KEGG pathway analysis revealed that the upregulated mRNAs were mainly involved in complement and coagulation cascades, coronavirus disease 2019, peroxisome proliferator-activated receptor (PPAR) signalling pathway, influenza A and measles (Fig 2C), while the downregulated genes were involved in antigen processing and presentation, graft-versus-host disease and rheumatoid arthritis (Fig 2D). Here, PPARA is linked to rheumatoid arthritis.