In general, people with Lupus and/or Sjogren's should avoid things that are promoted as 'boosting' the immune system -- for the exact reason you pointed out. Most of us are on some sort of anti-inflammatory, if not regularly then at least from time-to-time as flares occur.
I myself am not sure of the antioxidants because they seem to me to be a step removed -- they indirectly, rather than directly, affect the immune system.
In any case, *always* consult with your medical team before making drastic changes in food, vitamins/supplements, OTC meds -- it is quite possible that the "standard" claims/recommendations for some of these substances are exactly the opposite if you have an autoimmune disease.
And even when you get clarifying direction from your Dr, it should not be applied to another patient -- it is the combination of meds, supplements, and how your particular instance of the disease acts that makes each of us unique in fighting these diseases.
Lynnwood, Lupus & Sjogren's ModeratorDIAGNOSING-LUPUS & LUPUS-RESOURCES
"Life is far too important to be taken seriously" - Oscar Wilde