The Day the Military Force Explained the Fundamentals of the Immune System

“Eat probiotic yoghurts and drink zested juices to boost your immune system!” You probably heard this on multiple occasions. Yet, many judge the immune system a too obscure and complex concept for a non-life-scientist to understand. Perhaps thinking of it as a military force training for battles may help.

For starters, think of your body as a unique nation with globally conserved but country-specific attack and defense strategies. Your immune system, the nation’s military force, is responsible for maintaining your health by constantly fighting off invaders.  We are routinely exposed to attacks from bacteria, viruses and parasites with our every touch, every breath and every bite. 

Our immune system relies on a highly organised military-like structure and network. The lymphatic and circulatory system act as the immune army’s infrastructure allowing the transport of cells (soldiers), messenger molecules (orders, signals) and nutrients (provisions). Romans conquered with their rigorous military training and discipline. Our soldiers are no exception and sent to boot camps in specialised immune organs. 

The mucosa-associated lymphoid tissues (MALT) such as the reproductive or gastrointestinal tracts acts as the body’s front lines. Analogous to castle walls, they are a physical barrier and directly in contact with the external environment. If the wall is trespassed, the invaders attract the patrolling infantry soldiers.

Granulocytes, infantry soldiers, receive basic training in the bone marrow (spongy bone portion) and are deployed in the blood. They are then recruited to infected tissues to fight off intruders. Granulocytes respond within hours of infection via the non-specific innate immune response ie targets all enemies indiscriminately. This response explains the redness, heat and pain right after a paper cut for example.

Antigen-presenting cells (macrophages and dendrocyte cells) are secret agents, found at the walls. They collect information about the enemies (profiling) and deliver this information to B and T cell officers. Such officers belong to the adaptive immune response ie selective targeting and enemy elimination. B cell officers produce specific ammunition (antibodies) against the pathogenic invaders (antigen).

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Such weapons support the infantry and T cells. T cells, field officers undertaking more dangerous missions, are further trained in the thymus (organ beneath breastbone). Treacherous T cells capable of attacking host cells are executed in the thymus, prior to their release in the circulation. Thus, only trained and loyal T cells are released in the battlefields. 

After each battle, some B and T cells that have reacted against the pathogen are retained “memory cells” while all the others are destroyed to prevent damage to nearby healthy tissues. If the same invader attacks a second time, the soldier cells react faster with more ammunition to destroy it.  The storage of such memory cells diversifies attack and defense strategies. The memory cell palette is specific to the individual and remodeled during their lifetime. 

Vaccine development makes use of this field training. By injecting small viral doses, the body produces antibodies (ammunition stock) so that when the same virus attacks the immune response is faster and efficient.