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Overview of the Immune System

December 2020

What is the function of the immune system?


In the simplest terms, the immune system’s function is to prevent or limit infection. The immune system can distinguish between healthy cells and “unhealthy” cells. It distinguishes between the two by recognizing a variety of “danger” cues. Cells may recognized as “unhealthy” because of infection or cellular damage caused by non-infectious agents like sunburn or cancer.


When the immune system first recognizes these “danger” cues, it responds to address the problem. If the immune response cannot be activated when there is a need, infection can arise. However, when an immune response is activated when there is no threat or does not stop after the “danger” passes, allergic reactions and autoimmune disease can arise.


The immune system is extremely complex. There are multiple types of cells that either circulate throughout the body or reside in a particular tissue. Each type plays a different role with unique ways of recognizing issues, communicating with other cells, and performing their functions.

Where is the immune system located?

All immune cells begin in the bone marrow and undergo maturation that can occur in different parts of the body. The different parts of the immune system include:

Skin – Skin helps prevent germs from entering the body.

Mucous membranes - Mucous membranes are the moist, inner linings of some organs and body cavities like the mouth and nose. They make mucus and other substances which can trap and fight germs.

White blood cells - White blood cells have many types that are each designed to fight germs.

Organs and tissues of the lymph system - The organs and tissues include the thymus, spleen, tonsils, lymph nodes, lymph vessels, and bone marrow. They produce, carry, and store white blood cells.

Image Credit: https://clinicalinfo.hiv.gov/en/glossary/immune-system

How does the immune system work?


The immune system defends the body against foreign or harmful substances called antigens. Antigens could be bacteria, viruses, chemicals, or toxins. As stated earlier, it can also perceive damaged cells as antigens. When your immune system recognizes an antigen, it attacks it, which is an immune response. Part of the response involves making antibodies. Antibodies are proteins that work to attack, weaken, and destroy antigens.


The immune system remembers antigens, so that if it sees the antigen again, it can recognize it. This allows for a quicker immune response of sending the right antibodies out to prevent reinfection. This protection against a specific disease or antigen is called immunity.

What are the types of immunity?

Innate Immunity

This is the body's first line of defense and is the nonspecific defense mechanisms that come into play immediately or within hours of an antigen's appearance in the body. Mechanisms include physical barriers like the skin, chemicals in the blood, and white blood cells.

Adaptive immunity

Adaptive immunity is also called active immunity. It develops when you are infected with or vaccinated against a foreign substance. It is usually long-lasting, and in some cases may last your entire life.

Passive immunity

Passive immunity is "borrowed" from another source and only lasts for a short period of time. For example, antibodies in a mother's breast milk give a baby temporary immunity to diseases that the mother has been exposed to.

What can go wrong with the immune system?


Sometimes a person may have an immune response even though there is no real threat. This can lead to issues like allergies, asthma, and autoimmune diseases. Autoimmune diseases, like rheumatoid arthritis or psoriasis, cause your immune system to attack healthy cells.


When your immune system does not work correctly, it can lead to other problems. Immunodeficiency diseases weaken the immune system and oftentimes are genetic. If you have an immunodeficiency disease, you get sick more frequently. Infections can also last longer, be more serious, and harder to treat. Certain diseases can cause your immune system to not work correctly. For example, HIV is a virus that destroys white blood cells.

Sources:

https://www.niaid.nih.gov/research/immune-system-overview

https://medlineplus.gov/immunesystemanddisorders.html

https://ciiid.washington.edu/content/what-innate-immunity

http://www.biology.arizona.edu/immunology/tutorials/immunology/page3.html#:~:text=Innate%20immunity%20refers%20to%20nonspecific,foreign%20cells%20in%20the%20body.

https://kidshealth.org/en/parents/immune.html

Stay tuned for more on how to recognize a weakened immune system as well as how to boost your immune system.

The next 2 blog posts will cover those topics.