SFTPD and idiopathic interstitial pneumonia: Moreover, some blood biomarkers such as monocyte count, circulating protein fragments degraded by matrix metalloproteases (MMPs) MMP1 and MMP7, C–C motif chemokine ligand 18 (CCL18), Krebs von den Lungen-6 (KL-6), surfactant protein D (SP-D), and surfactant protein A (SP-A) were reported to be associated with decreased pulmonary function, incidence of acute exacerbation, and/or mortality in IPF patients16–24.