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The Immune System Explained I – Bacteria Infection


Every second of your life, you are under attack. Billions of bacteria, viruses, and fungi are trying to make you their home. So our bodies have developed a super complex little army with guards, soldiers, intelligence, weapons factories, and communicators to protect you from…well…dying For this video, let’s assume the immune system has 12 different jobs. For example, kill enemies, communicate, etc. And it has 21 different cells and 2 protein forces These cells have up to 4 different jobs. Let’s assign them. Here are the interactions. Now, let’s make this understandable. First of all, let’s add colors 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 awesome? For this video we will only talk about these cells and ignore the rest. So, what happens in the case of an infection? It’s a beautiful day, when suddenly, a wild rusty nail appears and you cut yourself. The first barrier of the immune system is breached: your skin. Nearby bacteria seize 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 is reached 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 can suffocate 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 enzymes and is killed. On top of that, they cause inflammation by ordering the blood vessels to 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. Neutrophils leave their patrol routes in the blood and move to the battlefield. The neutrophils 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 pieces and present the parts on their outer layer. Now the dendritic cell makes a crucial decision. Should they call for anti-virus forces that eradicate infected body cells… or an army of bacteria killers? In this case, anti-bacteria forces are necessary. It then travels to the closest lymph node in about a day. Here, billion of helper and killer T cells are waiting to be activated. When T cells are born they go trough a difficult and complicated training process and only a quarter survives. The surviving cells are equipped with a specific set-up. And the denditric cell is on its way looking for a helper T cell with the set-up that’s just right. It’s looking for a helper T cell that can bind 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 T cell is activated, it quickly duplicates thousands of times. Some become memory T cells that stay in the lymph node and will make you practically immune against this enemy, Some travel to the field of battle to help out. And the third group goes on to travel to the center of the lymph node to activate a very powerful weapons factory. Like the T cells, they are born with a specific set-up and when a B cell and a T cell with the same set-up meet, hell breaks loose. The B cell duplicates rapidly and starts producing millions of little weapons. They work so hard that they will literally die from exhaustion very fast. Here helper T cells play another important role, they stimulate the hard working factories and tell them: “Don’t die yet, we still need you, keep going!” This also ensures that the factories die if the infection is over so the body doesn’t waste energy or hurt itself. But what is produced by the B cells? You’ve heard of them of course, antibodies, Little proteins that are engineered to bind to the surface of the specific intruder. There are even different kinds of antibodies that have slightly different jobs. The helper T cells tell the plasma cells which type is needed the most in this particular invasion. Millions of them flood the blood and saturate the body. Meanwhile, at the site of infection, the situation is getting dire. The intruders have multiplied in number and start hurting the body. Guard and attack cells fight hard, but also die in the process. Helper T cells support them by ordering them to be more aggressive and to stay alive longer. But without help they can’t overwhelm the bacteria. But now, the second line of defense arrives. Billions of antibodies flood the battlefield and disable lots of the intruders, rendering them helpless or killing them in the process. They also stun the bacteria and make them an easy target. Their back is built to connect to killer cells, so they can connect and kill the enemy more easily, Macrophages are especially good at nomming up the bacteria which antibodies have attached to. Now the balance shifts, in a team effort, the infection is wiped out. At this point, millions of body cells have already died, no big deal, the losses are quickly replenished. Most immune cells are now useless and without the constant signals they commit suicide, so as not to waste any resources. But some stay behind: the memory cells. If this enemy is encountered ever again in the future, they will be ready for it and probably kill it before you even notice. This was a very, very simplified explanation of parts of the immune system at work. Can you imagine how complex this system is, even at this level, when we ignore so many players and all the chemistry. Life is awfully complicated, but if we take the time to understand it, we’ll encounter endless wonders and great beauty.

Randall Smitham

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100 COMMENTS

  1. Kurzgesagt – In a Nutshell Posted on February 8, 2019 at 4:12 pm

    There's brand new stuff in the Kurzgesagt Merch Shop. Check it out here: shop.kurzgesagt.org

    Reply
  2. Anas Qasim Posted on September 1, 2019 at 6:34 pm

    I need an online teacher

    Reply
  3. Tim Rogers Posted on September 1, 2019 at 7:54 pm

    This shows how complex our body is without us noticing that’s partly why we need a healthy lifestyle!!!!!!!!!!!

    Reply
  4. Tim Rogers Posted on September 1, 2019 at 7:57 pm

    Parents show your kids these videos the they will know why you say eat ya vegetables

    Reply
  5. Đỗ Tiến Anh Posted on September 2, 2019 at 12:43 am

    Thank you :> I feel like watching film in cinema :>

    Reply
  6. awaludin iskandar Posted on September 2, 2019 at 2:01 am

    Explain about HIV please

    Reply
  7. Asteroid Arts Posted on September 2, 2019 at 2:44 am

    Our Immune System… the best friend you never knew you had 🤣

    Reply
  8. 6969 subscribers with 0 videos challenge Posted on September 2, 2019 at 2:52 am

    this makes me feel weirdly uncomfortable

    Reply
  9. Danny Schatz Posted on September 2, 2019 at 3:24 am

    But I want to know it all!

    Reply
  10. Charlie Angkor Posted on September 2, 2019 at 3:49 am

    explain passive verbs: "the brain kicks in" vs. "the brain is kicked in" 😂😂😂

    Reply
  11. Cranks Posted on September 2, 2019 at 5:50 pm

    "only a quarter of Killer T cells survive" does anyone else realize how badass this is

    Reply
  12. Frasier Gallacher Posted on September 2, 2019 at 9:29 pm

    Why won’t nobody talk about that pokeball belt

    Reply
  13. Derppay Posted on September 3, 2019 at 4:08 am

    I love to see how the art style has changed through the time, I love these videos~

    Reply
  14. Daniel Evans Posted on September 3, 2019 at 4:34 am

    my blood cells really must be thinking why they have to protect such a dumb fucking idiot

    Reply
  15. favoritekidskinlem10 Posted on September 3, 2019 at 5:07 am

    Blue and green is the hole body in a nutshell tell us that.

    Reply
  16. Elizabeth Sumalinog Posted on September 3, 2019 at 6:36 am

    Hataraku Saibo gang, where you at??

    Reply
  17. Ahmed Falahy Posted on September 3, 2019 at 7:54 am

    Bacteria enters body through a cut wound

    Immunity System: plays Giorno piano "I, Immunity System, have a dream!"

    Reply
  18. Ahmed Falahy Posted on September 3, 2019 at 7:57 am

    Is there a D&D RPG based on the human's immunity system?
    Someone should make a game

    Reply
  19. ZiggyZagga Posted on September 3, 2019 at 8:11 am

    5:52 Who got the refrence? For Aiur!

    Reply
  20. Nailul-Hafiz Saifudin Posted on September 3, 2019 at 8:40 am

    Imagine is this applied to actual wars…

    Reply
  21. Areee Ash Posted on September 3, 2019 at 9:37 am

    As a sucidal person, i feel bad for my poor immune army

    Reply
  22. Zainul hussain Posted on September 3, 2019 at 9:42 am

    Subhanallah

    Reply
  23. Enigma BGR Posted on September 3, 2019 at 10:39 am

    The best explaining animations.

    Reply
  24. Mustaf 415 Posted on September 3, 2019 at 12:05 pm

    You are smizing thank yo6 very mush you guys geat tired to help us to now every thing thank you very mush

    Reply
  25. Burcu Kapıcı Posted on September 3, 2019 at 12:18 pm

    This is overkill.

    Reply
  26. spacenutcj plays Posted on September 3, 2019 at 12:54 pm

    This would be an epic movie.

    Reply
  27. SSV Posted on September 3, 2019 at 5:19 pm

    Bacteria: Lets kick some butt!

    Bacteria:Hey wants that banging?

    Immune System:FBI OPEN UP!!!

    Bacteria:Oh shoot.

    Immune System:You messed with the wrong body!

    Reply
  28. G A Y fish G A Y Posted on September 3, 2019 at 7:31 pm

    Bruh now I feel sad for my cells

    Reply
  29. Corner tree Posted on September 3, 2019 at 8:10 pm

    Immune system is incredible. I spent my childhood around hospitals till at age 11…my immune system evolved so much I haven't had any fever or infection for the last 14 years….I got symptoms of major disease but immune system fought back before it took over my body…..

    My doctor used to say never use medicine until no options left because our immune system evolves to defend us.

    Reply
  30. Squilliam Posted on September 4, 2019 at 8:31 am

    get paper cut
    Me: meh nothing bad…

    Immune stystem: WE ARE FIGHTING A LITERAL WAR DOWN HERE!!!!

    Reply
  31. richard fang Posted on September 4, 2019 at 10:22 am

    Me: gets cut

    My mind: it's alright

    My immune system: now this is an avengers level threat

    Reply
  32. Reiven Wee Posted on September 4, 2019 at 10:38 am

    "Everyone dies "
    Memory cells be like: nope were good

    Reply
  33. Gina Forrisuelo Posted on September 4, 2019 at 10:41 am

    Me: Gets cut
    Me: Okay this is fine
    Immune System: THIS IS NOT FINE

    Reply
  34. Jordany Paez Posted on September 4, 2019 at 12:06 pm

    wow we got tha, that cool

    Reply
  35. LyricLuke. Posted on September 4, 2019 at 1:02 pm

    Kurzgesagt has grown since then!

    Reply
  36. Deadlyninja_death Roblox Posted on September 4, 2019 at 2:21 pm

    I just noticed the person at the beginning is a Pokémon trainer…

    Reply
  37. sunkist Posted on September 4, 2019 at 2:23 pm

    now i think my inside look like this

    Reply
  38. Tsuki Hoshi Posted on September 4, 2019 at 4:02 pm

    I want to be a teacher and flex how informative your video are

    Reply
  39. Gwo Gaming Posted on September 4, 2019 at 4:24 pm

    Naughty bois: we gonna enter
    Immune system: No, i dont think you will

    Reply
  40. Heavenly Demon Posted on September 4, 2019 at 10:32 pm

    Virgin b cell

    Reply
  41. BicMacVal KFC Posted on September 5, 2019 at 3:16 am

    This is basically "Cells at work" in 6 minutes

    Reply
  42. RG Posted on September 5, 2019 at 5:57 am

    Top 5 youtube channels 🙂

    Reply
  43. chetan singh Posted on September 5, 2019 at 6:23 am

    reading or watching won't work , to understand our body we have to experience it by looking inside, will take hard practice of meditation

    Reply
  44. Hema Pandey Posted on September 5, 2019 at 6:31 am

    That explanation was pretty cool!
    I have today seen a first youtuber who has completely explained a concept!!!

    Reply
  45. Xxblackwiddow 69 Posted on September 5, 2019 at 9:30 am

    Lol who watches this when there sick?

    Reply
  46. Antoan's Gaming Posted on September 5, 2019 at 9:33 am

    5:26 target detected , go go go

    Reply
  47. A random Agent Posted on September 6, 2019 at 1:21 am

    If only I had a microscopic probe to see these battles, so I don’t need to watch any more battles on YouTube anymore…

    Reply
  48. Twig Posted on September 6, 2019 at 4:53 am

    Lol I'm gonna get sick soon

    Reply
  49. A Blind Kid Posted on September 6, 2019 at 7:58 am

    So it’s like WW2 in your body…

    Reply
  50. Rishab Posted on September 6, 2019 at 8:42 am

    Who else is watching the video with an infection?

    Reply
  51. Tiss fant Posted on September 6, 2019 at 9:22 am

    Watching this while sick is like being patriotic for your immunse system. Like, you go guys, please save me I'm counting on you immune bros, I'll drink water and stay warm to help anyway I can!!!

    Reply
  52. Kasey Marriott Posted on September 6, 2019 at 10:28 am

    i havent got my flu shots yet oof

    Reply
  53. ProperGoodDishcloth Posted on September 6, 2019 at 11:07 am

    Thank you body, you the best

    Reply
  54. NASRO RIVA Posted on September 6, 2019 at 11:26 am

    سبحان الله الخالق

    Reply
  55. ItzJoiegaming Offline channel Posted on September 6, 2019 at 12:12 pm

    Show: Shows Macrophag
    Cells at work: ara ara
    Me: Cells at work confirmed

    Reply
  56. Drape Nailed Talaoha Posted on September 6, 2019 at 2:39 pm

    5:52 one literally says
    "killing was the best part"

    boomers: "say what again?"

    Reply
  57. Hammer Bro 19 Posted on September 6, 2019 at 11:53 pm

    Trillions of skin cells play pokemon

    Reply
  58. Damla Bahri Posted on September 7, 2019 at 4:58 am

    My father is in the hospital right now because he has an infection in his blood. Therefore the white blood cells are eating the red blood cells. This can be very dangerouse, even to the point of death. I'm really scared and I don't know what to do anymore. I'm trying to stay strong when i'm with him and my other family members but, when I'm alone I just can't help but beak down and cry.

    Reply
  59. Xiaowu Zhu Posted on September 7, 2019 at 5:17 am

    Every time I watch this video I feel healthy

    Reply
  60. Indria Retnowati Posted on September 7, 2019 at 10:30 am

    I like this vidio… because complate the are subtitle indonesia..

    Reply
  61. TheLegend27 Posted on September 7, 2019 at 11:59 am

    so like agario

    Reply
  62. Vanessa Zhou Posted on September 7, 2019 at 1:45 pm

    Don't die yet, we still need you, keep going!

    – T helper Cells

    Reply
  63. Gideon Parmonang Posted on September 7, 2019 at 4:18 pm

    Nail use scratch. It's very effective.

    Reply
  64. SuperKarolinaB Posted on September 7, 2019 at 6:29 pm

    6:15 Whats the pokeball cell caled?

    Reply
  65. Fox Cyano Posted on September 7, 2019 at 8:52 pm

    I love this animation so much it's brilliant! And the witty comments! This is the best way for modern education I'm mind blown😍😍😍

    Reply
  66. Fox Cyano Posted on September 7, 2019 at 8:57 pm

    An app for tablets? Hell yess interested! 🎆

    Reply
  67. Meowjelly Pusheen Posted on September 8, 2019 at 12:59 am

    Wow there is a little war in my body every time I get hurt o ma gaddddddddddd

    Reply
  68. Rainbow,Frosty&Raingirl Gachalife Posted on September 8, 2019 at 1:05 am

    WhiteSetsuna that is a Funniest Joke!!! So funny!

    Reply
  69. Fong SK Posted on September 8, 2019 at 2:54 am

    That is your name

    Reply
  70. Gazelle Tanglao Posted on September 8, 2019 at 3:45 am

    I'm currently dying for my sickness but my immune system is doing great

    Reply
  71. Sean Perez Posted on September 8, 2019 at 5:19 am

    Hataraku Saibouuuuuuu, Saibouuuuu

    Reply
  72. Aziz & Serg Posted on September 8, 2019 at 1:56 pm

    1 like 1 Rip for all these tiny soldiers who died for the sake of us 🙏

    Reply
  73. Alex Racioppa Posted on September 8, 2019 at 2:21 pm

    Wend I was watching this I had a cut

    Reply
  74. うた Posted on September 8, 2019 at 6:14 pm

    面白い!実に興味深い最近かウイルスかを判断するなんてことが体の中で行われてるなんて驚きです‼️

    Reply
  75. Angry oofling The first Posted on September 8, 2019 at 8:34 pm

    Honestly, the effort put into your videos is amazing.

    Reply
  76. TheGrtfy Posted on September 8, 2019 at 9:23 pm

    Immune system… Assemble!!!!

    Reply
  77. johnbillybob bro Posted on September 9, 2019 at 12:23 am

    I wish there was some way I could say thank you to my immune system

    Reply
  78. Remedy Posted on September 9, 2019 at 8:49 am

    Someone: gets a cut
    Immune system: GOGOGOGOGOOGO ATTACK THERES A WAR HERE!

    Reply
  79. Patrick Ma Posted on September 9, 2019 at 12:44 pm

    5:53: 'For Aiur' that one cell is a Protoss main I see.

    Reply
  80. Daneil - Roblox Posted on September 9, 2019 at 1:59 pm

    Our cells is smarter that us

    Reply
  81. Nicholas Gerry Posted on September 9, 2019 at 3:46 pm

    I take Immunology this year. It's so exhausting and so many things to get inside my head sigh

    Reply
  82. Deemuel Dean Calumpang Posted on September 9, 2019 at 6:25 pm

    I was gonna commit suicide today, but I saw this vid, and felt bad for my younglings. I am never gonna kill myself now.

    Reply
  83. SCP Time Posted on September 9, 2019 at 6:29 pm

    Please, i know this is an old video, but i really want a vid on the other cells…

    Reply
  84. Rawenhappy2 Posted on September 9, 2019 at 8:04 pm

    Wow my body is constantly committing sucide just to save me

    Reply
  85. Hosuh M Posted on September 10, 2019 at 2:26 am

    The Vietnam war is on our bodies

    Reply
  86. Jean Pierre maximus Posted on September 10, 2019 at 4:15 am

    Get hurt by nails
    Me: hmph it's nothing.

    Immune system: going defcon 3, deploying countermeasure, sending troops at sector 3.

    Reply
  87. theonlyguitarperson Posted on September 10, 2019 at 4:28 am

    Great animations and easy to digest the material.

    Reply
  88. Shiny shield Posted on September 10, 2019 at 10:13 am

    where is part 2?

    Reply
  89. Lina Lab Posted on September 10, 2019 at 2:17 pm

    1:16 Poke Mon Game Started Rusty Nail Vs Skin Rusty Nail: Use Uno Reverse Skin Fainted Rusty Nail Got 100 Point And New Fungus

    Reply
  90. Mel C Posted on September 10, 2019 at 2:35 pm

    Omg they try so hard 😭😭😩❤️

    Reply
  91. Sadiq Khan Posted on September 11, 2019 at 12:37 am

    Wondering how and who has designed, developed and implemented this system? It cannot be a self implemented/autopilot process that evolved over thousands of years.

    Reply
  92. Mr Godzilla Posted on September 11, 2019 at 2:04 pm

    Bacteria: * invades again*
    Immune system:*freaks out *
    Memory T cells: Guys hold by blood cells

    Reply
  93. 빵빵이폭주 Posted on September 11, 2019 at 2:22 pm

    와 시발 개쩐다

    Reply
  94. The Gaming Lamb Posted on September 11, 2019 at 2:52 pm

    Subscribe to the gaming lamb

    Reply
  95. Frances Atty Posted on September 11, 2019 at 5:19 pm

    when you're trying to make your a levels easier

    Reply
  96. Frances Atty Posted on September 11, 2019 at 5:29 pm

    1:59 my biology textbook calls this "engulf and digest"

    Reply
  97. jungefrau Posted on September 11, 2019 at 5:37 pm

    As impressive as this is, it works like shite. Before vaccinations and antibiotics our ancestors dropped like flies. Whole villages died of the flu. And you can still die from tetanus…almost 40k ppl do every year.

    Reply
  98. Serenity Guerrero Posted on September 11, 2019 at 6:00 pm

    why did iy have to end like that

    Reply
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