TNF-alpha and ghrelin: opposite effects on immune system, metabolism and mental health.

Tumor necrosis factor-alpha (TNF-alpha) is a glycoprotein hormone with important functions in inflammation and apoptosis. It plays a significant role as a pro-inflammatory cytokine in the defense against viral, bacterial and parasitic infections and autoimmune disorders. Furthermore, it influences energy homeostasis and has an anorexigenic effect on the hypothalamus. TNF-alpha has also been shown to be involved in the pathogenesis of psychiatric disorders such as depression or narcolepsy. Ghrelin is a peptide hormone which primarily regulates eating behavior through modulation of expression of orexigenic peptides in the hypothalamus. Ghrelin administration increases food intake and body weight, while weight loss in turn increases ghrelin levels. Secondly, it posesses anti-inflammatory properties. It also seems to have an impact on mental health as it is has been suggested to have antidepressant and anxiolytic properties. Therefore, TNF-alpha and ghrelin seem to have opposite effects regarding the hypothalamic regulation of eating behavior, modulation of the immune response and the state of mental health.