Other pro-inflammatory signals, such as ROS [165] and colony-stimulating factors [166], are significantly raised in CF; likewise, levels of the bioactive fragment of collagen called proline-glycine-proline (PGP) which is generated by the activity of both prolylendopeptidase and matrix metalloproteinase-9 (MMP9), are also raised [167]. Here, MMP9 is linked to cystic fibrosis.