Could your gut bugs change your mind?

Emerging research suggests that the bacteria in your stomach could be influencing your mood, as Emma Sackville found out when she spoke to Graham Rook...

Graham - It's as though the stress resilience of the people in the rich western countries has been decreasing with time. And in fact, there's good evidence that if your immune system doesn't switch itself completely when not required, then the inflammatory responses that are chuntering along there in the background lead to changes in your brain, and lead to depression. So, it looks as though if your background activity of your immune system doesn't switch off completely when you don't need it, then your stress resilience is reduced. You are more likely to suffer bad consequences of being stressed.

The immune system is rather like the brain. It has to learn, it has to have the appropriate educational inputs put into it, especially during the first two or three years of life. Now what we think is happening in the developed, rich countries is that the control mechanisms that switch off the immune system when it's not required are not being properly educated in the early years of life.

Graihagh - What does he mean when he says our immune systems aren't being educated in the early years of life - I don't quite get it?

Emma - It's what Graham calls the 'old friends' hypothesis - it's also sometimes known as the hygiene hypothesis. This is the idea that kids aren't exposed to microorganisms anymore like our ancestors were and this suppresses the natural development of our immune system.

Graihagh - Ah ok I see where you're going with this because before,  Angela said that stress reduces our ability to inhibit inflammation and inflammation is all to do with the immune system, right?

Emma - Yeah, so the scientists were wondering what would happen if they reintroduced these 'old friends'. In particular, they were interested in one particular microorganism found in soil called Mycobacterium vaccae...

Graham - Now what we've done in these experiments is use a microorganism which we know switches on certain cells that regulate the immune system. They're like the police force of the immune system and they're called regulatory T cells, and it increases the number and activity of these cells, and increases the release of mediators that are anti-inflammatory. And it turns out that by giving this organism to theses animals, when they were then exposed to as stress, it blocked the development of anxiety, it blocked the development of the coelitus and it stabilised, to some extent, the changes that stress causes in the gut.

Emma - What's interesting about this is that it may no just make us more resilient to stress but might also help dampen down the effects of stress. Graham was working with a team from University of Colorado, and they found that mice immunized with this bacteria were also protected against colon inflammation and anxiety - side effects of stress.

Graihagh - I still find this slightly bonkers that one bit of bacteria found in soil of all places can have such a huge impact... Next question - this is in mice, so how do we know this is going to a) work in humans and b) be safe?

Emma - Great minds think alike, as I also wondered this and it turns out there was a previous trial where they looked at it to try and help treat cancer...

Graham - This material has indeed been used in humans before and that was one of the reasons for using it in these animal experiments because that should make it easier to move back to human clinical trials. The point being it was used in a clinical trial for a condition where, in fact, it didn't help the condition that was being treated. That aspect of the trial failed, but the patients had been subjected to a quality of life questionnaire and although this has to be regarded as very preliminary data, it did appear to be making it easier for them to put up with the stress of the condition itself.

Graihagh - Let me guess, next step is human trials?

Emma - Yeah but it's not quite that simple...

Graham - Well, you're really looking way into the future now. Since the material is available in what is called good manufacturing practice, that is to say manufactured to the regulatory level required for trial in humans, then it should be possible, with appropriate funding, to do some such study. Designing the ideal study is very difficult. Clinical trials are extremely difficult to do well, particularly when one's looking at an end point which is something a little bit nebulous like the extent of the detrimental effects of stress.