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Bacterial immunization and PTSD-like symptoms in mice

A paper published today in the Proceedings of the National Academy of Sciences has reported that injecting mice with a heat-killed version of the bacteria Mycobacterium vaccae can reduce stress and inflammation in the animals, preventing them from developing post traumatic stress-like conditions. In response to this report, the BSI has issued the following statement:

Dr Sheena Cruickshank, British Society for Immunology spokesperson and Senior Lecturer in Immunology at The University of Manchester said:

"It is clear that, in developed countries, there is an increased incidence of allergy and inflammatory autoimmune disorders, although the reasons for this are not fully understood. One popular theory is that we have become too clean and the types of germs we are exposed to has changed, meaning that our immune system becomes ‘faulty’ and reacts inappropriately – this idea is sometimes called the ‘Old Friend's’ hypothesis.

"In this study, Reber and colleagues have set out to investigate this ‘Old Friend’s’ hypothesis by repeatedly vaccinating mice using a heat-killed environmental microbe and then studying their response to stressful situations.

"The study’s findings that injecting mice with this particular bacterium can reduce stress and inflammation are intriguing, but it is early days yet. The gut inflammation characterised in this study appears to be only mild in nature.  Additionally, the outcomes observed between the different gut inflammation models used are inconsistent, making it hard to come to an overall conclusion on treatment effects.  The study was conducted over a relatively short time frame, so it remains to be seen whether there is any long-lasting protective effect, how wide-ranging any effects may be (particularly against other types of inflammation) and how applicable the findings are to humans.”


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