses of total cell and differential cell counts and collagen I degradation with and without aminophenyl mercuric acetate (APMA) treatment were performed. Correlations between cell counts and percentage of degraded collagen I in BALF were studied. Collagenase activity detected in BALF was characterized by Western immunoblotting for collagenase-2 (MMP-8) and collagenase-3 (MMP-13), and their cellular location was studied by immunocytochemical means. Collagenolytic activity was significantly increased in cell-free and native BALF of PE dogs compared to healthy controls. APMA treatment had no significant effect on BALF collagenase activity, indicating that collagenolytic activity occurred in diseased BALF in vivo in active form. Western immunoblotting identified the presence of MMP-8 and MMP-13 immunoreactivities, of which the latter was converted to active form. Major immunoreactivity for MMP-8 was observed in macrophages and epithelial cells, and major immunoreactivity for MMP-13 was observed in macrophages. A significant positive correlation was noted between the percentage of degraded collagen I and the counts of eosinophils, macrophages, lymphocytes, and mast cells. These findings suggest that the up-regulation of collagenolysis eventually contributes to pulmonary tissue destruction in canine PE.