What is "boosting immunity?"?

There are a lot of questions here about immunity boosting and I'd really like to know what they mean? Is it pseudoscientific concept much like "flushing out toxins" or is it a real scientific concept? How do you know your immune system is "boosted?" Can this boosted immunity be... show more There are a lot of questions here about immunity boosting and I'd really like to know what they mean? Is it pseudoscientific concept much like "flushing out toxins" or is it a real scientific concept?

How do you know your immune system is "boosted?"

Can this boosted immunity be measured?

If yes, then how? Number of B and T cells? NK cells?

If you boost the immune system of a person who has autoimmune disease, will you end up hurting him?

Is it entirely possible that boosting the immunity is totally bogus since your immune system is like a binary system (it either works or doesn't)?
Update: thanks, SkepDoc. Here's hoping.
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