The Immune System Explained I - Bacteria Infection

Hard words

The longest, least common words in this video. Say them slowly before you start.

• understandable
• communicators
• inflammation
• intelligence
• interactions
• encountered
• environment
• explanation

Transcript: 86 sentences

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1. 0:01 Every second of your life, you are under attack.
2. 0:03 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
3. 0:14 to protect you from...well...dying.
4. 0:18 For this video, let's assume the immune system has 12 different jobs.
5. 0:23 For example, kill enemies, communicate, etc.
6. 0:25 And it has 21 different cells and 2 protein forces These cells have up to 4 different jobs.
7. 0:32 Let's assign them.
8. 0:34 Here are the interactions.
9. 0:35 Now, let's make this understandable.
10. 0:38 First of all, let's add colours to the jobs.
11. 0:41 Now, let's illustrate the cells.
12. 0:43 The central colour represents the main job of the cell, while the surrounding ones represent secondary duties.
13. 0:50 Now the immune system looks like this.
14. 0:53 Now the interactions.
15. 0:55 Isn't this complexity just awesome?
16. 0:58 For this video we will only talk about these cells and ignore the rest.
17. 1:03 So, what happens in the case of an infection?
18. 1:06 *Intro*
19. 1:13 It's a beautiful day, when suddenly, a wild rusty nail appears and you cut yourself.
20. 1:18 The first barrier of the immune system is breached: your skin.
21. 1:22 Nearby bacteria seize on the opportunity and enter your wound.
22. 1:26 They start using up the body's resources and double their numbers about every 20 minutes.
23. 1:31 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.
24. 1:40 The immune system has to stop them as fast as possible.
25. 1:44 First of all, your guard cells, known as macrophages, intervene.
26. 1:48 They are huge cells that guard every border region of the body.
27. 1:52 Most of the time, they alone can suffocate an attack because they can devour up to 100 intruders each.
28. 1:59 They swallow the intruder whole and trap it inside a membrane.
29. 2:02 Then the enemy gets broken down by enzymes and is killed.
30. 2:05 On top of that, they cause inflammation by ordering the blood vessels to release water into the battlefield so fighting becomes easier.
31. 2:12 You notice this as a very mild swelling.
32. 2:15 When the macrophages fight for too long, they call in heavy backup by releasing messenger proteins that communicate location and urgency.
33. 2:22 Neutrophils leave their patrol routes in the blood and move to the battlefield.
34. 2:27 The neutrophils fight so furiously that they kill healthy cells in the process.
35. 2:31 On top of that, they generate barriers that trap and kill the bacteria.
36. 2:35 They are, indeed, so deadly that they evolved to commit suicide after five days to prevent them from causing too much damage.
37. 2:42 If this is not enough to stop the invasion, the brain of the immune system kicks in.
38. 2:47 The dendritic cell gets active.
39. 2:49 It reacts to the signals of the soldiers and starts collecting samples from the enemies.
40. 2:53 They rip them into pieces and present the parts on their outer layer.
41. 2:57 Now, the dendritic cell makes a crucial decision.
42. 3:00 Should they call for anti-virus forces that eradicate infected body cells or an army of bacteria killers?
43. 3:07 In this case, anti-bacteria forces are necessary.
44. 3:10 It then travels to the closest lymph node in about a day.
45. 3:13 Here, billions of helper and killer T cells are waiting to be activated.
46. 3:17 When T cells are born they go trough a difficult and complicated training process and only a quarter survives.
47. 3:23 The surviving cells are equipped with a specific set-up.
48. 3:27 And the denditric cell is on its way looking for a helper T cell with the set-up that's just right.
49. 3:32 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.
50. 3:39 When it finally finds one, a chain reaction takes place.
51. 3:42 The helper T cell is activated.
52. 3:45 It quickly duplicates thousands of times.
53. 3:47 Some become memory T cells that stay in the lymph node and will make you practically immune against this enemy.
54. 3:52 Some travel to the field of battle to help out.
55. 3:55 And the third group goes on to travel to the center of the lymph node to activate a very powerful weapons factory.
56. 4:01 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.
57. 4:08 The B cell duplicates rapidly and starts producing millions of little weapons.
58. 4:13 They work so hard that they would literally die from exhaustion very fast.
59. 4:18 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!"
60. 4:26 This also ensures that the factories die if the infection is over so the body doesn't waste energy or hurt itself.
61. 4:32 But what is produced by the B cells?
62. 4:35 You've heard of them of course, antibodies.
63. 4:38 Little proteins that are engineered to bind to the surface of the specific intruder.
64. 4:42 There are even different kinds of antibodies that have slightly different jobs.
65. 4:46 The helper T cells tell the plasma cells which type is needed the most in this particular invasion.
66. 4:52 Millions of them flood the blood and saturate the body.
67. 4:55 Meanwhile, at the site of infection, the situation is getting dire.
68. 5:00 The intruders have multiplied in number and start hurting the body.
69. 5:04 Guard and attack cells fight hard, but also die in the process.
70. 5:08 Helper T cells support them by ordering them to be more aggressive and to stay alive longer.
71. 5:12 But without help they can't overwhelm the bacteria.
72. 5:16 But now, the second line of defense arrives.
73. 5:18 Billions of antibodies flood the battlefield and disable lots of the intruders, rendering them helpless or killing them in the process.
74. 5:25 They also stun the bacteria and make them an easy target.
75. 5:29 Their back is built to connect to killer cells, so they can connect and kill the enemy more easily.
76. 5:34 Macrophages are especially good at nomming up the bacteria which antibodies have attached to.
77. 5:40 Now the balance shifts.
78. 5:41 In a team effort, the infection is wiped out.
79. 5:44 At this point, millions of body cells have already died.
80. 5:48 No big deal, the losses are quickly replenished.
81. 5:51 Most immune cells are now useless and without the constant signals they commit suicide, so as not to waste any resources.
82. 5:59 But some stay behind: the memory cells.
83. 6:02 If this enemy is encountered ever again in the future, they will be ready for it and probably kill it before you even notice.
84. 6:10 This was a very, very simplified explanation of parts of the immune system at work.
85. 6:14 Can you imagine how complex this system is, even at this level, when we ignore so many players and all the chemistry.
86. 6:21 Life is awfully complicated, but if we take the time to understand it, we'll encounter endless wonders and great beauty.

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