It has been demonstrated that levels of matrix metalloproteinase-2 (MMP-2), matrix metalloproteinase-9 (MMP-9), IL-6, and TGF-β were significantly elevated, along with an increase in the numbers of leukocytes, neutrophils, and lymphocytes in the lung tissues and BALF of mice with BO. Here, MMP2 is linked to bronchiolitis obliterans syndrome.