MMP9 and chronic obstructive pulmonary disease: Increased numbers of neutrophils, macrophages, and lymphocytes in the airways are found associated with COPD [1-3], and various mediators derived from these cells, such as interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF)-α, monocyte chemoattractant protein (MCP-1), and matrix metalloproteinase (MMP)-2, MMP-8, and MMP-9, are suggested to contribute to the development of COPD [4,5].