A lot has been said about the immune system and how to strengthen it. There are countless books, articles, podcasts, and TV documentaries about it. Some doctors have devoted their entire careers to finding ways to boost and improve this amazing system, which does a remarkable job defending us against disease-causing pathogens. There are diets, herbal preparations, supplements, and vitamins explicitly designed to increase immunity. But while the idea of supercharging the immune system might be enticing, it is only...