The Immune System Explained I – Bacteria Infection
Kurzgesagt – In a Nutshell
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1.Immune System Complexity Overview
0:00 / 1:42This chapter introduces the immense complexity of the immune system, highlighting its numerous jobs, cell types, and protein forces. It uses a visual analogy of colors and shapes to represent different functions and interactions, simplifying the system for better understanding.
- Immune System
- Immune Cells
- Protein Forces
What's inside this course
- 0:00
1. Immune System Complexity Overview
This chapter introduces the immense complexity of the immune system, highlighting its numerous jobs, cell types, and protein forces. It uses a visual analogy of colors and shapes to represent different functions and interactions, simplifying the system for better understanding.
- 1:42
2. Initial Bacterial Invasion and Macrophage Response
This chapter describes the initial breach of the body's defenses, such as a skin cut, allowing bacteria to enter. It details how macrophages, the body's guard cells, are the first responders, engulfing intruders and initiating inflammation to aid the fight. If the infection persists, neutrophils are called in as heavy backup.
- 4:02
3. Dendritic Cells and T Cell Activation
This chapter explains the role of dendritic cells as the 'brain' of the immune system. They collect samples of the enemy, travel to lymph nodes, and activate specific helper T cells. This activation leads to the rapid duplication of T cells, some becoming memory cells, others joining the battle, and a third group activating B cells.
- 6:39
4. B Cell Activation and Antibody Production
This chapter focuses on the activation of B cells by helper T cells, leading to the rapid production of millions of antibodies. It describes how these antibodies are specifically engineered to bind to intruders, disabling them and making them easier targets for other immune cells like macrophages.
Every chapter ends with a checkpoint (quiz, flashcards, retell, diagram, or prediction) and the course closes with a final boss-fight. More courses →
Full transcript of “The Immune System Explained I – Bacteria Infection”
— 96 segments
0:01Every second of your life, you are under attack.
0:03Billions of bacteria, viruses, and fungi are trying to make you their home,
0:08so our bodies have developed a super complex little army with guards, soldiers, intelligence, weapons factories, and communicators
0:14to protect you from...well...dying.
0:18For this video, let's assume the immune system has 12 different jobs. For example, kill enemies, communicate, etc.
0:25And it has 21 different cells and 2 protein forces
0:29These cells have up to 4 different jobs.
0:32Let's assign them. Here are the interactions.
0:35Now, let's make this understandable.
0:38First of all, let's add colours to the jobs.
0:41Now, let's illustrate the cells.
0:43The central colour represents the main job of the cell,
0:46while the surrounding ones represent secondary duties.
0:50Now the immune system looks like this.
0:53Now the interactions.
0:55Isn't this complexity just awesome?
0:58For this video we will only talk about these cells and ignore the rest.
1:03So, what happens in the case of an infection?
1:06*Intro*
1:13It's a beautiful day, when suddenly, a wild rusty nail appears and you cut yourself.
1:18The first barrier of the immune system is breached: your skin.
1:22Nearby bacteria seize on the opportunity and enter your wound.
1:26They start using up the body's resources and double their numbers about every 20 minutes.
1:31At first, they fly under the radar, but when a certain bacteria population is reached,
1:36they change their behavior and start to damage the body by changing the environment around them.
1:40The immune system has to stop them as fast as possible.
1:44First of all, your guard cells, known as macrophages, intervene.
1:48They are huge cells that guard every border region of the body.
1:52Most of the time, they alone can suffocate an attack
1:56because they can devour up to 100 intruders each.
1:59They swallow the intruder whole and trap it inside a membrane.
2:02Then the enemy gets broken down by enzymes and is killed.
2:05On top of that, they cause inflammation by ordering the blood vessels to release water into the battlefield
2:10so fighting becomes easier.
2:12You notice this as a very mild swelling.
2:15When the macrophages fight for too long,
2:17they call in heavy backup by releasing messenger proteins that communicate location and urgency.
2:22Neutrophils leave their patrol routes in the blood and move to the battlefield.
2:27The neutrophils fight so furiously that they kill healthy cells in the process.
2:31On top of that, they generate barriers that trap and kill the bacteria.
2:35They are, indeed, so deadly that they evolved to commit suicide after five days to prevent them from causing too much damage.
2:42If this is not enough to stop the invasion, the brain of the immune system kicks in.
2:47The dendritic cell gets active.
2:49It reacts to the signals of the soldiers and starts collecting samples from the enemies.
2:53They rip them into pieces and present the parts on their outer layer.
2:57Now, the dendritic cell makes a crucial decision.
3:00Should they call for anti-virus forces that eradicate infected body cells
3:04or an army of bacteria killers?
3:07In this case, anti-bacteria forces are necessary.
3:10It then travels to the closest lymph node in about a day.
3:13Here, billions of helper and killer T cells are waiting to be activated.
3:17When T cells are born they go trough a difficult and complicated training process
3:21and only a quarter survives.
3:23The surviving cells are equipped with a specific set-up.
3:27And the denditric cell is on its way looking for a helper T cell with the set-up that's just right.
3:32It's looking for a helper T cell that can bind the parts of the intruders which the dendritic cell has presented on its membrane.
3:39When it finally finds one, a chain reaction takes place.
3:42The helper T cell is activated. It quickly duplicates thousands of times.
3:47Some become memory T cells that stay in the lymph node and will make you practically immune against this enemy.
3:52Some travel to the field of battle to help out.
3:55And the third group goes on to travel to the center of the lymph node
3:58to activate a very powerful weapons factory.
4:01Like the T cells, they are born with a specific set-up
4:04and when a B cell and a T cell with the same set-up meet, hell breaks loose.
4:08The B cell duplicates rapidly and starts producing millions of little weapons.
4:13They work so hard that they would literally die from exhaustion very fast.
4:18Here, helper T cells play another important role; they stimulate the hard working factories and tell them:
4:23"Don't die yet, we still need you, keep going!"
4:26This also ensures that the factories die if the infection is over so the body doesn't waste energy or hurt itself.
4:32But what is produced by the B cells?
4:35You've heard of them of course, antibodies.
4:38Little proteins that are engineered to bind to the surface of the specific intruder.
4:42There are even different kinds of antibodies that have slightly different jobs.
4:46The helper T cells tell the plasma cells which type is needed the most in this particular invasion.
4:52Millions of them flood the blood and saturate the body.
4:55Meanwhile, at the site of infection, the situation is getting dire.
5:00The intruders have multiplied in number and start hurting the body.
5:04Guard and attack cells fight hard, but also die in the process.
5:08Helper T cells support them by ordering them to be more aggressive and to stay alive longer.
5:12But without help they can't overwhelm the bacteria.
5:16But now, the second line of defense arrives.
5:18Billions of antibodies flood the battlefield and disable lots of the intruders,
5:22rendering them helpless or killing them in the process.
5:25They also stun the bacteria and make them an easy target.
5:29Their back is built to connect to killer cells, so they can connect and kill the enemy more easily.
5:34Macrophages are especially good at nomming up the bacteria which antibodies have attached to.
5:40Now the balance shifts.
5:41In a team effort, the infection is wiped out.
5:44At this point, millions of body cells have already died.
5:48No big deal, the losses are quickly replenished.
5:51Most immune cells are now useless and without the constant signals they commit suicide, so as not to waste any resources.
5:59But some stay behind: the memory cells.
6:02If this enemy is encountered ever again in the future, they will be ready for it and probably kill it before you even notice.
6:10This was a very, very simplified explanation of parts of the immune system at work.
6:14Can you imagine how complex this system is, even at this level, when we ignore so many players and all the chemistry.
6:21Life is awfully complicated, but if we take the time to understand it, we'll encounter endless wonders and great beauty.