The Invisible Kingdom: Reimagining Chronic Illness

by Meghan O'Rourke

The innate system we are born with is our first line of defense, responding immediately to pathogens and foreign matter, deploying natural killer cells and phagocytes like macrophages and neutrophils—types of white blood cells—to fight off pathogens, frequently by ingesting or engulfing them. Acquired (also known as “adaptive”) immunity is our second and more sophisticated line of defense: it mounts a response specific to the pathogen encountered, and then remembers those pathogens. Adaptive immune cells include B cells and T cells, which help fight off infections in concert with our innate immune system. The primary organs of the immune system, I learned, are the bone marrow and the thymus, a soft, pinkish-gray triangular gland above our heart. (It resembles a thyme leaf, hence its name.) It is one of the few organs that grows smaller after puberty, the point at which many of our immune cells have been made. In the bone marrow and the thymus, hordes of B and T cells, named for the parts of the body from which they come, are born and educated. Both kinds of cells attack infections, heal wounds, and more. B cells make antibodies: Y-shaped proteins that target specific pathogens by locking into them in ways that bring the video game Tetris to mind. Each antibody is specific to a given pathogen; measuring them gives doctors a record of the body’s encounters—the body’s memory of the foes it has faced.