Stephen Buhner recommends astragalus as an immune modulator, although he doesn't suggest it's use by people with chronic lyme because it may produce too much of a Th1 response.
For chronic lyme he recommends cordyceps, also a mushroom, and the ginsengs. We personally use all of the herbs I have listed in rotatation, including astragalus (which we are able to handle 3x weekly).
I didn't realize how important the immune system was in combating these illnesses until I read Buhner's books. I just thought that we could throw abx at our daughter's infections, and they would resolve. That's what many doctors tell us, right? 3 weeks, 1 year, 2 years and then you will be OK.
The immune system is SO important, and we are killing the good bacteria in our guts by eating pesticides. We are stifling our natural immune reactions with vaccinations and fever supressants.
It's little wonder we have so many chronic illnesses that our immune systems should be able to take care of.