Here is an animation of the role or regulatory T-cells in the homeostatis of the immune system:
This is kind of an old presentation, but you can see that in the mechanism of Treg suppression #2, the enzyme idoleamine 2,3-dioxygenase is responsible for initiation of the anti-inflamitory regulation or effector T-cells.
Fast forward to more recent data.
The paper above concludes:
"Finally, 1,25(OH)2D3 also increased the expression and biological activity of indoleamine 2,3-dioxygenase, mediating significant increase in the number of CD4+CD25+ T regulatory cells."
Clearly, Vitamin D has a role in autoimmunity. The key thing is that your immune cells metabolize 1,25(OH)2D3 locally from 25(oh)D3.
Thus, your Calcitriol levels in your tissues may be quite different than that found in your serum.
So, any reccomendations for Vitamin D (Calcidriol) levels by your doctor is not based on the optimum to maintain immune system homeostasis.