The Immune System — How Does It Works? | Bacteria Infection | Ft.LearniCulture

What Is The Immune System?

The human immune system is the most complicated and complex biological system after the brain. The immune system is a complex network of cells, tissues, organs and the substances they make that helps the body fight infections and other diseases. Our bodies have developed a super complex little army with guards, soldiers, intelligence, weapons factories and communicators to protect us from dying, seriously~

So, first of all, what does the word "Immune" mean? Well, someone is immune when he is resistant to a particular infection or toxin owing to the presence of specific antibodies. 

Fact Time: Did You Know What The Basic Difference Between An Infection And A Disease Is?

Infection, often the first step, occurs when bacteria, viruses or other microbes that cause disease enter your body and begin to multiply. Disease occurs when the cells in your body are damaged — as a result of the infection — and signs and symptoms of an illness appear.

The immune system has a lot of jobs. Like kill enemies, produce antibodies, communicate, remember enemies etc. etc. The immune system has 21 different cells and 2 protein forces. And now, these cells have up to 4 different jobs.

Now, let's say one day you wound yourself. The layer of your skin gets breached and blood is dripping out. The first barrier of the immune system is destroyed. Nearby bacterium and other organisms seize this opportunity and get inside your wound. They start using all the resources in your blood and started multiplying and dividing themselves into double number every 20 minutes. When a certain bacteria population is reached, they start to damage the body's inner part by destroying things around them.

The Guard Cells — Macrophages

The immune system needs to do something fast. So, firstly, the guard cells also known as the Macrophages start intervening in there. Their size is just 21 micrometers, but in the point of view of our human body, they are huge cells that guard every border region of our body. For reference, average bacterial cell size is around 1 micrometers. In Biology, we represent a micrometer with the symbol — "μ". They act like the soldiers standing on the borders of their country protecting us from invaders. That is why they are known as Guard Cells.

Most of the time, the Macrophages alone can suffocate or, kill the intruders as they can kill up to 100 intruders each. They first swallow the bacteria, then trap it in a membrane. Then the bacterium gets broken down or killed by the secreted enzymes and game over. On top of that, they also cause inflammation by ordering the blood vessels to release water into the battleground through the messenger proteins so that the fighting becomes easier and the invaders can be defeated successfully. You can notice this as a mild swelling.

If the bacterium still does not give up and if the macrophages somehow fight for too long, then they need heavy backup army and signals the whole body communicating for help, urgency and location. The macrophages release messenger proteins to do so. Yeah, so that's basically the task of the messenger protein in our story of the immune system.

Neutrophils

Neutrophils leave their patrol routes and move towards the battlefield or the place where bacteria has invaded once it gets the signals from the messenger proteins. Now neutrophils are the most abundant type of granulocytes and make up half of the white blood cells in humans. Wait, what are these "granulocytes" now? Granulocytes are a classification of white blood cells in which granules are present. Basically, there are 5 types of white blood cells based on the presence of granules. Three of them, which are the Neutrophils, the Eosinophils and the Basophils are Granulocytes (with granules) whereas the other two, which are the Monocytes and the Lymphocytes are Agranulocytes (without granules). 

To have a complete overview, read our Components Of The Blood article. And now, let's move ahead. The Neutrophils fight so furiously that they even kill healthy cells in the process. That's unpleasant. Well, on top of that, they generate barriers that trap and kill the bacteria. They are so so vigorous and violent, that they have adapted or evolved themselves to commit suicide after 4 to 5 days so that they do not cause too much damage to the healthy cells in our immune system. And even if this is not enough to stop the invasion, then the Dendritic cells hops in.

Dendritic Cells

The brain of the immune system, also known as the Dendritic cells gets active when things start getting too serious. What it does is that it reacts to the signals of the soldiers and starts collecting samples from the enemies. They rip them into pieces and present the parts on their outer layer. Okay, then the dendritic cells either calls the anti virus force or the anti bacteria forces. Well, in the case of a bacteria invasion, of course the dendritic cells would call the anti bacteria forces. The dendritic cells then travel to the closest lymph node in about a day. Here billions and billions of helpers like the super soldiers Killer T Cells wait to get activated.

Killer T-Cells

When Killer T Cells are born, they go through several difficult training processes and once they are ready to fight for the world, only a quarter of them are selected as all others die. Only the strongest of them survives and are then given the respect to be called the Killer T Cells. The surviving cells are equipped with a specific set-up. And the dendritic cell looks for a helper T Cell with just the right equipment and power.

Basically, as I told you just now in the dendritic cells section, that they present the parts on their membrane. Therefore they search for a helper T Cell that can attach, bind the parts of the intruders which the dendritic cell had presented on its membrane. When it finally finds one, a chain reaction takes place. The helper T Cell gets activated and it quickly duplicates itself thousands of itself.

Now, some of them become memory T Cells that just stay in the lymph node and make you immune against the enemy. For your knowledge, a lymph node is A small bean-shaped structure that is part of the body's immune system. Lymph nodes filter substances that travel through the lymphatic fluid, and they contain lymphocytes (white blood cells) that help the body fight infection and disease. There are hundreds of lymph nodes found throughout the body.

Coming back, as we saw some T Cells become memory T Cells whereas some others become the soldiers and proceed to the battlefield to help out. Then the third group of T Cells goes on to travel to the center of the lymph node to activate another powerful weapon factory: The Virgin B Cells.

Virgin B-Cells

Just like the T Cells, they are born with a specific setup. Now when a B Cell and a T Cell with the same setup meet, the B Cell duplicates rapidly and starts producing millions of little weapons. They work very hard and die. This also ensures that the factories die if the infection is over so the body doesn't waste energy or hurt itself.

You must've heard of antibodies. Yeah! The B Cells produce them, exactly! Little proteins that are engineered to bind to the surface of the intruder. There are different types of antibodies as well and the helper T Cells tell the plasma cells which type is needed the most in any particular invasion.

The Final Fight

But back to the battlefield, when all the soldiers of the army get tired and couldn't fight anymore from the bacteria that starts hurting the body, then the helper T Cells orders the army to be more aggressive and fight. But without any support or help, they can not withstand the fight anymore. So, here only the next line of defense comes into play.

Billions of antibodies flood the battlefield and kill the intruders. Macrophages and the Killer T Cells get support and kill them more successfully then. Especially, the macrophages are good at choosing the bacteria which antibodies have attached to.

Finally, with a full team effort and support of all these guys, the infection gets kicked out of our body. But a consequence of this is that many healthy cells die in the process. But that's not a problem, they get replenished very quickly. Most immune cells, then become useless and without any signals, they commit suicide so they do not waste any resources in our blood. But yeah, if you remember, you will know that there were some T Cells known as Memory cells who were left behind. These guys do not die because they play a very important role for our future immunity purposes. And, if the same enemy is encountered ever again in the future, the Memory T Cells will remember them and will be ready to eradicate them even before you notice.

Conclusion

Its just so amazing, right? Our body's immune system's cells protects and even dies for us. But this topic is still complicated as immune system is a very vast subject. That is why studying everything in detail is very complicated. However, here in this post, you now how the immune system works when you get wounded. The Basics! Life is awfully complicated and exploring it is the beauty of biology.

Special Thanks to @SpandanSaha for making an amazing thumbnail for us! Check out his blog: www.learniculture.blogspot.com

Thank you so much reading and learning something new. We will meet you in our next post.

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