There is evidence that the brain's own immunological function is involved in the genesis of PD. Microglial cells can exist in different states that trigger different brain activities. (I think I made a post about this once.) In one state, they can trigger immune responses, cytokines, inflammation, the release of strong oxidants (!!), and programmed cell death.
In simple language, there is growing evidence that the nerve cells that die in Parkinson's disease were marked for death. Yes, they may have already been struggling, but the body actually is the cell executioner.
But, in another mode, microglial cells DON'T do these aggressive things, but instead signal the brain to do nice things like cell repair.
This brings us to the present article.
Neuroimmune Activation Drives Multiple Brain States
It says that in some cases, the immune response in the brain can be turned on chronically! Long term! This may be really important for people with PD.
(Note, the present paper does not itself mention Parkinson's).
I think there's a very real chance that some people with PD had their brains' immune systems chronically activated.
From Wikipedia: "Cytotoxic secretion is aimed at destroying infected neurons, virus, and bacteria, but can also cause large amounts of collateral neural damage. As a result, chronic inflammatory response can result in large scale neural damage as the microglia ravage the brain in an attempt to destroy the invading infection."
The role that microglial can play in cell death in Parkinson's is not speculation.
This paper mentions another example of autoimmune brain cell death, that of the partial brain damage that can be associated with the West Nile Virus infection. In that case, the brain's own microglial infiltrate and cause "loss of hippocampal synapses and spatial memory impairment".
More on this topic in a 2009 review:
Neuroinflammation in Parkinson's disease: a target for neuroprotection?
"In vivo imaging studies of microglial activation using positron-emission tomography (PET) showed that PD patients have markedly increased neuroinflammation in various brain regions, including the basal ganglia and striatum, regardless of the number of years with disease. Studies have determined that inhibiting or preventing microglial activation renders PD mouse models resistant to neuronal death. "
The document popped up during a search for citations of the paper you linked to in your previous thread i.e. this document cites the paper titled "Striatal blood–brain barrier permeability in Parkinson's disease (2015)".
And yes, it talks about some aspects of the innate immune system (e.g. microglia), as well as some aspects of the adaptive immune system (e.g. T cells).
This is an interesting field of research involving autoimmune responses which cause inflammation. I'm tempted to think there might be a link between diet, inflammation, leaky gut and BBB and the intensity and progression of Parkinson's symptoms. The link could be twofold :
1) Positive : eating food rich in antioxidants, anti-inflammatory agents etc. This comes down to lots of fresh fruit and vegs, rich in polyphenols, omega 3, especially from seafood at the bottom of the food chain; small fish, krill etc.
2) Negative : avoiding eating foods known to provoke intolerance or allergies in certain people. The mechanism of intolerance acts through certain toxic food metabolites passing through the gut into the blood and generating cytokines via an autoimmune reaction. The cytokines cause a massive inflammation attack.
This may be just anecdotal, but I have a friend with Gougerot Sjogen disease which is a rare debilitating autoimmune + neurological disease. There is no treatment, but in the case in question, it is 80% controlled by avoiding certain foods that cause inflammation.
These are : all dairy foods, eggs, certain fish, but not other non-fish seafood or shellfish, and sunflower oil. There is a simple blood test that can show what you are intolerant to.
"Heightened innate immune responses are seen in the CNS of PD patients. There is an increase in the levels of proinflammatory cytokines in the CSF and nigrostriatal regions of PD brains.60 Furthermore, extensive amounts of reactive microglia are found in the substantia nigra of PD patients.61 These may chronically produce ROS, resulting in depletion of antioxidant stores that may jeopardize mitochondrial activity. Since aerobic respiration in mitochondria is responsible for most of the ROS produced in cells, abnormalities in these organelles may exacerbate oxidative stress. Thus, parallel to AD, NSAIDs and antioxidant therapy may benefit PD patients."
source:
Campbell, Arezoo. "Inflammation, neurodegenerative diseases, and environmental exposures." Annals of the new york academy of sciences 1035.1 (2004): 117-132.
This is all very interesting and could cause a result that we call Parkinson's.
I rattle on all the time about our own built-in repair or replacement kit known as GDNF. For some reason, I can only guess it is because the drug industry does not want to find a way of overcoming the dame caused by Pd; nobody wants to find a way of getting the brain to produce MORE GDNF.
I think fast walking does that, because it is what I have been doing for the past 25 years and what I think has helped me to be able to live without any Pd medication since 2002. That also appears to me to be something the drug industry does not want us to do.
Why do I think that fast walking causes the brain to produce GDNF? I think it has something to do with the FIGHT OR FLIGHT condition. Walking fast is not natural! If we are in a hurry we would normally run. Walking fast is not easy.
I am very aware that many people either have no interest in walking or have other problems that prevent them from walking. But there are a large number of people with Pd, who are able to walk and can learn how to walk fast, which requires the use of the conscious brain to control the movements, instead of the normally used subconscious brain. But there I go again rattling on about ways to overcome the effects of Pd. It's NOT GOOD FOR BUSINESS!
Yes, it would effect people's jobs but what is more important? A better quality of life for people with Pd or jobs for others?
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GPT PD Coach - Enhancing Neuroplasticity in Parkinson's Disease 
Informative article with links re PD and Gut microbiome
