Is There a Way to Train the Immune System?

People in the rain forests have been doing it for centuries, where you eat little bits of the leaf to be able to train your immune system not to become a lurgic. I've been interested in that since i first watch princess bride. Exactly a i was made himself immune to the poison. Exactly alexander the great did it. So this is kind of a natural item that our great grandparents probably did and knew to do. But nevertheless, how do we put it into action and explore it as a therapy and use it to train the immune system in a good way? Because these epidemics are rising, ed to think about how to prevent them, but also how do we stem