Where immune system/autoimmune dysfunction (diseases) exist, how do they further contribute to destruction at the cellular level?

How does the Central Nervous System, Brain, Spine and overall blood/brain/barrier, HPA axis' decrease in overall and combined functioning?

The immune/autoimmune response or dysfunction appears to be of systemic origins, so my question is what is the connections of the above conditions at the basis of cellular levels and destruction. (ie. demyelinating) Can they be repaired and if so how?

When the Central Nervous System and all of its components combined with the genetic predisposition of hereditary characteristics(ie, Autosomal dominant or recessive) does the cellular function already predispositioned to defaults of functioning?