This is why studies in the lab, and even in animals, still need to be repeated in people before we can be sure the findings apply. This same feature that makes the immune system flexible also makes it difficult to study. The same is true of the cells and proteins of our immune system most “jobs” of the immune system can be done by more than one part of the immune system although some parts are better at certain jobs than others. The substitute may or may not be as efficient, but it still allows you to complete your task. If you need to go to the store, but your tire is flat, you may go by another method of transportation - another motor vehicle, a bicycle or walking. Think of it like a trip to the grocery store.
One of the amazing aspects of the immune system is that it is compensatory, meaning that when one part is weak or non-functional, typically another part can step in. This can result from immune deficiencies present at birth medications that suppress the immune system, like steroids unnecessary or overzealous immune responses, such as allergies or immune responses to one’s self, called autoimmunity. Sometimes a person’s immune system does not work properly.