MAPK3 and infection: According to the comparison of enrichment results between adolescents and adults with MDD, we found that the results of MDD adolescents were more enriched in synthesis and metabolic processes of cellular nitrogen compound, heterocycle metabolic process, cellular aromatic compound, organic cyclic compound, organic substance, nucleobase-containing compound, etc. While MDD adults were more enriched in immune and infection-related processes, such as: regulation of phagocytosis, leukocyte chemotaxis, monocyte chemotaxis, ERK1 and ERK2 cascade, and defense response to virus by host.