SDC4 and chronic obstructive pulmonary disease: When comparing E-COPD to controls, we found that CXCL10-mediated interactions (e.g., SDC4, DPP4, CXCR3), and ligand-receptor pairs associated with immune checkpoint molecules (CD48-PDCD1, PVR-CD96, CD274-PDCD1) were upregulated in E-COPD (Fig. 8f).