Lesson video

Hi there, I'm Mrs. Kemp, and welcome to today's lesson, all about responses of the human immune system to specific pathogens.

This fits into the unit of defences against pathogens, the human immune system and vaccination.

So let's get started then.

Now, today's lesson, our main outcome is, I can describe parts of the human immune system and how they respond to specific pathogens.

We'll be using some key terms today and here they are for you.

And if you would like to pause the video and read those in a bit more detail, please do.

If not, do rest assured that I will go through each one of these as we move through the slide deck.

So we've got two learning cycles for today, antigens, and antibodies and antitoxins.

Of course, we will be starting with our first learning cycle, which is antigens.

So the human body, as we know is made up of cells.

Every part of our body is made up of a cell and these cells make up tissues.

The tissues make up organs, the organs make up organ systems, and then we make up an organism.

But actually a lot of pathogens, they're also made up of cells.

An example of a pathogen would be a bacterial cell, and on the surface of all cells we find these things called antigens.

Antigens are proteins and they have a particular structure to them, a particular tertiary structure.

We can see here on the image that different cells have these different antigens.

We can see that in the shape of them.

Now blood is transported to all parts of our body by the circulatory system.

Remember that the circulatory system is made up of our heart and also all those blood vessels, so arteries, veins, and capillaries, and that blood travels around our circulatory system in order to deliver oxygen and also to sort of take away waste, things like carbon dioxide.

The blood contains different parts and for different functions, our red blood cells carry oxygen, our platelets are used for clotting the blood, and we also have phagocytes and lymphocytes which are types of white blood cells.

These are make up part of our immune system and they make sure that any pathogen that has entered the blood or the body is destroyed.

So lymphocytes can recognise the antigens on the surface of different sorts of cells.

And lymphocytes don't usually respond to any antigens that are on our own body cells because otherwise we would start, our immune system will start attacking our own body.

There are certain diseases that people can have where this might happen.

So an example of one of those is type 1 diabetes.

However, most of the time, in healthy people, actually they only respond to the antigens that are on the surface of pathogens and we can see a pathogen there that has a different shape of antigen than the body cell, and so that lymphocyte can only identify that pathogen.

All right, onto our first check.

True or false? Only pathogens have antigens on their surface.

Is that true or is that false? I'll give you a moment to think about it, but if you need more time, please pause the video.

Did you realise that that one was false? What I'd like you to do now is try to justify your answer.

So again, I'll give you some time.

Did you realise that that was b, all cells have antigens on their surface.

Excellent, well done.

So different pathogens, as I said, do have different antigens on their surface because they're made of proteins and they have different shapes.

Here's some example of some different pathogens then, some different cells, and on their surface, look, every single one of those is a slightly different shape.

The lymphocytes, which is the type of white blood cell, will recognise different pathogens by the shape of their antigens.

There's our lymphocyte there reminding us that it is a white blood cell.

Each lymphocyte though will only respond to one specific antigen.

So for example, look, we'll look at lymphocyte A and it is able to recognise and respond to that triangular-shaped antigen on the surface of pathogen A.

However that circular-shaped one, it will not recognise, and therefore it will not respond to it.

Lymphocyte B is a different lymphocyte, so it will not recommend, it will not recognise pathogen A, however it can recognise pathogen B by the antigen.

So we can see that only one type of lymphocyte will respond to one type of pathogen.

This means that each lymphocyte then will only respond to one specific pathogen.

Who do you think is correct? We've got Andeep, he says, "Lymphocytes have antigens that respond to pathogens." Jacob, "Lymphocytes recognise the antigens on pathogens." Sofia, "One lymphocyte can respond to lots of different pathogens." I'll give you a moment to think about it, but if you need more time, please pause the video.

Did you realise that it was b, Jacob, "Lymphocytes recognise the antigens on pathogens? Excellent.

Really well done.

Onto our first task of the day then.

And if you'd like to get your worksheet out, you can record your answers on there.

So very rarely, lymphocytes attack body cells in the pancreas that secrete the hormone insulin.

This can lead to type 1 diabetes.

That's where somebody is not able to control their blood sugar levels.

Number 1, explain why the lymphocytes have respond, explain what the lymphocytes have responded to.

And number 2, suggest why this does not happen in most people.

We can see in the image there that we've got the pancreas showing so we know which part of the body normally produces insulin.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Did you remember then that explaining what lymphocytes have responded to? Of course, lymphocytes are adapted to respond to the antigens.

So it's important that we've used that term there, antigen.

In this case, the lymphocytes have responded to self antigens on the body cells in the pancreas.

Number 2, suggest why this does not happen in most people, and that's because usually lymphocytes only respond to non-self antigens on pathogens.

They don't normally respond to self antigens on the body unless there is some kind of problem or disease, so for example, with type 1 diabetes in this case.

If you need to add any more into your answer, please do that now.

Otherwise we're going to move on.

Well done.

So onto our second learning cycle of the day.

This one is antibodies and antitoxins.

So there are actually different types of white blood cell.

We've just met the lymphocytes, haven't we? But there's also the phagocytes.

Now the job of the phagocyte is a non-specific response, and what they do is that they will engulf by changing shape.

They change the shape of their cytoplasm to engulf any pathogen into a vesicle.

They then release enzymes into that and digest and destroy that pathogen.

So lymphocytes are adapted to respond to only a specific antigen on specific pathogens.

We go back to that example where we've got lymphocyte A will recognise the shape of the antigen on pathogen A, but it will not recognise the shape of the antigen on pathogen B.

Lymphocyte B is different then, it will recognise pathogen B by the antigen but not pathogen A, 'cause it has a different shape antigen.

Now lymphocytes are actually able to produce things called antibodies.

Antibodies, we can see there in the image that is being shown and they have that funny Y shape and on the end of each of the Ys they have a little binding site.

That binding site is able to bind to specific antigens, and again, that will be because of their shape.

Antibodies are also proteins, so they have a specific 3D shape that will able to fit and be complimentary to that antigen.

It can actually take a few days for the antibodies to be produced.

So once that lymphocyte has recognised that that pathogen has invaded us, it will take a while for it to start producing those antibodies to help to destroy the pathogen.

In that period of time, that's when we start to feel poorly.

So that's when we're going to have symptoms. Let's say that it was a virus that produces the common cold, actually we might start sneezing, we might have a high temperature, we might have a cough, and that's because our lymphocytes need a little bit of time in order to start producing those antibodies so that then they can destroy that pathogen.

Onto a true or false.

Antibodies are proteins found on the surface of a pathogen? Is that true or is that false? Justify your answer for me, a, antibodies are not proteins, b, antigens are found on the surface of pathogens.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Did you get false? And that is because obviously antigens are found on the surface of pathogens, not antibodies.

Antibodies are proteins, but they're produced by the lymphocytes in response to those antigens.

So what do antibodies actually do? One thing that they can do is they can cause the pathogen to clump together.

So we can see that what that those antibodies down there have done is they've collected up two or three of bacterial cells and they've made them clump together.

The reason why this is a good thing then is that actually it makes it much easier for phagocyte, remember, that's the other type of white cell, to come along and engulf all of those bacteria in one go.

It then needs to produce some enzymes in order to break down those bacteria and destroy them.

But because they haven't had to keep going and getting them separately and they're all in one place, it makes it much easier for that process to happen.

Each lymphocyte then only produces one specific type of antibody.

Again, we've got those different types of lymphocytes, we've got A, B, and C here, and you can see that at the end of those Y-shaped antibodies we can see that those binding sites on each one of those antibodies is a slightly different shape and that shape is complimentary to the shape of the antigen so that they fit together.

When they fit together then, that's then bound together and that can form that clumping of the different pathogens.

Can you match the antibody to the correct antigen? I'll give you a moment to think about it, but if you need more time, please pause the video.

Have you got it correct? Now actually they're not only just the correct shape, they've also got matching colours, so it makes it slightly easier as well.

So we've got that green one at the top, going to the middle, we've got the blue one in the middle going to the bottom cell, and then we've got the bottom purple one going to the top purple cell.

Excellent, I hope you realise that those antigens and antibodies there are complimentary and they're able to fit together.

Excellent, well done.

Now, bacteria can make us feel poorly because actually what they do is they produce these poisons called toxins and those toxins can damage living tissue and make us feel poorly.

That is different from how viruses, for example, make us feel poorly.

Remember that how viruses make us feel poorly is 'cause they invade our cells and then use the cellular processes to replicate themselves, when they burst out of the cell, it kills our cells.

Bacteria make us feel poorly for a different reason, and that's because of producing these things called toxins.

White blood cells, then, as well as being able to produce antibodies, they can also produce these things called antitoxins.

The antitoxin, just like the antibody is actually specific for its own toxin.

So it'll only neutralise one type of toxin.

So what they do is they neutralise that toxin and then they makes the bacterium no longer harmful to us.

So if you can neutralise that toxin that's being produced by the bacteria, it's no longer going to be damaging your tissues, and therefore you are not going to feel unwell.

What do white blood cells produce to neutralise toxins? A antibodies, b, antigens, or c, antitoxins? I'll give you a moment to think about it but if you need more time please pause the video.

Did you realise that it was antitoxins? Those are the ones that are able to respond to toxins.

Antibodies, remember, they're complimentary to the antigens that we find on the surface of pathogens.

Onto our final task of the day, then.

We can see that we've got two different white blood cells here.

We've got phagocytes and we've got lymphocytes.

You can open up your worksheet because you can record your answer on there.

What I would like you to do then is to explain two ways that white blood cells can protect the human body from bacterial infection.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Excellent, well done.

Let's go over these answers then.

So you can choose any two from, first of all we've got a phagocyte, and a phagocyte, what they can do is engulf and digest the bacteria.

You may have actually mentioned the enzymes there as well that actually do that digesting inside the little vesicles.

You may have mentioned the type of lymphocyte that can make specific antibodies that bind to the antigens on the surface of pathogens.

You might have mentioned that both of those are made of proteins.

They cause the bacteria to clump together so phagocytes can then engulf them much more easily, digest them and destroy them.

You might have also mentioned that bacteria can produce toxins that cause damage to the body and make a person feel ill.

White blood cells can make antitoxins to neutralise that toxin so they cannot cause any harm.

Hopefully you've got all of those points down.

Now if you haven't, what you might want to do is you might want to pause the video and add a couple more into your answer, but I'm sure that you've done really well on that, so excellent, well done.

We are very close to finishing, then.

And what I'd like to do is just go over those key learning points from today.

So all cells, including our body cells and pathogens have molecules called antigens on their surface.

Lymphocytes are a type of white blood cell.

Lymphocytes recognise pathogens by their specific antigens.

Lymphocytes produce specific antibodies that clump pathogens together to be engulfed and destroyed by phagocytes.

White blood cells can also produce antitoxins that neutralised toxins produced by bacteria.

So there's been a lot of new information there and I hope you've managed to keep on track with it all.

I'm sure you've done really well.

I've really enjoyed learning with you.

Thank you very much and hopefully I'll see you again soon.

Bye now.