Immune System Components

Here is an excerpt from Module 1 of the new Education Modules. One can purchase Modules 1–3 for general education about the immune system, food allergies and sensitivities, and inhalant allergies and sensitivities. The complete set includes two Modules that show one how to implement SET-DB™ and so are for SET-DB™ practitioners only. One can become a Certified SET-DB™ Practitioner by scoring 70+ on each of the Module quizzes. (The quizzes are not mandatory; one can go through the Modules for education purposes only.)

The immune system doesn’t have one central regulating organ like the heart for the circulatory system and the lungs for the respiratory system. Instead, the immune system is dispersed throughout the body. Its functional units are immune cells and their supporting tissues. Its primary function is to recognize invaders and other cells and substances that aren’t “self” and get rid of them. Once a potential enemy has been identified, a complex immune response kicks in to neutralize it and prepare it to be removed from the body.

Let’s review the immune system’s components.

The lymphatic system is the body’s filtration system. It helps sample incoming substances, filter out waste products from cells, regulate fluid homeostasis, and prime the immune system for action when a threat is located. Central to the system is the transportation of lymph, a clear fluid that stores and transports white blood cells, proteins, salts, glucose, bacteria, and certain waste products.

 Lymphatic vessels  perform a little like blood vessels, carrying lymph to virtually all areas of the body, other than bone marrow. Unlike blood vessels, however, a series of valves force lymph to travel in just one direction, always toward the neck where it re-enters the venous circulatory system. New lymph is formed when specialized lymphatic capillaries allow soluble materials and cells to work their way back into lymphatic vessels.

The lymph fluid, along with lymphatic vessels and nodes, comprise one-sixth of the weight of the body. The major lymphatic vessels generally run parallel to blood vessels.

Lymphatic vessels are connected to lymph organs, which we’ll talk about. Lymph is filtered and lymphocytes are created in these organs.

Lymph nodes dot lymph vessels throughout the body, but namely in the armpits, groin, throat, at the base of the lungs, and in the abdomen. They filter lymph and act as traps for pathogens, preventing them from entering the bloodstream and allowing mature lymphocytes, primarily macrophages, to attack. They also contain antibody-producing cells called B-lymphocytes, or B-cells. 


Tonsils and adenoids, at the back of the throat, act as barriers to infectious organisms we inhale or ingest.

Thymus gland, the master gland of immunity, is the principle activator of the immune system. It’s composed of two gray lobes located at the base of the neck under the sternum, at about the 2nd rib. Its primary function is the maturation of T-lymphocytes, which can directly attack antigens without producing antibodies. As these lymphocytes get older, they’re sent into the lymphatic vessels to hunt down and attack infected or cancerous cells. 

The thymus also releases hormones that regulate the immune system. These include thymosin, thymopoietin, and serum thymic factor. Lastly, it initiates the differentiation of white blood cells into different types, as needed.

The spleen, weighing in at seven ounces, is the largest lymphoid organ. It lies in the upper left abdomen, behind the lower ribs. It’s functions include producing white blood cells that can engulf and destroy bacteria and cellular debris; destroying worn-out blood cells and platelets; and acting as a blood reservoir. Like the thymus, the spleen releases many potent substances that enhance immune function.

The small intestines are only nine feet long, but the absorptive surface is 600 times longer because the inner lining is highly folded. Peyer’s patches, in the lining of the small intestines, contain both T- and B-cell lymphocytes. It’s one of the largest and most important interfaces between you and your environment. We’ll be discussing it at length in the food allergy module.

Bone marrow is the production site for two types of white blood cells: antibody-secreting B-cells and foreign cell-devouring neutrophils.

Skin is considered part of the immune system because it’s a barrier against potential invaders.

The mucus membrane contains immune cells that produce chemicals, like histamine, during an allergy reaction and secrete mucous that engulfs microorganisms and moves them along for elimination.

The appendix has long been thought to be vestigial, that humans evolved in a manner that made it obsolete. However, recently it’s been proposed that the appendix serves as a haven to useful bacteria when illness flushes the bacteria from the rest of the intestines. A “safe house” or “back-up” system, so to speak that serves to repopulate the gut flora when needed.

And finally, the liver. During an immune response, it’s stimulated to release large numbers of protein molecules known as acute phase proteins. They exert an important influence on tissue repair, immune cell functions, and the inflammatory process. It’s also involved in ongoing detoxification, which takes a load off the immune system by breaking down immune complexes, which you’ll learn about soon.