MMP-9 possessing high gelatinolytic activity can cleave collagen before prolyl endopeptidase further degrades the gelatin fragments to form neutrophil chemoattractant proline–glycine–proline (PGP), which contributes to the chronic neutrophilic inflammation in CF patients (Gaggar et al., 2008). The gene discussed is PREP; the disease is cystic fibrosis.