Is Parkinson’s an autoimmune disease? What does the current research say?

Evidence in recent years suggests that Parkinson’s disease could be an autoimmune disease

For decades, scientists and doctors alike have known that inflammation causes changes in the brains of Parkinson’s disease (PD) patients. However, it is only in recent years that they have come to understand that this inflammation is part of the cause of the progressive nature of PD and is not merely a result of the disease.

In 2018, a study conducted by researchers in Germany found further evidence supporting the idea that Parkinson’s could in fact be an autoimmune disease. By examining a stem cell model, they demonstrated how immune cells attacked dopamine-producing cells taken from PD patients but not from people who did not have PD.

Dopamine is a neurotransmitter (a chemical messenger) made in the brain that supports a number of functions, including those that deal with emotions, reward, pleasure, and movement control. In Parkinson’s disease, the cells that make dopamine, the midbrain neurons, die off. 

As more and more dopamine cells die over time, the neurotransmitter levels decrease, leading to a number of symptoms including tremors, balance issues, muscle rigidity, and slow body movement. Swallowing and speech issues also occur, as well as several non-movement symptoms, such as distorted or lost sense of smell, sleep disturbances, fatigue, confusion, and anxiety.

It is not yet clear what exactly causes this midbrain neuron death.

What is autoimmunity? How does it link to Parkinson’s disease?

The immune system is a network of biological processes that protects the body from illness. It is able to detect and respond to a number of pathogens, ranging from viruses to parasites, from cancer cells to even foreign objects such as wooden splinters, and distinguish them from the body’s own healthy tissue. When the immune system makes a mistake and misidentifies and attacks the body’s own organs or tissues, this is called autoimmunity, and can lead or develop into an autoimmune disease.

There are at least 80 different types of known autoimmune conditions, including type 1 diabetes, Crohn’s disease, vitiligo, multiple sclerosis, lupus, and rheumatoid arthritis.

As mentioned previously, the thought that Parkinson’s disease could be an autoimmune disease is not new, but evidence supporting the claim is only now coming to light.

In 2017, for example, a US study found that fragments of the protein that builds up in the dopamine cells in the brains of Parkinson’s patients (alpha-synuclein) trigger T cells to launch an immune system attack.

Researchers have also in recent years established a link between the use of immunosuppressant drugs and a lower risk of developing Parkinson’s disease.

A stem cell model to understand Parkinson’s disease

The previously cited 2018 study conducted by researchers at Friedrich-Alexander-Unversität (FAU) in Germany, has allowed scientists to definitively prove that T cells are involved in causing Parkinson’s disease.

The FAU researchers were motivated into this area of investigation by a previous discovery of higher levels of T helper 17 (T_h17) cells in the brains of people with PD, a phenomenon that is also observed in people with rheumatoid arthritis and other autoimmune conditions.

To drive their explorations further, the research team developed a stem cell model, taking skin cells from people with and without Parkinson’s and induced them into pluripotent stem cells (iPS). These cells are capable of developing into any other type of cell. 

They then encouraged the stem cells to develop into dopamine producing midbrain neurons and exposed the resulting patient-specific dopamine cells to T_h17 cells also taken from each patient. 

The results showed that these immune T cells attack and kill off dopamine cells derived from PD patients but not cells derived from patients who do not have PD.

Findings such as these have significantly helped to advance research and development of new Parkinson’s treatments, giving hope that one day a cure may be possible.

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