I Contain Multitudes: The Microbes Within Us and a Grander View of Life

by Ed Yong

The immune system, for all its intricacy, is a lot like that dial. It works like an ‘immunostat’, which, rather than stabilising temperature, stabilises our relationships with our microbes.15 It manages the benign trillions that live with us, while thwarting invasions by an infectious minority. If it is set too low, it becomes relaxed, missing threats and leaving us open to infections. If it is set too high, it becomes jumpy, falsely attacking our own microbes and triggering chronic inflammation. It must tread a fine line between these extremes, balancing the cells and molecules that induce inflammation with those that repress it. It must react without overreacting. But over the last half-century, we have gradually pushed our immunostats to higher settings through a combination of sanitation, antibiotics, and modern diets. We’ve ended up with immune systems that go berserk at harmless things like dust, molecules in our food, our resident microbes, and even our own cells.