Does the Immune System Play a Role in Parkinson’s Disease?
Research sheds light on one potential cause of this mysterious condition, which could open new avenues for treatment.
Parkinson’s disease (PD) is widespread and well-studied, but its origins remain somewhat of an enigma to the medical establishment. Around 60,000 Americans are diagnosed with PD each year, and nearly a million people in the U.S. are living with the disorder.
Yet, as of now, there is no cure for PD, in part because the root cause is still a mystery, explains James Beck, PhD, chief scientific officer at the Parkinson’s Foundation in Miami, FL. “We know that 10 to 15% of people who develop PD have a genetic mutation that predisposes them to the disease, but even then, we do not fully understand how their disease starts.”
Scientists know that Parkinson’s symptoms (tremors, loss of coordination, speech problems) are brought on by some combination of genetic and environmental factors. These trigger a loss of nerve cells in one specific part of the brain that is responsible for producing dopamine–a chemical that plays a role in regulating bodily movements.
There’s also increasing evidence that PD may be tied to an immune response in the body–which could change the way doctors look to treat it in the future. A new study from the La Jolla Institute for Immunology in San Diego, CA discovered a sign of autoimmunity in Parkinson’s patients, years before their official diagnosis. Long before Parkinson’s symptoms appear, T cells in the brain are activated to attack other brain cells, contributing to the onset of the disease. It is still unclear what activates this T cell response in the first place. Still, this opportunity for early detection of PD could open the door for doctors to prevent it.
Parkinson’s Disease and Autoimmunity
This autoimmune component of PD may only be one piece of a larger puzzle. “It has long been suspected that immune alterations are an important part of the development of PD,” says Maureen Leehey, MD, professor of neurobiology at the University of Colorado School of Medicine in Aurora, CO. She notes previous research that has linked ibuprofen use in mid-life with lower PD risk. “And studies have shown that in the early stages, but not the late stages, there is activation of immune fighting cells in the brains of persons with PD,” Dr. Leehey says. “I think that immune alterations are an important part of the progression of central nervous system damage in PD.”
This isn’t the first research being done on Parkinson’s and autoimmunity – there have been multiple studies in this vein in recent years. In 2017, the same researchers from La Jolla and Columbia University identified a specific protein that drives the T cell response in early Parkinson’s disease. Further work has suggested that Parkinson’s could be triggered by bacterial infection.
Experts are looking more closely at gut symptoms, which are often the first noticeable changes that people with Parkinson’s observe in their body. “Researchers are turning their attention to understand the role that the microbial gut population or microbiome might play in the initiation and progression of PD,” says Daniel Paredes, PhD, assistant research professor at the Knoebel Institute for Healthy Aging at the University of Denver in Denver, CO.
Paredes explains that changes in the gut bacteria population can cause chronic inflammation that might influence Parkinson’s symptoms. An April 2020 study in Nature Genetics theorized that Parkinson’s may start in the gut, due to evidence that neurons (nerve cells) in the gut are directly associated with the onset of disease.
The Future of Parkinson’s Treatment
While this research doesn’t prove anything definitive, it’s definitely promising. “These studies on autoimmunity could open new avenues on how PD can be treated, especially at the early stages, and even diagnose it before the motor symptoms appear,” Paredes says. In the future, doctors may be able to intervene with early therapies when they start noticing early symptoms of Parkinson’s, such as changes in the gut microbiome or T cells attacking the brain. Paredes explains that these treatments could involve immunomodulatory drugs, antibiotics or antivirals, or probiotics.
Still, there is much for researchers still to learn. “The immune system is very complex, and our understanding is imperfect at best,” Beck notes. He calls to mind autoimmune diseases like rheumatoid arthritis and juvenile diabetes, which are still at varying stages of treatment development and prevention research. “I am hopeful that progress will be made,” Beck asserts. “However, like a financial portfolio, a diversity of research investments will be the key to understanding and stopping PD.” This research represents another critical step forward in combatting Parkinson’s disease, so that hopefully younger generations will be able to halt the disorder before it progresses.
About Parkinson’s: Parkinson’s Foundation. (n.d.) “Understanding Parkinson’s.” parkinson.org/understanding-parkinsons
Parkinson’s Basics: United Kingdom National Health Service. (n.d.) “Parkinson’s Disease.” nhs.uk/conditions/parkinsons-disease/
La Jolla Study: Nature Communications. (2020.) “α-Synuclein-specific T cell reactivity is associated with preclinical and early Parkinson’s disease.” nature.com/articles/s41467-020-15626-w
Parkinson’s and Ibuprofen: Neurology. (2011.) “Use of ibuprofen and risk of Parkinson disease.” ncbi.nlm.nih.gov/pmc/articles/PMC3059148/
Parkinson’s T-Cell Response: Nature. (2017.) “T Cells From Patients With Parkinson's Disease Recognize α-Synuclein Peptides.” pubmed.ncbi.nlm.nih.gov/28636593/
Parkinson’s Environmental Influence: Neurology Today. (2019.) “Is Parkinson's Disease an Autoimmune Disorder?” journals.lww.com/neurotodayonline/Fulltext/2019/09050/Is_Parkinson_s_Disease_an_Autoimmune_Disorder_.3.aspx
Parkinson’s and GI Symptoms: Parkinson’s Disease. (2016.) “Gastrointestinal Dysfunctions in Parkinson’s Disease: Symptoms and Treatments.” hindawi.com/journals/pd/2016/6762528/
New Study on Parkinson’s Gut Link: Nature Genetics. (2020.) “Genetic identification of cell types underlying brain complex traits yields insights into the etiology of Parkinson’s disease.” nature.com/articles/s41588-020-0610-9