December 9, 2025 • 12 mins
Your adaptive immune system remembers specific germs and fights them really effectively -- but it can sometimes make mistakes and attack your own healthy cells. Learn how the adaptive immune system works (and how it can go wrong) in this episode of BrainStuff.
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Episode Transcript
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Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff Lauren Bogelbaum. Here,
you might think of your body sort of like a
fabulous estate with a lot of different departments and individual
workers that keep the household running. For this metaphor, whether
you want to imagine yourself as a medieval castle or
(00:24):
a countryside manor, or more of a well staffed but
nonetheless haunted mansion is up to you. You might say
that you've got a kitchen staff in your digestive system,
because it prepares nutrients for the whole household to use.
Organs like your kidneys, are part of the cleaning staff.
Your body also keeps a sharp security staff on hand
(00:45):
in the form of your immune system. There are two
subdepartments or branches within the immune system, the innate and
the adaptive. A lot of germs that enter your body
get dealt with with a swiftness by your innate immune system.
This is a whole organization of defenses that keep out
and kick out any sort of home invader at the home,
(01:07):
in this case being you. Your innate immune system includes
your skin and mucous membranes, which are physical barriers, and
some cells and enzymes that scan for attack and kill
any germs that do make it in of like in
the state's physical walls and its camera network and security guards.
The innate immune system is fairly automated and can't distinguish
(01:29):
between different types of invaders that well, but it's really
effective at stopping them before they make you sick. Unfortunately
for us, some germs have evolved to evade our innate
immune system. When for whatever reason, a germ survives in
your body and keeps multiplying, the security guards of the
innate immune system call into action that second branch, your
(01:52):
adaptive immune system. It's called adaptive because it can learn
about different germs and respond specific to each. It functions
sort of like a network of live in detectives or
special agents that build a database of all the germs
they fought off over the course of your life. This
is super cool because I mean, A, it keeps us alive,
(02:15):
but B it also prevents us from getting sick from
certain diseases twice like chicken pox. Once you've had it,
you'll probably never get it again. The adaptive immune system
is also why vaccines work. We can introduce a harmless
version of a germ or bits of a germ to
our adaptive immune system, and it'll learn how to recognize
that germ, so should the real thing try to invade
(02:38):
at a later time and date, your body can spring
into action and fight it off quick You can see
our whole episode on vaccines for more about that. The
immune system and its two branches are hugely complex and interrelated.
When it's all working correctly, it sets up a lot
of checks and balances so that the cells, the workers
within the system are aggressive about fighting off invaders, but
(03:01):
also don't make mistakes in the form of friendly fire
or too much collateral damage. But because of that complexity,
there's also a lot of things that can go wrong. Today,
let's talk more about how your adaptive immune system works
and what can happen when it turns against you. The
(03:22):
primary workers in your adaptive immune system, your detectives or
special agents, are a category of cells called lymphocytes. They're
called that because when they're not actively fighting off an infection,
they mostly hang out dormant in your lymph nodes. These
are small organs that you have many of throughout your body,
though you might be most familiar with the two in
(03:44):
your upper neck on either side of your windpipe. You
might have had a doctor or parent feel for those
when you've had a cold, because during an infection, they're
a base of operations for lymphocytes, so if you're fighting
something off, they tend to swell up. There are two
categories of lymphocytes, B cells and T cells. T cells
(04:05):
are called that because they mature in the thymus after
having been created in your bone marrow. B cells are
created and mature in the bone marrow, which is why
they're called B cells. That's not super important, but I
just learned that, and I had always wondered about the names,
so I thought i'd share. Anyway, In their downtime, your
lymphocytes are mostly hanging out in their headquarters, your lymph nodes,
(04:29):
waiting for a call to action. When your innate immune
system encounters germs, specialized security guard cells come to lymph
nodes to tell the lymphocytes about it. What's technically happening
is that the innate immune cell eats the germ and
breaks it apart and displays bits of the germ on
its surface. But that gets real grizzly for our metaphor,
(04:53):
So let's say it's like showing some security cam footage.
These germ bits or identic buying footage are what's called antigens.
We've talked about antigens on the show before. There are
molecules that occur on the surface of germs and cells
and other stuff that your immune system can use to
(05:13):
id whatever it is. If the thing in question is
from your own body and thus belongs there, your immune
system should recognize that. If it's not, your adaptive immune
system's job is to create a specific attack against germs
bearing that antigen and then remember it later. Here's how
(05:34):
it works. The T cells in your lymph nodes can
test a presented antigen and see whether they recognize it
because your body has fought a germ with it before.
Each individual T cell tests for, or recognizes, or fits
to a single antigen like a key in a lock.
Even if it's a new to you antigen, that's okay.
(05:56):
Eventually your system will find a T cell that fits
well enough as a remembered antigen. That's great. The whole process
can go quicker. When a T cell fits to an antigen,
it activates a response like a red alert. The T
cells starts to replicate rapidly, producing copies of itself that
are all custom fitted to that particular antigen. This is
(06:18):
really helpful because T cells are sort of like your
body's targeted assassins. They seek out and attack germs and
infected cells directly based on the particular antigen that they recognize.
T cells can also chemically signal other immune cells to
come help and can help activate your B cells. B
(06:39):
cells are sort of like your weapons experts. They create
what's called antibodies. Antibodies are specific proteins that your body
builds to match specific antigens. Antibodies can bind to their
matching antigen on the surface of a germ, rendering the
germ unable to do any harm, and also serve to
(07:00):
flag that germ or a germ infected cell for destruction.
At this point in the estate metaphor, I'm not sure
exactly what kind of household we're running here, maybe a
supervillain's compound, but let's just roll with it. So, after
your immune system has cleared an infection, it will stockpile
(07:21):
that particular antibody and keep around some T cells that
recognize that antigen in most cases forever. So if your
immune system encounters antigens of the same type later on
Bada bing Bada boom, where Bada bing boda boom indicates
that networks within networks of intracellular communication and coordinated efforts
(07:43):
will occur. It's all again really complex, which means a
lot of different things can go wrong. For example, not
everything that your immune system IDs using antigens as not
self and thus potentially unsafe, is actually a threat. This
is how we wind up with allergies to not just
(08:05):
harmless but actively adorable things like cats and flowers. For
some reason, your immune system looks at a granule of
pollen or pet dander and tries to clear it out
of your body with the same kind of extreme prejudice
it would a disease causing germ. Your innate immune system
triggers lots of inflammation to help get fighting resources to
(08:26):
the area, say your nose, but there's really nothing to fight,
so you just wind up swollen and itchy. There are
also some types of germs that actively mess with your
immune system. That's what originally made the human immuno deficiency
viruses or HIV so scary. HIV infects and kills immune
(08:48):
system cells like T cells in order to spread. There
have been some amazing advances in treating and preventing HIV
in recent years. It's very manageable. Now I'll have to
do a whole episode about it. Anyway. There are also
a number of conditions that happen when the adaptive immune
system starts confusing your own cells for invaders. Every cell
(09:10):
in our bodies should be coded as self thanks to
antigens on the cell's surface. It's sort of like wearing
an id. Bad antigens tell your immune system at a glance,
hey I'm cool, I work here. There are entire processes
in your body to curate your T cells and B cells,
but keep their activity in check and make sure that
(09:31):
ones that seem to want to attack self codd cells
don't get into circulation in the first place. But it
still happens, and this category of conditions is called autoimmune disorders.
It includes things like arthritis, in which your immune system
attacks your joints, type one diabetes in which it attacks
(09:51):
your pancreas, multiple sclerosis which damages nerve cells, and psoriasis,
which damages the skin leading to scaly, pass or other problems.
Autoimmune disorders tend to be frustrating to treat, after all,
You can't just remove and replace a malfunctioning immune system
the way you might a kidney. Also, we don't understand
(10:14):
exactly why any given autoimmune disorder happens. There is a
lot of research going into this, and we've got a
lot of good starting concepts, but again, the entire immune
process is so complex that it's hard to nail things down.
For example, researchers have identified sets of genes that code
for things like how your immune cells recognize antigens or
(10:37):
how your body's cells produce their self ID. It makes
sense that errors in this coding could lead to problems.
Other research has looked into malfunctions in T cells that
lead them to overproduce those signal molecules that call in
the troops, which also leads to inflammation, which tends to
be an issue in autoimmune disorders. Yet other research is
(11:00):
diving in two malfunctions in a subset of T cells
called regulatory T cells, that are supposed to regulate their
fellow workers in the immune system, shutting down the red
alert after an infection has been cleared, and suppressing excess activity.
Even when we do have a decent idea of what's
going wrong, immune disorders of all types can be difficult
(11:21):
to treat, but there are increasingly effective therapies that can
ease symptoms or even target particular immune system activities to
help bring it back closer to normal. As always, if
you or a loved one is experiencing strange inflammation or
other irritating or painful symptoms with no obvious cause. You
(11:42):
know you didn't stub your skin, definitely get in touch
with a healthcare professional. They'll be able to help you
get a diagnosis and a treatment plan, even if your
body is a supervillain's layer that may or may not
be haunted. Today's episode is an original written by me.
(12:04):
Brain Stuff is production of iHeart Radio and is produced
by Tyler Klang. Four more podcasts from iHeartRadio visit the
iHeartRadio app, Apple Podcasts, or wherever you listen to your
favorite shows.
Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff Lauren Bogelbaum. Here,
you might think of your body sort of like a
fabulous estate with a lot of different departments and individual
workers that keep the household running. For this metaphor, whether
you want to imagine yourself as a medieval castle or
(00:24):
a countryside manor, or more of a well staffed but
nonetheless haunted mansion is up to you. You might say
that you've got a kitchen staff in your digestive system,
because it prepares nutrients for the whole household to use.
Organs like your kidneys, are part of the cleaning staff.
Your body also keeps a sharp security staff on hand
(00:45):
in the form of your immune system. There are two
subdepartments or branches within the immune system, the innate and
the adaptive. A lot of germs that enter your body
get dealt with with a swiftness by your innate immune system.
This is a whole organization of defenses that keep out
and kick out any sort of home invader at the home,
(01:07):
in this case being you. Your innate immune system includes
your skin and mucous membranes, which are physical barriers, and
some cells and enzymes that scan for attack and kill
any germs that do make it in of like in
the state's physical walls and its camera network and security guards.
The innate immune system is fairly automated and can't distinguish
(01:29):
between different types of invaders that well, but it's really
effective at stopping them before they make you sick. Unfortunately
for us, some germs have evolved to evade our innate
immune system. When for whatever reason, a germ survives in
your body and keeps multiplying, the security guards of the
innate immune system call into action that second branch, your
(01:52):
adaptive immune system. It's called adaptive because it can learn
about different germs and respond specific to each. It functions
sort of like a network of live in detectives or
special agents that build a database of all the germs
they fought off over the course of your life. This
is super cool because I mean, A, it keeps us alive,
(02:15):
but B it also prevents us from getting sick from
certain diseases twice like chicken pox. Once you've had it,
you'll probably never get it again. The adaptive immune system
is also why vaccines work. We can introduce a harmless
version of a germ or bits of a germ to
our adaptive immune system, and it'll learn how to recognize
that germ, so should the real thing try to invade
(02:38):
at a later time and date, your body can spring
into action and fight it off quick You can see
our whole episode on vaccines for more about that. The
immune system and its two branches are hugely complex and interrelated.
When it's all working correctly, it sets up a lot
of checks and balances so that the cells, the workers
within the system are aggressive about fighting off invaders, but
(03:01):
also don't make mistakes in the form of friendly fire
or too much collateral damage. But because of that complexity,
there's also a lot of things that can go wrong. Today,
let's talk more about how your adaptive immune system works
and what can happen when it turns against you. The
(03:22):
primary workers in your adaptive immune system, your detectives or
special agents, are a category of cells called lymphocytes. They're
called that because when they're not actively fighting off an infection,
they mostly hang out dormant in your lymph nodes. These
are small organs that you have many of throughout your body,
though you might be most familiar with the two in
(03:44):
your upper neck on either side of your windpipe. You
might have had a doctor or parent feel for those
when you've had a cold, because during an infection, they're
a base of operations for lymphocytes, so if you're fighting
something off, they tend to swell up. There are two
categories of lymphocytes, B cells and T cells. T cells
(04:05):
are called that because they mature in the thymus after
having been created in your bone marrow. B cells are
created and mature in the bone marrow, which is why
they're called B cells. That's not super important, but I
just learned that, and I had always wondered about the names,
so I thought i'd share. Anyway, In their downtime, your
lymphocytes are mostly hanging out in their headquarters, your lymph nodes,
(04:29):
waiting for a call to action. When your innate immune
system encounters germs, specialized security guard cells come to lymph
nodes to tell the lymphocytes about it. What's technically happening
is that the innate immune cell eats the germ and
breaks it apart and displays bits of the germ on
its surface. But that gets real grizzly for our metaphor,
(04:53):
So let's say it's like showing some security cam footage.
These germ bits or identic buying footage are what's called antigens.
We've talked about antigens on the show before. There are
molecules that occur on the surface of germs and cells
and other stuff that your immune system can use to
(05:13):
id whatever it is. If the thing in question is
from your own body and thus belongs there, your immune
system should recognize that. If it's not, your adaptive immune
system's job is to create a specific attack against germs
bearing that antigen and then remember it later. Here's how
(05:34):
it works. The T cells in your lymph nodes can
test a presented antigen and see whether they recognize it
because your body has fought a germ with it before.
Each individual T cell tests for, or recognizes, or fits
to a single antigen like a key in a lock.
Even if it's a new to you antigen, that's okay.
(05:56):
Eventually your system will find a T cell that fits
well enough as a remembered antigen. That's great. The whole process
can go quicker. When a T cell fits to an antigen,
it activates a response like a red alert. The T
cells starts to replicate rapidly, producing copies of itself that
are all custom fitted to that particular antigen. This is
(06:18):
really helpful because T cells are sort of like your
body's targeted assassins. They seek out and attack germs and
infected cells directly based on the particular antigen that they recognize.
T cells can also chemically signal other immune cells to
come help and can help activate your B cells. B
(06:39):
cells are sort of like your weapons experts. They create
what's called antibodies. Antibodies are specific proteins that your body
builds to match specific antigens. Antibodies can bind to their
matching antigen on the surface of a germ, rendering the
germ unable to do any harm, and also serve to
(07:00):
flag that germ or a germ infected cell for destruction.
At this point in the estate metaphor, I'm not sure
exactly what kind of household we're running here, maybe a
supervillain's compound, but let's just roll with it. So, after
your immune system has cleared an infection, it will stockpile
(07:21):
that particular antibody and keep around some T cells that
recognize that antigen in most cases forever. So if your
immune system encounters antigens of the same type later on
Bada bing Bada boom, where Bada bing boda boom indicates
that networks within networks of intracellular communication and coordinated efforts
(07:43):
will occur. It's all again really complex, which means a
lot of different things can go wrong. For example, not
everything that your immune system IDs using antigens as not
self and thus potentially unsafe, is actually a threat. This
is how we wind up with allergies to not just
(08:05):
harmless but actively adorable things like cats and flowers. For
some reason, your immune system looks at a granule of
pollen or pet dander and tries to clear it out
of your body with the same kind of extreme prejudice
it would a disease causing germ. Your innate immune system
triggers lots of inflammation to help get fighting resources to
(08:26):
the area, say your nose, but there's really nothing to fight,
so you just wind up swollen and itchy. There are
also some types of germs that actively mess with your
immune system. That's what originally made the human immuno deficiency
viruses or HIV so scary. HIV infects and kills immune
(08:48):
system cells like T cells in order to spread. There
have been some amazing advances in treating and preventing HIV
in recent years. It's very manageable. Now I'll have to
do a whole episode about it. Anyway. There are also
a number of conditions that happen when the adaptive immune
system starts confusing your own cells for invaders. Every cell
(09:10):
in our bodies should be coded as self thanks to
antigens on the cell's surface. It's sort of like wearing
an id. Bad antigens tell your immune system at a glance,
hey I'm cool, I work here. There are entire processes
in your body to curate your T cells and B cells,
but keep their activity in check and make sure that
(09:31):
ones that seem to want to attack self codd cells
don't get into circulation in the first place. But it
still happens, and this category of conditions is called autoimmune disorders.
It includes things like arthritis, in which your immune system
attacks your joints, type one diabetes in which it attacks
(09:51):
your pancreas, multiple sclerosis which damages nerve cells, and psoriasis,
which damages the skin leading to scaly, pass or other problems.
Autoimmune disorders tend to be frustrating to treat, after all,
You can't just remove and replace a malfunctioning immune system
the way you might a kidney. Also, we don't understand
(10:14):
exactly why any given autoimmune disorder happens. There is a
lot of research going into this, and we've got a
lot of good starting concepts, but again, the entire immune
process is so complex that it's hard to nail things down.
For example, researchers have identified sets of genes that code
for things like how your immune cells recognize antigens or
(10:37):
how your body's cells produce their self ID. It makes
sense that errors in this coding could lead to problems.
Other research has looked into malfunctions in T cells that
lead them to overproduce those signal molecules that call in
the troops, which also leads to inflammation, which tends to
be an issue in autoimmune disorders. Yet other research is
(11:00):
diving in two malfunctions in a subset of T cells
called regulatory T cells, that are supposed to regulate their
fellow workers in the immune system, shutting down the red
alert after an infection has been cleared, and suppressing excess activity.
Even when we do have a decent idea of what's
going wrong, immune disorders of all types can be difficult
(11:21):
to treat, but there are increasingly effective therapies that can
ease symptoms or even target particular immune system activities to
help bring it back closer to normal. As always, if
you or a loved one is experiencing strange inflammation or
other irritating or painful symptoms with no obvious cause. You
(11:42):
know you didn't stub your skin, definitely get in touch
with a healthcare professional. They'll be able to help you
get a diagnosis and a treatment plan, even if your
body is a supervillain's layer that may or may not
be haunted. Today's episode is an original written by me.
(12:04):
Brain Stuff is production of iHeart Radio and is produced
by Tyler Klang. Four more podcasts from iHeartRadio visit the
iHeartRadio app, Apple Podcasts, or wherever you listen to your
favorite shows.
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Host
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