The top 10 genes that were most hypermethylated by both morphine treatment and Alkbh5 knock-down are listed in Fig. 4C. The genes that were commonly hypermethylated by both morphine and Alkbh5 knock-down were associated through KEGG pathway analysis with MAPK signaling pathway, adhesion (e.g., focal adhesion, adherens junctions, and leukocyte transendothelial migration), regulation of actin cytoskeleton, and inflammation-related terms (e.g., Staphylococcus aureus infection, HIV-1 infection, and Epstein-Barr virus infection) (Fig. 4D). Here, ALKBH5 is linked to Epstein-Barr virus infection.