REN and idiopathic interstitial pneumonia: In this context, some proteins evaluated as possible biomarkers of IPF include surfactant proteins A and D (SP-A and SP-D), Krebs von den Lungen 6 (KL6), C-C motif chemokines (CCL16, CCL18), matrix metalloproteinases (MMP7, and MMP28), renin and soluble (pro) renin receptor [29,30,31,32].