Mind your Immune System

Another significant piece in the mind-body puzzle comes from this new study where obsessive-compulsive behavior in mice was cured by a bone marrow transplant.

A rare form of a genetic disorder in mice causes a “hair pulling” disorder, very similar to its human counterpart trichotillomania. In their new findings published in Cell, Mario Capecchi and his team at Salt Lake City, Utah found that the basis of this psychological aberration was a reduced population of microglia, which are the immune system cells in the brain. These cells have been long known to be the brain’s scavenger system, playing a vital role in clearing breakdown products and microbes, but its surprising that its depletion leads to a specific form of behavioral disorder.

The genetic mutation responsible was pinpointed to the Hox8 gene, which belongs to a family of genes that determine body plan and architecture in all vertebrates, apart from regulating development and growth of organs. The brain microglia cells are thought to originate from the bone marrow, and are the only brain cells that express this gene — thus they are thought to play a key role in the brain’s development.

The study found that if bone marrow containing Hox8 expressed stem cells (early forms which give rise to microglia) were transplanted to affected mice, their hair pulling disorder was cured within four months. By contrast when bone marrow from affected mice was transplanted into normal ones, the disorder appeared in normal ones.

Apart from the fact that this is the world’s first reported behavior transplant, this finding is an important landmark in our understanding of the genetic basis of behavior. To what extent are our behaviors pre-determined by our immune system and our mine interconnected? To what extent does a malfunction of one lead to problems with the other?

To quote Capecchi,

We know a lot more about the immune system than we know about our brain. We know almost nothing about how the brain works and less about how drugs work. If we say the immune system is important, this opens up a whole new vista of things we can do simply because we know more about the immune system.


Chen SK, Tvrdik P, Peden E, Cho S, Wu S, Spangrude G, & Capecchi MR (2010). Hematopoietic origin of pathological grooming in Hoxb8 mutant mice. Cell, 141 (5), 775-85 PMID: 20510925

  • There’s some research on testicular transplants (from what I found on a brief google search, in salamanders, mice, rats, and frogs) going back several years. As the presence of gonadal hormones greatly influences behavior (and these are often done to investigate sex-typical behavior), I’d call these “behavioral transplants.”

    Also, your first paragraph refers to “obsessive-compulsive behavior” in mice – this is a misnomer, as what we’re really talking about is “hair-pulling behavior”. While the mice in question may model certain aspects of a certain type of OCD, they are not themselves obsessive-compulsive; at best, they have certain characteristics that are approximately analogous to the human disorder. It is misleading to talk about these animals as if they somehow actually have the disorders whose symptoms they model.

  • Helena Vidaurri

    Impressive paper!
    Indeed, we ignore a lot about our brain and its many misteries. Our nervous and immune system are closely related and both can be affected by environment and genetic disorders.

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  • Hi Brian Blogger –

    Would the work by Swedo, wherein strep antibodies were capable of causing OCD in animals count as a ‘behavioral transplant’?


    – pD

  • ferkan

    This article is a bit credulous.

    Firstly Trichotillomania is not normally classed as part of OCD. It has been suggested that it is part of an Obsessive–compulsive spectrum. However, this spectrum is not universally accepted to exist as a valid concept. Trichotillomania is more normally classified as an impulse control disorder.

    Secondly, OCD is a disorder that generally responds very well to psychological treatment and has a well characterised cognitive model (please see: Salkovskis, P. M. (1999). Understanding and treating obsessive-compulsive disorder. Behaviour Research and Therapy, 37, s29-s52.) Thus, although more research is always useful, the need to reduce everything to a simple biological substrate is simplistic and unhelpful. That the whole article makes no comment to psychological mechanisms is problematic.

    Next and perhaps most relevant. There is little evidence to suggest that the mouse model described here has anything to do with trichotillomania, let alone typical OCD. Just because a behaviour has a similar form does not mean it has a similar aetiology or function. There may well be some overlap with trichotillomania, but that remains to be proven.

    It’s undeniably interesting work, but the implications are overplayed.

  • Very interesting. It really makes me wonder how many other psychological problems actually have a physiological cause (and cure). Thanks for posting this.

  • Sophie

    There are so many things to talk about regarding health… And it is always a great honor for me to read materials such as this. I believe that health is wealth and we should not neglect the treats around us. Nothing beats a healthy living.

  • Jarred Neil

    Once in a while people get sick because of too much stress or because of working too much. Sometimes weather changes can cause a person’s immune system to weaken making the person more susceptible to diseases. The usual diseases include cough and colds and the occasional fever but wouldn’t it be hard if a person would get hit by his very own immune system? Unfortunately, this happens to people sometimes. There are even times when a person gets attacked by his immune system every single day as long as there are triggers, the immune system will react. It is unfortunate that for some people, getting immune system diseases is inevitable.

Sudip Ghosh, MD

Sudip Ghosh, MD, is a surgeon at the University of Manchester, UK and a medical writer.

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