Pratique du Shadowing: The Real Reason Why You Have Allergies - Apprendre l'anglais à l'oral avec la vidéo

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An allergy is like finding a spider in your bedroom and exploding a nuclear bomb.

Sure, spiders are upsetting and now dead, but so are all of your neighbors and your dog.

You can be allergic to an incredibly diverse and weird amount of stuff: pollen, dust, insect stings, animal hair, any kind of food, latex and even your own sweat.

One of the wildest things about allergies is how fast they are, breaking out suddenly and violently.

And you can develop new allergies.

One moment you're enjoying a shellfish you ate thousands of times before, and the next moment you wake up in an ambulance.

A shrimp can kill you.

How bizarre!

But, like, what are allergies?

Why do our bodies flip the table on harmless stuff?

There's a wild and interesting idea we want to share with you.

Humans might have created allergies by accident by getting rid of worms.

For your ancestors, being infected by worms was a reality of life.

We won't get into the disgusting details, but in a world where drinking water and our poo were close buddies, some species of worms found just the perfect cycle of life.

They enter your bodies with the water and make themselves at home, sometimes for decades, and then release their eggs or larvae with your poo, which used to go back to the water we drank.

So, until recently, in evolutionary terms, our ancestors had to deal with frequent or permanent worm infections.

This caused all kinds of unpleasant health effects.

Our immune system had to find weapons to get rid of them.

But how do you do that?

From the perspective of a cell, worms are cities-scale kaiju reaching beyond the horizon.

Worse, instead of skin, parasitic worms have an elastic protective layer that withstands even stomach acid.

You really need to pack some punch to cause damage.

It takes an army to kill a worm.

We're simplifying but, basically, when a worm enters your body for the first time, intelligence cells notice their presence.

They move to your lymph nodes and activate specialized antibody factories called "B cells".

We explain them in detail in this video.

These B cells are told that they need to fight parasites and start producing a special class of weapons, IgE antibodies tiny protein crabs with two pinches that connect to worms like magnets to metal.

IgE floods your entire body and basically begin arming a nuclear bomb, an army of really scary cells called "mast cells".

Mast cells are huge bloated fellows filled to the brink with histamine and other nasty chemicals.

They pick up the IgE floating around and cover themselves with them like angry Hedgehog Grenades without their safety pins.

And then they just lie and wait, angrily.

So now you have millions of bombs, in your skin lungs or gut.

Until the day the mast cells meet a worm trying to enter your body.

There's not much time to get rid of it so things escalate rapidly.

The mast cells with their IgE spikes grab onto the worm particles and… kind of explode.

They release all of their dangerous chemicals all at once.

A few things now happen in rapid succession.

First, some of the mast cell chemicals wound the worms, ripping wounds into them and making them really unhappy.

Then emergency chemicals like histamine cause massive and rapid inflammation ordering your blood vessels to flood the battlefield with water to flush the worms out.

They also order your cells that make mucus to go into overdrive and cover the worms in sticky slime.

Other chemicals are like air raid sirens, screaming loudly throughout your body for anti-parasite soldiers: eosinophils.

First thousands, then hundreds of thousands hear the alarm leave your blood vessels to where the mast cells are causing inflammation.

Not only do they make the inflammation worse, they carry extremely toxic chemicals that they vomit at the worm, ripping open its defensive layer and causing horrible injuries.

Sometimes this will straight up kill the parasite.

Lastly the anti-worm coordination cell arrives: the basophil.

It makes sure that the immune system doesn't slow down but keeps attacking with violence.

It keeps the inflammation going and alerts more and more attack cells to the sight of battle.

Zooming out, we see that the chemicals from your anti-parasite forces make your smooth muscles contract rapidly, pushing everything that's inside, outside.

In your intestines, combined with all the water, you notice this as diarrhea.

as your body tries to expel the stressed parasite.

In your respiratory tract loads of mucus and water flood outside trying to take the worm with them.

If this happens under your skin, your tissue is red, hot and itchy as your immune system is trying to commit murder.

It takes a fierce army to kill a worm and your anti-parasite forces have the license to act rapidly and with intense violence.

Okay, this is nice and all, but what does all this have to do with killer shrimps?

Parasitic worms don't love being ripped apart by millions of bombs, and as all living things do, they adapted to the deadly attacks on them.

In a nutshell, worms release a plethora of chemicals to manipulate your immune system.

They make it weaker and much less angry like immune system weed.

Which is pretty bad for your survival because you have to fight off all sorts of intruders every day.

Our ancestors were basically unable to prevent regular worm infections, so, as the worms adapted to us, our bodies had to adapt to them.

To balance out any weakening worm chemicals, one adaptation might have been to make our immune system more aggressive so it could still defend against other invaders.

And then, a hot second ago in evolutionary terms, everything changed.

We suddenly invented soap and hygiene but, most importantly, the separation of poop and drinking water.

This destroyed the life cycles of parasitic worms and the ones that remained were eradicated by modern medicine.

Worms still infect up to 2 billion people, mostly in undeveloped rural regions or slums with unsanitary conditions and dirty water.

The people who escaped these conditions now face an interesting problem.

An immune system without a major enemy that had kept it down for millions of years.

It could very well be that our immune system still operates assuming that worms are making it weaker, and that it has to be overly aggressive because of that.

And while IgE, mast cells, basophils and eosinophils also have other jobs, a major reason for their existence has now gone away.

But they kind of act as if worms are around, only that they now attack other dangerous foes, like shrimps.

This is exactly what happens when you have an allergic reaction to a shrimp.

Your immune system picks up shrimp proteins and produces IgE antibodies against shrimps.

The antibodies then arm mast cells, turning them into bombs.

So you have millions of bombs in your skin, your lungs or your gut with a license to choose violence, even when provoked a little bit.

Until one day you eat another shrimp, your anti-parasite forces flip on like a switch.

Only there is no kaiju to attack.

This is what you experience when you have an allergic reaction.

Extremely powerful weapons now target your own body.

Under your skin, your blood vessels suddenly turn leaky.

Fluid streams into your tissue, your skin swells up and turns red, often in itchy hives.

You immediately feel hot and unwell.

In your digestive system, the mast cells can cause nausea, cramps and sharp pain as water floods into your intestines and triggers intense diarrhea and vomiting.

Your respiratory tract swells up making breathing hard.

Way more dangerously, histamine and other chemicals can cause the smooth muscles in your lungs to tense up.

In the best case, you get a stuffy nose.

In the worst case, you're suddenly fighting for your life.

Mast cells all over your body unload their bombs all at once, causing an anaphylactic shock.

Your blood loses so much water that your blood pressure drops to dangerous levels.

This alone is life-threatening.

In combination with the things going on in your lungs, anaphylaxis is a life or death emergency, often with just a small time window to do anything about it.

Allergic reactions truly are no joke.

Even the deadliest diseases like Ebola need days to kill you, but your immune system can kill you within a few minutes.

And this is why a shrimp can kill you.

Because, on a fundamental level, an ingenious defense system, vital for our species survival for millions of years, is fighting imaginary kaijus.

Yet we still don't know why some people produce a lot of IgE antibodies against certain substances and others don't.

We don't know why some adults develop new allergies later in life or why some allergies disappear over time.

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And we're not sure if the lack of worms is the main culprit, only that the cells that evolve to fight them are responsible for the symptoms of allergies.

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There are other ideas, like less diverse microbiomes or increased pollution.

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Maybe it's just a combination of all of them.

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But what we clearly see is that allergies and their more serious cousin, autoimmune diseases, have been rising massively in the last 100 years.

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Wherever humans moved into more sanitary conditions and got rid of some of the horrible parasites hunting us.

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Hopefully we'll figure it out and prevent allergies forever Because one thing's for sure: we don't want to get worms back.

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That would really be like finding a spider and exploding a nuclear bomb.

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📺 Même chaîne

Mot	Prononciation	Sens
worm nom	/wɝm/	ver
mast nom	/mɑːst/	mât
allergy nom	/ˈæl.əɹ.d͡ʒi/	allergie
shrimp nom	/ʃɹɪmp/	crevette
antibody nom	/ˈæn.tɪˌbɑ.di/	anticorps
donation nom	/doʊˈneɪʃən/	donation, don
inflammation nom	/ɪnfləˈmeɪ̯ʃən/	inflammation
allergic adjectif	/əˈlɝ.d͡ʒɪk/	allergique
ancestor nom	/ˈæn.sɛs.tɚ/	ancêtre
histamine nom	/ˈhɪstəmiːn/	histamine
parasitic adjectif	/ˌpæɹ.əˈsɪt.ɪk/	parasite, parasitaire
explode verbe	/ɪkˈsploʊd/	détoner, exploser
donor nom	/ˈdəʊnə/	donateur, donneur
adapt verbe	/əˈdæpt/	adapter
basophil nom	/ˈbeɪsəfɪl/	basophile

Mot	Prononciation	Sens
pick up verbe		soulever
break out verbe		s'échapper, s’évader
go away verbe		partir, s'en aller
slow down verbe		ralentir, décélérer
zoom out verbe	/ˌzuːm ˈaʊt/	dézoomer

Structure	Dans la vidéo
Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait	being infected · are told · being ripped
Present perfect have/has + participe passé — une action passée qui compte encore maintenant	has now gone · have now spent

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