KEGG pathway enrichment analysis revealed that differentially expressed proteins were mainly involved in complement and coagulation cascade, COVID-19, PPAR signalling pathway, mineral absorption, cholesterol metabolism, ferroptosis, staphylococcus aureus infection, bile secretion, systemic lupus erythematosus, folate biosynthesis, and proximal tubule bicarbonate reclamation (Figure 4(D)). The gene discussed is PPARA; the disease is COVID-19.