When the anthropologist Emily Martin asked an array of scientists to discuss descriptions of the immune system that depended on the metaphor of a body at war, some of them rejected the idea that this was a metaphor. It was, they insisted, “how it is.” One scientist disliked the war metaphor, but only because he objected to the way war was being waged at that moment. In her study of how we think about immunity, which was conducted during the first Iraq war, Martin found that metaphors of military defense permeate our imagination of the immune system.“Popular publications,” Martin observes, “depict the body as the scene of total war between ruthless invaders and determined defenders.” Our understanding of disease as something that we “fight” invites an array of military metaphors for the immune system. In illustrated books and magazine articles, the body employs some cells as “infantry” and others as the “armored unit,” and these troops deploy “mines” to explode bacteria, while the immune response itself “detonates like a bomb.”But this war imagery does not reflect the full diversity of thinking Martin discovered in her interviews. Alternative medicine practitioners, as a group, consistently refused to use war metaphors in their descriptions of the immune system. Most other people, scientists and non-scientists alike, tended to gravitate toward militaristic terms, but many were able to suggest different metaphors and some explicitly resisted military metaphors. “My visualization would be much more like a piece of almost tides or something… the forces, you know, the ebbs and flows,” a lawyer remarked, clarifying that by forces she meant “imbalance and balance.” A number of other people, including scientists, echoed this idea of a body striving for balance and harmony, rather than engaging in armed conflict. The inventive metaphors with which they imagined the immune system ranged from a symphony to the solar system to a perpetual motion machine to the vigilance of a mother.The term immune system was used for the first time in 1967 by Niels Jerne, an immunologist who was trying to reconcile two factions of immunology – those who believed that immunity depended largely on antibodies and those who believed it depended more on specialized cells. Jerne used the word system to unite all the cells and antibodies and organs involved in immunity into one comprehensive whole. This idea what immunity is the product of a complex system of interdependent parts acting in concert is relatively new to science.Even so, what we know of this system is staggering. It begins at the skin, a barrier capable of synthesizing biochemical that inhibit the growth of certain bacteria and containing, in its deeper layers, cells that can induce inflammation and ingest pathogens. Then there are the membranes of the digestive, respiratory, and urogenital systems with their pathogen-ensnaring mucous and their pathogen-expelling cilia and their high concentration of cells equipped to produce the antibodies responsible for lasting immunity. Beyond those barriers, the circulatory system transports pathogens in the bloody to the spleen, where the blood is filtered and antibodies are generated, the lymphatic system flushes pathogens from body tissues to the lymph nodes, where the same process ensues – pathogens are surrounded by an assortment of cells that ingest them, eliminate them, and remember them for a more efficient response in the future.Deep in the body, the bone marrow and the thymus generate a dizzying array of cells specialized for immunity. These include cells that can destroy infected cells, cells that swallow pathogens and then display pieces of them for other cells to see, cells that monitor other cells for signs of cancer or infection, cells that make antibodies, and cells that carry antibodies. All of these cells, falling into an intricate arrangement of types and subtypes, interact in a series of baroques dances, their communication depending in part on the action of free-floating molecules. Chemical signals travel through the blood from sites of injury or infection, activated cells release substances to trigger inflammation, and helpful molecules poke holes in the membranes of microbes to deflate them.Infants have all the components of this system at birth. There are certain things the infant immune system does not do well – it has trouble penetrating the sticky coating of the Hub bacteria, for example. But the immune system of a full-term infant is not incomplete or undeveloped. It is what immunologists call “naïve.” IT has not yet had the opportunity to product antibodies in response to infection. Infants are born with some antibodies from their mothers already circulating in their systems, and breast milk supplies them with more antibodies, but this “passive immunity” fades as an infant grows, no matter how long it is breast-fed. A vaccine tutors the infant immune system, making it capable of remembering pathogens it has not yet seen. With or without vaccination, the first years of a child’s life are a time of rapid education on immunity – all the runny noses and fevers of those years are the symptoms of a system learning the microbial lexicon.When I asked for help understanding the basic mechanics of immunity, a professor of immunology gave me a two-hour explanation of the immune system in a coffee shop. He never once, in those two hours, used a military metaphor to describe the workings of the body. His metaphors tended to be gastronomic or educational – cells “ate” or “digested” pathogens and “instructed” other cells. When he spoke of something being killed or destroyed, he was referring to literal death or destruction. The scientific term for a type of white blood cell capable of destroying other cells, he told me, is natural killer.Later, I attended a series of lectures by the same professor. While I was learning the distinction between innate immunity and adaptive immunity and trying desperately to keep track of a proliferation of acronyms – NLRs and PAMPs and APCs – I would note that the cells of the immune system lead lives in which they kiss, are naïve, eat purge, express, get turned on, are instructed, male presentations, mature, and have memories. “They sound like my students,” a friend of mine, a poetry professor, would observe.If a narrative of any kind emerged from those lectures, it was the drama of the interaction between our immune system and the pathogens with which it coevolved. This drama was sometimes characterized as an ongoing battle, but not the kind that involves Apache helicopters and unmanned drones – this was clearly a battle of the wits. “And then the viruses got even smarter,” my professor would say, “and did something ingenious – they used our own strategies against us.” In his telling, our bodies and the viruses were two competing intelligences locked in a mortal game of chess.
Eula Biss, excerpt from On Immunity. Copyright © 2014 by Eula Biss. Reprinted with the permission of Graywolf Press, Minneapolis, Minnesota, www.graywolfpress.org.