Narrator: Every second of your life youare under attack. Billions of bacteria, viruses, and fungi are trying to make youtheir home. So our bodies have developed a super complex little army with guards,soldiers, intelligence, weapons factories and communicators to protect you from uh,well, dying. For this tutorial, let's assume the immune system has twelve different jobs. For example, kill enemies, communicate etc. And it has 21 different cells and twoprotein forces. These cells have up to four different jobs. Let's assign them. Here are the interactions. Now let's make this understandable. First of all, let's addcolors to the jobs. Now let's illustrate
the cells. The central color represents the main job of the cell, while the surrounding ones represent secondary duties. Now the immune system looks like this. Now the interactions. Isn't this complexity just awesomeé For this tutorial we will only talk about these cells and ignore the rest. So what happens in the case of an infectioné Music It's a beautiful day when suddenly a wild rusty nail appears and you cut yourself. The first barrier of the immune system isbreached: your skin. Nearby bacteria sieze
on the opportunity and enter your wound.They start using up the body's resources and double their numbers about every 20 minutes. At first they fly under the radar but when a certain bacteria population isreached, they change their behavior and start to damage the body by changing the environment around them. The immune system has to stop them as fast as possible. First of all your guard cells, known as macrophages, intervene. They are huge cells that guard every border region of the body. Most of the time they alone cansuffocate an attack because they can devour up to 100 intruders each. They swallow the intruder whole and trap it inside a membrane.
Then the enemy gets broken down by enzymesand is killed. On top of that, they cause inflammation by ordering the blood vesselsto release water into the battlefield so fighting becomes easier. You notice this as a very mild swelling. When the macrophages fight for too long, they call in heavy backup by releasing messenger proteins that communicate location and urgency. Neutrophiles leave their patrol routes in the blood and move to the battlefield. TheNeutrophiles fight so furiously that they kill healthy cells in the process. On top of that, they generate barriers that trap and kill the bacteria. They are indeed so deadly that they evolved to commit suicide
after five days to prevent them from causing too much damage. If this is not enough to stop the invasion, the brain of the immune system kicks in. The dendritic cell gets active. It reacts to the signals of the soldiers and starts collecting samples from the enemies. They rip them into piecesand present the parts on their outer layer. Now, the dendritic cell makes a crucial decision. Should they call for antivirus forces that eradicate infected body cells,or an army of bacteria killersé In this case, antibacteria forces are necessary.It then travels to the closest lymph node in about a day. Here billions of helper andKillerT cells are waiting to be activated.
When TCells are born they go through adifficult and complicated training process and only a quarter survives. The survivingcells are equipped with a specific setup. And the dendritic cell is on its way lookingfor a helper Tcell with a set up that's just right. It's looking for a helper Tcellthat combines the parts of the intruders which the dendritic cell has presented on its membrane. When it finally finds one, a chain reaction takes place. The helper Tcell is activated. It quickly duplicates thousands of times. Some become memory Tcells that stay in the lymph node and will make you practically immune to this enemy.Some travel to the field of battle to help
I think we've all heardof the word bacteria. And we normally associateit with negative things. You say bacteria, those aregerms. So we normally associate those with germs, andthey indeed are germs, and they cause a whole setof negative things. Or at least from the standardpoint of view, people believe
that they cause a whole bunchof negative things. So let's just list them alljust to make sure we know about them, we're allon the same page. So the bad things they do, theycause a lot of diseases: tuberculosis, Lyme disease. I mean, I could go on and on. You know, pretty muchany time well,
I'll be careful here. Whenever people talk about aninfection, it's often caused by a bacteria. It can also be causedby a virus. An infection is, in general,anything entering you and taking advantage of your bodyto kind of replicate itself, and in the process,making you sick. But bacterial infections,let me write that down.
And this whole perception ofbacteria being a bad thing is probably a good reason whyalmost any soap you see now will say antibacterial on it. Because the makers of the soapknow that in conventional thinking, bacteria are viewedas a negative thing. And you're like, OK,Sal, I know where
you're going with this. Bacteria isn't all bad. There are some good traitsof bacteria. For example, I could stick someyogurt in some or I could stick some bacteria insome milk and it'll help produce some yogurt, sometimesspelled yoghurt. And that's obviouslya good thing.
It's a delicious thing to eat. You say, well, I know I havebacteria in my gut. It helps me digest food. And these are all true, butyou're like, look, you know, on balance, I still thinkbacteria is a bad thing. I'm not going to take sides onthat debate, as I tend to avoid taking sides on debatesin these science tutorials. Maybe I'll do a whole playlistwhere I do nothing but take