Depression and bipolar disorder have been linked to high levels of inflammatory proteins in the blood (namely CRP, IL-1, IL-6, and TNF-alpha), but the relationship between these illnesses and inflammation in the brain has not been well-characterized.
At the 2015 meeting of the Society for Biological Psychiatry, researcher Ghanshyan Pandey discussed findings from autopsy studies of people who died with a diagnosis of unipolar depression or bipolar disorder, and teens who died of suicide. The studies compare data from these ill people with those of controls who are matched for demographic characteristics.
Pandey found that the brains of those who died of unipolar depression and bipolar disorder showed more signs of inflammation compared to the controls. This included elevated levels of the inflammatory proteins IL-1B, IL-6, and TNF-alpha, in addition to elevated levels of the mRNA that leads to their production. Pandey also found that those with depression and bipolar disorder had higher levels of mRNA for the receptors to which TNF-alpha and other inflammatory proteins attach themselves.
Pandey performed similar autopsy studies of teens who died of suicide, the second leading cause of death for this age group, compared to teens who died of other causes. There were more signs of inflammation in the prefrontal cortices of teens who died of suicide. These included mRNA and proteins for IL-1B and TNF-alpha, and IL-6 proteins. In contrast to the ill adults, the teens who died of suicide had lower levels of the receptors for inflammatory proteins than controls. Another type of receptor known as toll-like receptors was higher in the ill teens, particularly the mRNA and proteins TLR3 and TLR4.