Obsessive-compulsive disorder is a complicated illness, and the cause, or causes, remain unknown. Research has shown that OCD is seen more frequently than usual in those with various physical disorders, such as muscular dystrophy. An October 2018 study published in Frontiers in Immunology highlights a connection between OCD and another disease – multiple sclerosis.
Multiple sclerosis (MS) is a debilitating autoimmune disorder, where the body’s immune system goes haywire and attacks healthy cells. It affects over two million people worldwide and has no known cure. Patients with multiple sclerosis and other autoimmune disorders are known to suffer from OCD, anxiety and depression. However, the relationship between these illnesses and the immune system has been somewhat of a mystery.
In the above-mentioned study, scientists found a direct link. They discovered that a class of cells that defends the body against invaders also triggers obsessive-compulsive behavior. In mice exhibiting symptoms of multiple sclerosis, the researchers noted that immune cells called Th17 lymphocytes induced behaviors characteristic of OCD. Th17 cells infiltrated the mice brains, and the researchers believe they likely disrupted nerve circuits involved in controlling obsessive behavior.
Specifically, the researchers found that the diseased mice (with symptoms of MS) spent 60 to 70 percent more time grooming themselves compared to healthy ones. They also buried a greater number of glass marbles and shredded more of their bedding to make nests—signs that are suggestive of OCD, which is partially defined by uncontrollable, repetitive behaviors known as compulsions.
To identify the trigger for such behavior the team focused on Th17 cells because previous studies showed they can penetrate the blood-brain barrier. They also play a key role in the progression of MS. The researchers infused diseased mice with Th17 cells and subsequently found an increase in the compulsive behaviors mentioned above. Moreover, brain tissue analysis in these mice showed that large numbers of Th17 cells were found lodged in the brainstem and cortex, which are involved in regulating grooming.
The study’s senior author, Avadhesha Surolia , said:
“For the first time, we are reporting a likely link between OCD and an important arm of cell-mediated immunity. Until now, we have looked at neuropsychiatric diseases as purely a neurological problem, ignoring rather completely the immunologic contribution.”
Interestingly, when the mice were given an antidepressant such as fluoxetine which boosts the uptake of serotonin, their obsessive grooming reduced. This suggests that Th17 cells eventually disrupt serotonin uptake, giving rise to OCD-like symptoms. Researchers believe other neurotransmitters such as glutamate might also be involved.
The team also gave the diseased mice digoxin, a molecule that inhibits Th17 development, and then found that the time spent on grooming was almost cut in half. This finding could be an important step in the development of medications that might be helpful for those with OCD and autoimmune disorders. You can read more about this interesting study here.
As is the case with research, we are often left with more questions than answers. But thanks to dedicated researchers we are moving forward and slowly peeling away some of the complicated layers of OCD.