The immune system is a complex system of cells and defence mechanisms working together. It is one of those things that is extremely important for our health, but not many people understand how it works. So today, I am going to tell you more about the immune system, the different parts of the immune system, and what happens if an attacker enters the body!
What is the immune system?
Your immune system works hard to keep you healthy. Its job is to keep germs out of your body, destroy them or limit the extent of their harm if they CAN get in. it is a complicated system made up of cells with specialized jobs. In a way, it is a lot like an army. As Kurzgesagt put it, “the whole thing goes and attacks a foreign invader with different types of warriors, such as captains, intelligence officers, soldiers, suicide bombers, and heavy weapons! The immune system is a defence mechanism that protects you from any sort of invasion.” It is made up of many cells, such as these:
Phagocytes: Simple warriors. Grabs onto bacteria and digests them.
Neutrophils: Suicide warriors that only live to kill.
Compliment: A system of proteins that rips holes in bacteria.
Dendritic Cells: The brain of the immune system. Controls the activation of helper T cells.
Helper T cells: Duplicates to help out at the infection site. Also activates B cells.
Memory T cells: Stays around to remember enemies.
Killer T cells: Kills infected/cancer cells
Virgin B Cells: Idle cell waiting to be activated.
B cells: Create antibodies.
Memory B cells: Stays around to remember enemies.
Antibodies: Proteins produced by B cells to defend against attackers.
But the immune system is more than that. It is a delicate mechanism that works hard every day to keep you healthy.
According to Cleveland Clinic, “there are two subsystems within the immune system, known as the innate (non-specific) immune system and the adaptive (specific) immune system. Both of these systems are closely linked and work together whenever a germ or harmful substance makes the Immune system react.“
The adaptive immune system creates antibodies and uses them to specifically fight certain germs that the body has previously come into contact with. This is also known as an “acquired” or specific immune response.
Because the adaptive immune system is constantly learning and adapting, the body can also fight bacteria or viruses that change over time.
Now, let us look at different parts of the immune system and an overview of how they work.
The Complement System
The complement system is one of the most important (and largely unknown) parts of the immune system. According to Kurzgesagt, “the complement system has three jobs: to cripple enemies, to activate the immune system, and to rip holes in them.” The complement system is very complicated, so we can simplify it, and you will get a general idea of how it works.
Complement proteins have two states, passive and active. They can switch between these two states by changing their shape. The shape is important to proteins because shape determines what you can interact with.
The story starts with the C3 protein. This protein is floating around in the bloodstream, casually minding its own business. C3 needs to change from passive to active to start the complement system. The way that this can happen is quite complex, so let us just say that it can happen randomly.
When the C3 protein becomes active, it splits into two parts, C3a and C3b. C3b is more like a seeker missile that tries to latch itself onto bacteria. It only has a fraction of a second to find an intruder before it gets neutralized by water molecules.
If C3b DOES find a target, it anchors itself very tightly to the surface of the intruder and does not let go. After that, C3b starts a small cascade that connects to other molecules and eventually turns into a protein called C3 Convertase. This new protein is like a recruiting platform and activates other C3 proteins to start the chain of events all over again. Soon, thousands of proteins cover the bacteria, crippling it.
But wait. Do you remember the other part of C3? The C3a? Well, all this time, the C3a protein has been moving away from the site of infection calling for help. Thousands of these proteins rush away from the battlefield to help activate the rest of the immune system. Passive immune cells that notice the C3a proteins become active and follow the trail of the proteins back to the site of infection. The more C3a proteins they meet, the more aggressive they get. The first cells to get there are Phagocytes. We will discuss them more later, but the basic idea is that they grab onto enemies, trap them in a tiny prison, and then kill them with acid.
However, these Phagocytes cannot eat intruders without grabbing them first. And bacteria are slippery and do not like to be grabbed. That is where the C3b protein comes in. C3b acts as a hook or an anchor for the Phagocytes to grab onto.
But now it gets even better. The C3 Convertase changes its shape AGAIN to turn into a protein called C5 Convertase. It begins to recruit more proteins to form a structure called the Membrane Attack Complex. This structure pokes a hole into the bacteria, and then “calls over” a set of proteins that look like spears, which makes the hole in the bacteria larger and larger until it cannot be closed again. The “guts” of the bacteria rush out, and fluid rushes in. They essentially bleed to death.
That is how the complement system works to protect against intruders. Now, let us look at other types of immune responses. What happens when your body is invaded with bacteria or viruses?
The Defence Network
The first layer of defence is your skin. The skin is the envelope of your insides, covering almost all the parts that you perceive are your insides. But for the bacterium, it is a giant desert for miles and miles, filled with geysers that spit out toxic fluid and wash enemies away. But what happens if your skin is breached?
Let us imagine that you are having a wonderful day on the beach. It is a gorgeous day, the sand is warm, and you take off your shoes to walk along the shore. Then, you feel a sharp pain in your foot! You have cut yourself on a rusty nail. How annoying. However, there is a different story inside your wound. There is blood and sand everywhere, not to mention countless dead cells.
Immediately, your immune response kicks in. The cells that have survived the “attack” started to scream out, alerting your first line of defence cells, which will be Macrophages. A Macrophage is a gentle fellow, but you do not want to annoy him, sort of like how bacteria do. Within seconds, these large cells grab bacteria and consume them whole, and digest them alive. These Macrophages can digest over 100 invaders before they are exhausted.
But their efforts are not enough, so the Macrophages call for reinforcements. In the blood, hundreds of thousands of Neutrophils pour out and move to the battlefield. Neutrophils are very different from Macrophages. While Macrophages are like giants that do not hurt civilians, Neutrophils are crazy suicide bombers, and only live to kill things. They are so excited about killing things that they kill themselves a few days after birth so that they do not start destroying your body from the inside.
As soon as Neutrophiles arrive on the scene, they begin to vomit out deadly chemicals that trap and kill the bacteria. Some Neutrophiles have so much fun killing that they go as far as to push their suicide button and self-destruct, casting deadly nets of acid everywhere.
While the battle goes on, your blood vessels let fluid out onto the battlefield, sort of like a dam. This is inflammation, which is important because it warms up the area and makes it hard for bacteria to do much of anything. Inflammation also releases a weapon into the battlefield; millions of complement proteins are about to rip holes in enemies.
Here, there is a crossway. If things go well, our defences defeat the invader and we can go about our normal lives. But if the bacteria overwhelm the defences, there is a big problem. This is the hour of the Dendritic cell. The Dendritic cell is the intelligence officer. While the battle goes on, the Dendritic cell was also devouring enemies. But after killing them, the Dendritic cell covers itself with dead bacteria parts. The cell then leaves the battle and enters the super-highway of the immune system, which connects all the immune headquarters to your tissues, called your lymph nodes.
The Dendritic cell travels to the closest lymph node in about a day. The Dendritic cell is looking for a Helper T cell. A Helper T cell is sort of an all-purpose commander. It can help activate B cells and it can help the Phagocytes and Macrophages fight. But the Dendritic cell is looking for the ONE specific Helper T cell that has the right proteins to battle the specific bacterium. So it goes around and rubs itself – still covered in bacteria guts – on every T Cell it meets. Most T cells are not interested, but after a few hours, a T cell recognizes the bacteria part. The Dendritic cell is overjoyed and activates the T cell.
As soon as the T cell is activated, it starts duplicating itself. One becomes two, two becomes four, four becomes eight, eight becomes 16, and so on. After there are thousands, half of the cells move to the battleground to help out.
On the battlefield, things are getting severe. There are dead cells and bacteria everywhere. A tired Macrophage is ready to give up and go to sleep, as many of its buddies have done already. But then, the T cells arrive at the scene. One of the T cells comes to the tired Macrophage and whispers something (using special chemicals). In an instant, the discouraged warrior feels fresh again. But along with that energy comes a newfound rage. The Macrophage throws itself against the invaders. All over the battlefield, this begins to happen.
The second group of T cells was working on activating another line of defence, B cells, which produce antibodies. Antibodies are produced by B cells, and antibodies look like little crab pincers with two ends to grab enemies. Once the T cells find the right B cell to create the right type of antibodies, the B cell starts to clone itself. Thousands of B cells head to the site of infection. Each B cell can create up to 2000 antibodies per second!
Now, the tide is turning. A week after you injured your foot, the antibodies swarm the battlefield and clump together bacteria so that it is easier to clean them up. Now, your defences realize that they are no longer needed, and begin to kill themselves to save resources. But not all of them. A few T cells and B cells stick around and become Memory T and B cells. They will guard the tissue for years, with the B cells producing a low amount of antibodies at all times, making you mostly immune from this bacterium or virus again.
Now, the battle is over. You had no idea what was going on inside your wound. All it was for you was a cut and a band-aid. But I hope, after reading this, that you have a better appreciation for the Immune System. And it is a thing to be respected, too! It is an amazing system of cells working together in harmony to defend your body from foreign invaders.
Sources:
Tiny Bombs in your Blood – The Complement System
How The Immune System ACTUALLY Works – IMMUNE
The Immune System Explained I – Bacteria Infection
The Immune System | Johns Hopkins Medicine
The immune system: Cells, tissues, function, and disease
How does the immune system work? – InformedHealth.org – NCBI Bookshelf
Immune System and Disorders | Autoimmune Disease | MedlinePlus
Dettmer, Philipp. Immune, A Journey into the Mysterious System That Keeps You Alive, New York, Random House, 2021
Recent Comments