MMP9 and pulmonary fibrosis: As an example, Secretory Leukocyte Protease inhibitor (Slpi), which regulates serine proteases involved in the activation of MMP-2 and MMP-9, protected against an increase in Col1a1 mRNA levels observed in wild type mice having bleomycin-induced pulmonary fibrosis in comparison to Slpni knock-out mice [102].