There are explanations, see here, but they aren't widely accepted yet. This particular explanation is that most things considered auto-immune, are an infection of the immune system itself, by bugs that are heard to detect.
There are several forms of bacteria and mycoplasma that can shed their cell walls, and go into a spore-like form that is very slow growing and small enough that they can't be seen by visible microscopy, and are also too small to be filtered out of vaccines, and aren't killed by chorination or floridation. One of the things that can provoke these organisms to go into CWD form is the use of beta-lactam antibiotics like penicillin which attack the cell wall of bacteria.
Why some people fight off this infection and others don't isn't explained yet.
The good news is that this particular explanation is not just a guess, but based on solid research, and has provided a therapy that works.
That last phrase is based on personal experience with sarcoid.
Luke would you post the link about sarcoid again please?