In M.S., the immune system is thought to strip the insulation, called myelin, off neurons, leading to progressive disability. One possibility is that toughening the immune system early in life alters how we respond to hits later, making those viral infections less likely to provoke autoimmunity. When we don’t encounter the attendant stimulation early in life, the immune system can become unsteady. Lifestyle seems to be the major determinant — how the way you live guarantees (or doesn’t) exposure to a rich variety of microbes that favorably sculpt the immune system. The world today is very different from the one our immune system evolved to anticipate — not just in what we encounter, but in when we first encounter it.

Source: New York Times June 03, 2016 12:00 UTC