Week 3 - How Does The Immune System Work?

 Hello guys! After a 1-week poll of fourteen votes, the results are....., A TIE!

5 people wanted an Immune System explanation, 5 on how stars form, and 4 on how does colors work (from the last poll). I did a 50/50 wheel, and the immune system one won, so we will do that. Let's go!

The Immune System is a vital biological system in our body. A biological system is a group of organs that together work for one common purpose. For example, The Digestive System is the easiest example of one. There are many organs in the digestive system (e.g Intestines, Liver, Stomach, etc) but they all have one goal: to turn food into nutrients and energy.

The Immune System's goal as a biological system is to protect the body from illness, disease, and other inconveniences. It is one of the most complex ones, but this will be a more easy to understand version of it.

The Immune System is composed of several organs, and millions of cells. Let's go through a story to see how the Immune System works. When germs enter our body, let's say in this case our skin tissue, they begin to pollute it and they kill the cells there with toxic stuff. Cells release cytokines, a signal that travels around our body. 

When an immune cells "smell" cytokines, they follow a track of cytokines and they enter the infected area. The immune cells are more specifically called White Blood Cells, and the type of white blood cell that reacts first to an infection is a Macrophage, a large white blood cell that kills germs in a process called Phagocytosis, basically "consuming" the germs. They can't eat all of them and have their limits, so they too call for more immune response. 

Macrophages are a type of phagocytes, a subclass of immune cells that use Phagocytosis to kill germs. Another type of phagocytes, coming early aswell is the Neutrophil, which is also a phagocyte and uses phagocytosis but it has a few other ways to kill: it can release toxic stuff which kill bacteria, but it sometimes accidentally also kills your own cells.

During this time, another type of cell, related to the Macrophage is the Dendritic Cell. It collects dead  germ parts and stick with them, and goes to a lymph node, a mini-organ with lots of immune cells to call for (there are many lymph nodes in your body). The story of the Dendritic Cell will be continued later.

Now, we want to introduce the Adaptive Immune System - there are two subsystems of the Immune System, the Innate and Adaptive. The Innate one is ready when you were born and kills every type of germ, while the Adaptive takes years to prepare and each adaptive cells specializes against one specific species of germ.

The Dendritic Cell is searching for the T-Cell, an adaptive cell, that can recognize that certain germ that infected you. After lots of searching, it eventually finds a match, and the T Cell begins to duplicate itself, and the group of T cells that recognize this germ split into two halves. The type of T Cell in this case is the Helper T Cell.

The first half goes to the site of infection to revitalize Macrophages, since they have limits in killing. They also enforce inflammation, which makes the environment harder for the germs to live in and to fight in. Around this time, proteins in the bloodstream called Compliment Proteins flow into the site of infection to disable germs and debilitate their ability.

The other half of T Cell is searching for the right match of another adaptive cell, the B Cell. After searching, the B cell with the right receptor to recognize the infecting disease is picked and duplicates. They then begin to produce antibodies, which flow around the body, grabbing and killing germs. Typically  by the point B Cells are called, the situation is over. (This is mostly applicable to bacteria).

Let's do one more scenario: A Viral Infection. Viruses are small and have a different kind of attack than bacteria. They infect the insides of cells and make them virus-creation machines. They begin when they enter your body, let's say into your lungs. They infect the epithelial cells there, and enter them. They change their functions to create more viruses, and then when there is enough, they order the cell to explode, so they can go and infect more.

This repeats and repeats, and it takes time for the immune system to recognize it. The epithelial cells send out interferons, which harden their defenses. Dendritic Cells eventually get viral samples, and they call for an adaptive response. Killer and Helper T cells are called.

The Killer T Cells go around the site of infection and look at the receptor molecules of cells to see what they are producing. If its something like a virus, it orders the cell to kill itself in an orderly way - a process called apoptosis. 

NK Cells (Natural Killer Cells) are another anti-viral cell. Since viruses can make the infected cell hide its receptors so Killer T Cells can't kill them, there needs to be a counter solution for that. Luckily, there is - the Natural Killer Cell. It goes around, checking if there are molecular receptors on the cell. If there are none or little, it kills them. 

That was a simple part of the Immune System! That is only 2 scenarios, and this is an extremely incomplete version.

Fun Fact: Once defeating a pathogen, our immune cells remember the pathogen, so when it comes again, we can quickly and easily respond against it. The cells that preserve information on past pathogens are called Memory Cells, and they turns from adaptive cells.

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