What is the Immune System?

The immune system is a complex, intricate system that researchers are still learning more about. The following information regarding our immunity is a brief overview and while a “little” technical, it will illustrate the relationship between stress and the immune system and how managing our stress can help our immunity.

Think of our immune system as being like a huge defensive army for our body. It has all sorts of personnel that are deployed when our body is attacked by foreign invaders such as viruses, bacteria, parasites, and fungi. It also scavenges dead or dying body cells and destroys abnormal or cancerous cells. The immune system is made up of specialized organs, cells, and tissues that all work together as an organized team to destroy these invaders.  Specifically, the parts that play a role include our bone marrow, lymphocytes, thymus, lymphatic nodes and vessels, tonsils and adenoids, spleen, appendix, and Peyer’s patches (gut-associated lymphoid tissue).^[1]

Let’s talk about each of these units and their functions.

If the immune system is the army, the bone marrow is where basic training boot camp occurs, as all of the different types of immune system cells are created here. All cells in the body are derived from stem cells, which are cells with the potential ability to transform into many different types of cells in the body.^[2] In the future, the stem cells develop into specialized cell types, including red blood cells (erythrocytes), part of our blood; platelets (thrombocytes), which are necessary for blood clotting; and white blood cells (leukocytes), which are the front lines of the immune response.^[3] As we grow older, only some of our bones such as the ribs, sternum, and pelvis still contain red bone marrow, and the rest turns into fatty tissue.^[4] Thus, one of the consequences of aging is the decline in our immune function with resulting increased vulnerability to infections.^[5] That being said, our immune system cells are constantly replenished for as long as we live.

Lymphocytes are a sub-type of white blood cells that are mainly formed into B-cells, T-cells, and natural killer (NK) cells. B-cells mature in the bone marrow and, among other tasks, are responsible for humoral (antibody-driven) immunity. . Cells that will turn into T-cells travel from the bone marrow to the thymus via the bloodstream where they mature.^[6] As we age, the thymus starts to slowly shrink and become replaced by fat. However, the thymus produces all of the T-cells we need by the time we reach puberty, as by age 75, the thymus is little more than fatty tissue.^[7] Once T-cells have fully matured in the thymus, they travel to the lymph nodes of the Lymphatic System. Natural killer cells respond rapidly to many pathogens, and are especially adept at killing virally infected cells, and detecting and controlling early cancerous cells.^[8] We will delve deeper into B and T-cells later when we talk about the specific acquired defense portion of our immune system.

The Lymphatic system is essentially our “drainage system” and consists of a network of tissues, vessels, nodes, and organs that assist our body to expel toxins, waste and other undesirable things.^[9] This network transports these wastes via lymph, a clear, watery fluid. Lymphatic fluid collects waste from the tissues, and then filters this fluid through the hundreds of lymph nodes that we have throughout our body.^[10] The most notable groups of lymph nodes are found in the throat, groin, armpits, chest, and abdomen, and are particularly prevalent in the digestive tract and genital region, as this is where pathogens most often enter the body.^[11] If pathogens are detected, the immune system is activated, and the number of immune system cells are increased. This results in enlarged nodes that are painful due to the increased space they take up. Most of us are familiar with “swollen glands” on our neck if we have a cold, or sore throats due to swollen tonsils and adenoids.

Once the lymph fluid is filtered, lymph vessels carry the lymph back to the heart to return to the blood stream for another trip through the body. Lymph is not circulated like blood; it doesn’t have a pump like our heart to push it through our body. It only flows in only one direction – upward – towards our heart.

There are other lymphatic organs that are part of the lymphatic system.  The tonsils and adenoids protect the entrance to the digestive system and lungs.^[12] The spleen is the largest filtering organ in the lymphatic system and is located on the left side of the abdomen under the diaphragm. It not only destroys aged or damaged red blood cells, it also can remove dangerous pathogens.^[13] It also produces macrophages, a type of white blood cell that engulfs and destroys bacteria, dead cells, and foreign matter from the body, as well as B-cells and T-cells.^[14]

The appendix, an organ that many think is useless, actually has been found to be important after all.  The appendix is believed to store beneficial bacteria so it can restore intestinal normal flora in case it’s destroyed by an infection.^[15]

Most people may not be familiar with Peyer’s patches, which are lymph nodes that line the small intestine, most notably the ileum, which is the last portion of the small intestine. Peyer’s patches contain different types of immune cells that sample material within our small intestine, so it’s theorized that they play a role in controlling which substances require an immune response.^[16]

You got this far! Great job! Continue on to read more about the Immune System Lines of Defense.