It is important to underline that, in our in vitro studies using MRC5 and primary IPF, we were unable to detect the active form of both MMP-2 and MMP-9 by zymography, as reported by other authors (Habelhah et al., 1999; Hostettler et al., 2014). This evidence concerns the gene MMP2 and idiopathic pulmonary fibrosis.