Your immune system may play a bigger role in depression than previously thought.
A new study of stress-related behavior in mice suggests that levels of a certain cytokine could help determine whether an individual is prone to depression.
Cytokines are proteins involved in the inflammatory process of the immune system, and are responsible for the inflammation seen in psoriasis and psoriatic arthritis. Previous studies have linked inflammation to depression and anxiety, the researchers note. Depression is also a comorbidity of psoriatic disease.
The study, published in October in Proceedings of the National Academy of Sciences (PNAS), found that mice with higher levels of a cytokine called interleukin-6 (IL-6) were particularly sensitive to stress, said Dr. Georgia Hodes, a neuroscientist at the Icahn School of Medicine at Mount Sinai in New York and the lead author of the study.
When exposed to stress, mice with elevated IL-6 became uninterested in social interactions, the researchers report. But when these mice were given an IL-6 antibody, which neutralized the effect of the cytokine, they no longer developed this depression-like behavior.
Prior to this study, Hodes explained, stress was thought to trigger an inflammatory response in the immune system. But her findings indicate that some individuals’ immune systems may be primed to respond to stress in a certain way.
“What we’re saying is that before there is any stress, there is already sensitivity of the immune system,” Hodes explained. “And because it’s more revved up, when you’re stressed it over-responds and leads to depression.”
Hodes describes this sensitivity as similar to an allergy to stress. Because of this “allergy,” the body may launch a stronger immune response by producing more IL-6.
These findings indicate that IL-6 could be a biomarker for depression, Hodes said, and they also suggest that reducing inflammation could help heal depression.
It turns out that people who are depressed also have elevated IL-6. When researchers tested the blood of people with major depressive disorder, they found high levels of IL-6, even following treatment with anti-depressants.
New treatments for depression targeting inflammation are currently in development, Hodes said.
These findings could also help explain the connection between psoriatic disease and depression, according to Dr. Theoharis Theoharides, a researcher at Tufts University who received a $200,000 Translational Research Grant from the National Psoriasis Foundation in 2013 to study the connection between psoriasis and stress.
Further studies examining IL-6 levels in people with psoriatic disease and depression could reveal new insights about the role of IL-6 in the development of this comorbidity, he said.
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