Reading Susannah’s story in Brain on Fire got me really interested in ways that a person’s immune system can have an effect on their neurological and psychological status. One study I found, by Capecchi et al., was able to show a direct link between a problem in the immune system and obsessive compulsive grooming behavior in mice. This excessive grooming behavior was characterized by excessive grooming to the point of hair loss and lesion development.
Mice with obsessive-compulsive grooming behaviors were found to have a Hoxb8 mutation. In the brain the only cells that would express this mutation are microglial cells. Microglia are basically the macrophages of the brain as they clean up debris and pathogens. Through a series of experiment Capecchi et al., found that mice with the Hox8b mutation had 15% less microglia than normal mice. As the microglial lineage often originates in the bone marrow mice with the mutant Hox8b were given a bone marrow from a “normal” mouse. Over the following months the mutant mice stopped the obsessive compulsive recovered from the hair loss and lesions. These results show strong evidence that the obsessive compulsive grooming behaviors are a result of microglial deficiencies in the brain.
I think that this is really interesting. A small deficiency, one mutation, can cause such harmful behavior. It makes me wonder what other disorders can be attributed to problems within the immune system.
Chen, Shau-Kwaun, Petr Tvrdik, Erik Peden, Scott Cho, Sen Wu, Gerald Spangrude, and Mario R. Capecchi. “Hematopoietic Origin of Pathological Grooming in Hoxb8 Mutant Mice.” Cell 141.5 (2010): 775-85. Print