Introduction: Your Immune System

Your immune system is the second most biologically complicated system after the brain. It involves multiple cells that have different ways of activating and attacking to save your body from unwanted invaders, such as pathogens. Today we’ll talk about how this amazing system works and how it copes with different diseases. Let’s begin!

Macrophages: The “Eating Cell”

Macrophages belong to a group called the “phagocytes”. Not the worst names in biology, it actually means “eating cell.” Macrophage also means “great eater”. Anyway, they stick out weird arms and grab the pathogen. Then it shoves the pathogen into itself, creating a small pocket in the cell. It then merges with several other pockets containing acid that destroys the pathogen. After this, it takes in some nutrients and vomits the rest out for the other cells to eat. One macrophage can eat up to 100 bacteria before it dies of exhaustion.

Neutrophils: Crazy Suicide Warriors

Neutrophils only exist to kill. In fact, they are so dangerous that they commit suicide after a few days. Although macrophages respond to pathogens first, neutrophils respond to tissue damage first. Anyway, these guys vomit acid, swallow enemies and cause damage to your own cells. When they are about to die, they vomit their DNA, creating a NET that traps and kills bacteria. Rarely, the neutrophil is still alive and dies because of exhaustion. DNA is for making protein and as a result the neutrophil doesn’t need any new ones and can still survive.

Dendritic Cells: Your Adaptive Immune System

Your immune system is split into 2 parts. The innate immune system and the adaptive immune system. The innate system comes when you are born and your adaptive system slowly builds up. More on this later. Anyway, the dendritic cell rips and eats pathogens and covers itself with dead pathogen guts. Then it goes into the lymph nodes, the channels that allow your immune system to travel, to find the right t-cell. When the t-cell recognises the bacterium, it activates and multiplies.

T-cells: The Helper

T-cells are like helpers. They are activated by the dendritic cell and they can help in the immune response. When they are activated, they multiply to thousands and split up into 2 groups. The first one rushes to the battle site and the other activates the b-cells. The first group makes macrophages hungry, and inside is a hot white anger. It rushes and kills everything it sees, killing more than ever before. The other t-cells are finding the correct b-cell to activate.

B-Cells: Protein Missiles

B-Cells create antibodies that stun bacteria and disable bacteria. They can release up to 2000 antibodies every second. Plasma cells are basically upgraded versions. Anyway, these fellows are activated by the t-cells. They are created in the bone marrow. They have to go through different proteins in the bodies. If they recognise it, they die. This prevents autoimmunity, when the body thinks a part of itself is a pathogen, where your body keeps making more and it gets slaughtered. Sometimes, they escape, recking havoc.

Killer T-cells and Natural Killer Cells

Killer T-cells (right) are activated when your body develops cancer. Normal cells show correct bunches of protein on MHC class II molecules. Killer T-cells check if they are normal and the natural killer cell checks if there are even any. It is a step to stop cancer, and it is likely these cells killed some tumour a few minutes ago. Anyway, they fight cancer. You’ll probably be dead in a  few days if you don’t have them. They both also kill infected cells.

Your Skin: Acidic and Unstable

Your skin starts at the basal layer, where the cells multiply to make more skin cells. They then become stronger and drier. They eventually lock together and release fat to fill in any gaps. Then they die, shedding off. Below are your receptors. Worse, your skin is acidic! Around 5.4 pH. You wouldn’t survive for more than 12 minutes without your skin! Most pathogens can’t resist the acid and if they do, they can’t infect or kill dead cells! Also, the skin is constantly shedding. A nightmare for pathogens. 200,000,000 a day! 

Complement: Loads of Mini Bombs

Complement proteins can be deadly. It first starts with the C3 protein with then activates to become C3a and C3b. C3a alerts the immune system and C3b attaches itself to a pathogen. Then, more proteins come to make a C3 convertabase. It will activate more C3 proteins, increasing the potential. Then, another C5 protein can come to become a C5 convertabase, which can become a membrane attack complex, which sticks a hole into the bacteria and more C9 proteins come and make the hole larger. The bacteria bleeds to death. I recommend watching the Kurzgesagt video for more info.

Only Top Results Accepted

Teachers can kill you. A T-cell has to start in the thymus. Then it is seen if the receptors work. If it is a no, it is forced to kill itself. Can it recognise any of the proteins in the body? If it can, it dies*! After that, only 2% of the T-cells make it. Well, around 10-20 million T-cells are created every day. Where do the dead cells go? They are eaten! Sadly, this school closes at 85 because your thymus is constantly shrinking, replaced by useless tissue. Well, now you know how your super-weapon is made!

*There’s a 5-10% chance it will become a regulatory T-cell.

Cancer: Mini Rebel Towns

Cancer starts when a cell is corrupted. This can happen because of radiation, age, or literally just an error when a cell duplicates. It starts out as a little tiny tumour. It needs resources to grow! Most of them die and the problem fixes itself. But wait! One has evolved to ability to order blood vessel growth! It then supplies the tumour to grow more. The tumour grows once again, only to be able to grow more. This time, cells are dying causing immune responses. They come in with macrophages and natural killer cells.

Uncontrollable growth

These cells kill cancer. Macrophages gobble them up and natural killer cells recognise them in the absence of MHC class II molecules. Dendritic cells take samples of cancer. Cancer has been killed! Except, this time, some survived and made another community. This time, the immune system responds with T-cells and B-cells. Most die, and this repeats till the cancer dies or it evolves to turn immune cells off. It triggers inhibitor receptors. These are a good idea, and is like an off switch for your immune cell. And then cancer grows. Time to see the doctor!

I’m just a skin cell…

Attack!

Stop!

Auto-Immunity

Right. Nothing is perfect. Sometimes, a t-cell escapes that could be hazardous. It starts recognising a part of the body as a pathogen. It orders Macrophages to come attack. If it is your skin, this could be bad. They attack your cells while your body keeps producing more. This gets worse and worse there’s no more left of that part and what really happens now is if that part was important. Normally, it happens with insulin to form type 2 diabetes. So, I hope you don’t have it!

Why You are Weak Against Diseases

If you have all these awesome defences against pathogens, why do you get badly sick in the first place? Well, Let’s take a look at some particular examples. 

MEASLES: The most contagious disease

Measles is terrible for a number of reasons. Lets infect you and see what happens.

Nothing Happens

Measles infects through the eyes, nose or mouth.  It then makes it into your lungs where it infects your first line of defence, your macrophages. They helplessly get turned into dangerous virus production machines, where more viruses are created to infect more cells. But the natural killer cells step in and kill all the infected cells so efficiently that you feel nothing for the first ten days until the macrophages call for the dendritic cells. The virus infects the dendritic cell and spreads through to other lymph nodes, where t-cells are.

A Catastrophe

Measles is now infecting your weapon against measles. This is what makes it so bad and it starts spreading more and infects the lungs, intestines, spleen and liver. Symptoms range from high fever, headache, bronchitis and definitely a rash. This time, millions attack a second time, overwhelming your defences. But some dendritic cells make it. While you’re still coughing giving other unvaccinated people a 90 percent chance of being infected, your super weapons kick in. Plasma cells produce antibodies and you take over. Sometimes, the virus reaches your brain giving a 20-40 percent chance of death.

Rabies: >99.99% Lethality

Rabies is the ultimate lethal disease. This virus first infects you when an animal bites you. It is easily destroyed if it comes in from the mouth, nose or eyes, but rabies has a trick. It sneaks into your neurons and tries to reach the cellular machinery. But there’s a problem. It is really long. Fortunately, there are dynein motors walking on cables. It is made of 52 proteins (while rabies only has 5 different ones) and is like a pair of shoes. Rabies hijacks this system and uses it to transport rabies to the cellular machinery. It keeps going like this without killing anything until it reaches your brain.

You Will Die

Rabies has now reached your brain stem, which can take weeks, months and rarely years. Now, you start feeling all sorts of symptoms from hydrophobia, (fear of water) confusion, aggression, paralysis and seizures. Now, your immune system responds. Killer t-cells rush to work trying to kill cells infected with viruses. They fail, getting killed by the neurons seeing them as crazy. Just before you die, rabies retreats and heads for your saliva glands. They get infested by rabies and if you are an animal you will bite. After feeling the symptoms, you’ll probably die. There’s one thing to save you. A vaccine! Rabies is slow, so you can still get a vaccine after you’re infected. YAY!

Smallpox: Eradicated and forgotten

Smallpox was one of the most feared diseases of the past. It was more feared than rabies because of the fact that it literally spread like crazy, and still had so 30% fatality rate. Also, you might be scared, blind, or deaf after surviving it. Let me explain. This virus first comes in from the nose or mouth. It then infects your throat and causes massive disturbance. Your immune system is distracted and checks out the scene. Then smallpox infects your dendritic cells, which then travel to the lymph nodes, where all your t-cells and b-cells are stored.

Smallpox is Everywhere

Now smallpox is everywhere. It kills more t-cells and b-cells infecting everything as it travels around the whole body. It infects capillaries making them die, attracting something you don’t want to. Neutrophils come in and vomit deadly chemicals that do nothing but hurt you more. They order inflammation causing a high fever. Either your body fights back or you die. But the world decided to say NO! Smallpox only infects humans which means it is easy to eradicate through vaccine. Chinese have practiced inoculation, drying scabs of an infected person and grinding it up. It is blown through someone’s

NOOOO!

Smallpox is Gone

nostril making a milder version, which made you immune in a less painful way. However, 2-3% would still die, but smallpox was so bad it was worth doing it. It spread across Europe and America but stuff began when Edward Jenner came in. He used cowpox, a very minor disease that only causes a few blisters. He noticed people with cowpox don’t get smallpox. He has just created the first ever vaccine! WHO then used this vaccine to immunise everyone around infected places to starve the virus. In 1980, smallpox was declared eradicated! There is only two more samples left, in Koltsovo and Atlanta.