Scientists discover 'immune scars' on patients with lung infections

It is not likely this can be solved as easily as re-activating the immune cells, the switch off is part of the natural response after an infection is controlled, and it prevents the immune system from over damaging the organs and prevent the appearance of self-immunity, so activating them again can have quite serious unintended consequences.

It probably more useful to think about dialing it up a little faster than normal without just going from 0 to 100%.