Hi. It’s Mr. Andersen and welcome
to the immune system podcast. In this podcast I wanted to start with a little history. These
are some beautiful illustrations from the Florentine Codex which is thousands of pages
long. It was created over about 45 years by this guy, this friar. And basically what we
did was he studied Aztec culture and how it changed over his lifetime. So we’ve converted
a lot of this to English and you can find some if it on Wikipedia. It’s just fascinating.
So you could see these rituals and these chieftains. And he would describe all of it. But a sad
part of that is that he describes how small pox came and devastated the Aztec. And it’s
one of the reasons why the Spanish were able to conquer them. And so they didn’t have a
immunity to it. And that’s what this is about. So basically what happens with any kind of
a infection, a viral infection like this, is you have a virus. And that virus is essentially
going to gain entry inside your cells. It’s going to use the machinery of your cell to
make copies of itself. And more copies of itself. And more copies of itself. And eventually
it’s going to destroy the cell and it’s going to spread off to infect other cells. And so
that seems awful. In other words when you get a cold what’s happening is that your cells
are making viruses which are spreading to more cells. And if it weren’t for our immune
system we would be devastated by all the viruses that are around us. And so we have to have
protection. And so I like the analogy of a castle. A castle needs protection as well.
And so if you’re building a castle, you have to think about a few ways to defend yourself.
First of all you have to defend yourself from the outside. So it’s good to have a moat.
It’s also good to have a really large wall. So it’s hard for people to get over it. And
this castle’s great because it’s got water on all sides of it. You also have to have
soldiers. So if anybody were to ever get close to the gate you could shoot them with arrows
or pour hot tar on them. But if they were to breach the wall you have to be able to
fight them there as well. But probably when you’re defending a castle a more important
thing is you have to have intelligence. You have to have spies that are sent out to surrounding
areas to do reconnoissance and figure out what’s going on. To recognize invaders when
then come. And so I’m going to quit talking about castles and we’re going to talk about
the immune system. But the same thing works inside us. And so the idea of a castle wall.
Let’s start with that. And so what protects us from infection, our castle wall is going
to be our skin. And so what our skin provides us with is it provides us with a barrier.
So there’s going to be a barrier of cell, dead cells, on the top. And keratin on the
top. It’s also going to have a really low pH which makes it hard for any kind of bacteria
to live there. And we’re also going to have chemicals on the surface of our skin that
are going to disrupt certain viruses. And also we’re going to have bacteria that crowd
out our skin. And so it makes it hard for other bacteria to gain entry. We have what
are called normal flora that just live on our skin. And so all of this is going to provide
protection against infection. But occasionally you know that that get’s breached. Occasionally
you cut yourself or a pin prick or something like that gains entry. And so that would be
just like the soldiers making it over the wall. And so what do we have? Well we have
a call to arms. We have inflammation. So basically we have chemicals that are released that cause
our body to respond to that. Now you constantly are being infected, especially if you are
a teenager because you get acne. So what is acne? Acne is essentially an infection in
the pores of your skin. So it’s bacteria that are living and feeding inside our body. And
so how do we fight that? Well we’ll plug it up for one thing, but we have swelling. So
we’re going to increase the heat. But basically we’re going to send soldiers in there. And
those soldiers are the macrophages. Those are going to be the eaters or the big eaters.
And what they’re going to do is they’re going to find anything that’s not part of our body
and they’re going to eat it. So any invader is called antigen. And so basically what a
macrophage will do is it will notice that this is not part of our body. It will grab
on to it. It will take it into the macrophage. It’ll secrete lysosomes and enzymes into it
which break it up. It will lots of times present that on its surface, but eventually gets rid
of it. And so this is an actual picture of a macrophage. And you can see it’s grabbing
I don’t know if it’s viruses or bacteria on either side. And so that’s great. But the
one thing about it is it attacks anything that’s not us. In other words if you get a
heart implant from someone else, or you get a heart transplant, those macrophages are
going to attack it as well. It’s going to kill that. And so we also have what’s called
a specific immune response. Specific immune response is more like the spies. And so basically
here’s an antigen again. An antigen is going to have specific proteins on its surface.
But to fight that we use what are called antibodies. And so the name antigen means an antibody
generator. In other words it generates the formation of antibodies. So what are antibodies?
Antibodies are going to be proteins produced by our body. And basically they all look the
same. They’re this Y kind of a shape. So they’re a Y shape like this. We produce almost an
infinite number and an infinite variety of them. But at the top of the Y you’re going
to have different shapes. In other words, you’re going to have a shape that looks like
this. But you’re also going to have an equal shape that might look like this. And you’re
going to have an equal shape that might look like this. And so we’re going to have all
of these different shapes at the top. But we’re only going to produce the shape for
the one thing that we’re infected by. So basically the antibody will dock to the antigen. And
when it does that basically it marks the antigens so macrophages can find it. And it also makes
it harder for them to do their job. Imagine if I had another antibody here. And another
antibody here. And another antibody here. It’s hard for them to do their job. And so
when you gain immunity, specific immunity or specific immune response what that means
is you have the ability to produce these antibodies. And that’s why when you have a cold you’re
not going to get that same cold again. And so basically how do we do this? Or how does
this work? Well we need what are called lymphocytes. Lymphocytes are a type of white blood cells.
And so basically there are two types of lymphocytes. There are B lymphocytes and then there are
T lymphocytes which will get to in just a second. Okay. So B lymphocytes are made in
the bone marrow. And they’re responsible for a humoral response. Now this term I’m going
to show you a couple more times in this podcast. Humoral means in the fluid or in the humers
of your body. So that means in the blood. In the lymph material. In the lymph vessels.
In the interstitial fluid. And so humoral response, what I want you to think about is
going to be anytime there are viruses free in the fluids of our body. And what the B
lymphocytes do is they produce antibodies. So how does that work? Basically you have
a naive B cell. It’s going to sense the shape of the antigen. I’ll tell you how that works
in just a second. But basically what it’s going to do is it’s going to produce antibodies.
And so what B lymphocytes do is they produce all of these antibodies that are specific
for the antigen. So in other words if we’re infected by this virus, we’ll call this virus
A1, then we’re going to produce antibodies for that specific antigen. We’re also going
to produce memory B cells so that we have that immunity for the rest of our life. So
those are the B lymphocytes. And so you might think, if they attack the viruses out inside
our body then what do the T lymphocytes do? Well the T lymphocytes are responsible for
cell mediated response. What does that mean? They’re going to target and kill the cells
inside our body that are already infected. Okay. So what are the T lymphocytes? Where
are they made? They’re made in the thymus gland which kind of sits on the top of our
heart. Basically what they do is they create what are called kill T cells or killer T lymphocytes.
And so a killer T cell is an activated T cell. Basically what it will do is it’ll find any
of the cells inside our body that are infected with a virus. It’ll dock next to them and
it will kill our own cells. And so it’s going to kill any of the cells inside our body that
are infected by the virus. Or even cancerous cells, it’s going to kill them. So it’s made
in the thymus and it produces cell death inside us. And so the T lymphocytes are responsible
for this cell mediated, I mean killing cells inside, our cells that are infected. B lymphocytes
are going to be in the humers of our body. And so if I were to summarize this a little
bit, this would be the humoral response up here. So what type of cells are responsible
for that? Those is going to be the B cells. And here’s the cell mediated down here. Those
are going to be the killer T cells. And so before we get to that let’s look over here
on the left side. So basically what’s happening? We have an antigen that is eaten by a macrophage.
That macrophage is going to chop up that antigen. It’s going to present pieces of it on its
surface. And so we use a chemical called MHC2. It’s major histocompatibility complex 2. It’s
going to present the shape of that antigen on it’s surface and now we get this cell right
here which is super important. It’s call the T helper cell. What the T helper cell is going
to do is it’s going to dock and it’s going to physically sense the shape of that antigen.
It uses another protein called CD4. And it’s going to sense the shape of that antigen.
The helper T cell is responsible for initiating both the humoral and the cell mediated immune
response. So let’s see what helper T cell is going to do. Helper T cell is going to
tell that shape to the B cells. And so it can produce more antibodies. It’s going to
activate macrophages. So it can kill more of them inside the humers of our bodies. So
it’s responsible for that humoral response. And the helper T cell is also going to activate
the killer T cells. So they can kill the cell mediated, or excuse me, the cell’s that are
infected by a virus. And so if isn’t for these guys, if it isn’t for the helper T cells,
we’re out of luck. Now sadly, helper T cells are the cells that are infected by HIV or
people who have AIDS. And so you can see why that’s a really bad thing. Because without
the helper T cells we can’t fight normal infections. So if you have HIV you don’t die of that.
You’re dying of normal infections that we would fight off. So let me kind of do this
in cartoon style. If we were to animate it again. So what we’ve got here is our antigen.
Remember that’s our invader. And so basically what’s going to happen is it is going to be
eaten by a macrophage. So the macrophage will take it in. It will secrete enzymes into to
it which are going to digest that antigen. It will get rid of it. But it’s also going
to grab on to a little bit of that. It’s going to grab on with this major MHC. It’s going
to take it’s shape out to its surface and now we have helper T cell. What’s helper T
cell going to do? Helper T cell is going to dock with that macrophage. And it’s going
to sense the shape of that antigen. It’s now going to become an activated helper T cell.
So thinking back to that flow chart just a second ago, where does it go next? Well it
can activate macrophages. But more importantly it’s going to activate B cells. So now we’ve
got an activated B cell. It’s going to activate killer T cells. And now through clonal selection
it’s basically, they’re going to make clones of themselves. We’re going to have a whole
bunch of activated B cells. We’re going to have a whole bunch of activated killer T cells.
So now, thinking about it, this on the top is going to be the humoral response up here.
And this down here is going to be the cell mediated response. And so basically we can
fight those antigens out here in the humers of the body. We do that by sticking antibodies
to it so macrophages can eat it, break it down. We also inactivate them a little bit.
But if you look down here, that killer T cell is docked with a cell inside our own body
that’s already infected by an antigen. And so it’s going to secrete enzymes into it that
are going to break that down. So it’s going to kill that. And so basically what we have
done is we’ve killed them in the humers or in the fluids of the body and then we’ve killed
cells that are infected. And so this takes awhile. But it’s going to be your immune response.
And it’s specific to that antigen. Until we get that specific antigen, we’re not going
to produce the antibodies for it. So let’s talk about a cold, because I’m getting a cold
right now. So basically what happens is you’re exposed to the cold right here. The virus
is going to start reproducing inside my body and it’s going to take me a little while for
me to start building memory, excuse me, B cells and killer T cells. And so there’s going
to be a lag time but essentially I’m going to produce a whole bunch of antibodies and
effector T cells. So that’s going to increase inside my body. And this time right here is
where I actually feel like I have a cold. So this is me feeling like I have a cold,
but really what’s happening is it’s my body fighting and killing off all the viruses.
And so let’s say I get exposed to that same cold again in the future. Well in the future
I’m going to get exposed to it. But since I have so many antibodies I’m going to produce
them so quickly. And since I have these memory B cells and memory T cells that are just hanging
out, I’m going to fight off and kill that infection before I even realize that I have
a cold. And this could be years later. Now how could colds get around this, and they
do get around it? Well they can have a bunch of different types and colds I think have
a hundred different types of rhinoviruses. But they also can mutate. And if they mutate
they change the shape of the antigen. And now those antibodies aren’t going to work
anymore. And so that’s the immune response. If you think of it this way, it’s like keeping
the invaders out of the castle. You’re at least one step closer to understanding the
immune system. And I hope that’s helpful.