Immunology icon Immunology Notes

Some Topics

  • Immune Networks

    Medical textbooks refer to the "immune system", although this is not the best description of immune function. A more meaningful description is immune networks (IN) which are collections of different, diverse, often unstable, components. When the term "system" is used we may get the wrong image of a well-defined, orderly device, perhaps similar to a new car or a computer with an instruction manual. We are not quite the coherent entity that we like to think we are. We are really a community of cells in prodigious array. Immune networks are unlike other body systems that have well defined locations and stay in one place. Immune activity is distributed through all body systems and involves large, diverse populations of migratory cells.

    Lymphocytes are important immune players and to get an idea of the size of immune populations, think of a young tadpole as containing about one million lymphocytes. Human immune networks contain about 10 trillion cells. Some of our cells stay in one place and do more or less predictable things. Immune cells tend to wander around and, like bees, forage in our various body parts looking for items of interest. An appropriate image of immune networks would be the foraging and swarming of bees, each moving about, with different job descriptions in the colony and a meta order achieved by the collective behavior of many individuals. The overall activity of the hive or colony decides how the society or system looks and acts. They have the property of getting excited, recruiting their peers and attacking interlopers.

    The main purpose of immune networks is to wage war against invading aliens. Once engaged, orderly behavior tends to become chaotic with destruction of normal tissue structures. Fantasies about boosting your friendly, cooperative immune system have little biological basis. Another analogy that helps us relate to the changeable patterns of immune response is the weather. We regularly observe periodic and chaotic changes in the symptom patterns of patients, especially if we observe them over years. As Alan Perelson, an immunologist, suggested: "Immune activity never settles down to a steady-state, but rather, constantly changes with local flare ups and storms, and with periods of relative quiescence."

    Fessenden wrote about the complexity of immune networks: "The human immune system is incredibly diverse. Each class of immune cell is actually an army of subtypes. The elite forces — the lymphocytes, which recognize specific pathogens or wayward body cells — consist of natural killer (NK) cells, which quickly dispatch infected or cancerous cells, and B and T cells, which bear receptors on their surfaces designed to recognize specific invaders. There are regulatory T cells, T helper cells, memory B cells, naive B cells and more, each with its own unique role. These lymphocytes coordinate in turn with cells such as macrophages and monocytes, which are further specialized for other functions. Diversity manifests between people. Even identical twins vary in terms of the exact molecules and cell profiles that fight off disease. Gender, ethnicity, genetic background and disease history all affect a person's immune response in unpredictable ways. They influence whether a vaccine will work, and whether someone has allergies or an autoimmune disease — both resulting from an overactive immune system — or whether a person will develop cancer, which is caused in part by an inattentive system that fails to remove errant cells."

    [i] Fessenden, M. The cell menagerie: human immune profiling. Nature 525, 409–411 (17 September 2015)