TNF and chronic obstructive pulmonary disease: We performed KEGG pathway enrichment analysis using these COPD-related genes and noted that the top 20 KEGG pathways were markedly enriched with COPD genes, which could be categorized as related to inflammation regulation (cytokine–cytokine receptor interaction, TNF signaling pathway, chemokine signaling pathway, hematopoietic cell lineage, HIF-1 signaling pathway, mitogen-activated protein kinase (MAPK) signaling pathway, and PI3K-Akt signaling pathway), cancer, and infections, among other roles (Figure 3A).