When treating debilitating mental disorders, researchers look not only to the brain, but also to the body for answers. A new study in mice shows that levels of the inflammatory cytokine interleukin-6 (IL-6), a molecule that is produced and secreted by white blood cells of the immune system, can be used to predict how animals might react to social stress. The findings were presented at Neuroscience 2013, the annual meeting of the Society for Neuroscience and the world’s largest source of emerging news about brain science and health. 30,000 scientists are attending this meeting. More than 350 million people worldwide suffer from clinical depression and between 5 and 25 percent of adults suffer from generalized anxiety, according to the World Health Organization. The resulting emotional and financial costs to people, families, and society are significant. Further, antidepressants are not always effective and often cause severe side effects. Social stress is one of the most significant contributors to depression in humans, yet some individuals experience no adverse effects, while others are vulnerable. Understanding the differences could drastically affect how depression is treated. In the IL-6 study, the researchers found that higher levels of IL-6 released by stimulation of the white blood cells before a defeat experience predicted depression-like behavior, while lower levels predicted stress-resistance. They also showed that reducing IL-6 in the body made mice immune to social stress. Conversely, increasing IL-6 with a bone marrow transplant from a stress-susceptible mouse had the opposite effect, provoking depression-like behavior. The results suggest that measuring stimulated IL-6, a chemical easily found in the blood, could serve as a biomarker for stress sensitivity.
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