The Immune System Explained I – Bacteria Infection — Transcript

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1. 0:00Every second of your life, you are under attack.
2. 0:03Billions of bacteria, viruses, and fungi are trying to make you their home,
3. 0:07so our bodies have developed a super complex little army with guards, soldiers, intelligence, weapons factories, and communicators
4. 0:14to protect you from...well...dying.
5. 0:17For this video, let's assume the immune system has 12 different jobs. For example, kill enemies, communicate, etc.
6. 0:25And it has 21 different cells and 2 protein forces
7. 0:29These cells have up to 4 different jobs.
8. 0:32Let's assign them. Here are the interactions.
9. 0:35Now, let's make this understandable.
10. 0:38First of all, let's add colours to the jobs.
11. 0:40Now, let's illustrate the cells.
12. 0:43The central colour represents the main job of the cell,
13. 0:46while the surrounding ones represent secondary duties.
14. 0:49Now the immune system looks like this.
15. 0:52Now the interactions.
16. 0:54Isn't this complexity just awesome?
17. 0:58For this video we will only talk about these cells and ignore the rest.
18. 1:02So, what happens in the case of an infection?
19. 1:05*Intro*
20. 1:12It's a beautiful day, when suddenly, a wild rusty nail appears and you cut yourself.
21. 1:18The first barrier of the immune system is breached: your skin.
22. 1:22Nearby bacteria seize on the opportunity and enter your wound.
23. 1:26They start using up the body's resources and double their numbers about every 20 minutes.
24. 1:31At first, they fly under the radar, but when a certain bacteria population is reached,
25. 1:35they change their behavior and start to damage the body by changing the environment around them.
26. 1:40The immune system has to stop them as fast as possible.
27. 1:44First of all, your guard cells, known as macrophages, intervene.
28. 1:48They are huge cells that guard every border region of the body.
29. 1:52Most of the time, they alone can suffocate an attack
30. 1:55because they can devour up to 100 intruders each.
31. 1:58They swallow the intruder whole and trap it inside a membrane.
32. 2:01Then the enemy gets broken down by enzymes and is killed.
33. 2:05On top of that, they cause inflammation by ordering the blood vessels to release water into the battlefield
34. 2:10so fighting becomes easier.
35. 2:12You notice this as a very mild swelling.
36. 2:14When the macrophages fight for too long,
37. 2:16they call in heavy backup by releasing messenger proteins that communicate location and urgency.
38. 2:22Neutrophils leave their patrol routes in the blood and move to the battlefield.
39. 2:26The neutrophils fight so furiously that they kill healthy cells in the process.
40. 2:31On top of that, they generate barriers that trap and kill the bacteria.
41. 2:35They are, indeed, so deadly that they evolved to commit suicide after five days to prevent them from causing too much damage.
42. 2:42If this is not enough to stop the invasion, the brain of the immune system kicks in.
43. 2:47The dendritic cell gets active.
44. 2:48It reacts to the signals of the soldiers and starts collecting samples from the enemies.
45. 2:53They rip them into pieces and present the parts on their outer layer.
46. 2:57Now, the dendritic cell makes a crucial decision.
47. 3:00Should they call for anti-virus forces that eradicate infected body cells
48. 3:04or an army of bacteria killers?
49. 3:06In this case, anti-bacteria forces are necessary.
50. 3:09It then travels to the closest lymph node in about a day.
51. 3:12Here, billions of helper and killer T cells are waiting to be activated.
52. 3:17When T cells are born they go trough a difficult and complicated training process
53. 3:21and only a quarter survives.
54. 3:23The surviving cells are equipped with a specific set-up.
55. 3:26And the denditric cell is on its way looking for a helper T cell with the set-up that's just right.
56. 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.
57. 3:38When it finally finds one, a chain reaction takes place.
58. 3:42The helper T cell is activated. It quickly duplicates thousands of times.
59. 3:47Some become memory T cells that stay in the lymph node and will make you practically immune against this enemy.
60. 3:52Some travel to the field of battle to help out.
61. 3:54And the third group goes on to travel to the center of the lymph node
62. 3:57to activate a very powerful weapons factory.
63. 4:00Like the T cells, they are born with a specific set-up
64. 4:03and when a B cell and a T cell with the same set-up meet, hell breaks loose.
65. 4:08The B cell duplicates rapidly and starts producing millions of little weapons.
66. 4:12They work so hard that they would literally die from exhaustion very fast.
67. 4:17Here, helper T cells play another important role; they stimulate the hard working factories and tell them:
68. 4:23"Don't die yet, we still need you, keep going!"
69. 4:25This also ensures that the factories die if the infection is over so the body doesn't waste energy or hurt itself.
70. 4:32But what is produced by the B cells?
71. 4:34You've heard of them of course, antibodies.
72. 4:37Little proteins that are engineered to bind to the surface of the specific intruder.
73. 4:42There are even different kinds of antibodies that have slightly different jobs.
74. 4:46The helper T cells tell the plasma cells which type is needed the most in this particular invasion.
75. 4:51Millions of them flood the blood and saturate the body.
76. 4:55Meanwhile, at the site of infection, the situation is getting dire.
77. 4:59The intruders have multiplied in number and start hurting the body.
78. 5:03Guard and attack cells fight hard, but also die in the process.
79. 5:07Helper T cells support them by ordering them to be more aggressive and to stay alive longer.
80. 5:12But without help they can't overwhelm the bacteria.
81. 5:15But now, the second line of defense arrives.
82. 5:18Billions of antibodies flood the battlefield and disable lots of the intruders,
83. 5:22rendering them helpless or killing them in the process.
84. 5:24They also stun the bacteria and make them an easy target.
85. 5:28Their back is built to connect to killer cells, so they can connect and kill the enemy more easily.
86. 5:34Macrophages are especially good at nomming up the bacteria which antibodies have attached to.
87. 5:39Now the balance shifts.
88. 5:41In a team effort, the infection is wiped out.
89. 5:44At this point, millions of body cells have already died.
90. 5:47No big deal, the losses are quickly replenished.
91. 5:51Most immune cells are now useless and without the constant signals they commit suicide, so as not to waste any resources.
92. 5:59But some stay behind: the memory cells.
93. 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.
94. 6:09This was a very, very simplified explanation of parts of the immune system at work.
95. 6:14Can you imagine how complex this system is, even at this level, when we ignore so many players and all the chemistry.
96. 6:20Life is awfully complicated, but if we take the time to understand it, we'll encounter endless wonders and great beauty.