On Immunity : An Inoculation (9781555973278) (7 page)

O
UR UNDERSTANDING OF IMMUNITY remains remarkably dependent on metaphor, even at the most technical level. Immunologists describe the activities of our cells with terms like
interpretation
and
communication
, imbuing them with essentially human characteristics. Three immunologists on a road trip in 1984 became excited about the possibility that the cells of our bodies might, like the humans they compose, use a system of signs and symbols—a kind of language—in their communication with each other. After traveling for seventeen hours in a VW bus with a ripe wheel of Taleggio cheese and an Italian edition of Umberto Eco’s
A Theory of Semiotics
, they determined, through some rough translations performed by the Italian among them, that a better understanding of semiotics, the study of how signs and symbols are used and interpreted, might enhance their work in immunology.

When I learned of the resulting conference on “immunosemiotics,” I was excited by the possibility that it was devoted to the discussion of metaphor, a semiotic device. I thought I had found a group of immunologists interested in dissecting their own metaphors. To my disappointment, the conference papers revealed that they were much more concerned with the question of how our bodies, not our minds, interpret symbols. But as the immunologist Franco Celada proposed in a paper titled “Does the Human Mind Use a Logic of Signs Developed by Lymphocytes 10
⁸
Years Ago?” our minds may have learned the ability to interpret from our bodies.

“Immunologists are forced to use unusual expressions in order to describe their observations,” the semiotician Thure von Uexküll observed at the conference. “Expressions like ‘memory,’ ‘recognition,’ ‘interpretation,’ ‘individuality,’ ‘reading,’ ‘inner picture,’ ‘self,’ ‘nonself,’” he maintained, were unknown in physics or chemistry. “Atoms and molecules have no self, memory, individuality, or inner pictures,” he said. “They are not able to read, to recognise or to interpret anything and cannot be killed either.” Some of the other semioticians at that conference, most notably Umberto Eco, would question whether the cells of the body were literally engaged in acts of interpretation, but the immunologists seemed less skeptical.

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 nonscientists 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 that 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 biochemicals 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 blood to the spleen, where the blood is filtered and antibodies are generated, and 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 baroque 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 Hib bacteria, for example. But the immune system of a full-term infant is not incomplete or undeveloped. It is what immunologists call “naive.” It has not yet had the opportunity to produce 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 naive, eat, purge, express, get turned on, are instructed, make 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.

I
WALK THE EDGE OF A LARGE CEMETERY whenever I walk north along Lake Michigan, which is nearly every day when the weather is warm. One high summer morning when my son was clamoring to get out of his stroller, I turned through the iron gate of the cemetery so that he could run on its paths under the shade of its trees. “Hi,” he called out brightly, waving into space as we entered the empty cemetery. “Hi,” he kept saying as he toddled down the path, pausing to smile and wave at nothing. I had only ever heard him say “hi” to people, so I knelt down to catch his sight line and saw that he was staring at the doors of a tomb. “What’s that?” he asked, and I chilled. But now he was careening down the path and I followed him, pausing in front of a granite obelisk that caught my eye because it was inscribed with the first name WILLIE in large letters where the family name appeared on other stones. Willie had died in 1888, at the age of eight.

“Hi,” my son was saying again, somewhat insistently, a few feet away, “hi!” He was standing in front of a marble statue of a little boy. The boy had the full cheeks of a baby and his marble eyes stared gravely into the middle distance. An eroded stone at my feet revealed that his name was Josie and he had died in 1891 at nine years old. As my son reached out his hand toward the boy I caught his wrist, in a rising panic, saying, “No, don’t touch that!” I still cannot say exactly what scared me in that moment. Did I worry that my son would catch death if he touched the marble boy?

After leaving the cemetery I remarked to my father that I had noticed the graves of five-year-olds and ten-year-olds and a number of teenagers, but that I was surprised not to have seen, in one of the oldest cemeteries in Chicago, the graves of any babies. This, my father reminded me, was probably because infants died in such large numbers during the nineteenth century that they were not routinely buried in marked graves. Later, I would learn that one out of every ten children born in 1900 died before their first birthdays. I would read this in a report on vaccine side effects, which concluded its brief historical overview of child mortality with the observation that now “children are expected to survive to adulthood.”

The first night my son slept farther than an arm’s length from me, I fell asleep with the baby monitor pressed painfully against my ear. When the monitor ran out of batteries and began to beep I woke in alarm, but my son continued to sleep. His crib was no more than twelve feet from my bed, with an open door between us, and I could hear him crying quite well without a monitor, but I wanted to hear him breathing. I understood that this was an absurd indulgence but it was one I could not resist. The monitor, when it was turned up loudly enough for me to imagine I could hear breathing, produced a thick static that hosted a range of otherworldly sounds. I heard low muttering and whispering, clicks and bumps and sometimes crashes that were, when I rushed to see, nothing. Occasionally the monitor picked up phone conversations and I heard voices clearly for a few moments. I often woke in the night to crying that disappeared as soon as I was fully awake, and this happened, I began to notice, at the same time every night, just as a jet plane came in low over the lake to land at O’Hare. My sleeping mind, I realized, was choosing the frequencies it was listening for and manufacturing the crying of a baby out of the combination of the whine of the jet plane’s engines and the static of the baby monitor.
Psycho acoustics
, a musician friend of mine once called this phenomenon.

I stopped using the baby monitor finally because I had to admit to myself that I did not know what I was listening for. But I continued to listen. One evening shortly after my son turned two, I heard a strange sound from his room just as I was getting into bed. I was no longer finding crying in the whine of jet planes, but I still sometimes woke with a start from a dream of crying. This sound I heard could have been a dog in the courtyard or it could have been a chair scraping the floor upstairs. I was only certain that I had really heard it because I heard it once more, and then there was a long silence. I walked to my son’s door and listened. He was asleep, I was certain.

It was dark and quiet in his room, as usual, but he was sitting up in bed. Tears were running down his face and his mouth was wide open, gasping silently. I grabbed him, heard a thin whine of breath pulling through his throat, and laid him over my knees in an attempt at the Heimlich maneuver. This had worked for me in the past, but it produced nothing this time and only further alarmed my boy, whose body was quivering with fear. My husband, out of bed now, swept the back of his throat, found nothing, and carried him directly out the door for the hospital.

When I ran into the emergency room ten minutes later with my son’s mouth next to my ear, saying, “He’s having trouble breathing!” the triage nurse was unimpressed. “It’s probably stridor,” she said to her computer screen. Stridor, I would learn, is the high-pitched wheezing sound that indicates an obstructed airway. But as the nurse could see, my son’s color was good and his breathing was better, having improved, to my surprise, after we took him out into the cold night air. By the time the doctor arrived, my son was coughing the strange, barking cough I had heard from his room. “I’d know that cough anywhere,” the doctor said cheerfully. “I don’t even need to look at him to make this diagnosis.” It was croup, a swelling of the throat caused by a viral infection. Croup can be mild or severe, depending on the size of a child’s airway, and it produces a distinctive cough that can lead to stridor and difficulty breathing. Beyond being what the doctor termed “moderately severe,” this was a typical case of croup, having appeared at night in a toddler who seemed well when he was put to bed. Cold air, a traditional treatment for croup, had eased the swelling and reduced his stridor on the way to the hospital.