In a review article by Katarzyna Grzela et al. based on some research from Cataldo et al. 2002, Gagliardo et al. 2009, Lee et al. 2001 and Lem-jabbar et al. 1999, there were elevated levels of MMP-9 found in serum, sputum and bronchoalveolarlavage from patients with asthma exacerbations. Here, MMP9 is linked to asthma.