SFTPD and chronic obstructive pulmonary disease: Among circulating biomarkers, several have proven useful in reflecting systemic inflammation in COPD [11], including peripheral eosinophil count, C-reactive protein, elevated plasma fibrinogen, soluble receptor for advanced glycation end products (sRAGE), surfactant protein D (SP-D) and Clara cell protein 16 (CC16), as well as IL-6 and IL-8.