Current understanding of the bi-directional relationship of major depression with inflammation

Consistent evidence links major depression and its affective components to negative health outcomes. Although the pathways of these effects are likely complex and multifactorial, recent evidence suggests that innate inflammatory processes may play a role. An overview of current literature suggests that pathways between negative moods and inflammation are bi-directional. Indeed, negative moods activate peripheral physiologic mechanisms that result in an up regulation of systemic levels of inflammation. Conversely, peripheral inflammatory mediators signal the brain to affect behavioral, affective and cognitive changes that are consistent with symptoms of major depressive disorder. It is likely that these pathways are part of a complex feedback loop that involves the nervous, endocrine, and immune systems and plays a role in the modulation of peripheral inflammatory responses to central and peripheral stimuli, in central responses to peripheral immune activation and in the maintenance of homeostatic balance. Further research is warranted to fully understand the role of central processes in this feedback loop, which likely contributes to the pathophysiology of mental and physical health.