Super fruits are your best bet to boost immunity (blueberry, acai berry)... Its funny, I just posted a link on my facebook to this article on the best herbs to boost immunity.
HERE.
Its an assumption that our immune systems are over active, but idealy, its the fact that the immune system has been triggered to release many white blood cells that are fighting off harmless body tissue, because they are confused at what to attack. That's why when I went to get a blood cell study done before even being diagnosed with colitis, my doctor couldn't find alot of white blood cells, and same with eye doctor -probably because they were mostly concentrated in the colon.
Immune Suppressors can be dangerous, and bring on infection in other areas of the body because you're basically warding off those white blood cells (that are mistakenly attacking your body) but in a healthy person, actually ward off disease and infection.