Chapter 11.1b - Maturation and Activation of B Lymphocytes | Cambridge A-Level 9700 Biology

Summary

This educational video script delves into the maturation and activation of lymphocytes, crucial for the immune system's specific response to pathogens. It explains the differentiation of stem cells into naive B and T cells in the bone marrow and thymus, respectively. The script highlights the specificity of lymphocytes, with each type responding to a unique antigen. It details the process of clonal selection and expansion, leading to the formation of plasma cells for antibody production and memory cells for long-term immunity. The video also covers the structure and functions of antibodies, including their role in neutralizing toxins and facilitating pathogen engulfment by phagocytes.

Takeaways

• 🔬 Lymphocytes play a crucial role in the immune system by responding to specific antigens, highlighting the body's ability to combat a vast array of pathogens.
• 🌟 Each type of lymphocyte is specific to one antigen, ensuring a targeted immune response, which is why lymphocytes are involved in specific immune responses.
• 🧬 Lymphocytes originate from stem cells in the bone marrow and mature in specific organs: B cells in the bone marrow and T cells in the thymus.
• 🛡️ Antibodies, also known as immunoglobulins (Ig), are glycoproteins with a Y-shape structure, consisting of two heavy and two light chains, providing them with a quaternary structure.
• 🔒 The variable region of antibodies is responsible for antigen binding, with each type of B cell having a unique variable region that binds to a specific antigen.
• 🔗 The constant region of antibodies is involved in various functions, such as binding to phagocytes for opsonization or attaching to the B cell surface membrane.
• 🏃‍♂️ Upon antigen invasion, specific B lymphocytes are activated through a process called clonal selection, leading to clonal expansion and differentiation into plasma and memory cells.
• 💊 Plasma cells are short-lived but produce a large amount of antibodies rapidly, while memory cells provide long-term immunity and a faster response to subsequent infections.
• 📈 The primary immune response is slower with fewer antibodies, whereas the secondary response, facilitated by memory cells, is faster and more robust, often preventing the disease from manifesting.
• 🛡️ Antibodies have multiple actions including neutralizing toxins, preventing pathogens from binding to cells, and enhancing phagocytosis through processes like agglutination and opsonization.

Q & A

What is the primary function of lymphocytes in the immune system?

Lymphocytes play a crucial role in the immune system by responding to specific antigens. They are involved in a specific immune response, producing antibodies that can neutralize pathogens.

How many types of lymphocytes are there, and why is this diversity important?

There are millions of types of B and T lymphocytes, each specific to different antigens. This diversity is important because it allows the body to respond specifically to a vast array of pathogens, providing a tailored defense mechanism.

What is the difference between B cells and T cells?

B cells mature in the bone marrow and produce antibodies upon activation, while T cells mature in the thymus and can differentiate into various types such as T helper cells, T cytotoxic cells, and T memory cells to perform different immune functions.

What is the process of maturation for B cells?

B cells mature in the bone marrow from stem cells. They become mature B cells that can circulate in the lymph and carry out immune responses upon encountering their specific antigen.

How does the body ensure that only the specific lymphocytes respond to a particular antigen?

The body ensures specificity through the unique antibody receptors on the surface of B cells. Each B cell has one type of antibody receptor that can only bind to its complementary antigen, a process known as clonal selection.

What is the structure of an antibody, and how does it contribute to its function?

An antibody is a globular glycoprotein with a Y-shaped structure, consisting of four polypeptide chains: two heavy chains and two light chains. It has a variable region for antigen binding, a constant region for effector functions, and a hinge region providing flexibility.

What are the various actions of antibodies in the immune response?

Antibodies can prevent pathogens from entering cells, attach to bacterial flagella to hinder movement, agglutinate bacteria for easier phagocytosis, cause lysis of pathogens, opsonize pathogens for enhanced phagocytosis, and neutralize toxins.

What is clonal expansion, and why is it significant in the immune response?

Clonal expansion is the process where an activated B cell rapidly divides by mitosis to produce many identical cells. This is significant as it allows for a rapid and specific response to an antigen, increasing the production of antibodies.

How do memory cells contribute to long-term immunity?

Memory cells are long-lived and remain in circulation, providing long-term immunity. They enable a faster response during a subsequent invasion of the same antigen by rapidly dividing and forming more plasma cells to produce antibodies.

What is the difference between the primary immune response and the secondary immune response in terms of memory cells?

In the primary immune response, there is a slower production of antibodies due to the limited number of specific B cells. In contrast, the secondary immune response is faster and produces a higher concentration of antibodies because of the presence of memory cells from the initial exposure.

Outlines

00:00

🌟 Introduction to Lymphocyte Maturation and Activation

The video begins by introducing Chapter 11, Part 1b, focusing on the maturation and activation of lymphocytes. It emphasizes the importance of lymphocytes in the immune system, highlighting that they are crucial for fighting pathogens. The narrator explains that the body is constantly exposed to various pathogens, and to combat these, the body has a diverse range of B cells and T cells, each specific to different antigens. The video then delves into the concept of lymphocyte specificity, explaining that each type of lymphocyte responds to a single type of antigen, exemplified by the production of a single type of antibody receptor by a B cell. The video concludes this section by discussing the maturation process of lymphocytes, stating that only mature lymphocytes can circulate in the lymph and carry out immune responses. It outlines the journey of B cells and T cells from their origin in the bone marrow to their maturation and subsequent activation upon encountering specific pathogens.

05:00

🔬 Maturation of Lymphocytes and Structure of Antibodies

Paragraph 2 delves into the maturation process of lymphocytes, explaining that all cells are formed in the bone marrow before birth. It details the role of B cells, which have specific antibody receptors that can bind to complementary antigens, providing the B cells with their specificity. The paragraph further discusses the structure of antibodies, also known as immunoglobulins (Ig), which are glycoproteins with a Y-shaped quaternary structure. Antibodies consist of four polypeptide chains, including two heavy chains and two light chains, held together by disulfide bonds. The variable region of the antibody, which is crucial for antigen binding, is formed by both heavy and light chains and varies among different antibodies. In contrast, the constant region, which is the same across all antibodies of the same type, plays a role in the antibody's function in the immune response, such as binding to phagocytes or serving as a B cell receptor.

10:03

🛡️ Functions and Actions of Antibodies

Paragraph 3 explores the functions and actions of antibodies. It mentions the constant region's role in classifying antibodies into different classes like IgM and IgG, which have distinct constant regions. The paragraph describes the actions of antibodies in the immune response, including preventing pathogens from reaching cells, immobilizing bacteria by binding to flagella, promoting agglutination to facilitate phagocytosis, causing lysis of pathogens, opsonization to enhance phagocyte engulfment, and neutralizing toxins. The video uses a diagram to illustrate these actions, emphasizing the textbook's effective visualization of the process. The paragraph concludes by noting that antibodies can act both as freely circulating molecules and as receptors on the B cell surface, with the context determining their specific function.

15:04

🧬 Clonal Selection and Memory Cell Function in B Cell Response

Paragraph 4 discusses the activation and response of B cells upon pathogen invasion. It explains the process of clonal selection, where only B cells with receptors specific to the antigen are activated. This leads to clonal expansion through mitosis, resulting in many identical B cells. These activated B cells then differentiate into plasma cells, which produce and secrete antibodies, and memory cells, which provide long-term immunity. Plasma cells are short-lived but produce a large number of antibodies rapidly, while memory cells remain in circulation for many years, enabling a faster response to subsequent exposures to the same antigen. The paragraph includes a graph illustrating the difference between the primary immune response and the secondary immune response, highlighting the increased speed and effectiveness of the response due to the presence of memory cells.

20:05

🔄 Summary of B Lymphocyte Activation and Response

Paragraph 5 provides a summary of the activation and response of B lymphocytes. It reiterates that B cells mature and, upon pathogen invasion, undergo clonal selection and expansion, leading to the differentiation into plasma cells and memory cells. Plasma cells produce and secrete antibodies into the bloodstream, while memory cells enable a faster response during a second invasion of the same antigen. The paragraph succinctly encapsulates the key points discussed in the video, reinforcing the viewer's understanding of B lymphocyte function in the immune system.

Keywords

💡Lymphocytes

Lymphocytes are a type of white blood cell that plays a crucial role in the immune system. They can be found in the blood, lymph, and lymphoid tissues. In the video, lymphocytes are discussed in the context of their maturation and activation, highlighting their importance in responding to pathogens. The script mentions B cells and T cells, two main types of lymphocytes, which are specific to different antigens.

💡Antigens

Antigens are substances that can trigger an immune response, such as foreign substances from bacteria, viruses, or other pathogens. The video script explains that the body has millions of different types of B cells and T cells, each specific to a particular antigen, demonstrating the specificity of the immune response.

💡Maturation

Maturation, in the context of the video, refers to the process by which naive B cells and T cells develop into mature cells capable of carrying out immune responses. The script describes how B cells mature in the bone marrow and T cells in the thymus, preparing them for circulation in the blood and lymphatic system.

💡Activation

Activation is the process by which lymphocytes become stimulated to perform their immune functions. The video script details how specific B cells are activated when they encounter their corresponding antigen, leading to a series of immune responses.

💡Clonal Selection

Clonal selection is a principle in immunology where only those lymphocytes with receptors that match a specific antigen are activated. The video script uses this term to explain how the immune system selectively activates the appropriate B cells to respond to a particular pathogen.

💡Clonal Expansion

Clonal expansion is the rapid proliferation of a specific set of lymphocytes in response to an antigen. The video script mentions this process as a way for the activated B cell to divide and produce many identical cells, all capable of responding to the same antigen.

💡Plasma Cells

Plasma cells are differentiated B cells that produce and secrete large amounts of antibodies. The video script describes how activated B cells can differentiate into plasma cells, which are short-lived but play a critical role in the immune response by secreting antibodies into the bloodstream.

💡Memory Cells

Memory cells are a type of lymphocyte that remain in the body after an initial immune response, providing long-term immunity. The video script explains that memory cells enable a faster response during a subsequent exposure to the same antigen, contributing to the body's ability to remember and respond more effectively to previous infections.

💡Antibodies

Antibodies, also known as immunoglobulins, are proteins produced by B cells that recognize and bind to specific antigens. The video script discusses the structure and function of antibodies, including their role in neutralizing pathogens and marking them for destruction by other immune cells.

💡Opsonization

Opsonization is a process where antibodies coat the surface of pathogens, making them more recognizable and easier for phagocytic cells to engulf and destroy. The video script uses this term to illustrate one of the mechanisms by which antibodies aid in the immune response.

Highlights

Lymphocytes are crucial for the body's defense against pathogens, with a specific response to different antigens.

The body has millions of types of B cells and T cells, each specific for different antigens.

Each type of lymphocyte responds to only one type of antigen, ensuring a specific immune response.

Lymphocytes undergo a maturation process in the bone marrow before they can circulate in the lymph and carry out immune responses.

B cells mature in the bone marrow and can differentiate into plasma cells and memory B cells upon antigen attack.

T cells mature in the thymus and can differentiate into various types including T helper cells and cytotoxic T cells.

Antibodies, also known as immunoglobulins, are glycoproteins with a Y-shaped structure.

The variable region of antibodies provides two identical antigen-binding sites, crucial for specificity.

The constant region of antibodies allows them to bind to receptors on phagocytes and facilitate pathogen engulfment.

Antibodies can prevent pathogens from entering cells, bind to bacterial flagella, and cause agglutination to restrict movement.

Memory B cells provide long-term immunity and enable a faster response during a second invasion of the same antigen.

The primary immune response is slower and results in illness, while the secondary response is faster and can prevent symptom development.

Clonal selection refers to the activation of only the specific B lymphocytes that have receptors matching the antigen.

Clonal expansion is the process where one activated B cell divides by mitosis to produce many identical cells.

Plasma cells are short-lived but produce and secrete a large amount of antibodies rapidly.

Memory cells remain in circulation, providing a quicker response and long-term immunity to specific pathogens.

Transcripts

hi everyone and welcome to chapter 11

part 1b on the maturation and activation

of lymphocytes yes i know you have heard

about lymphocytes already this

we heard about it in last video we also

heard about it in chapter 8 but i'm

telling you this is way more detailed

now

before we go into lymphocytes we need to

talk about what happens to our body

every single day every single day we are

exposed to so many different types of

pathogens you don't know it but we our

body is constantly fighting a war here

now but there's so many million types of

pathogen there's so many out there

and if you are smart

you know

country you would have many many special

task forces

to combat the many many enemies you have

right so the same idea here your body

will have many many types

of b cells and t cells specific

for different antigens

if there are millions of pathogens out

there it will have million types of

billion b cells and t cells

now

each type of lymphocytes would respond

to only one type of antigen only this is

why we say that lymphocytes are involved

in specific response it is this specific

for example if you have one type of b

cell it will only produce one type of

antibody receptor so like this y shape

just one type not just one there are

many many y's around the cell

but you get it there's only one type of

antibody receptor

and this one type of antibody receptor

would respond to one type of antigen

only don't worry about antibody term

antibody receptor i'm going to get to

that later on

but the point is

if we have million types of b and h

cells which are specific this means that

our body can respond specifically to

almost any type of pathogenous that we

are ready for the war

now that is about the millions of

different types of bnt lymphocytes

but the reality is they don't just

you know

they don't just sit there and do their

job and that's pretty much it there's

actually a growing process a maturation

process

an activation process

for lymphocytes only the mature

lymphocytes can actually circulate in

lymph and carry out the immune responses

okay

so

what do we mean by maturation this is

what we mean okay

they are

once upon time there is stem cells in

the bone marrow

all your t cells and b cells are

produced before birth

but this b cells and t cells are naive

they are not mature yet they are naive b

cells b cells will mature in the bone

marrow made in the bone marrow mature

and the bone marrow become mature b

cells

when the pathogen that is specific to

attacks the body

then it will get activated

to form

plasma cells which are still b cells by

a specific type of cell

these plasma cells can produce

antibodies and also

metro b cells for different shape to

become b memory cells which does a

different function

how about t cells t cells also the same

idea they are made in the bone marrow

from the stem cell forms naive t cells

and it undergoes a maturation process in

the thymus to form mature t cells then

it can circulate in a blood and lymph

but it doesn't really differentiate and

activate until

the pathogen that is specific for

attacks the cell

then it's activated putting

it

different shades into t helper cells

t-haber cells later on can differentiate

the t helper memory cells

true t cells also can differentiate into

t killer cells or what we call cytotoxic

t cells which then also differentiates

into t killer memory cells

so

this chart here is very very useful and

i recommend that you sort of uh remember

these types and remember this chart so

that the future parts processes that i'm

going to talk about around now it's

going to be easier for you okay

we are going to be talking about b link

both sides first

and then the t lymphocytes

so all the b cells would have a one at

the like left hand corner here and all

the

t cells related would have a two car two

in blue

at the top left corner here

so let's talk about it

in more detail let's go maturation of

the lymphocytes

now again all cells are formed

in bone marrow before birth it was

formed in your bone marrow before you

were born

what happens there there are millions of

type right so you expect that genes in b

cells

called for different type of antibodies

four different types of b cells

now

each b cell will have a specific

antibody which acts as a glycoprotein

receptor

antibodies are glycoproteins which has a

protein it also has a carbohydrate

attached to it and this is on the cell

surface membrane of b cells

and the specific antibody receptor would

bind to the antigen that is

complementary in shape

this gives the specific b cells its

specificity

yeah so one type of b cell

has one type of antibody receptor

can only respond and be activated by one

type of antigen

after that building for sites can divide

and mature in the bone marrow and these

mature brain lymphocytes can circulate

the blood and concentrate in liver

spleen and the lymph nodes

now let's talk about antibodies when we

say antibodies what do we mean you now

know that is a glycoprotein

okay

and

here's more information it is also

globular the carbohydrate part is

usually not shown in diagrams when you

see the protein parts here just so you

know another name for antibodies is

immunoglobulins and sometimes it can be

summarized into the word the

abbreviation ig so immunoglobulins or ig

anyways

what is it made of what kind of level of

structure it has it is made up of four

polypeptide chains

and this is just a representative

diagram but generally all antibodies are

represented by this y shape here

it's four polyploid chains two heavy

chains which are in blue here

and two light chains

that is green

now because it has four polypeptide

chains this obviously is a protein with

a quaternary structure don't forget it

has a glycol part which is not shown in

the diagram as well how is it held

together it's held together by

diosulfite bonds which give its limit

there are three regions on the

antibiotic bodies number one is a

variable region

now variable region is these parts here

in yellow

there is a light chain variable region

here and here

and a heavy chain variable region here

and here so they are formed by both

heavy and light chains

this variable region is important to

provide

two identical antigen binding sites so

this is one binding site this is another

antigen binding site

and

that means each antibody has two binding

sites left

it is specific for binding antigen as

this particular part is complementary in

shape to the antigen

and the shape here is determined by the

specific sequence of amino

acid you can see here that it's a little

bit jagged um and this is to show you

that hey this one has a specific site

for specific antigens

the r groups of the antigen binding site

would form hydrogen bonds and ionic

bonds with the specific antigen that it

binds to

now again it's specific which means that

the sequence of amino acids at the

variable region is different for each

type of antibody

each type of antibody would bind to

different antigens

again

one type of b cell one type of antibody

receptor

okay

one type

of antigen

so different

different b cells

will have antibodies

with a slightly different

primary structure beside these different

specific sequence of amino acids add

this variable region

so this one differs from different b

cells

different type of b cells

now the constant region however here in

blue

the primary structure of the protein or

the sequence of amino acids is the same

so blue regions

again

sequence of amino acid is the same for

all the antibodies all the different

types but a variable region for

different types

would have a different sort of sequence

of amino acids

so speaking of constant region

constant region is formed by heavy and

light chains just like the variable

region

and what does it do when it circulates

in blood okay when antibodies are

circulating but

these antibodies can actually bind to

um receptors on phagocytes so you can

see this picture right

here you can see that here the

antibodies these y-shaped things are

bound to this antigen or pathogen here

and then this

the constant region of the antibody is

actually binding to a receptor on a

phagocyte

and this helps the phagocytes

engulf

the pathogen

now but when the antibody acts as a b

cell receptor so something on the b

salvia an antibody receptor

this constant region is a region that

attaches to the cell surface membrane of

the b cell so there are two functions

here depending on the question depending

on the context

one is when the antibody is freely

circulating the other is when it's

acting as a receptor

now another function of the constant

region is to really give the antibody

different

classes

no it's not the same as your m1 m2 s1 s2

s3 something no no different

class as in types

so you can see here igm igg okay these

are immunoglobulin m okay short for that

and they have sort of different constant

regions

okay you don't need to remember this i'm

just showing you how what different

shapes antibodies can take

now there is a third part here for

antibodies there's the variable region

there's the constant region and then

there is the hinge region hydrogen is

pretty easy it is held by disulfide

bridges it is this area here

and what it does it just gives some

flexibility when binding to antigens

that's funny

now let's talk about the action of the

antibodies we saw a little bit of

the

action just now

this is the same picture here

but let's do a sort of a range of

different things

now um these parts here are

important but i feel like the textbook

did a very good job at making this

diagram so i just copy pasted it and

added some title typography

okay so actions antibodies how do

antibodies work these are antibodies

that are freely circulating okay

now antibodies can prevent engine to

cell

okay it can bind the virus or the toxin

and prevent it from getting to the cell

it can attach to flagella of bacteria

and prevent it from moving around so if

it's less active it is easier for the

phagocytes to engulf

number three it can bind

um

agglutinate sorry it can clump together

those bacteria or pathogens so that it's

also easier for engulf and restricts the

movement so this is called arblutination

therefore it can cause pathogens to lies

so it actually can poke a little hole

and when water moves in pathogen can

rise

number five they do something called

opsonization optionalization

is the process that describes just now

the antibody would

bind to the receptor of the phagocyte

membrane

okay

and

facilitate the engulfment of pathogen

makes it easier for the macrophage to

find it and to ingest

the pathogen and number six is to

neutralize toxins

so 3d protein toxins can affect our

cells and enter our cells so

by binding it it makes the toxins not

toxic so

some people say that antibodies also act

as anti-toxins

so

that was

antibodies

and sort of the maturation of feminine

facade if it's too long they don't hear

they read

feed for sides they've produced in their

bone marrow

they mature in the bone marrow each of

them have an antibody receptor of a

different shape on their cell membrane

antibody structure and action you need

to know

but one exactly is antibodies secreted

when exactly is it acting as a receptor

what when how

okay we'll get there here

so let's talk about the action of

beating for sights this is after

maturation

after modulation let's say that's a

pathogen that invades the body

what will happen first is that the

antigen presenting cell

will fall

so this could be

a phagocyte

maybe a macrophage

engulfs the pathogen and presents the

antigen to the b lymphocytes

only the specific b lymphocytes has

receptors

with the complementary shape to that

particular antigen will be activated

because there are many many types of b

lymphocytes

right

only this specific special task force

will be activated

so this is selected so that's why it's

called clonal selection

this activated b cell then divides by

mitosis

and

this is called clonal expansion so many

that you will result with many type

sorry many

of the same type of these cells

so one b cell

that is activated become many many

activated b cells

now activated b cells then

can develop or differentiate into plasma

cells and memory cells let's talk about

plasma cells plasma cells are

short-lived they are only a few weeks

but their main

main function is to produce and secrete

antibodies rapidly they produce a lot

and they do this by exocytosis

okay again antibodies are globular

glycoproteins

which means they will have to undergo

modification in the goji and then secret

by exocytosis something you have learned

in chapter one

secret to wear secret to blood plasma

limb lungs it's not linings and it's

going to circulate in the blood

now because

this requires a lot of energy and a lot

of

processing you expect plasma cells to

have a lot of er and golgi as seen here

that's plasma cells

now again the activated b cells also

differentiated into memory cells so what

do memory cells do memory cells are

long-lived they remain in circulation of

blood and length

and it actually provides long-term

immunity

that's why it's called memory cells

and what they do is they last for many

years and lifetime and they enable a

faster response during a second invasion

of the same antigen

because they are

memory cells circulating already

during the second invasion of the same

pathogen it can divide rapidly

okay or clonal expansion it can form

more plasma cells which forms more

antibodies and this speeds up the

response

and the infection is actually destroyed

before symptoms develop this is why this

is

where we call

um

when we say that the host already has

immunity or the host is immune towards a

certain thing maybe because the host has

been infected with the same thing before

or similar thing and has the mean cells

in the body

now this is a graph of what memory cells

does this is what happens with the

primary response you can see that this

is a graph of concentration of antibody

against time

the primary response is a slower

response here

it um quite

a less steep

graph compared to this

only if this is because only a few b

cells specific to antigen is present

and as a result the individual does

become ill and takes some time before

the individual becomes healthy again

however

memory cells are produced here and

during the second exposure to antigen

you can see that it's a steeper curve

faster response and actually a bigger

response you can see the concentrated

antibody is much higher here

and this is because many memory cells

are circulating only so it detects it

faster there's a higher chance of

encountering those pathogens quickly

more plasma cells are formed compared to

the primary response and therefore even

more antibodies are produced in the

response as a result the individual do

not develop any symptoms

the pathogen will be killed and dealt

with even before symptoms develop

so this is a summary of action by

lymphocyte building foresight

first of all they mature

second law when the end when the

pathogen invades there is a binding

okay

with the specific antigen on abc this is

called clonal selection

and there's division by mitosis

this is called clonal expansion

and then there is differentiation into

plasma cells which produce and secretes

antibodies here into the bloodstream

and also there will be the formation of

memory cells which enable the faster

response during the second invasion of

the same antigen and that's it that is

the summary of action by gameplay being

impossible