Immunohistochemical localisation of the matrix metalloproteinases MMP-3 and MMP-9 within the airways in asthma

Abstract

Background - The matrix metalloproteinase (MMP) enzymes IMMP-3 and MMP-9 have relevance to the chronic structural airway changes in asthma. These proteinases can be generated by structural and inflammatory cells, and have the ability to degrade proteoglycans and thus potentially enhance airway fibrosis and smooth muscle proliferation through their ability to release and activate latent matrix bound growth factors. Methods - Immunostaining for MMP-3 and MMP-9 as well as for mast cells, eosinophils, and neutrophils was undertaken in acetone fixed and glycolmethacrylate embedded endobronchial biopsy specimens obtained by fibreoptic bronchoscopy under local anaesthesia. The findings from 17 asthmatic subjects (nine with mild to moderate non-steroid treated asthma and eight with chronic persistent steroid-dependent asthma) were compared with those from eight healthy controls. The cell associated MMP immunoreactivity was co-localised to mast cells, eosinophils, or neutrophils and represented as cells/mm2, based on the area of the biopsy specimen. Extracellular matrix immunoreactivity was assessed by an image analysis system and visually with ranking and the two approaches were compared. Results - The biopsy specimens from asthmatic subjects contained significantly more eosinophils (p < 0.001) than those from the non-asthmatic subjects. Both MMP-9 and MMP-3 immunoreactivity could be identified in endobronchial biopsy specimens. Gelatinase B (MMP-9) immunoreactivity was prominent within the extracellular matrix as well as exhibiting distinct cell immunoreactivity which predominantly co-localised to neutrophils. Stromelysin (MMP-3) was co-localised to mast cells, eosinophils, and neutrophils as well as being present in the epithelium, the lamina reticularis and, to a lesser extent, the extracellular matrix. There was no significant difference in the extent of matrix immunoreactivity for either MMP-3 or MMP-9 between healthy controls or subjects with mild or severe asthma. Conclusion - Although immunostaining cannot distinguish between active and inactive forms of MMPs, the presence of MMP-3 and MMP-9 within endobronchial biopsy specimens, the co-localisation to inflammatory cells of relevance to asthma (mast cells and eosinophils), and the identification of matrix binding, indicative of MMP-matrix interactions, points to the potential for disease related changes in MMP release that influence airway remodelling in asthma.