Vitamin C does seem to stimulate lymphocyte activity - which was one of the reasons that Linus Pauling thought that it was so good in the prevention of malignancy. The flip to that, of course, is when the malignancy is in the lymphocytes and then it is not a good idea to stimulate them any further than already are.
One of the issues then is the fact that we all need vitamin C to live. So - what to do. I would stick with theprinted recommended daily allowance and not go too high above that. Does that mean I don't gorge on fresh oranges when we get them? No - but I don't do it on a daily basis either.