@pawprintpeg

"Why and how might accumulated stress trigger an autoimmune response?"
---------------------
I don't think stress causes an autoimmune response directly. I think chronic stress impacts the delicate balance of the immune system because of the production of cortisol which is called the stress hormone.
https://pmc.ncbi.nlm.nih.gov/articles/PMC11546738/
-------------------------
I'm going to turn it over to artificial intelligence to explain what stress does:

"The Cortisol Shift:
In response to chronic stress, the brain's Hypothalamic-Pituitary-Adrenal (HPA) Axis continuously stimulates the adrenal glands to produce cortisol.

Receptor Desensitization:
Under short-term stress, cortisol helps suppress inflammation. However, prolonged exposure causes immune cells to become resistant to cortisol's anti-inflammatory signals, leading to glucocorticoid receptor impairment.

Immune Dysregulation:
This resistance means cortisol can no longer properly regulate the immune system. Consequently, cytokines—proteins that mediate immune responses—become imbalanced, promoting systemic inflammation and reducing the body's ability to tell the difference between "self" and "non-self".
===================
From my personal experience I think genetics and an infection were causal factors for my first autoimmune condition. It was called "reactive arthritis" which derives its name from a reaction to an infection in genetically predisposed people.
https://www.ncbi.nlm.nih.gov/books/NBK499831/
Reactive arthritis is plagued by the same diagnostic problems and treatment difficulties as PMR/GCA.
--------------------------------
There are other various reasons that have been hypothesized for why the body might lose the ability to differentiate between "self" and "non self." There are only theories so nobody knows for sure.

The way that Prednisone further disrupts the delicate balance of the HPA axis and the immune system ability to regulate systemic inflammation makes me think that prednisone isn't the best solution to the problem of autoimmunity. My body didn't "reset itself" until I was able to wean myself off Prednisone.