TNF and depressive disorder: Among the studies conducted in adolescents, Zhao and colleagues identified enrichments in genes involved in apoptosis, TNF signaling pathway, and NF-kb signaling pathway in MDD adolescents compared with controls [36], and the study by Chiang and colleagues observed an up-regulation of inflammation-related genes and a down-regulation of antiviral-related genes in adolescents with depression compared with their non-depressed peers [34].