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Mental maladies and the role of our immune system

Research from IISc finds a vital link between immune system disorders and psychological conditions like OCD.

Our body and mind have a unique connection; perturbations in one has ramifications on the other. Many chronic physical health problems cause severe psychological stress, and vice-versa. Sometimes, our immune system can mistakenly attack our body, which it is meant to protect in the first place. Autoimmune disorders like rheumatoid arthritis affecting the joints, or multiple sclerosis affecting our nerve cells, are a result of such unintentional attack by our immune system. In a recent study, researchers at the Indian Institute of Science, Bengaluru, have shown how our immune system can also trigger mental health conditions like obsessive-compulsive disorder (OCD).

Obsessive-compulsive disorder is a condition marked by uncontrollable, reoccurring thoughts and behaviours with an urge to repeat again and again. Studies in the past have shown associations between disorders of the immune system, called autoimmune diseases, and mental health problems like depression and OCD. However, the precise role of the immune system in causing such conditions was not clear. In the current study, published in the journal Frontiers in Immunology, Prof. Avadhesha Surolia and his group at IISc have thrown some insights into how immune system disorders affect mental health. The study was funded by the Council of Scientific and Industrial Research (CSIR) and the Science and Engineering Research Board (SERB).

The researchers of the study artificially induced autoimmune encephalomyelitis—a condition where the immune system attacks the brain cells—in mice. They carefully observed the psychological impact of this condition and found that the mice started showing unexpectedly high levels of grooming activities. Their repetitive grooming behaviour was quite similar to symptoms exhibited by individuals affected with OCD.

The researchers further investigated which component of the immune system was responsible for triggering OCD-like behaviour in the mice. When they looked closely at the brains of the mice that showed OCD-like behaviour, they saw a marked increase in the levels of T helper 17 cells (Th17)—a type of cell in our immune system. Studies have shown that apart from Th17, another kind of cell, called Th1, also causes autoimmune responses. The researchers then experimentally transferred more of Th17 and Th1 cells into mice and found that Th17 was indeed the only one responsible for inducing OCD-like behaviour.

“This is the first study where we found Th17 cells to be intimately associated with OCD-like disease in mice”, shared Prof. Surolia in an interview with Research Matters. “However, OCD has been reported as a co-morbid condition in autoimmune diseases like inflammatory bowel disease, systemic lupus erythematosus and rheumatoid arthritis, where certain other components of the immune system (such as auto-antibodies or cytokines) may also be involved,” he added.

The study also found many other pieces of evidence that linked Th17 to inducing OCD. For instance, when the affected mice were treated with fluoxetine, an antidepressant that boosts the absorption of the neurotransmitter serotonin, they observed reduced OCD-like behaviour. Serotonin is a chemical produced by the nerve cells that regulates our mood. “The levels of serotonin are usually much lower in the brains of OCD patients. Hence, they respond positively to treatments with a chemical like this”, explained Prof. Surolia. The researchers also tried to eliminate Th17 cells using a drug called digoxin and observed that the mice significantly reduced their abnormal grooming behaviour.

The findings of the study could help design new approaches to treat conditions like OCD, hope the researchers.

“The present study, in my view, will change our perspective, where until now, we have looked at neuropsychiatric diseases as purely a neurological problem ignoring rather completely the immunologic contribution. Our findings will thus open up new avenues for treating OCD by developing effective therapeutic molecules that target Th17 cells. We can thus treat the root cause of the malady rather than targeting its manifestation and symptoms”, signs off Prof. Surolia.