Tweaking immune system provides vaccine hope for post-traumatic stress

TWEAKING the immune system could be key to treating, or even preventing, post-traumatic stress disorder (PTSD). Research in rodents suggests that immunizing animals can lessen fear if they are later exposed to stress.

Researchers have known for some time that depression and immune-system health are linked and can affect each other. Early clinical trials have shown that anti-inflammatory drugs can reduce symptoms of depression, raising hopes that such treatments might be useful in other types of mental illness, such as PTSD.

“I think there’s kind of a frenzy about inflammation in psychiatry right now,” says Christopher Lowry, a neuroscientist at the University of Colorado Boulder. He presented results of experiments probing the link between fearful behaviour and immune response at a meeting in Victoria, Canada, last week of the International Behavioral Neuroscience Society.

Studies of military personnel suggest that immune function can influence the development of PTSD. Soldiers whose blood contains high levels of the inflammatory protein CRP before they are deployed, or who have a genetic mutation that makes CRP more active, are more likely to develop the disorder.

To directly test whether altering the immune system affects fear and anxiety, Lowry and colleagues injected mice with a common bacterium, Mycobacterium vaccae, three times over three weeks to modulate their immune systems. The scientists then placed these mice, and a control group of unimmunized mice, in cages with larger, more aggressive animals.

Mice that had received the injections were more ‘proactive’ in dealing with the aggressor, Lowry says, rather than simply surrendering, as most mice do. And the guts of the immunized mice remained healthy, whereas the animals in the control group developed inflamed colons and their gut bacteria shifted to favour species associated with stress.