Immune system involved in depression, animal study suggests

The research was presented at Neuroscience 2010, the annual meeting of the Society for Neuroscience, held in San Diego.

Activation of the immune system caused mice to learn to run less on wheels in their cages -- an activity they normally like. The mice resumed their normal activity when the action of interleukin-6, an immune hormone that carries "sickness" signals to the brain, was blocked.

"Our findings suggest that blocking the action of interleukin-6 might reduce depression symptoms, like fatigue or loss of interest in pleasurable activities, in people who are depressed and who have elevated levels of interleukin-6," said Simon Sydserff, PhD, a senior research scientist at BrainCells Inc., who conducted the research while with AstraZeneca Pharmaceuticals.

Scientists previously observed that some people became depressed due to an immune response to illness or stress. Elevated levels of immune hormones like interleukin-6 have been found in some depressed patients who are otherwise healthy. In addition, people who have never had a mental illness, but who are treated for other illnesses with immune- stimulating cytokines, often become depressed.

"These observations support the idea that depression may be caused in part by a breakdown in the normal communication between the immune system and the brain, causing people to experience the feelings associated with sickness even when they are medically healthy," Sydserff said.

Research was supported by AstraZeneca Pharmaceuticals.