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Background: Atopic dermatitis (AD) is a chronic inflammatory skin condition that is characterized by a defective skin barrier. Despite the well-recognized role of proteases in skin barrier maintenance, relatively little is known of the contribution made by matrix metalloproteinases (MMPs) to the inflammatory process in AD., Objectives: To test a simple, novel ex vivo bioassay technique in an analysis of the MMPs present in wash samples taken from the skin surface of patients with AD., Methods: Saline wash samples were collected from eczematous and unaffected areas of the skin of patients with AD and from the skin of normal controls. Wash samples were analysed for their MMP content using a functional peptide cleavage assay, gelatin zymography and an antibody array., Results: Using a functional substrate cleavage assay, skin wash samples from AD lesions were shown to contain 10- to 24-fold more MMP activity than those from normal control skin (P < 0.02) and fivefold more than those from unaffected AD skin (P < 0.05); this activity was inhibited by a broad-spectrum MMP inhibitor Ro 31-9790. Gelatin zymography and antibody array analysis revealed substantial levels of MMP-8 (neutrophil collagenase) and MMP-9 (92-kDa gelatinase) in AD skin wash samples as well as lower levels of MMP-10 (stromelysin 2) and tissue inhibitor of metalloproteinases (TIMP)-1 and TIMP-2; low levels of MMP-1 (fibroblast collagenase), MMP-3 (stromelysin 1) and TIMP-4 were also detected., Conclusions: A simple skin wash technique suitable for the quantitative and functional analysis of biomolecules in AD is described. Using this method we show that MMPs, and in particular MMP-8 and MMP-9, represent an important potential component of the pathology of AD. The method is expected to prove useful in advancing our understanding of AD and in identifying biomarkers for the evaluation of new therapies.