As if being stuck sick in bed wasn’t bad enough, several studies conducted during the past few years have found that the immune response to illness can cause depression. Recently scientists have pinpointed an enzyme that could be the culprit, as it is linked to both chronic inflammation—such as that found in patients with coronary heart disease, type 2 diabetes and rheumatoid arthritis—and depressive symptoms in mice.

In the new study, immuno­physiologist Keith Kelley and his colleagues at the University of Illinois exposed mice to a tuberculosis vaccine that produces a low-grade, chronic inflammation. After inocu­lation, production in the mice brains of an enzyme called IDO, which breaks down tryptophan, spiked. The animals exhibited normal symptoms of illness such as moving around and eating less. Yet even after recovering from the physical illness induced by the vaccine, they showed signs of depression—for example, struggling less than control mice to escape from a bucket of water. Surprisingly, their listlessness was solved relatively simply. “If you block IDO, genetically or pharmaceutically, depression goes away” without interfering with the immune response, Kelley explains.

The research makes a solid case that the immune system communi­cates directly with the nervous system and affects important health-related behaviors such as depression. The findings could bring relief to patients afflicted with obesity, which leads to chronic inflammation, as well as to cancer patients treated with radiation and chemotherapy drugs that produce both inflammation and depression. “IDO is a new target for drug compa­nies to aim for, to treat patients with both clinical depression and systemic inflammation,” Kelley says.

This article was originally published with the title Inflammation Brings on the Blues.

6 Comments

1. 1. Burn Doubt 11:04 AM 9/24/09

   Great! I look forward to drugs targeting IDO to be released in 19 years, and then finding out they cause horrible side effects like liver damage, stroke, and death another 8 years after that.

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2. 2. Holli Thompson, Nutritional Style 01:24 PM 9/24/09

   I wonder if natural holistic anti inflammatory remedies would work as well. This is such an interesting article - seeing the science behind the depression is oddly comforting. Now we work on fighting it.
   Holli Thompson- Nutritional Style

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3. 3. sunny strobe 01:54 PM 9/25/09

   Species-specific nutrition for our primate body constitution works wonders also for our immune system! It makes biological sense to eat mainly fruits and vegetables, with enzymes & vitamins undamaged by cooking & frying. Medical tests done by Kourtchakioff in the 1930s showed that our white blood cells are reacting to cooked and processed food like an inflammatory foreign body invasion. I personally can attest to the fact that eating raw fruits and vegetables contributes lifts my mood.

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4. 4. Chrisfs 06:11 PM 9/25/09

   This may answer why Omega 3 fatty acids combat both inflammation and depression.

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5. 5. Hilly1609 05:13 PM 9/28/09

   There is evidence already of the link between the immune system - both nervous systems and our emotions. Dr Ester Sternberg has issued a book on the subject that is supported by empirical evidence not only her work but much by other researchers. A fascinating and informative read that is highly recommended.

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6. 6. b_johnson 06:52 PM 10/5/09

   Maybe this is why they say taking fish oil lessens depression; because it reduces inflammation.

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