Specific (Adaptive) Immunity | Humoral and Cell-Mediated Responses

Summary

This script delves into the intricacies of the human immune system, focusing on specific or adaptive immunity. It explains how the body recognizes and combats pathogens using antigens, macrophages, T helper cells, and B cells, leading to the production of antibodies. The process highlights the development of humoral and cell-mediated responses, as well as the formation of memory cells to provide long-term immunity against future infections. The educational narrative is interspersed with humor, making complex biological concepts accessible and engaging.

Takeaways

• 🤒 The speaker discusses feeling sick, likely due to a virus or bacteria that bypassed their innate immune defenses.
• 🛡️ The video focuses on specific immunity or adaptive immunity, which is the immune system's way of learning to fight off specific pathogens.
• 🦠 Pathogens, like bacteria or viruses, have unique antigens on their surfaces that the immune system can learn to recognize.
• 🍽️ Macrophages are big eater cells that consume pathogens and present their antigens on the surface to alert the immune system.
• 🧬 T helper cells recognize the antigens presented by macrophages and clone themselves to fight off the specific pathogen.
• 💉 B cells, which mature in the bone marrow, produce antibodies that are specific to the pathogen and help neutralize it.
• 💧 The humoral response involves B cells producing antibodies in the body's fluids, such as blood and lymphatic system.
• ⚔️ Cytotoxic T cells target and kill infected cells by detecting antigens on their surface and releasing destructive chemicals.
• 🔄 Memory B cells and memory T cells remain in the body to quickly respond if the same pathogen invades in the future.
• 🧪 The video provides an overview of how the body transitions from a non-specific immune response to a specific immune response, ensuring better protection against future infections.

Q & A

What is the primary focus of this video?

The primary focus of this video is to explain specific immunity or adaptive immunity, which involves the immune system learning how to fight off a particular pathogen.

What are antigens, and why are they important?

Antigens are proteins on the surface of pathogens that help the immune system identify the pathogen. Recognizing antigens allows the immune system to target and fight off specific bacteria or viruses.

What role does a macrophage play in the immune response?

A macrophage is a type of white blood cell that engulfs and digests pathogens through a process called phagocytosis. It then presents the antigens from the pathogen on its surface to help other immune cells recognize and fight the invader.

What is the significance of the Major Histocompatibility Complex 2 (MHC2)?

MHC2 is a protein found on the surface of macrophages that presents antigens to T helper cells. This process is crucial for activating the specific immune response by allowing T cells to recognize and respond to the pathogen.

How do T helper cells contribute to the immune response?

T helper cells recognize the antigens presented by macrophages and then clone themselves to produce more cells that can identify the pathogen. They also release cytokines, which activate other immune cells, including B cells and cytotoxic T cells.

What is the function of B cells in the immune system?

B cells produce antibodies that specifically target the pathogen identified by the immune system. These antibodies neutralize the pathogen and make it easier for other immune cells to destroy it.

Why is it important for B cells to be specific in the antibodies they produce?

Specificity is crucial because if B cells produced antibodies that targeted any protein, they could mistakenly attack the body's own healthy cells. The specificity ensures that only the pathogen is targeted.

What are memory B cells, and what is their role in immunity?

Memory B cells are long-lived cells that remain in the body after an infection. They are ready to respond quickly if the same pathogen invades the body again, providing immunity to future infections by that pathogen.

How does the immune system handle cells that are already infected by a pathogen?

Infected cells present antigens on their surface, signaling for help. Cytotoxic T cells recognize these antigens and release perforins and enzymes that kill the infected cells, preventing the pathogen from replicating and spreading.

What is the difference between humoral and cell-mediated immune responses?

The humoral response involves B cells producing antibodies to neutralize pathogens in body fluids like blood. The cell-mediated response involves T cells killing infected cells to stop the spread of intracellular pathogens like viruses.

Outlines

00:00

🤒 Feeling Sick and the Role of Specific Immunity

The speaker starts by describing their current illness, highlighting how a pathogen bypassed their innate immune defenses like skin and stomach acid. Despite this, they emphasize the role of specific or adaptive immunity, which is now developing to fight the pathogen. The speaker explains the importance of specific immunity in recognizing and fighting off specific bacteria or viruses, setting the stage for a deeper exploration of how the immune system learns to combat pathogens through specialized responses.

05:01

🦠 Introduction to Pathogens, Antigens, and Immune Responses

The speaker introduces the concept of pathogens and antigens, explaining how pathogens such as bacteria and viruses have unique proteins on their surfaces called antigens. These antigens help the immune system identify the pathogen. The speaker then differentiates between the non-specific immune response, which reacts the same way to all pathogens, and the specific immune response, which targets particular pathogens. This sets the foundation for discussing how the immune system transitions from a general to a more specialized response to fight off specific invaders.

10:02

🍽️ Macrophages: The Big Eaters of the Immune System

The speaker explains the role of macrophages in the immune system, describing how these 'big eater' cells engulf and digest pathogens through a process called phagocytosis. The macrophage then presents antigens from the pathogen on its surface using a protein called MHC2, effectively turning into an antigen-presenting cell. This presentation of antigens is crucial for alerting other immune cells, like T helper cells, which begin to learn how to recognize and fight the pathogen. This marks the beginning of the specific immune response.

👨‍🏫 T Helper Cells: The Commanders of Specific Immunity

The T helper cells play a central role in the specific immune response. After recognizing the antigen presented by the macrophage, they clone themselves to increase their numbers and release cytokines, signaling molecules that activate other immune cells. One of the key players activated by these cytokines is the B cell. B cells, which mature in the bone marrow, are responsible for producing antibodies specific to the pathogen. These antibodies neutralize the pathogen and mark it for destruction by other immune cells. This paragraph highlights the coordinated effort of the immune system in mounting a targeted defense.

🔬 B Cells and the Humoral Immune Response

B cells are a critical part of the humoral immune response, which occurs in the body's fluids, such as blood and lymph. The speaker explains the 'three B's' of B cells: they mature in the bone marrow, produce antibodies, and operate in the body's fluids. The antibodies they produce are specific to the pathogen, neutralizing it and marking it for destruction. Some B cells become memory B cells, remaining in the body long-term to provide immunity against future infections by the same pathogen. This paragraph underscores the importance of B cells in both immediate and long-term immunity.

🔪 Cytotoxic T Cells and the Cell-Mediated Immune Response

The cell-mediated immune response is essential for dealing with cells already infected by pathogens, particularly viruses. The speaker describes how cytotoxic T cells, stimulated by cytokines from T helper cells, identify and destroy infected cells by releasing perforins and enzymes that break down the cell membrane and kill the infected cell. This prevents the pathogen from replicating and spreading. Some of these T cells also become memory T cells, ready to respond to future infections by the same pathogen. This paragraph highlights the aggressive but necessary actions of cytotoxic T cells in protecting the body.

📜 Recap: From Non-Specific Defense to Long-Term Immunity

The speaker recaps the immune response process, starting with the non-specific response by macrophages and ending with the specific immunity developed by T and B cells. They summarize how the immune system learns to recognize a pathogen, mounts a specific response, and retains memory cells to prevent future infections. The recap emphasizes the complex coordination between different immune cells and the importance of both the humoral and cell-mediated responses in protecting the body from pathogens. The speaker closes by lightheartedly reflecting on their 'fake' sickness and the importance of understanding immunity.

Keywords

💡Pathogen

A pathogen is any organism, such as a bacteria or virus, that can cause disease in a host. In the video, the pathogen is the invading entity that the immune system is trying to fight off. The concept is central to the video’s discussion on how the body’s immune system, both non-specific and specific, works to identify and eliminate these harmful invaders.

💡Antigen

An antigen is a molecule or a part of a pathogen that the immune system recognizes as foreign. The video discusses antigens as the specific markers on the surface of pathogens that allow the immune system to identify and target them. The ability of the immune system to recognize these antigens is crucial for the activation of specific immune responses.

💡Macrophage

A macrophage is a type of white blood cell that engulfs and digests pathogens through a process called phagocytosis. In the video, macrophages are described as 'big eater cells' that consume pathogens and then present their antigens to alert other immune cells, marking the beginning of the adaptive immune response.

💡T Helper Cells

T helper cells are a type of white blood cell that play a key role in the immune system by recognizing antigens presented by macrophages and then coordinating the immune response. The video explains how these cells clone themselves once they recognize a pathogen, thereby enhancing the body's ability to fight off the infection through both humoral and cell-mediated responses.

💡B Cells

B cells are a type of white blood cell that are responsible for producing antibodies, which are proteins that specifically target and neutralize pathogens. In the video, B cells are activated by T helper cells and then produce antibodies that are specific to the pathogen, playing a critical role in the humoral response.

💡Antibodies

Antibodies are proteins produced by B cells that specifically bind to antigens on pathogens, neutralizing them and marking them for destruction by other immune cells. The video highlights how antibodies are crucial in preventing pathogens from infecting other cells and making it easier for other immune cells to eliminate them.

💡Humoral Response

The humoral response is the part of the immune system that involves B cells and the production of antibodies, which circulate in the body’s fluids (like blood) to fight off pathogens. The video explains this as one of the specific immune responses that target pathogens in the body's fluids, distinguishing it from the cell-mediated response.

💡Cell-Mediated Response

The cell-mediated response is a type of specific immune response that involves T cells directly attacking infected cells. In the video, this response is described as being crucial for dealing with cells that have already been infected by pathogens, especially viruses, by killing the infected cells to prevent the spread of the infection.

💡Cytokines

Cytokines are signaling molecules released by immune cells that help coordinate the immune response by activating and directing other cells to the site of infection. The video discusses how T helper cells release cytokines to activate both B cells in the humoral response and cytotoxic T cells in the cell-mediated response, making them a key component in mobilizing the immune system.

💡Memory Cells

Memory cells are long-lived immune cells that 'remember' a pathogen after the initial infection has been cleared, allowing the body to respond more quickly if the same pathogen invades again. The video emphasizes the importance of memory B cells and memory T cells in providing immunity, explaining that these cells lie in wait to fight off the same pathogen in the future, helping to prevent reinfection.

Highlights

Introduction of specific immunity: The video is all about specific or adaptive immunity, where the immune system learns to fight off a particular pathogen.

Difference between innate and adaptive immunity: The speaker distinguishes between the body's innate immune defenses and the adaptive immune system, which develops specific immunity to pathogens.

Role of antigens: Antigens on the surface of pathogens are crucial for the immune system to recognize and target specific bacteria or viruses.

Function of macrophages: Macrophages are large white blood cells that engulf pathogens through phagocytosis, breaking them down into smaller pieces, including antigens.

Presentation of antigens: Macrophages present antigens on their surface using a specialized protein called MHC2, turning them into antigen-presenting cells.

Role of T helper cells: T helper cells use their CD4+ protein to recognize antigens presented by macrophages and then clone themselves to fight off the specific pathogen.

Cytokines and B cells: T helper cells release cytokines that activate B cells, which are responsible for producing antibodies specific to the pathogen.

Function of antibodies: Antibodies neutralize pathogens by binding to them, preventing them from infecting cells, and making them targets for other immune cells.

Memory B cells: Some B cells become memory B cells, ready to fight off the pathogen if it invades the body again in the future.

Humoral response: The humoral response involves B cells and antibodies acting in the fluids of the body, such as blood and lymphatic system.

Cell-mediated response: The cell-mediated response targets cells already infected by pathogens, especially important for fighting viral infections.

Cytotoxic T cells: Cytotoxic T cells detect infected cells by recognizing antigens on their surface and release perforins and enzymes to kill the infected cell.

Memory T cells: Some T cells become memory T cells, providing immunity against future infections by the same pathogen.

Recap of the immune process: The video recaps the entire immune process, from pathogen entry to the development of specific immunity and memory cells.

Educational approach: The speaker uses a clear, step-by-step explanation and diagrams to break down the complex process of adaptive immunity.

Transcripts

hey everyone i gotta admit i'm feeling

pretty

sick today i feel kind of achy all over

whatever virus or bacteria

got into my bloodstream it had to make

it past my innate immune defenses

my skin my stomach acid if it got in

that way

a bunch of white blood cells like

neutrophils and natural killer cells

somehow it's lingered on past all of

those

sorry but the good thing is that i've

got specific immunity that's developing

right now so hopefully

i won't have a problem with it next time

so this video is all about specific

immunity or adaptive immunity my immune

system is learning how to fight off this

particular pathogen

calling in the big guns you might say

so let's jump to the the white board or

whatever

and get started so let's say we have a

pathogen invading the body it could be a

bacteria it could be a virus

but it's something in our bodies that

shouldn't be there i've got the

pathogens drawn in green

and on the surface of the pathogens i

have these little orange circles which

are the antigens

antigens are just little proteins that

are on the surface of the pathogen

that we can use to identify what that

pathogen is all of the bacteria and

viruses that can make it into our body

have different antigens that present on

their surface and so if we can learn to

recognize

each bacteria or viruses antigens we can

fight off that specific bacteria or

virus and that's what this whole process

is about

learning to recognize a particular virus

or bacteria

and then recruiting cells that are ready

to fight it off as quickly as possible

now in this diagram on the top left we

have a non-specific response

that means that this top left part of

the diagram

all the stuff that happens there would

happen no matter what the pathogen is

that's entered into our body it could be

this specific one i've got drawn in

green

or it could be covet or it could be

chickenpox it could be anything

then we have a humoral response as well

as a cell mediated response

those are both specific immune responses

meaning that we're going to develop some

cells

there that are specific to this pathogen

it's like they're just going to train

in fighting off this one pathogen and

not worry about anything else

they're going to be specific to this

pathogen and so this is all about

converting from our non-specific

response

to our more effective specific responses

to the pathogen

so the first thing that's going to

happen is we're going to have a special

cell called a macrophage

macro means big and phage means to eat

so this literally means a big cell

that's going to eat

the bacteria or the pathogen that's

invaded our body you can see it wrapping

its cell membrane around that pathogen

in a process called endocytosis we call

it specifically phagocytosis

and phago just meaning to eat and cyto

meaning a cell so this

literally means to eat another cell so

that macrophage or big eater cell is

going to phagocyticize the bacteria

and it's going to store it in what we

call a vacuole at that point it's going

to take these little

compartments called lysosomes that are

filled with enzymes and it's going to

inject those enzymes

into the vacuole and those enzymes are

going to break apart that pathogen

it's going to break it into little

pieces and some of those pieces will be

the antigens that are found on the

surface

of the pathogen the macrophage is going

to have a specialized protein which is

called

mhc2 or major histocompatibility complex

2

and that mhc2 protein is going to grab

onto some of those antigens and present

those antigens on the surface of the

macrophage because they're presenting

this antigen or saying

hey here's how you can recognize this

pathogen we're going to call the

macrophage an antigen

presenting cell it's presenting the

antigen now once the macrophage is

presenting

this antigen another cell is going to

come along called a t helper cell

now the macrophage and the t helper cell

are both white blood cells they're just

different types of white blood cells

and the t helper cell is going to use

its specialized protein called cd4 plus

to recognize and learn what that antigen

looks like now on the diagram i drew

that as an orange circle but in reality

it's detecting the shape of it it's not

just going to be a

circle like that it's going to be a

protein which folds lots and lots of

times to make these really complex and

strange

shapes it's learning what that shape is

at that point this t helper cell which

now knows what the antigen looks like so

it could recognize the pathogen

it's going to clone itself it's going to

make a whole bunch of copies of itself

because the more of these t helper cells

that we have the better we're going to

be able to fight off

the bacteria or virus that's entered the

body now again these t

helper cells have just learned the

specific pathogen

what it looks like so we're now into

what we call specific immunity

which is going to be this humoral

response and our cell mediated response

okay so all of these t helper cells

they're going to go around now and

release something called

cytokines so cytokines are these little

chemicals

cyto means cell and kine or kina

means to move and so these are gonna

sort of move other cells

into action that's where they get the

name cytokines they cause cells to move

into action one of the cells these get

released to are called b cells

now for b cells which are another type

of white blood cell you need to remember

the three b's

the first b is that these mature or

differentiate and become

b cells in the bone marrow t cells

although all white blood cells come from

the bone marrow originally

t cells are going to develop or mature

into t cells in the thymus gland hence

the name t

so b cells bone marrow t cells thymus

gland that's where they get their names

the second b

is that b cells are going to make

antibodies b for bodies

and antibodies that b cells make are

going to be specific for the pathogen

that we're trying to fight off the b

cell has learned what this pathogen

looks like it's been called into action

by the t helper cells and their

cytokines and it's going to make

antibodies

they're going to latch on to this

specific pathogen now this needs to be

specific

because if it wasn't if this b cell was

making antibodies it latched on to just

any old protein on the surface of a cell

and that would be attacking our red

blood cells it would be attacking our

normal healthy cells that would be bad

so this has to make antibodies that are

specific for

this pathogen now that'll do a couple

things one it's going to neutralize this

pathogen think about it if that pathogen

is covered in these antibodies

then it can't infect other cells and it

can't grow

it can't do any of the things it

normally would do in our bodies having

these antibodies also makes it a target

for some of our own cells

if other macrophages or natural killer

cells or neutrophils come along and they

see something with a bunch of antibodies

attached to it

they know it's time to strike so other

cells will kill off this pathogen more

easily because of the antibodies the

third b to remember is that this happens

in the fluids of our body

and an example of that would be our

blood that's what humoral response

means humoral means happening in our

fluids so that includes our blood but

also includes our lymphatic system our

lymph nodes

and lymph vessels as well as the

interstitial fluid which is all the

fluid like between the cells throughout

our body so remember for b

cells they mature in the bone marrow

they make antibodies

and this all happens in our blood now

this is all well and good we're going to

fight off this pathogen really well with

our

newly specialized b cells that are

making antibodies for that pathogen but

we want to be able to fight off this

bacteria or virus again in the future

and not have to get sick again so a lot

of these b cells are going to stick

around as what we call

memory b cells they're just going to be

chilling in our body

hanging out ready to fight off that

pathogen if it ever makes it into our

bodies again

we're waiting for you so that's our

humoral response and we're gonna be

ready to fight off that pathogen again

if it ever gets into our body let's say

a year or two down the road now this is

all happening in the fluids of our body

but unfortunately

some of our cells may have already been

infected and the antibodies

can't really make it into our infected

cells to fight off the pathogen that's

infected those cells so we have to have

a separate system or a separate response

which is going to take care of our cells

that have already been infected so here

we have a normal cell in the body this

could be a skin cell or a digestive

system

cell or whatever cell in the body and

it's been infected with this

bacteria or virus so we have to do

something about that this is especially

important for viruses because what

viruses do

is they make it into our own cells and

they'll use the machinery of our cells

like ribosomes and stuff

in order to make lots of copies of

themselves then they'll kill the cell

burst open and go infect a bunch of

other cells so if we're able to

neutralize this before the virus is ever

able to make copies of itself in

infected cells then we're gonna be able

to fight off this viral infection a lot

more effectively now our infected cell

won't call for help like this but it

will

present some of the antigens from those

pathogens on the surface of it

it's sort of a call for help so our t

helper cells during this are going to be

releasing cytokines

which are going to stimulate cytotoxic t

cells

into action the cytotoxic t cells are

going to detect this antigen which is

presenting on the surface of our

infected cell

and that's how it's going to know that

this is a cell that it needs to

neutralize

so a couple things to remember about t

cells t cells mature in the thymus gland

that's where they get the name t cell

and what they do is they kill

infected cells and so this is going to

release

these specialized chemicals called

perforins which will break open the cell

membrane and a bunch of enzymes as well

which are going to kill

this infected cell for infected cell

this is not how you probably thought the

story was going to end it's a tragic

ending for our infected cells but for us

it's a happy ending because

it's better off if these cells die if we

can kill them off really quickly

before this virus is able to replicate

and destroy the rest of our cells so

bad for that cell good for us and so

some of those are going to stick around

is what we call memory t

cells so if we get sick in the future

these are ready lying in wait

to fight off that particular pathogen

we're waiting for you and so that's how

we go from a non-specific response to

developing immunity

to some bacteria or virus that we've

been exposed to in the past

all right let's do a quick recap so

we've got some pathogen that's entered

into the body

and a macrophage or dendritic cell is

going to phagocytosize or eat that

bacteria or pathogen then it's going to

release

enzymes from lysosomes those enzymes

will break that pathogen

apart into its little pieces a

specialized protein in our macrophages

called an mhc2 is going to grab on to

the antigens

and it's going to present those antigens

on the surface of

the macrophage or dendritic cell which

we call antigen presenting cells because

they're presenting the antigen t helper

cells are going to come along

and the t helper cells will use cd4 plus

their specialized protein

to detect the shape of that antigen once

they know the shape of that antigen

they're going to start cloning

themselves so we have a whole bunch of t

helper cells that know what that antigen

looks like the t helper cells are going

to release

cytokines to stimulate b cells to make

antibodies

and those antibodies will be specific to

that pathogen they'll neutralize it by

locking on to it as well as make it

easier for other cells such as

macrophages and neutrophils to destroy

that pathogen some of those b cells will

stick around as memory b cells so we can

fight off this pathogen in the future

and remember the three b's of b cells

they mature in the bone marrow they make

antibodies and all this happens in our

fluids particularly our blood

that's our humoral response now onto the

cell mediated response which is what we

do to cells that have already been

infected by this pathogen the t helper

cells

release cytokines to stimulate cytotoxic

or killer t

cells the killer t cells will detect

which cells have been infected by

looking for antigens presenting on the

surface of those infected cells once

they detect one they'll release

perforins which

poke holes into the cell membrane as

well as enzymes which will make it into

the cell

and destroy that cell so that bacteria

or virus can't replicate within that

cell

and can't go out to infect other cells

in the body t cells of course mature in

the thymus gland which is where they get

the name t and some of those t

cells are going to stick around as

memory t cells so their body is able to

fight off this pathogen again in the

future

without having to go through all this

process and getting sick again

so how convincing was my fake coughing

and fake sickness do i have a career in

acting

all right thanks for watching good luck

fighting off those pathogens