Of all the proteins above 30% FDR, PD-L1 (immune checkpoint marker), CD68 (a marker of functionally active macrophages (29), CD163 (a marker of functionally inactive macrophages (29), CD40 and CD44 (co-stimulatory B and T cell molecules expressed during viral infections), CD45 (pan-leukocyte marker), and Human Leukocyte Antigen–DR isotype (HLA-DR, ligand of T cell receptor) were significantly higher in the GOLD 1–2 COPD group vs. smokers (Fig. 2A) and GOLD 3–4 COPD group (Fig. 2B) across all the ROIs. This evidence concerns the gene CD68 and viral infectious disease.