The Human Immune System

By: Tony Wang


Image Credit: flickr @ Nenad Stojkovic

There are so many viruses, parasites, and bacteria in our world, all of which are determined to wreak havoc on our body; the only thing stopping them from doing so being our own immune system. Lately, the human immune system has been a prevalent topic in the news, primarily due to the fear and uncertainty surrounding the COVID-19 pandemic.

But what exactly is the immune system? To put it simply, the immune system is a complex network of cells that works to defend your body against infections and disease. Additionally, the immune system also has special cells that keep a record of any infectious viruses and/or bacteria that have been detected in your body. This is done so that your body will be better equipped to deal with these same viruses and/or bacteria in the future. Based on this, it’s clear that the immune system is an integral part of the human body. It is for this same reason that an abnormal immune system can be so harmful; autoimmune disorders, allergic diseases, and immunodeficiencies are all results of abnormal immune systems. Now, let’s take a closer look at how the immune system actually functions. The immune system is composed of several different parts, the first of which being the lymphatic system. The lymphatic system contains lymphocytes, which are the various types of white blood cells. White blood cells, as you probably already know, are responsible for combating infectious viruses and bacteria that enter our body. The two most notable types of white blood cells reside in lymph nodes. These white blood cells are known as B and T cells; B and T cells are cells that fight viruses by targeting particular viral epitopes. Additionally, some B and T cells are responsible for keeping a “memory” of any notable infection the body has experienced. Lymph nodes are found throughout the body, and each human body contains approximately500 lymph nodes in total. They are aided by antibodies, which help fight off infections. These are the main components of the immune system; let’s now take a look at how the immune system responds once a bacteria and/or virus has been detected.


Image Credit: flickr @ Lars Plougmann

Once a bacteria and/or virus enters a human body, most of the body’s cells will begin to release a chemical called histidine, which sends signals to the brain in order to start the inflammatory response and activate the secondary response. After this signal has been sent out, macrophages, which are a type of white blood cell, come and begin to “eat” the bacteria/virus cells by engulfing them. In a majority of cases, this is a sufficient response for small cuts and minor infections. However, sometimes, when the body is dealing with a virulent illness, the macrophages are unable to completely wipe out the infection. This is when the third line of defense, which is known as adaptive immunity, is activated. The adaptive immunity response involves B cells—white blood cells that are produced in bone marrow—and T cells—white blood cells that are also produced in bone marrow, but mature in the thymus. There are two stages of adaptive immunity: cell-mediated response and humoral response. In the cell mediated response, cytotoxic T-cells are released into the bloodstream. They destroy infected cells by injecting a protein called perforin, which causes the infected cell to undergo apoptosis (to self-destruct). In the humoral response, helper T-cells bind to antigens—flag-like structures—and stimulate B cells to produce antibodies which will destroy infectious cells. Along with both these responses, memory B and T cells keep a “memory” of the infection. As mentioned previously, they do this so that in the case of another infection by the same bacteria/virus, the memory cells will be able to recognize the bacteria or virus and stimulate a faster and more efficient immune response. These same memory cells are why vaccines work.


Overall, the immune system is a very complicated system that is essential to our survival. It, combined with the advancements of modern medicine, are why so many humans are able to live long and fulfilling lives nowadays.


Citations:

www.health.harvard.edu/staying-healthy/how-to-boost-your-immune-system

https://www.youtube.com/watch?v=fSEFXl2XQpc

https://www.youtube.com/watch?v=GIJK3dwCWCw&t=487s

https://www.youtube.com/watch?v=2DFN4IBZ3rI&t=513s

https://www.youtube.com/watch?v=rd2cf5hValM&t=507s

No changes were made, https://flic.kr/p/2kV2TSi, License: Creative Commons Legal Code

No changes were made, https://flic.kr/p/dmmP7P, License: Creative Commons Legal Code



What Did You Learn?

Questions:

1. How do you build a strong immune system?


There are several ways one can build a strong immune system in order to fight off diseases and infections. Some common tips are to avoid smoking, eat lots of vegetables and fruits, exercise frequently, and get sufficient sleep (at least 8 hours per night for teens). Although doing these things won’t keep you from getting sick, they’ll definitely strengthen your immune system.


2. Is our skin a component of the immune system?


Yes, our body’s skin and mucosal membranes are actually the first line of defense in our body in regards to the immune system. Both prevent bacteria and viruses from getting inside our bodies. In the case that you scrape your knee while playing soccer, that area on your knee will become exposed to harmful bacteria due to the skin being removed. Once those pathogens get inside of your body, white blood cells and antibodies will then activate in order to protect the body.


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