Autoimmune disease as a risk factor for mood disorder?

Autoimmunity, the process by which the immune system fails to recognise self as self and subsequently targets those self tissues and cells, is something talked about quite a lot on this blog with autism specifically in mind. Part of the very wide and diverse immune-related features which have been discussed with at least some of the autisms in mind, it's not yet altogether clear exactly how and why autoimmunity is linked to behaviour but the association is an interesting one.

Sally? @ Wikipedia  

The paper by Michael Benros and colleagues* expands that autoimmune - behaviour interest and their observations suggesting: "Autoimmune diseases and infections are risk factors for subsequent mood disorder diagnosis". Their conclusion is based on the analysis of a huge patient set from which nearly 100,000 people had a hospital contact for mood disorder. Mood disorder by the way, is an overarching term for quite a few conditions (see here) which as the name suggests, affect mood; be it an unusual 'high' or an unusual 'low'.

"A prior hospital contact because of autoimmune disease increased the risk of a subsequent mood disorder diagnosis by 45%". To me this is a really interesting association. OK I know correlation does not equal causation, but added to the association they made between hospitalisation for infection and subsequent mood disorder (62% increase) and the large participant numbers, there is lots to ponder here.

I've gone on a few times on this blog about the bi-directional link between our physiology and the presentation of more psychiatric or behavioural 'symptoms'. Be it C.diff infection and depression or the skin-brain axis (see here), the connections are starting to be formed and examined. I'm just remembering back to some interesting research on allergic disease and neurodevelopment as also potentially being relevant to this post (see here) with the focus on allergy and its potential developmental effects and indeed the implication of some interesting potential interventions too.

So what could be the mode of action for this autoimmune-infection-mood disorder link? Well, we have some contenders but at the moment nothing concrete. That the immune system might be doing so much more than protecting against disease is already pretty well known about as for example with the rise and rise of research into microglia (see here) and some other areas of interest** particularly with a focus on a very nebulous term: inflammation.

Regular readers might know about my views and opinions on the role of food and the gut to behaviour - no really -  and certainly when it comes to certain autoimmune conditions like coeliac (celiac) disease, we have a body of research suggesting how food, certain elements of food, under the right circumstances might be able to affect behaviour. Think Marios Hadjivassilliou for example.

Even more outlandish, how about some role for those HERVs - human endogenous retroviruses - which seem to be cropping up with lots of conditions in mind (see here) and in particular autoimmune conditions***? Too speculative? Whether any of these areas overlap with the Benros paper is something as yet unknown. But the association posited between autoimmune conditions / infections and subsequent mood disorders is really, really interesting.

To close, with the new Stone Roses inspired movie on the horizon, how about a song about Sally Cinnamon?

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* Benros ME. et al. Autoimmune Diseases and Severe Infections as Risk Factors for Mood Disorders. JAMA Psychiatry. 2013;():1-9. doi:10.1001/jamapsychiatry.2013.1111.

** del Rey A. et al. A cytokine network involving brain-borne IL-1β, IL-1ra, IL-18, IL-6, and TNFα operates during long-term potentiation and learning. Brain, Behavior, and Immunity. 6 June 2013. http://dx.doi.org/10.1016/j.bbi.2013.05.011

*** Dreyfus DH. Autoimmune disease: A role for new anti-viral therapies? Autoimmun Rev. 2011 Dec;11(2):88-97. doi: 10.1016/j.autrev.2011.08.005.

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Benros ME, Waltoft BL, Nordentoft M, Ostergaard SD, Eaton WW, Krogh J, & Mortensen PB (2013). Autoimmune Diseases and Severe Infections as Risk Factors for Mood Disorders: A Nationwide Study. JAMA psychiatry (Chicago, Ill.), 1-9 PMID: 23760347