[Palomides]

calling the immune system simple and mechanical is completely wild, like half of americans have some kind of medically diagnosable immune dysfunction

[gcanyon]

The immune system operates at level far below where we get "tired" -- worrying that we'll "use up" the immune system seems similar to worrying that exercise will "use up" our lifetime allotment of heartbeats.

[empath75]

The concern isn't "using up" the immune system, the concern is the immune system gets all revved up looking for something to kill, and not finding pathogens handy, attacks your own organs.