A common misconception about auto immune diseases is that your immune system is weak. In fact, it is misdirected. The last thing you want to do is amp up the immune response until your immune system has normalized which might not happen for many of us. Taking immune system boosters is not a good idea and talk to your doctor before taking any mega doses of anything. If these treatments worked we would have done away with lupus and other AI diseases long ago.
Think about auto immune response as a gun with a miscalibrated gun sight. The gun works fine but it just misses the target and hits something else.
The vitamin C treatment was promoted by a very famous chemist, Dr Linus Pauling who won nobel prizes for chemistry and peace, and has gone in and out of favor. Dr Pauling died in the early 90s.
Here is an article on the subject and you can judge for yourself. Despite any validity of Dr Pauling's claims for cancer and heart disease I would not take high doses of anything to boost the immune response until there is definite scientific evidence that it works.
MCTD (lupus, scleroderma, polymyositis). Diagnosed 2005. Kidney, liver, GI tract, dysphagia, raynauds, Barretts esophagus, quadriplegic in 2005. Recovered and now active in skiing, tai, chi, hiking, golf. Meds: prednisone 2.5mg, imuran 25mg, amlodipine, benazapril, omeprazole, potassium, folic acid, vitamins, maxide and various supplements and vitamins.
Remain optimistic and you can overcome the odds.