During my first year of college I took a biochemistry course. On our final exam, there was a short answer question requiring an explanation of the adaptive immune system, and how is it different from the innate immune system. I saw this as a great opportunity to put this into language a Marine Corps infantryman could understand. The following was the answer I provided for the exam.
In order to summarize or provide an overview of the adaptive immune response, I’m going to draw a comparison between a group of frontline infantrymen and a special operations unit.
The innate immune system is feisty. It is ready to pounce at a moment’s notice and will attack any foreign element the body does not recognize. An aspect of the innate immune system is what we could call a defense in depth consisting of physical/structural barriers (mucous linings), chemical barriers (stomach acid), and finally our infantrymen, the NK (natural killer) cells – a type of white blood cell that stands ready to destroy foreign adversaries attempting to establish themselves within the host structure (our body). Like any defense in depth, over time, we have to continue to make improvements and we do this mostly with proper nutrition, thus getting the right vitamins and minerals that will strengthen the immune system.
At a young age, our special ops troops with their embedded intelligence cell (the adaptive immune system), are not yet fully trained. Although the innate immune system pounces on infections such as colds, ear infections, etc., these may come back repeatedly because the adaptive immune system is not yet capable of conducting the analysis needed to keep these invaders at bay or to repel the enemy’s assault by close combat when they have broken through the lines.
The adaptive immune system is our special operations shock troops who deploy with their own embedded intelligence cell.James Conner
What this means is when a pathogen, viral or bacterial, has broken through the front lines of the innate immune system, the more elite adaptive immune system springs into action to capture/kill the invader and exploit the intelligence.
This exploitation serves two purposes: a) prevent an invader from the same army from entering the body or b) in the event an invader does re-enter the body and gets passed the front line, a be on the lookout (BOLO) is issued in an effort to prevent the pathogen from loitering around longer than it normally would.
The base structure, or the headquarters for the adaptive immune system is made of white blood cells (WBC) called lymphocytes. From there the lymphocytes have two units, B cells and T cells, with specific missions.
B cells produce antibody responses by deploying immunoglobulin proteins whose mission involves binding to antigens and denying them the ability to connect to host cells. The binding of antigens is akin to detaining the viruses and microbial toxins, and processing them for deactivation and ultimately destruction by performing a detainee handover to phagocytic cells of the innate immune system.
*Phagocytes are cells of the innate immune system that eat infected cells. The word phagocyte comes from the Greek words phagein meaning “to eat” and cyte meaning cell which comes from the Greek word “kutos” which means vessel. People who engage in fasting or intermittent fasting experience autophagy. Auto meaning “self”, autophagy has been described as the body’s way of doing some spring cleaning – the body eats old and/or dying cells, recycles what it can, and eliminates the waste.
T cells are the highly lethal element of the adaptive immune system. They are designated to carry out the missions of a) commencing a direct action to kill a virus infected host cell, or b) give the order (via signaling molecules) directing the macrophages to kill invaders which have undergone phagocytosis.
(Graphic: Conner 2020)
Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. Chapter 24, The Adaptive Immune System. Available from: https://www.ncbi.nlm.nih.gov/books/NBK21070/
Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001. The structure of a typical antibody molecule. Available from: https://www.ncbi.nlm.nih.gov/books/NBK27144/