In vasculitis treatment, what is treatment with cellcept intended to improve? (ie joint/muscle pain, gi issues, lessen blood in urine, petechia etc)

Artery inflammation: In vasculitis there is inflammation of the blood vessel. The blood vessel swells, you can leak, and can clot, and so the idea of therapy is to stop that inflammation and stop these other issues The symptoms that you have a related to the inflammation in the spot assholes. Remember blood vessels travel all over your body and some of these blood vessels are involved in vasculitis

Cellcept : Is given as an immunosuppressive, it's mainly given post transplant, kidney, heart, etc..to help prevent rejection of the transplanted organ by the active immune system of the recepient. Its use in other autoimmune conditions as vasculitis is along the same principle: suppress the active immune system so it won't attack its own, (self) tissues, hence all the symptoms would improve, best wishes