Introduction to Your Immune System

Healthy Beings Staff
Sep 28, 2021 11:22:07 AM

Our immune system is one of the most important systems in the human body. We are constantly coming into contact with bacteria, fungi, amoeba, viruses, and other pathogens looking to invade our bodies and take over. Our only defense is the organs, cells, and substances that make up our immune system and that work together to eliminate these threats.

Innate vs. Adaptive

Within our immune system, there are two divisions: the innate and adaptive immune systems. The innate immune system fights off any general invaders. It is not specific in its defense, and it does not remember pathogens it has encountered before. It's what alerts our bodies to "stranger danger."

The adaptive immune system is more closely related to the America's most wanted list. Our bodies keep a list of "bad guys" that they know have committed crimes against them before, and they are on the lookout for their return. Each cell within our immune system remembers when they have met a specific bacterium, virus, amoeba, or fungus and stores that information for when they come back in order to activate an rapid immune response.

Organs of the Immune System

Anatomy-of-the-immune-system

Skin

Skin is our first line of immunity defense. It provides a physical barrier to infection. Skin cells also secrete oils and enzymes that can break down the outside wall of bacterium.

Mucous membranes

There are mucous membranes that line your respiratory, gastrointestinal, and genitourinary tracts. These membranes secrete mucus that traps small particles, including pathogens. They also have cilia (small hair-like projections), that move the mucus, and its trapped particles, out of the respiratory tract, and ultimately out of the body.

Tonsils

The tonsils are at the back of the throat (palatine tonsils, the pair of tonsils that we refer to most frequently), the base of the nasal passage into the throat (adenoids), and the base of the tongue (lingual tonsils). It is at these key points that the small pits on the tonsils' surfaces trap foreign particles that enter the nose and mouth. The palatine tonsils and adenoids often become infected because they are inefficient at destroying the substances they catch. Also, larger debris can get stuck in the pits and cause inflammation also known as tonsillitis. It is rare for the lingual tonsils to get infected because mucous glands drain them.

Lymph nodes

Lymph nodes are filters for blood circulating in the body. They are located where major junctions of the lymphatic system reside; in the neck, groin and armpits. They capture foreign substances in the blood and expose them to the cells of the immune system used for pathogen destruction. Both B and T cells, common immune system cells, can live here.

Thymus

Your thymus is behind your sternum, right by your heart. It is one of the most important organs in the immune system because it coordinates the entire system and develops specific immune cells known as T lymphocytes or T cells.

Spleen

The spleen is most known for being associated with mononucleosis (aka "mono" or the "kissing disease"). The spleen consists of two parts; the white pulp and the red pulp. The white pulp produces lymphocytes to fight infection directly. The red pulp monitors the red blood cells in our system and destroys old or damaged cells that could lead to disease. It also has phagocytes inside the tissue that eat microorganisms such as bacteria, fungi, and viruses.

Bowel

Your digestive tract houses millions of good bacteria that aid in digestion. In addition, they interact with our immune system in a way that protects us. They help train and develop our immune systems from birth forward. The immune system monitors the growth of the bacteria in the gut and keeps it in check, training it on how to ward off infection. Our gut and the microbiome that live there have a mutually beneficial relationship. Good bacteria may live in the gut and consume substances we cannot digest or other substances that move through the GI tract. In exchange, the good bacteria helps our immunity and other vital functions in our bodies. When we have plenty of "good" bacteria in our GI tract, the "bad" bacteria have less of a chance of survival.

There is also lymph tissue in the gut. It acts much like tonsils in capturing microorganisms and their antigens, destroying them and helping the immune system learn from their attack.

Bone marrow

Bone marrow is the soft tissue inside the bones that produces stem cells. These stem cells become red blood cells, white blood cells, and platelets. B lymphocytes (B cells), which are vital in the adaptive immune response, also originate here.

Cells of the Immune System

Basophil

Basophils are white blood cells produced in your bone marrow that release enzymes to attack all foreign organisms such as bacteria, fungi, and viruses. They are part of the innate immune system, meaning they cannot recognize specific pathogens and instead kill anything deemed foreign. Two of the notable enzymes they release are histamine and heparin. Allergic reactions involve histamine release whereas heparin prevents blood clotting.

B lymphocyte

The "B" in B lymphocyte points to the origin of the cell itself. B immune cells originate in the bone marrow. They are part of the adaptive immune system and develop antibodies to recognize specific pathogens. Each B lymphocyte creates antigens for a particular pathogen, allowing our immune system the ability to learn nearly limitlessly.

Memory B cell

Memory B cells or memory B lymphocytes circulate in the body, ready to wage war against a virus or other invader. They hold on to the antibodies created when they first encountered a pathogen and if they ever encounter the pathogen again, they are instantly ready to start an immune response and destroy the pathogen.

Dendritic cell

A dendritic cell is a type of antigen-presenting cell. It processes antigens from pathogens and presents them to T cells to activate them and their response.

Eosinophil

Eosinophils are part of the innate immune system. They are phagocytic, meaning they ingest (eat) the bacteria and parasites that they encounter. They also mediate allergic reactions by deactivating and consuming substances like histamine that are released by mast cells.

Natural killer cell

Natural killer cells are part of the same family as B and T cells. However, they are part of the innate immune system. Their purpose is to kill infected cells and detect early signs of cancer.

T lymphocyte

The "T" in T lymphocyte stands for thymus, as that is where the cells live. T lymphocytes are part of the adaptive immune system. When they encounter an antigen from a pathogen, they rapidly differentiate (transform from a general cell type to a specific cell type) and proliferate (make many copies of itself) in order to carry out their function within the immune system.

Cytotoxic T cell

Cytotoxic or killer T lymphocytes scan cells to see if a pathogen has infected them or if they have become cancerous. If either of these things has happened, they will kill the cell.

Memory T cell

Memory T cells are similar to memory B cells in that they remember antigens that they have encountered in the past, but they have a different response. They will rapidly multiply when they encounter that antigen again, in order to fight it.

Helper T cell

Helper T cells activate other cells in the immune response. They activate B cells to secrete antibodies and other cells to destroy viruses, bacteria and fungi.

Regulatory T cell

Regulatory T cells control the immune response so it does over react and they play a large role in preventing auto-immunity (condition whereby one's own immune system attacks one's own body).

Macrophage

Macrophages (literally meaning big eater) are cells that eat and destroy pathogens and damaged or dead cells. They can also present antigens to other cells to help the adaptive immune system learn and release substances like cytokines to initiate inflammation.

Mast cells

Mast cells live within the connective tissue throughout the body. They are in charge of mediating inflammatory and allergic responses by storing granules of enzymes and chemical mediators. When they encounter an allergen, for example, they release the contents of their cells and produce the symptoms that are typical of an allergic reaction.

Neutrophil

Neutrophils are the dominant white blood cell of the immune system. They have increased mobility and decreased limitations compared to other white blood cells. They destroy foreign invaders as well as communicate with other immunity cells to coordinate the immune response and repair cells.

Substances of the Immune System

Antigen

Antigens are substances that instigate an immune response. An antigen is anything foreign that invades the body. The body launches an attack when it detects antigens and produces antibodies for future encounters with that same antigen. There can also be self-antigens when the body recognizes something inside of us as foreign in a disease-state.

Antibody (aka Immunoglobulin)

Substances that are created by plasma cells to deactivate pathogens by binding to them. Each antibody is a different shape in order to bind to the correct pathogen. You may see certain structures of antibodies/immunoglobulins expressed as a shortening of immunoglobulin plus a letter assigned to their specific shape, such as IgE (immunoglobulin E). Antibodies also recruit white blood cells to attack the foreign invader in addition to binding to them.

Cytokine

Cytokines are substances used for cells to communicate during an immune response. They help move immune cells towards the site of inflammation. They are part of both innate and adaptive immune responses.

Sources

1. https://www.healio.com/hematology-oncology/learn-immuno-oncology/the-immune-system/components-of-the-immune-system

2. https://www.merckmanuals.com/professional/immunology-allergic-disorders/biology-of-the-immune-system/cellular-components-of-the-immune-system

3. https://www.healthline.com/health/basophils#:~:text=Basophils%20are%20a%20type%20of,to%20a%20severe%20allergic%20reaction.

4. https://www.medicinenet.com/what_is_the_function_of_basophils/article.htm

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8. https://www.news-medical.net/health/What-are-Dendritic-Cells.aspx

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