The Watchdog Within

The world of life is hungry. Soon after birth we begin to crave the breast, and the hunger never stops. Everything that lives draws sustenance. Plants absorb sunlight. Babies drink milk. It’s all very natural.

So too is the way bacteria digest their surroundings and absorb useful chemicals, whether in soil or human tissues. Or how parasites take residence in the bodies of mammals, growing to produce eggs that leave by one route or another, hatch, and follow complicated paths through the living world before finding another mammalian host. Or how viruses divert the deepest chemistry of our cells to their own ends, causing colds, flus, and many other diseases, which at times are life-threatening.

Think how quickly a body decays after death. Decomposition is a banquet for microorganisms and insects, one held at bay during life. And what protects the living? The immune system.

Health depends on functioning immunity. I attended medical school as the early years of the AIDS epidemic devastated the San Francisco gay community. I saw firsthand the tragic deterioration of health that ensues when an immune system is damaged. Young men my age wasted away and died over the course of a year or two. It was a painful lesson in how much we need protection from the ravenous world of life.

How does immunity work? In ways too complicated to explain in a short blog post. But it includes some key components worth mentioning. Some immunity results from barrier functions. Skin and intestinal linings are designed to discourage invasion. Other immunity depends on recognizing ancient threats. Bacterial cell wall construction hasn’t changed much, we assume, in billions of years. Our bodies take advantage of this stereotypy, and cell wall proteins invite immediate and vigorous attack. Of course, bacteria learn to evade these fixed defenses by disguising or coating their surfaces. So the body must adapt. It learns, and in this capacity we see the immune system at its most impressive.

Every year new viral strains emerge, and every year those of us who recover from infection retain cells that remember the uninvited guest and prevent it from crashing the party a second time. This is what makes vaccination effective: we give the body a disabled version of the pathogen, so when native infectious particle shows up the system can fend them off.

The immune system has been likened to a distributed brain. It possesses an intelligence, as we see from the way it learns from experience. But its modes of learning and memory are not similar to those employed by the more nimble brain. We might dismiss the slow, organic responses as rather dumb by comparison with the speed of neural response. But remember that the brain depends on the immune system for its very survival. How smart is a brain that minimizes the intelligence of a protector capable of fending off threats of vast variety?

The immune system’s intelligence depends on a complicated system of cells that communicate via numerous chemical messengers. It builds proteins (such as antibodies) that distinguish what belongs from what doesn’t: human from bacteria, healthy from cancerous, and so on. It adapts to changing circumstances and accommodates life forms that aid survival, such as the friendly bacteria in our guts. Some immune cells actively patrol the body; others wait in reserve until needed. There are local sentries in every tissue of the body, and garrisons lodged in lymph nodes as well as in patches of lymphoid tissue lining the gut.

The immune system’s chemical activities are monitored by the brain, which explains why we often feel blue when ill with a flu. What’s more, the brain’s changing states influence immunity. That’s why we tend to get sick after a major loss, and perhaps why we feel vigorous when falling in love.

The immune system, like so many of the body systems, operates mostly on its own. Our thoughts and feelings affect it, but it doesn’t depend on our attention. Which is a good thing. Imagine trying to monitor your body, detecting every foreign or damaged cell, and directing appropriate protective responses. We’d never have time to walk on the beach, or hug our loved ones, or read a blog post about our immunity.

If you have a moment now, sit back with eyes closed. As you slow your breathing a little, imagine the deep intelligence that is your immune system. Ever watchful, ever learning, it protects you each day of your life. On most days it keeps you healthy. And should you suffer illness or injury, it heals you. Imagine that!

Perhaps your immune system isn’t perfect. Maybe it’s failed to prevent a cancer. Or maybe it’s so enthusiastic it attacks your own tissues, causing arthritis, colitis, or one of the other autoimmune conditions. Remember, even so, that your immune system has kept you alive your entire life. It’s doing its best. Feel gratitude for what it does right, even as you encourage its improvement.

The body does its best. After you’ve felt appreciation for the floating brain of your immune system, remember how hard your body works in each of its systems. Even an ailing body strives to sustain life. You might want to send your organism tender wishes for wellness and heartfelt thanks for its support.